WO1987002438A1

WO1987002438A1 - Fluid filled device and valve therefor

Info

Publication number: WO1987002438A1
Application number: PCT/GB1986/000623
Authority: WO
Inventors: Richard Bernhard Richardson
Original assignee: Richard Bernhard Richardson
Priority date: 1985-10-15
Filing date: 1986-10-15
Publication date: 1987-04-23

Abstract

A device to be filled with fluid under pressure includes a plurality of low pressure segments (17), ports (14) and a low pressure compartment (13) interconnecting the segments, and a high pressure compartment (11) arranged such that filling of the high pressure compartment with a fluid to a pressure higher than that in the low pressure compartment is operative to close the ports (14) interconnecting the low pressure segments (17) thereby isolating the segments from one another. In its simplest form only a single segment (17) is provided. The device is made up of a valve and the segments (17) and in one example of the invention is a mattress.

Description

Fluid Filled Device and Valve Therefor

This invention relates to fluid filled devices and to a valve which may be attached to or an integral part of such a device. The invention is particularly, but not exclusively, concerned with inflatable apparatus, for example inflatable beds or mattresses for domestic, medical and other purposes, inflatable structures such as tents, inflatable boats and packaging material.

It is well known to provide an inflatable device such as an air-bed with a number of segments so as to provide the device with the requisite shape. In a first form of such a device the segments are all in fluid communication with one another and the air-bed is inflated through a single valve. A disadvantage of a device of this kind is that if any one of the segments should be punctured the entire device is depressurised and rendered useless until the puncture is mended. This disadvantage is overcome in a second form of device in which all the segments are isolated from one another and each segment has its own inlet/outlet valve. The disadvantage of the second form of device is that it is tedious to inflate or deflate because of the number of separate points at which this must be done.

It is an object of the invention to provide a fluid filled device and also a valve which may be attached to or an integral part of such a device, which enables a fluid filled device to have a number of segments which in use are isolated and yet which can be inflated in a simple manner. According to a first aspect of the invention there is provided a differential pressure valve comprising a low pressure compartment bounded by flexible material and having a first port and one or more further ports, and a high pressure compartment having an inlet port, the low and high pressure compartments being arranged such that filling of the high pressure compartment with fluid to a pressure higher than that in the low pressure compartment is operative to close the one or more further ports in the low pressure compartment. Usually the first port of the low pressure compartment will be the port through which fluid is inserted into or removed from the low pressure compartment and the one or more further ports of the low pressure compartment will, in use, be connected to respective segments. In certain applications of the invention, however, fluid may be inserted into or removed from a segment and in this case the first port of the low pressure compartment will also be connected to a segment.

When a differential pressure valve (which term is often abbreviated to dpv in this specification) according to the first aspect of the invention is attached to or an integral part of an inflatable device having a plurality of segments then the segments can be filled with fluid through a single inlet via the first port, the low pressure compartment, and the one or more further ports. If the high pressure compartment is then filled to a pressure higher than that in the low pressure compartment the one or more further ports in the low pressure compartment will be sealed, thereby isolating the segments from one another. If it is desired to empty the segments, the high pressure compartment can be depressurized and then the segments can. be emptied through a single outlet.

In many applications it is preferable for the fluid filled device to have many segments and accordingly the low pressure compartment may have a plurality of further ports.

While it is within the scope of the invention for the high pressure compartment to have a relatively rigid structure in most applications it is preferable for at least the port of the high pressure compartment which is operative to effect closure of the one or more further ports to be bounded by a membrane of flexible material. The membrane may itself form the closure of the ports or one or more closure members attached to or engaged by the membrane may effect the closure. In the case where one or more closure members are provided, a respective closure member may be mounted in each port and its move¬ ment between an open and closed condition guided by the port in order to promote sealing of the port when closed. The high pressure compartment may be contained substantially wholly within the low pressure compartment. In this case in particular, but not exclusively, the membrane may be in the form of a bladder.

Alternatively the high pressure compartment may be adjacent the low pressure compartment and the two compartments share a common flexible boundary wall. In this case in particular, but not exclusively, the membrane may be in the form of a diaphragm.

The high pressure compartment may be of elongate form. In this case the low pressure compartment is also preferably of elongate form and a plurality of further ports in the low pressure compartment distributed along the length thereof. The first port of the high pressure compartment may be at one end thereof and the first port of the low pressure compartment may be in the vicinity of the other end of the high pressure compartment. The one or more further ports in the low pressure compartment may be located adjacent a side of the high pressure compartment; in alternative arrangements, however, the ports are located all around the high pressure compartment.

The first port of the low pressure compartment and the inlet port of the high pressure compartment may be connected to a common conduit, valve means being provided for closing the fluid path between the low pressure compartment and the conduit. The valve means may also be operative to close the fluid path between the high pressure compartment and the conduit. Closure means for the first port of the low pressure compartment and/or the inlet port of the high pressure compartment, which may comprise the valve means referred to above, will normally preferably be provided adjacent the associated compartment. An alternative arrangement, however, and one that is preferable in certain cases is to provide the closure means at a location remote from the associated compartment. In this case one end of a conduit can be connected to the port of the compartment and the closure means provided at the other end of the conduit.

A plurality of differential pressure valves may be connected together. They may be connected with their low pressure compartments connected in parallel or series and with their high pressure compartments connected in parallel or series. Another alternative which is described later is to connect the "low" pressure compartment of one differential pressure valve, either directly or via a segment to which the compartment is connected, to the "high" pressure compartment of another differential pressure valve. Such an arrangement is referred to later as a "cascade". It will be understood that in such a case the "low" pressure compartment of one valve will be at substantially the same pressure as the "high" pressure compartment of the other valve.

Locking means may be provided for maintaining the one or more further ports closed, even if pressure in the high pressure compartment is reduced. Such locking means may act automatically upon initial closure of the ports or may be manually applied.

The present invention also provides a device to be filled with fluid under pressure, the device including a differential pressure valve as defined above and respective low pressure segments communicating with each of the one or more further ports of the low pressure compartment whereby the low pressure segments can be filled with fluid through the first port of the valve and filling of the high pressure compartment to a pressure higher than that in the low pressure compartment and the segments is operative to close the one or more further ports in the low pressure compartment thereby isolating the segments from one another.

The present invention further provides a device to be filled with fluid under pressure, the device including a plurality of low pressure segments, ports and a low pressure compartment interconnecting the segments, and a high pressure compartment arranged such that filling of the high pressure compartment with a fluid to a pressure higher than that in the low pressure compartment is operative to close the ports interconnecting the low pressure segments thereby isolating the segments from one another. That device may incorporate a dpv having any of the features of the dpv defined above.

According to another aspect of the invention there is provided a differential pressure valve comprising a low pressure compartment and having a first port and one or more further ports, for connection to or connected to segments, and a high pressure compartment having an inlet port, the low and high pressure compartments being arranged such that filling of the high pressure compartment with fluid to a pressure higher than that in the low pressure compartment is operative to close the one or more further ports in the low pressure compartment to isolate respective segments connected thereto. That dpv may have any of the features of the dpv of the first aspect of the invention.

By way of example certain embodiments of the invention will now be described with reference to the accompanying drawings, of which: Fig. 1 shows a theoretical model of a dpv and segment with the low pressure compartment pressurised.

Fig. 2 shows the same theoretical model as Fig. 1 but with the high pressure compartment pressurised. Fig. 3 shows the same theoretical model as Fig. 1 but with an impinging force on the segment. Fig. 4 shows a theoretical model of a dpv with a partial vacuum in the segment. Fig. 5 shows the partial vacuum in the segment of

Fig. 4 isolated by the dpv. Fig. 6 shows in section a uniport dpv with a bladder and opposing compartment valves. Fig. 7 is a cross-section along the lines XY of Fig. 6. Fig. 8 shows the dpv of Fig. 6 with a segment connected and pressurised. Fig. 9 shows in section the dpv of Fig. 6 with a segment as an integral part. Fig. 10 shows in section the dpv of Fig. 6 with the high pressure compartment pressurised.

Fig. 11 is a cross-section along the lines XY of

Fig. 10. Fig. 12 is a cross-section along the lines VW of Fig. 6 but to a larger scale than Fig. 7 with the bladder unpressurised.

Fig. 12A is a cross-section along the lines VW of

Fig. 12. Fig. 13 is a cross-section similar to Fig. 12 but with the bladder pressurised. Fig. 14 shows the use of a retaining collar on a tubular bladder dpv. Fig. 15 shows an alternative cross-section along the lines XY of Fig. 6 with the bladder unpressurised. Fig. 16 is a cross-section similar to Fig. 15 but with the high pressure compartment of the bladder dpv pressurised. Fig. 17 shows in section a uniport dpv with a diaphragm, opposing compartment valves and a pressurised segment attached.

Fig. 18 shows the uniport diaphragm dpv of Fig. 17 with the high pressure compartment pressurised. Fig. 19 is a detailed cross-section along the lines XY of Fig. 17 with the diaphragm unpressurised. Fig. 20 is a cross-section similar to Fig. 19 but with the diaphragm pressurised. Fig. 21 shows an alternative cross-section along the lines XY of Fig. 17 with the diaphragm unpressurised. Fig. 22 is a cross-section similar to Fig. 21 but with the high pressure compartment pressurised. Fig. 23 shows in section a multiport bladder dpv with opposing compartment valves. Fig. 24 shows the multiport bladder dpv of Fig. 23 with attached segments and the high pressure compartment pressurised. Fig. 25 shows in section a multiport diaphragm dpv with opposing compartment valves. Fig. 26 shows the multiport diaphragm dpv of Fig. 25 with attached segments and the high pressure compartment pressurised. Fig. 27 shows in section a multiport bladder dpv with coaxial compartment valve ports. Fig. 28 is a detail A of Fig. 27 showing the coaxial compartment valve ports with access to the low pressure compartment. Fig. 29 is a view similar to Fig. 28 but with access to the low pressure compartment blocked and with access to the high pressure compartment. Fig. 30 shows a multiport dpv operating with a single source of fluid and a sliding valve. Fig. 31 is a detail A of Fig. 30 showing the sliding valve. Fig. 32 shows in section a dpv operating with a single source of fluid and transfer valves. Fig. 33A shows in section a multiport dpv with various ports.

Fig. 33B shows in section a multiport dpv with extended compartmental valves. Fig. 34 shows a self-inflated cylinder with a multiport dpv. Fig. 35 shows in section another multiport dpv. Fig. 36 shows in section two dpvs connected in cascade. Fig. 37 shows in section a multiport bladder dpv with guided ports. Fig. 38 is a detail A of Fig. 37 showing one of the guided ports. Fig. 39 is a cross-section along the lines VW of Fig. 37 with the guided port open.

Fig. 40 is a cross-section similar to Fig. 39 but with the guided port closed (shown with the high pressure compartment pressurised). Fig. 41 shows in section a diaphragm multiport dpv with spring-loaded guided ports.

Fig. 42 is a cross-section along the lines XY of Fig. 41 showing a spring-loaded guided port with the low pressure compartment pressurised only. Fig. 43A is a cross-section similar to Fig. 42 but with the high pressure compartment of the spring-loaded guided port pressurised. Fig. 43B is a cross-section similar to Fig. 42 showing a modified arrangement of the spring-loaded guided port only. Fig. 44 shows in section a radial multiport dpv.

Fig. 45 is a plan view of the radial multiport dpv of

Fig. 44. Fig. 46 shows a radial multiport dpv with a handpump connected thereto. Fig. 47 shows in section a spherical multiport bladder dpv with the bladder depressurised. Fig. 48 shows a plan view of the spherical multiport dpv of Fig. 47 with the bladder pressurised by the high pressure compartment. Fig. 49 shows in section two "add-on" multiport dpvs connected together. Fig. 50 shows an "add-on" differential pressure mattress. Fig. 51 shows several uniport dpvs connected in series. Fig. 52 shows in section a uniport diaphragm dpv. Fig. 53 is a cross-section along the lines NM of

Fig. 52. Fig. 54 shows in section a uniport tubular bladder dpv with tubing. Fig. 55 shows in section the uniport tubular bladder dpv alone (without tubing). Fig. 56 is a cross-section along the lines XY of Fig. 55.

Fig. 57 shows in section a spherical uniport bladder dpv with tubing. Fig. 58 is a cross-section along the lines ST of

Fig. 57. Fig. 59 shows in section a spherical uniport diaphragm dpv. Fig. 60 is a cross-section along the lines GH of

Fig. 59. Fig. 61 shows in section a guided uniport dpv. Fig. 62 is a cross-section along the lines XY of

Fig. 61. Fig. 63 is a plan view of the guided uniport dpv of

Fig. 61. Fig. 64 is a plan view of several guided uniport dpvs combined to provide a design for a multiport dpv. Fig. 65 shows in section a guided uniport dpv with a manual locking device. Fig. 66 shows in section a guided uniport dpv with an automatic locking device.

Fig. 67 shows several serial segment dpvs with internal high pressure tubing. Fig. 68 shows several serial segment dpvs with external high pressure tubing. Fig. 69 shows in section a serial segment dpv with a tubular bladder, tubing and the low pressure compartment pressurised. Fig. 70 shows in section the serial segment tubular bladder dpv of Fig. 69 with the high pressure compartment pressurised. Fig. 71 is a cross-section along the lines XY of Fig. 70.

Fig. 72 shows in section a serial segment dpv with a spherical diaphragm and tubing. Fig. 73 is a cross-section along the lines ST of Fig. 72. Fig. 74 • shows a serial segment dpv in use with folding-segment (with end panels cut away) hung on rails. Fig. 75 shows in section a serial segment dpv with a diaphragm shown both unpressurised and pressurised.

Fig. 76 shows a plan view of a differential pressure mattress.

Fig . 77 shows a detail A of Fig. 76 as an oblique view,

Fig. 78 is a cross-section along the lines XY of Fig. 76.

Fig . 79 is a cross-section along the lines VW of Fig. 76.

Fig. 80 shows an alternative cross-section along the lines VW of Fig. 76 showing a mattress with segment walls.

Fig. 81 is a detail B of Fig. 76 showing a plan view of the segment walls. Fig. 82 is a cross-section along the lines XY of Fig. 81. Fig. 83 shows a plan view of a differential pressure mattress (dpv either side of transverse segments) with only the low pressure compartment pressurised. Fig. 84 is a cross-section along the lines XY of Fig. 83.

Fig. 85 is a plan view of the differential pressure mattress shown in Fig. 83 but with the high pressure compartment now pressurised. Fig. 86 is a cross-section along the lines XY of

Fig. 85. Fig. 87 shows schematically a plan view of a differential pressure mattress with a matrix of air-cells. Fig. 88 is a cross-section along the lines XY of

Fig. 87, also showing an internal and cushion-shaped dpv. Fig. 89 is a cross-section along the lines VW of Fig. 87 of a differential pressure mattress with an impact dpv. Fig. 90 shows a plan view of a landing area with a dpv attached to cylindrical segments. Fig. 91 is a cross-section along the lines XY of

Fig. 90. Fig. 92 shows an inflatable geodesic dome with a differential pressure valve around the base. Fig. 93 shows the geodesic dome of Fig. 92 in plan view. Fig. 94 shows a multiport dpv attached to inflated hoops of a structure. Fig. 95 shows uniport dpvs connected by tubing and attached to inflated hoops of a structure. Fig. 96 shows a dome with inflatable panels. Fig. 97A shows an inflatable dome with a circular multiport differential pressure valve at the apex. Fig. 97B shows the differential pressure dome of Fig. 97A in plan view. Fig. 98 is a plan view of an inflatable dome with a multiport radial or spherical dpv at the apex. Fig. 99 shows an inflatable tent groundsheet with a differential pressure valve. Fig. 100 is a detail A of Fig. 99 showing the differential pressure valve.

Fig. 101 is an end view of an inflatable tunnel tent with a multiport differential pressure valve. Fig. 102 is a detail A of Fig. 101 showing the differential pressure valve (high presure chamber partially inflated) as an integral part of an inflatable arch. Fig. 103 is a similar view to Fig. 102 but with the high pressure chamber of the dpv fully inflated isolating the inflatable arch. Fig. 104 is a side view of the inflatable tunnel tent showing a multiport dpv attached to each arch. Fig. 105 is a side view of a differential pressure tunnel tent with infill walls. Fig. 106 is a plan view of the differential pressure tunnel tent of Fig. 105. Fig. 107 shows an inflatable building made up of polyhedron cushions inflated via uniport dpvs.

Fig. 108 shows, partly cut-away, an amusement inflatable having several types of dpv. Fig. 109 is a front view of an immersion suit with dpv. Fig. 110 is a back view of the immersion suit with dpv. Fig. Ill shows a detail A of Fig. 110.

Fig. 112 shows a casualty bag (with mattress) with dpvs. Fig. 113 shows only the mattress of the casualty bag. Fig. 114 shows a single seat liferaft with dpvs. Fig. 115 shows a detail A of Fig. 114. Fig. 116 shows in plan view an inflatable floor of the liferaft of Fig. 114. Fig. 117 shows a detail A of Fig. 116. Fig. 118 shows a liferaft with uniport and multiport dpvs. Fig. 119 is a plan view of the liferaft of Fig. 118. Fig. 120 is a plan view of an inflatable boat with uniport dpvs connected to buoyancy tubes. Fig. 121 is a plan view of an inflatable floor of the boat of Fig. 120. Fig. 122 is a cross-section along the lines XY of

Fig. 121. Fig. 123 shows an alternative cross-section along the lines XY of Fig. 121 of a floor without a keel. Fig. 124 shows another alternative cross-section along the lines XY of Fig. 121 of a floor with a stretched keel. Fig. 125 is a plan view of an inflatable boat with a separate floor and stern cover. Fig. 126 is a plan view of an inflatable boat with a differential pressure floor, bow and stern as a single unit.

Fig 127 is a cross-section along the lines XY of Fig. 126.

Fig 128 is a plan view of an inflatable canoe with a dpv.

Fig 129 is a side view of the canoe of Fig. 128.

Fig 130 shows in section a differential pressure mattress for treating pressure sores.

Fig 131 shows an alternative construction for a part of the mattress.

Fig 132 is a plan view of a wheelchair cushion with a - dpv.

Fig 133 is a cross-section along the lines XY of Fig. 132.

Fig 134 is a plan view of an inflatable splint.

Fig 135 is a cross-section along the lines XY of Fig. 134 but showing the splint inflated and wrapped around a limb. Fig. 136 is a side view of a tank with a dpv. Fig. 137 is a detail A of Fig. 136. Fig. 138 is a cross-section along the lines XY of Fig. 137.

Fig. 139 is a sectional plan view of packaging material

(for a cube) incorporating a dpv. Fig. 140 shows the packaging material of Fig. 139 held around a cube. Fig. 141 is a sectional plan view of packaging material incorporating two multiport dpvs. Fig. 142 is a sectional plan view of packaging material (or a mat) incorporating a cushion-shaped dpv. Fig. 143 is a cross-section along the lines VW of

Fig. 142. Fig. 144 is a cross-section along the lines XY of Fig. 143.

Fig. 145 is a plan view differential pressure packaging material with a matrix of air-cells. Fig. 146 is a cross-section along the lines VW of Fig. 145. Fig. 147 shows a detail A of Fig. 146.

Fig. 148 is a cross-section along the lines XY of

Fig. 145. Fig. 149 is a cross-section along the lines VW of

Fig. 145 showing a modified version of the differential pressure packaging material.

Fig. 150 shows a detail A of Fig. 149.

The drawings are not drawn to scale and are schematic showing sufficient detail to demonstrate how the invention may be put into practice. The same reference numerals are used to designate corresponding parts in the various embodiments. Segments and the external part of dpvs including collapsible ports are shown throughout the drawings in their pressurised form even though when depressurized as in some of the drawings they may be collapsed and folded flat. In certain of the drawings the segments are omitted.

Theory

First the theory underlying embodiments of the invention will be explained. Referring to Fig. 1 there is shown a differential pressure valve 1 and a low pressure segment 2 both made of impermeable, non-elastic material. Only one segment is shown connected to the only port 3 of the dpv 1 although the principles described below apply to different kinds of dpv whether uniport or multiport. The dpv has a low pressure compartment 4, a high pressure compartment 5, a flexible diaphragm 6 separating the low and high pressure compartments, an inlet valve 7 for the compartment 4 and an inlet valve 8 for the compartment 5. The external pressure is Po, which may be for example zero in space, atmospheric pressure on earth or greater than atmospheric pressure under water.

First the case where the pressure in the segment 2 is greater than external pressure will be considered. Assume that the segment 2 is filled with fluid to a volume V, at pressure P, where P, ^ Po and that the low pressure compartment 4 of the dpv contains fluid of volume V_ at pressure P, . The diaphragm 6 is displaced away from the segment port 3.

When the high pressure compartment 5 is pressurised to a sufficient pressure the diaphragm 6 will move across to close the port 3 as shown in Fig. 2 and the pressure in the compartment 5 will then be P.,. By Boyle's law:

P₁(V₁ + v₂) = P₂v_χ

To close the port P^ ^"^- P„ Eq. 2)

If the internal volume of the dpv 1 is relatively small in comparison to that of the segment 2 say

V ₂ = V../100 than by equation (1) and (2)

3 -^ 100 *1

If the dpv is relatively large, say V₂ = V,/4 then

Therefore the smaller the volume of the dpv 1 the lower P-, in the high pressure compartment before the port(s) are closed. In use the segment may be subjected to a force F as shown in Fig. 3 which displaces fluid causing the pressure in the segment 2 to increase to a pressure of P. at a smaller volume V. as shown in Fig. 3,

where P. = — ^P -2z^V—1

^{4 v}4 For the port 3 to remain closed P₅ ^ P.

In practice the model given above is modified by many other factors including the characteristics of the materials (e.g. elasticity, permability, mass, leakage), the fluids (e.g. compressibility, density) and the design of the ports (e.g. resistance to flow).

Vacuums or partial vacuums can be isolated in the segment(s) by a dpv. In this case the segment 2 and dpv 1 need to be made of a non-collapsible material with a flexible diaphragm 6 or bladder as shown in Fig. 4.

Now the case where the pressure in the segment 2 is greater than the external pressure will be considered. Initially compartment 5 is partially evacuated and sealed. Spacers 9 may be necessary if there is more than one port 3 or dpv 1. Compartment 4 and the segment(s) 2 are evacuated to a desired pressure. Fluid is then allowed into the compartment 5 as a result of which the diaphragm 6 moves across to the position shown in Fig. 5 and isolates the segment 2. Simple Examples of Invention

The fluid-filled dpv in its simplest form comprises two separate compartments, with one segment only. One basic type of dpv, referred to herein as a bladder dpv, is shown in Figs. 6 to 11. Referring first to Figs. 6 and 7 the bladder dpv has a high pressure compartment 11 which is enclosed by a flexible membrane

12 in the form of a bladder which may be elastic or elastomeric and a low pressure compartment 13 with a single port 14. In addition to the port 14 the low pressure compartment 13 has a valve 15, and the high pressure compartment has a valve 16. The high pressure compartment 11 is shown depressurised in Figs. 6 to 9.

A single segment 17 is connected, in use, to the port 14 as shown in Figs. 8 to 11. Alternatively the segment may be an integral part of the dpv and permanently attached to the dpv. With the low pressure compartment valve 15 open, the low pressure compartment

13 and segment 17 are pressurised with fluid (a liquid or a gas) via valve 15, after which this valve is closed.

The high pressure compartment 11 is then pressurised with fluid via the valve 16, after which the valve 16 is closed. This condition is shown in Figs. 10 and 11. The pressurisation of the high pressure compartment displaces low pressure fluid that surrounds it and eventually the flexible bladder 12 seals off the low pressure fluid in the segment 17.

Fig. 12 which is a view similar to Fig. 7 but to a larger scale shows the high pressure compartment 11 depressurised with the flexible and elastic bladder

12 deflated and consequently spaced away from the port 14 which is non-collapsible. A non-elastic bladder 12A is also shown in Fig. 12 in dotted outline this being an alternative form of membrane that can be used. Fig. 13 shows the high pressure compartment 11 pressurised with the port 14 closed by the bladder 12. The bladder 12, which is of tubular form, is secured at the end away from the high pressure valve 16 by a perforated collar 18 (or other means) as shown in Fig. 14. Movement of air into the low pressure compartment 13 is shown by arrows in Fig. 14.

The bladder 12 may be secured down its longitudinal length to the boundary wall of the low pressure compartment 13 opposite the port 14. This arrangement is shown in Figs. 15 and 16, the high pressure compartment 11 being shown unpressurised in Fig. 15 and pressurised in Fig. 16.

An alternative basic type of dpv is the diaphragm dpv shown in Figs. 17 and 18. A flexible diaphragm 20 separates a low pressure compartment 13 and a high pressure compartment 11. A low pressure segment 17 is pressurised via a valve 15 and a port 14. Valve 15 is then closed and the high pressure compartment 11 pressurised via a valve 16 which moves the diaphragm 20 across to seal off the port 14 and segment 17 as shown in Fig. 18.

Figs. 19 and 20 show in more detail one form that the specially shaped port 14A and the diaphragm 20 may take. In Fig. 19 a flexible, non-elastic diaphragm 20 is shown in solid outline and an alternative flexible, elastic diaphragm 20A is shown in dotted outline. The diaphragm is secured above and below the port 14 at locations referenced 21. Fig. 19 shows the high pressure compartment unpressurised while Fig. 20 shows the compartment pressurized in which case the diaphragms 20 and 20A assume the same positions.

Figs. 21 and 22 are similar to Figs. 19 and 20 respectively but show a non-elastic diaphragm 20 secured at different locations referenced 22 which in the drawings are above and opposite the colapsible port 14B. The principles already described for the unisegment model will usually be of more practical use in a multisegmented version, several examples of which are described below.

Referring now to Fig. 23, there is shown a two compartment, multiport version of a dpv which has a flexible and possibly elastic bladder 12 with the compartmental valves 15 and 16 at opposing ends and a plurality of ports 14.

An example of the sequence of pressurisation and depressurisation of the multiport dpv is as follows. Initially fluid (gas or liquid) enters valve 15 illustrated in Fig. 24 into the low pressure compartment 13 and via the ports 14 into segments 17 which in Fig. 24 are shown connected to the ports 14. Valve 15 is then closed to prevent the loss of the low pressure fluid. Fluid is then introduced via the valve 16 into the high pressure compartment 11, and when pressure in that compartment reaches a sufficient pressure above that of the low pressure compartment, the bladder 12 seals off the segments of the low pressure compartment 13, as shown in Fig. 24, preventing redistribution of the low pressure fluid. Generally, the greater the difference in the pressure between the low pressure and the high pressure compartments the more effective the sealing off and isolation of the fluid within the low pressure segments. The valve 16 is then closed and allows the segments 17, which may together comprise a mattress, to retain their present form, if not disturbed by external influences. The differential pressure valve is depressurised by following a reverse procedure. The valve 16 is opened and the fluid in the high pressure compartment 11 is allowed to exit. All segments 17 of the low pressure compartment, which were previously sealed and isolated from each other, now reform as a fluid connected unit, and will deflate together via the ports 14 if the valve 15 of the low pressure compartment 13 is now opened.

The two compartmental, multiport dpv shown in Figs. 25 and 26 has low and high pressure compartment valves 15 and 16 at opposing ends of the differential pressure valve, ports 14 and a flexible (and possibly elastic) diaphragm 20 between the low and high pressure compartments 13 and 11. In Fig. 26 segments 17 are shown connected to the ports 14 of the dpv, the low pressure compartment 13 has been inflated via valve 15 and the high pressure compartment 11 subsequently inflated, causing the diaphragm 20 to be displaced towards, and close off the ports 14 causing the segments 17 to become isolated from one another.

The low and high pressure valves 15 and 16 may be arranged such that only one fluid supply is required. The use of one inflation point is especially useful for inflatable device for emergency or military purposes such as liferafts, rescue boats, assault boats and military dummy targets. The single inflation point for inflated devices may be connected permanently or temporarily, for example to a compressed air line or bottled gas. Two versions of a single inflation point dpv are described below.

Figs. 27 to 29 show a two compartment, multiport dpv having a single inflation point 30 and a combined low and high pressure compartment valve 31. With segments (not shown) connected to the ports 14 the low pressure compartment 13 is inflated with a moveable valve member 32 of the valve 31 spaced from a valve seat 33 defined at the open end of the bladder 12 as shown in Fig. 28. The valve member 32 can be screwed down on threads 33 to close off the low pressure compartment, as shown in detail in Fig. 29, allowing the high pressure compartment 11 to be further inflated to a higher pressure. Movement of fluid through the valve 31 is shown by arrows. The expansion of the bladder 12 closes off the ports 14 causing the segments to be isolated. The valve 31 may alternatively incorporate a push and slide arrangement and/or may have an automatic arrangement for changeover upon the required pressure being obtained in the low compartment.

Figs. 30 to 31 show a two compartment multiport dpv having a diaphragm 20, a single inflation point 30 and a sliding valve member 32. The dpv is operated from one fluid supply along a length of tubing 34. Fig. 31 shows the sliding valve+ member 32 allowing fluid into the low pressure compartment 13. The sliding valve member is slid across to the right when the low pressure compartment is at the required pressure, so that the high pressure compartment 11 is then pressurised. This action can be carried out automatically by conventional pressure operated transfer valves as illustrated in Fig. 32. Consider first the case in which only one valve 35 is present (valve 36 being omitted). Valve 35 is normally open but shuts upon the low pressure compartment 13 reaching a desired pressure P whereupon the high pressure compartment is then pressurised to a pressure greater than P. The additional valve 36, if provided, is normally closed but opens when the pressure P has been reached. This has the advantage that pressurising of the high pressure compartment 11 begins only after the low pressure compartment 13 has been pressurised. To depressurise the dpv the valve(s) need to be released manually or otherwise.

A number of variations of the multiport dpv will now be described.

Fig. 33A shows a multiport dpv with a bladder 12 and low and high pressure compartment valves 15 and 16 respectively at opposite ends. This version has ports 14 of various widths, of various lengths, extending in various directions, and extending from various different parts of the low pressure compartment.

Fig. 33B shows a multiport dpv with a diaphragm

20 and adjacent low and high pressure compartment valves 15 and 16 which are remote from the low and high pressure compartments 13, 11, being connected thereto by tubing 38. The dpv can, if required, be operated remotely by electrical or other means. Fig. 34 shows a self-inflated cylinder comprising a ring of longitudinal segments 17 to one end of which a circular multiport dpv 37 is connected. Impermeable fabric membranes 38 are provided over the ends of the cylinder with a self-inflation valve or stopper 39 in one of the membranes. In order to inflate the cylinder, the segments 17 are inflated through ports 14 and isolated by pressurising the dpv 37 through the low and high pressure valves 15, 16. During inflation air is drawn into the interior of the cylinder through the valve or stopper 39 which is then closed. The cylinder so formed is of much larger volume than the volume of fluid introduced into the segments 17 and dpv 37. Uses for the principle include inflatable structures such as military dummy targets and boat buoyancy tubes. Fig. 35 shows a multiport dpv with a diaphragm

20 and many inflated and isolated segments 17. The low pressure compartment valve 15 is provided on one of the segments 17. This illustrates how the low pressure valve 16 need not necessarily be on the low pressure compartment of the dpv. The posiiton of the high pressure valve 16 can also be varied.

Fig. 36 shows how two dpvs with segments connected can be joined together in series (cascaded). The principle of two (it can be more) cascaded dpvs can be applied to any of the dpvs described herein. Segments 17A are filled at a pressure Pi via a valve 15A. Then segments 17A are isolated by filling segments 17B at a pressure P2 via valve 15B where P2 is greater than Pi. Segments 17B are then isolated filling the high pressure compartment 11B via the valve 16B to a pressure P3 where P3 is greater than P2.

In order to ensure that the bladder or diaphragm closes the or each port 14, it may be desirable to guide the relative movement of those parts. Figs. 37 to 40 illustrate how such guiding may be incorporated in a dpv having a flexible and elastic bladder 12. The dpv has opposing low and high pressure valves 15 and 16 respectively. A plurality of valve members 42 are attached to the bladder 12, each valve member being associated with a respective port 14 and mounted for sliding movement relative thereto. When pressurising the low pressure compartment 13 fluid (shown by arrows in Fig. 38) passes through any of four circular apertures 40 in the hollow cylindrical body 41 of the valve member 42 into the segment (not shown). The bladder 12 is attached along its length to an external part of the dpv (see Figs. 39 and 40). With the high pressure compartment 11 depressurised as in Fig. 39, the bladder 12 biases the valve member 42 to the position shown causing the port to remain open. An integral collar 43 at the free end of the valve member 42 prevents it leaving the port. When the bladder 12 is pressurised the head 44 of the valve member 42 is pressed against the port shoulder 45 into the position, shown in Fig. 40, in which the port is closed.

Figs. 41, 42 and 43A show how such a guiding arrangement may be incorporated in a multiport dpv with a flexible and perhaps elastic diaphragm 20. In this example the diaphragm is not attached to the guided port valve member and the valve member 42 is gently biased by a compression spring 46. The low pressure compartment 13 is shown being pressurised in Fig. 42 with the diaphragm 20 opposite and free of the valve member. The light spring 46 keeps the port valve open and fluid passes through the apertures 40 of the hollow body 41 of the valve member into the segment (not shown). Fig. 43A shows the high pressure compartment 11 pressurised with the diaphragm 20 pressing the head 44 of the valve member 42 against the port shoulder 45. The spring 46 is compressed and therefore opens the port valve once the pressure in the high pressure compartment 11 is reduced.

Fig. 43B shows an alternative arrangement in which compression spring 46 is replaced by a leaf spring 47 extending between the port shoulder 45 and the head 44 of the valve member 42 which is shown in its closed position in Fig. 43B.

The multiport dpvs described so far have had ports diposed in substantially one direction only. It is however possible to arrange the ports 14 over a substantially two dimensional area as shown in the embodiment of Figs. 44 and 45. Fig. 44 shows a diaphragm 20, which may be elastic, in the position it adopts with the low pressure compartment 13 pressurised and the high pressure compartment 11 depressurised. The low pressure segment ports 14 and a high pressure port 49 are shown. Fluid supply to the low pressure compartment 13 may be from one of the segments (not shown) entering by one of the ports 14 and passing to the other ports, to pressurise the other segments (as shown by arrows). The ports 14 are isolated by pressurising the high pressure compartment 11 via the high pressure port 49 which in Fig. 45 is shown displaced 22 degrees from its actual position in the interest of clarity. An alternative version of a radial multiport dpv with diaphragm is shown in Fig. 46. A hand-pump 50 is attached to the high pressure compartment 11. An example of a use for such a valve is at the apex of an inflatable tent with the low pressure ports 14 attached to radial segments. Alternatively, the same dpv (but without the handpump) with a tube and a valve connected on the high pressure compartment can be inflated by mouth on the inside of the inflatable tent.

Figs. 47 and 48 illustrate an embodiment of the invention in which the ports 14 are arranged around a three dimensional space. A spherical multiport dpv with bladder 12 is shown with the high pressure compartment 11 depressurised in Fig. 47 and pressurised in Fig. 48. The low pressure ports 14 can be numerous and anywhere on the sphere (such as the alternative port 14A illustrated with dashed lines), apart from where the high pressure port 49 enters.

The dpv shown in the drawings in this particular example has four low pressure ports. The valve can be employed in a similar manner to the radial multiport dpvs described immediately above. Fig. 49 shows two multiport dpvs 51, 52 which are each constructed as an "add-on" unit with a flexible (and possibly elastic) diaphragm 20 and which are connected together in series. In a similar manner such "add-on" units can be made from bladder dpvs. There are low and high pressure valves 15 and 16 at both extremes of the extended differential pressure valve with interconnecting valve ports 53, 54 between adjacent units. This add-on version is suitable for building up a differential pressure valve of any required length (and any number of ports) .

Fig. 50 shows a mattress made up of a multiplicity of modules each of which comprises a dpv with segments connected thereto. In this way a mattress of as great an area as required can be built up. The chain dotted lines in Fig. 50 illustrate the boundaries of the modules. This form of differential pressure mattress makes use of "add-on" differential pressure valves as described in Fig. 49. Fig. 50 shows, by way of example, parallel differential pressure valves 55 and 56 each made up of several "add-on" differential pressure valves. They have their low and high pressure compartments (13 and 11 respectively), connected on one of the sides of the mattress to low and high pressure supply lines (57 and 58 respectively) which are pressurised and depressurised via valves 15 and 16. So as to form as continuous a surface as possible, the high pressure compartment would optimally be smaller in relation to the segments 17 than shown in Fig. 50.

A number of variations of the uniport dpvs shown in Figs. 6 to 22 will now be described.

Fig. 51 shows a plurality of uniport dpvs connected in series by tubing. Each segment port 14 is connected to a segment 17 (one only shown in dashed outline) . The low pressure compartments 13 have ports 60 which are interconnected by tubing 61 to a fluid supply connected to the low pressure valve 15. Similarly the high pressure compartments 11 are connected by tubing 62 to a high pressure valve 16.

The uniport dpvs described below have elastic membranes which is by way of example only as flexible and non-elastic membranes are equally suitable. Low and high pressure as applied to valves, compartments, tubing is relative only.

The high and low pressure valves 15, 15 can occur anywhere along the tubing 61 by making use of T piece connectors. Conventional transfer valves and a sliding-valve can be utilised, as described earlier for multiport dpvs, so that the uniport dpvs can be inflated and isolated from a single fluid supply. The distal uniport dpv from the fluid supply has stopper valves 63 and 64. Uniport dpvs can be used in series with multiport dpvs.

Figs. 52 and 53 show in some detail a suitable form for a uniport dpv having a flexible, elasticated diaphragm 20. Upon pressurisation of the low pressure compartment 13 via a low pressure compartment port 60 the diaphragm 20 moves away from the segment port 14.

Pressurisation of high pressure compartment 11 via the high pressure compartment port 63 causes the diaphragm 20 to close the segment port 14.

Figs. 54 to 56 show a uniport dpv with an elasticated bladder 12. Upon pressurisation of the low pressure compartment 13 via the tubing 61 the bladder 12 moves away from the segment port 14. Pressurisation of the high pressure compartment 11 via the high pressure tubing 62, which in this case is coaxial with and within the low pressure tubing 61, causes the bladder to close the port 14. The uniport dpv with tubular bladder 12 has coaxial low and high pressure compartment ports 60 and 63 respectively as shown in Fig. 55. There are spacers 65 between the low pressure compartment ports 60 and the high pressure compartment ports 63 as shown in Fig- 56. Figs. 57 and 58 show another form of uniport dpv having an elasticated spherical bladder 12. Upon pressurisation of the low pressure compartment 13 via the low pressure tubing 61 the segment is inflated via the segment port 14. Pressurisation of the high pressure compartment 11 via the high pressure tubing 62 causes the bladder to close the segment port.

Figs. 59 and 60 show a uniport dpv having an elasticated circular diaphragm 20 angled obliquely both to the segment port 14 and to high pressure compartment port 63. This uniport dpv is similar to the spherical uniport bladder dpv shown in Figs. 57 and 58 above. The low pressure compartment port 60 has been omitted from Fig. 59 for clarity. To provide efficient closing of the segment port

14 a close fitting guided port valve member may be attached to the diaphragm or bladder in a similar way to that already described above for a multiport dpv with reference to Figs. 37 to 43. Such an arrangement is shown in Figs. 61 to 63. Upon inflation of the low pressure compartment 13 via the low pressure compartment port 60 the guided port valve member 70 moves away from the port 14 allowing air (or other fluid) to enter the segment via apertures 40 in the hollow guided port valve member as shown by arrows in Fig. 61. Air also passes on to the next dpv.

Referring to Fig. 62, channels 71 are provided allowing air to pass around the guided port valve member 70 even if the port valve is in the closed position. Spacers 72 prevent the valve member 70 from leaving the port 14. In order to close the port 14 to isolate the segment connected thereto the high pressure compartment is pressurised via the high pressure compartment port 63 which forces the head 73 of the valve member 70 against a rubber "0" ring 74 providing an efficient seal.

Uniport dpvs of the kind shown in Figs. 61 to 63 can of course be made up into a multiport dpv with low and high pressure valves 15 and 16 as shown in Fig. 64.

Fig. 65 shows a guided uniport dpv in a closed position. The dpv is generally similar to that shown in Figs. 61 to 63 but has a security screw 75. After automatic closure of the valve member 70 and the apertures 40 by pressurisation of the high pressure compartment 11 the valve can be manually secured in the closed position, perhaps more firmly, by the security screw 75. The port valve 14 then remains closed and the segment isolated even if the high pressure is released. The security screw can be used to isolate a given segment, perhaps one which is punctured, and other interconnected uniport dpvs in use can still be inflated, isolated and deflated due to the fluid bypassing the secured dpv via the channels 71. In Fig. 65 the low and high pressure compartment ports are not shown.

Fig. 66 shows a guided uniport dpv with an automatic temporary locking device. The locking device shown as an example comprises a protrusion 76, which can be spring loaded, on the valve member 70 and a similarly shaped hollow 77 in the port 14. Other temporary locking devices could include a tapered port valve head. In the embodiment shown a part of the diaphragm 20 replaces the "0" ring 74. After the low pressure compartment 13 is inflated and the high pressure compartment 11 pressurised at pressure Pi causing the valve member 70 to close and lock, the high pressure compartment can be deflated and the valve member will remain in its closed position. The member 70 can be released either by applying pressure P2 to the low pressure compartment where P2" P1 or by apply- ing a partial vacuum to the high pressure compartment. Release by use of a partial vacuum can be carried out on a dpv where the high pressure compartment is of rigid or semi-rigid material such as moulded plastic rather than flexible sheeting such as PVC. Fig. 67 shows a plurality of dpvs and segments connected in series with the segments 17 alternating with the serial segment dpvs 80. A serial segment dpv such as that shown in Fig. 67 enables segments to be connected in series rather than in parallel. The dpvs are connected by high pressure tubing 62 from the high pressure valve 16 that goes through the centre of the segment. For all the dpvs the low pressure fluid supply to the dpv is via one or more of the segments 17. Upon the fluid entering the low pressure valve the segments 17 pressurise one after the other in series. The pres¬ surisation of the high pressure compartment via the tubing 62 isolates each of the segments 17 from each other. An example of such an arrangement is described in more detail below with reference to Figs 69 to 72. An alternative arrangement is for the high pressure tubing 62 to be external to the segments 17 as shown in Fig. 68. Details of a serial segment dpv of this sort are shown in Figs. 72 to 73.

Figs. 69 to 71 show a serial segment dpv having a flexible tubular bladder 12. Upon the pressurisation of the low pressure segment 17 the low pressure compartment 13 pressurises moving the bladder 12 to the position illustrated in Fig. 69. The pressurisation of the high pressure compartment 11 via the high pressure tubing 62 results in the bladder 12 filling out and obstructing the low pressure compartment 13 by pressing against the shaped walls thereof as shown in Fig. 70. There are spacers 65 between the coaxial low and high pressure ports 60 and 63 respectively as illustrated in Fig. 71. The serial segment dpv shown in Figs. 72 and 73 has an elastic spherical bladder 12. Upon pressurisation of the low pressure segment 17, the low pressure compartment 13 pressurizes. The high pressure tubing 62 is connected to the high pressure ports 63 externally of the segments 17. The high pressure compartment 11 is pressurised via the high pressure ports 63 causing the bladder 12 to adopt the position shown in Fig. 73 and isolate the adjoining segments 17.

Fig. 74 shows a serial segment dpv which has flat segments 17A that are hung on rails 81. Fluid enters the low pressure valve 15 and passes into the first segment and through an interconnecting aperture 82 to the next segment (air flow shown by dashed line in Fig. 74). The fluid then passes through a serial segment dpv 80 to the next segment (movement of segments shown by large arrow) . By pressurising the high pressure compartments of the dpvs through the pressure valve 16 segments are isolated in pairs.

Fig. 75 shows a suitable form of construction of a dpv with a diaphragm 20 for use in the embodiment of Fig. 74. Fluid entering the segment port 14 from a segment raises the diaphragm allowing the fluid through the low pressure compartment 13 (air flow shown by solid line in Fig. 75). When the high pressure compartment 11 is pressurised the diaphragm 20 is closed and the segment port 14 is sealed.

Three serial segment dpvs are described above as examples only. It will be appreciated that the various types of uniport dpv described earlier except those with guided segment ports can have their designs simply modified to be serial segment dpvs. The modification to the uniport dpvs involves the removal and closure of one of the three ports (low pressure compartment, high pressure compartment or segment ports) so that only two ports remain. General Comments

The external walls of the dpv comprising of the low pressure compartment and perhaps part of the high pressure compartment, can be made of flexible or non-flexible, elastomeric and non-elastomeric material impermeable material. Materials include coated, non-coated, impregnated, reinforced materials such as plastic sheeting, rubbers, synthetic rubbers, fabrics and metal foils for use with air mattresses, inflatable boats and other conventional inflatable devices, or more rigid materials such as unplasticised polyvinyl chloride and other thermoplastics or even metals if corrosive, toxic, or inflammable fluids are to be contained or armour plating is required. In embodiments of this invention, if an individual segment is punctured or damaged it can be replaced, rather than use patches or replace the whole device. The low pressure segments may be attached to the differential pressure valve and a permanent bond made between the segments and the ports at some stage in their manufacture or use. Indeed, in some applications the differential pressure valve may be made, at the same time, from the same piece of material, and be inseparable from, the low pressure segments. The segments themselves, whether or not permanently bonded to the ports, may be temporarily attached (using for example VELCRO fasteners) to each other along their entire length, or only partially attached with ventilation and drainage gaps, or not attached at all. The dpvs although often illustrated as being attached to the end of cylindrical segments can be attached in any position relative to the segments as long as the dpv (whether multiport or not) is attached by the segment ports to each segment. For example the multiport dpv may be positioned on top of and obliquely across the segments if required. The dpv can be on the exterior or on the interior of the segments. The segments, although in most cases shown as cylinders, can be of any shape or size. Individual segments may themselves be subdivided, quilted or provided with baffles in the manner of conventional inflatable devices.

The low pressure segments can be polyurethane foam-filled. When the foam-filled segments of the inflated device are transported or stored in a folded up or compressed manner there is relatively little air in the segments. Upon the foam-filled inflatable device being unfolded with the low pressure valve open, air is drawn into the segments as the foam expands. The segments can be isolated by the high pressure compartment in the usual way. Mattresses, such as those for hikers, are a suitable application for a dpv incorporated into a foam-filled device. A dpv can be attached to segments comprising impermeable fabric held together by continuous tie lines. These pneumatic sandwich plates with nylon threads between them are especially useful where additional strength and rigidity is required such as for inflatable structures.

To facilitate the conveyance of fluids through the ports, they can be designed and suitable material used, so as to make them non-collapsible. Collapsible ports, on the other hand, may create increased resistance to the filling and emptying of the segments (via the low pressure valve and the low pressure compartment) . Some form of collapsible ports or standard non-return valves with expanding slit apertures may be employed to prevent the rapid depressurisation of the segments. If rapid deflation were required when employing ports with high resistance such as collapsible or non-return valve ports, then deflation valves would be necessary on each segment. The portion of the port that forms a fluid-seal in contact with the inflated high pressure compartment can be specially shaped, and made from a suitable material, so as to provide an efficient seal (and similarly for the opposing surface of the high pressure compartment that forms a seal with the port) .

The use of the low pressure segments connected to the differential pressure valve can, for example, be load bearing where a load, force or pressure is applied externally to the segments. Another use of the low pressure segments is as a container or as a store of fluids. In most circumstances the overall volume of the container or load bearing low pressure segments, when connected and pressurised via the low pressure ports, will be of a much larger volume than that of the high pressure sealing compartment when inflated.

More complex forms of the differential pressure devices have one or more differential pressure valves. These can be "add-on" units arranged in series. Differential pressure mattresses for example can be made to cover any required area, and yet still be operated via one low and high pressure compartment valve. Any of the dpvs, such as uniport, multiport and serial segment dpvs can be joined to the same type or any different type of dpv directly or by tubing. By virtue of connectors, such as T pieces and tubing dpvs can occupy any position within reason in one dimensional (in series), two dimensional (in a plane) or three dimensional space. Tubing is connected from one dpv's low pressure compartment to that of another dpv's low pressure compartment. Similarly tubing connects high pressure compartments of dpvs. Fig. 108 illustrates this technique applied to an inflatable amusement apparatus. Although low and high pressure valves are illustrated both the low and high pressure fluid can be from a single source as described above.

Fluid-filled mattresses available at present have basically a two dimensional form with one layer of pressurised segments which are individually inflated. An embodiment of the present invention may comprise many layers of segments with each layer composed of multiple segments; the device can be pressurised through one or two inflation points.

Most applications of this invention are expected to employ the same fluid in each of the two basic compartments. However two different fluids may be utilised in the two basic compartments. For example a liquid can be used to pressurise the low pressure segments which can then be isolated by a gas in the high pressure compartment or vice versa.

In certain situations, where a permanent sealing of the low pressure segments is required or the risk of depressurisation of the high pressure sealing compartment is unacceptable; the fluid within the high pressure compartment may be such as would allow conversion, once the required pressure in that compartment was reached, into a gel or solid by chemical, thermal or other means. To aid acquiring adequate pressure for the high pressure compartment the dpv can be made of transparent or translucent material with the diaphragm or bladder made of a coloured material. This allows the user to distinguish when the high pressure compartment is pressurised enough to cause the diaphragm or bladder to close off the ports, thereby isolating the segments. The pressure of the fluid within the compartments may be controlled by a simple conventional pressure regulator, either placed within the valves or in a pump used to pressurise the compartments. The inclusion of pressure indicators would aid acquiring suitable differential pressures. As the volume of fluid contained by the high pressure compartment is generally small relative to that of the low pressure compartment, a small pump can be permanently attached to a high pressure compartment valve, to provide a small volume of fluid under high pressure when incorporated, for example, in the design of a fluid-filled mattress. Methods of providing fluid pressurisation can include breath (air), electrically or manually operated pumps (fluids) and pressurised bottles (gas).

The high pressure compartment effectively seals off the low pressure segments so that in certain situations the use of only a high pressure valve is adequate. However, the use of a low pressure valve has its advantages, in that it prevents foreign bodies, such as dirt, entering the low pressure segments. Also, if there is some leakage from the low pressure segments it prevents the loss of fluid to outside the device.

Leakages from the low pressure segments could occur when the differential pressuress are incorrect for the conditions of use or if the load upon one or more segments is so great that fluid is forced past the high pressure compartment seals. In this situation some loss from a particular segment would occur with the excluded fluid generally transferred to the neighbouring segments. With an impact upon a particular segment the transference of fluid acts as a shock absorber and subsequently reduces or dampens the impact and recoil to the impinging object. A valve on the low pressure compartment prevents loss of fluid when redistributing fluid among the low pressure segments, such as when employing the contouring properties of the differential pressure mattress. Non-return compartment valves (which can be "released" for the two-way movement of fluid if required) allow for the inflation of the differential pressure devices without a loss of fluid, for example in the case of an air mattress inflated by breath. i will be appreciated that the valves for the low and high pressure compartments may simply take the form of a stopper or similar device.

Uniport and multiport dpvs in general operate on the same principles. Some principles have been described above for uniport dpvs and not multiport dpvs and vice-versa. It should be undertand that features described above in respect of one embodiment may, where possible, be applied also to other embodiments.

Various properties and advantages provided by certain of the embodiments described above will now be indicated. The low pressure segments may provide a load bearing mattress which has the property, under certain conditions, of retaining the shape of the surface placed upon it. This is referred to herein as "contouring". Contouring is achieved by inflating the mattress with the load above the mattress at a height less than that achieved at the fullest extent of inflation. The low pressure segments are pressurised and follow the surface shape, that is the contour, of the load which is in contact with the mattress. The high pressure compartment is then inflated and the low pressure load segments thereby sealed. A property of a fluid is that equal pressure is exerted in all directions. Within the limitations of the flexibility and other properties of the impermeable material of the mattress the force per unit area exerted by the mattress on the load and, conversely, by the load on the mattress, is approximately the same on all parts of the surface in contact. When the load is removed the mattress retains the same basic shape of the surface that was in contact with the load, as when the load was upon it. This contouring property of the mattress is enhanced if the underside of the mattress, that is the side opposite to that surface in contact with the load, is adhered to a rigid structure and, more important, if the impermeable, flexible material of the mattress also has elastic properties.

The invention has the ability to produce a shaped surface, which can be reformed an almost infinite number of times by repeating the contouring procedure.

The mattress, after contouring has been carried out, gives greater stability and support to the load that it is shaped to and that is upon it.

A greater amount of contouring detail is achieved with as many and as small segments as possible. The low pressure segments can be arranged as a matrix and sealed, if required, by the high pressure compartment in the form of a grid. Within a given area, for example, a matrix of 10 by 10 (that is 100) low pressure segments would give greater surface detail than a matrix of 16 segments, arranged 4 by 4. Segments of the grid can be either adjacent and completely separate or attached to each other to form a continuous surface. Embodiments of this invention allow for the design and benefits of multi-segmented fluid-filled devices by the pressurisation of a minimum of two compartments, one of low and the other of high pressure. An advantage of this is that it allows for the low pressure compartment to be subdivided into an almost infinite number of load bearing or container segments connected via the low pressure ports and pressurised through a low pressure compartment valve and then for these segments to be sealed by high pressure fluid entering the high pressure valve into the high pressure compartment. The dpv allows the practical use of more pressurised segments, with fewer valves thereby reducing costs and the inconvenience of pressurisation or the containment of isolated pockets or segments of fluid through a large number of valves.

It is possible to employ a larger number of pressurised segments in the same volume, than has been practical hitherto, with the advantage that each individual segment is of smaller dimensions. In a mattress where the segments are basically of a cylindrical shape with hemispherical ends, the smaller lateral width across the cylinder also means a smaller vertical dimension, which is of the same order as the lateral width, resμlting in a thin-layer mattress. It is therefore possible to provide a practical multisegmented, thin-layer mattress.

The practical design of a fluid-filled device with a large number of segments enables any bulk flow or movement of the pressurising fluid in the low pressure segments to be contained within the small volume of that segment. The greater the number and the smaller the volume of an individual segment, the less bulk movement of the low pressurised fluid results. Bulk movement of fluid in the segments can, for example, be brought about by mechanical force upon the exterior of a differential pressure device (such as a mattress) or by thermal convection. A force applied over a small area of the surface of the load bearing or container segments could badly distort large volume segments of fluid-filled devices, such as mattresses, that are presently available. The greater practical number of pressurised segments now possible with this invention compared with conventional fluid-filled mattresses means that a force, over a relatively small area, impinging on the surface of the mattress causes less bulk movement of fluid and therefore less distortion of the mattress. The confinement of the bulk movement of fluid to within a smaller segment, also results in a reduction in convection currents and makes embodiments of the invention suitable for use in the field of thermal insulation. This is especially so in view of the poor thermal conduction of liquids and gases which generally have excellent properties of thermal insulation under the conditions described.

An advantage of embodiments of the invention is to provide a fluid-filled device where if one of the load or container segments is punctured, the remaining segments will remain pressurised.

The invention allows for the inflation, isolation and deflation of the low pressure compartments remotely, by the use of extended ports, for example, in the form of tubing between the dpv and the low pressure segments. If the segments are all in close proximity it is more economical in material to have just a pair of extensions (or one common extension) to the low and high pressure compartment valves.

The threshold pressure at which fluid is forced through a "closed" low pressure segment port from a segment back into the low pressure compartment of a differential pressure valve and then into neighbouring segments can be selected by adjusting the pressure in the high pressure compartment. The movement of fluid from the normally isolated segment(s) can act as a shock absorber and reduce recoil imparted by the impact cushion/mat/mattress upon the impinging object. The fluid within the low pressure segments (impact cushions) can thereafter be redistributed and the pressure equalized in all segments by the deflation and inflation of the high pressure compartment, in readiness for subsequent re-use.

Various specific applications of the invention will now be described. In the applications and the examples given below a particular dpv is shown by way of example only. Where a bladder dpv is shown a diaphragm dpv can be substituted and vice versa except where ports are required either side of the dpv, in which case a bladder dpv may be required. Where a multiport dpv has been illustrated, it can often be replaced by several uniport dpvs. Where one or more separate dpvs are illustrated these can be connected by tubing and inflated from one inflation point such as a compressed airline or by bottled gas as described earlier.

It is expected that this invention will have many more applications than mentioned here, for example specialised industrial applications.

Devices which utilize a dpv (for example a mattress) will on occasion but not always be prefixed by the term "differential pressure" (for example reference will be made to a "differential pressure mattress"). A. Fluid-filled beds/mattresses and furniture for use on land or water (including gymnasium, sports, camping and domestic use) .

The invention lends itself to the design of novel forms of fluid-filled beds/mattresses (such as airbeds/mattresses and waterbeds/mattresses) and inflatable furniture (e.g. seats) which are portable when depressurised, and have their use in leisure activities on land and water, gymnastics, sports, camping or domestic use. A dpv may be incorporated into many of the conventional inflatable articles currently available with the benefit of a reduced number of points of inflation (valves) but the provision of several isolated segments. The connections between the low pressure ports and load bearing segments would in most such cases be permanently bonded.

It is practical with a dpv to have a larger number of isolated compartments inflated through two valves to provide fluid-filled differential pressure beds/mattresses and other inflatable furniture which, compared to fluid-filled beds/mattresses available at present, will have a more even surface and less bulk movement of fluid if the individual's weight is poorly distributed over the uppermost surface. Inflatable furniture and inflatable novelty goods can be of more intricate shapes and have better pneumatic stressing due to the provision of many segments and less bulk movement of fluid. The smaller volume of an individual segment gives a relatively even surface even if one segment is deflated. The remaining inflated segments can still be used with a fair degree of comfort. The site of a puncture can be easily located for the repair to be made or the punctured segment can be replaced. The use of more segments than found on a conventional airbed, for example, would allow for a thin layer design with a smaller volume of air required to pump up the mattress. The designs shown below can be used as gymnasium mats, crash mats, trampoline spotting decks and landing areas. All designs are shown as having just one layer of differential pressure mattress. For sporting activities especially, two or more layer designs with one mat upon the other (enclosed together in a cover or taped etc. together), give less risk of bottoming out occurring due to loading or a punctured segment; this is especially so if the segments in adjacent layers are transverse to one another. The top mattress can be made to be softer than the bottom mattress by the low pressure segments of the top mattress being of lower pressure and/or of more flexible/elasticated material than the bottom mattress.

Fluid-filled beds/mattresses may be made for example from rubber, synthetic rubber or plastic sheeting with/without coatings or fabric reinforcement which has been high frequency or heat welded, glued and/or stitched together. Figs. 76 to 82 show an airbed/mattress which incorporates a dpv with a diaphragm 20, reinforced ports 14 and low and high pressure valves 15, 16 inflating and isolating many segments 17. A detail of the reinforced port 14 and welded/joined 100 material is shown in Fig. 77. Fig. 78 shows in cross-section the reinforced port 14, the high pressure compartment 11 and the three-quarter circum¬ ference diaphragm 20 joined to and between the external walls of the dpv. At each end of the dpv its opposing external walls are welded together forming a flat sandwich with the diaphragm in the middle. The segments 17 can be ribbed with the top and bottom sheets 101, 102 joined 100 directly together as shown in Fig. 79; alternatively, segment walls 103 may be welded/joined 100 between the top and bottom sheets 101, 102 to provide a more even surface as shown in Fig. 80. The segment walls 103 are folded and joined 100 together in between the top and bottom sheets at each end of the longitudinal segment 17 (see dotted lines in Fig. 81). The folded segment walls 103 joined 100 to the top and bottom sheets are shown in cross-section in Fig. 82. this is a suitable design for a water-bed/mattress with water in the segments and either air or water in the isolating high pressure compartment. A differential pressure mattress with a flexible and possibly elastic diaphragm 20 and transverse segments 17 is shown in Figs. 83 to 86. Figs. 83 and 84 show the low pressure compartment inflated and the high pressure compartment deflated, while Figs. 85 and 86 show the high pressure compartment inflated. Air movement from the low pressure valve 15 via the ports 14 to the segments 17 is shown by arrows. The cross-section in Fig. 84 shows the diaphragm 20 clear of the port 14 and separating the low and high pressure compartments 13, 11.

The mattress is formed as a whole, with the low pressure segments 17 an integral part of the low pressure compartment. The fluid-filled mats/mattresses shown in

Figs. 87 to 89 have a matrix of segment cells 17. The segments are inflated and isolated via low and high pressure valves 15, 16 causing bladders 12 to close the ports 14 of the dpv. The dpvs are shown in Fig. 89 within the inflatable segments 17 of the mat/mattress. As an alternative to the tubular bladder 12 a "cushion-shaped" dpv in the base of the mat with a diaphragm 20 between the low and high pressure compartments may be provided as indicated in Fig. 88 on the right hand side. The "cushion-shaped" dpv has the high pressure compartment at the base of the mat to prevent "bottoming-out" occurring and is similar to that shown and described in further detail in Figs. 142 to 144. A dpv with many ports instead of one or two ports is especially suited for impact absorption (described later) and is shown in cross-section in Fig. 89.

Figs. 90 and 91 show a mattress especially suited as a landing area which has inflatable cylinders 106 (or other convenient shapes) attached via the ports 14 to dpvs, all enclosed in a cover 107. The inflation and deflation via the low and high pressure tubing 61, 62 may be by a manual or electric pump 108 and controller 109. Tapes or VELCRO 110 may link the inflated cylinders 106 under impact as shown in the cross-section in Fig. 91. For optimum absorption of impact the cylinders are made from elasticated material, similar to that of bicycle inner tubes. The electric pump 108 and controller 109 are optional to facilitate impact absorption as described later with reference to impact cushions.

Designs shown in Figs. 113, 130, 131 and 139 to 150 are suitable as, or can be modified, for use as fluid-filled mattresses.

B. Impact Pillows and Landing Mats

The differential pressure valve can be attached to low pressure segments in the form of impact pillows for shock absorption. The dpv can be used with fluid-filled bags which inflate just before accidental impact, such as -an automobile passenger safety restraint device. The low and high pressure compartment valves can be, for example, of the extended type and controlled remotely by electrical means. All designs of fluid-filled beds/mattresses described above with suitably adjusted low and high pressure will act as impact landing areas. Differential pressure landing areas can be used for sports or by the fire-service for escape from high buildings. Impact cushions can be utilized with large parachuted loads, etc.

For certain applications it will be desirable to provide many large ports between the low pressure compartment of the dpv and the impact segments to facilitate the rapid transfer of fluid. Such an arrangement is shown in Fig. 89.

Recoil may be absorbed by fluid being allowed to transfer from the inflated segment under impact to a neighbouring segment. The difference in the low and high pressure compartments needs to be such as to provide efficient shock absorption. However, redistribution of the air and the equalization of pressure in the inflated cylinders is then necessary. This can be carried out by releasing and reapplying the high pressure by hand or by electrical means as shown in Figs. 90 and 91.

C. Inflatable Swimming Pool Cover In this application, the differential presure valve will normally be connected at one end of the pool to the floating low pressure segments which cover the pool's surface. When not in use the cover can be stored in its deflated form in a roll, for example, by. the side of the pool. The volume of the deflated pool cover is less than for conventional pool covers. When the cover is unrolled and inflated with air it provides a cover with excellent properties of thermal insulation. It will also float on the water surface and retain its shape over the whole of the pool's surface. If the final inflation takes place while it is on the surface of the water (and if its unrestricted size is slightly bigger than the surface area of the pool) it provides a relatively tight fit right up to the edges of the pool with improved thermal insulation. The provision of a reflecting surface on the differential pressure pool cover further enhances its properties of thermal insulation.

D. Inflatable Structures including Tents (with inflatable groundsheets) , Domes, Liferaft Canopies and Buildings.

These inflatable or pneumatic structures are suitable as permanent structures but are especially useful for temporary or emergency purposes. The structures described are suitable for camping, exhibition and sports covers, military storage, hospital units, greenhouses (transport polythene sheeting), radomes and other uses. They can be portable, have good thermal insulation, low cost, low storage volume, and are simple to erect. The invention allows for a large number of isolated segments, which makes possible the design of complex shapes which have good stability due to being pneumatically-stressed and bulk movement of fluid is inhibited. The low pressure segments when utilized as an inflated double skin gives good properties of thermal or acoustic insulation, especially if coated with reflective or other thermal or acoustic coatings. Windows, in the form of low pressure segments made from transparent plastic such as polythene sheeting will have similar properties to double glazed windows.

In structures which are air-inflated (but not air-supported), where metal or wooden supports have been replaced by inflated tubes, air beams, hoops or arches, these supports represent the segments of the low pressure compartment. These segments can be connected to the ports of a dpv and all inflated at the same time and sealed by the high pressure compartment instead of each individual support being inflated and sealed individually. The inflation, sealing and deflation can be carried out from just two compartment valves or by one source, such as bottled gas, with a changeover valve as described earlier.

Referring now to Fig. 92, a tent structure is formed from inflatable hoops 110, instead of poles, in sewn-in sleeves, to form a geodesic dome shown without an outer tent. There is the stability of the geodesic design but without the cost and weight of the poles. The differential pressure valve 109 with low and high pressure valves 15 and 16 is connected to each end of the hoops 110 at the base of the tent. The apex 111 of the dome, midpoint 112 and entrance 117 of the low hoops of the tent are also shown.

In the plan view the outer flysheet 113 is shown in Fig. 93 stretched over the inner tent 114 and separated by the low pressure inflatable hoops 110 which give even spacing for thermal insulation. Each hoop is divided, in this example, into two separate chambers at the apex 111. This results in 6 separate chambers which are initially inflated via the low pressure valve 15 and then isolated via the high pressure valve 16 in the dpv (109, bladder or diaphragm not shown) attached to the base of the hoops. The lower hoops may also be divided mid-way to give a total of 8 chambers in all. The inflation of the dpv causes the groundsheet (not shown) to spread out fully. The dpv can be away from ground providing additional bracing of the tent's structure. Continuous multiport dpvs or several uniport dpvs can be part of or connected to the inflatable hoops 110. A continuous multiport dpv with diaphragm 20 is shown in Fig. 94 connected to the inflatable hoops 110. Alternatively as shown in Fig. 95 low and high pressure tubing 61, 62 may be connected to individual dpvs shown with diaphragms located at the base of each hoop 110. Adjacent hoops may be suitable with continuous multiport dpvs while spaced hoops with infill cover are generally preferred with interconnected uniport dpvs (although where uniport dpvs may be preferred following figures may show a multiport dpv schematically). The high pressure compartment 11 of the dpv may be of such a quality and material as to almost exclude the possibility of puncture by accident (this applies to the high pressure connecting tubes and valve as well).

The inflatable hoops may be attached to either the inner or outer tent or attached to both the inner and outer tent fabric separating the two. Two superimposed hoops (in the radial direction if connected to a radial or spherical dpv) either independent or as interconnecting segments will provide a greater separation between the inner and outer tents.

Fig. 96 shows a tent structure with inflatable segments 17 forming panels. In this case the high pressure compartment 11 is located in the arches or hoops 110 of the dome. The low pressure inflatable panels act like inner and outer tent surfaces. The arches separate and give even spacing to the two layers of the low pressure panels providing efficient thermal insulation even in bad weather. All the panels are inflated initially via one low pressure valve 15 and the arches interconnected at the apex 111. The ports 14 of the panels are then isolated by the pressurisation of the high pressure compartment 11 via the high pressure valve 16.

In the arrangement shown in Figs. 97A and 97B the dpv is towards the apex 111 of the tent. The entrance 117 is also shown. The principles shown in Fig. 35 are utilised here for the dpv with one of the low pressure semi-hoops 110 having the low pressure valve 15. The high pressure valve 16 is attached to tubing 62 which goes to the high pressure compartment of an endless multiport dpv as seen in Fig. 97B. The low pressure air flow via the low pressure valve 15, one semi-hoop 110 and the ports 14 of the dpv to other semi-hoops is shown by arrows in Fig. 97B. A radial or spherical multiport dpv (see Figs.

44 to 48) with low and high pressure valves 15 and 16 is shown in the apex of an inflatable structure in Fig. 98. The use of a radial or spherical dpv 112 shown in Figs. 44 to .48 does away with the need for high pressure tubing 62 and allows the high pressure compartment to be pressurised by an attached hand pump or other means on the inside of the tent.

A differential pressure air mattress/groundsheet can be incorporated into a tent's design in the same way as a sown-in groundsheet. A design suitable for the domed tent described above is shown in Figs. 99 and 100. It is used as a groundsheet in its deflated form and when the segments 17 are inflated and isolated they provide a comfortable mattress. When inflated there is a minimum of bulk movement giving good feeling of stability to the occupant of the tent. It also has good properties of thermal insulation. The area covered by a tent's groundsheet can be relatively large in area, and if it was substituted by a conventional air mattress with a small number of compartments would make a bulky mattress. A conventional mattress of many separate compartments would be inconvenient in the number of valves to open, inflate and to close.

The differential pressure mattress/groundsheet could be also- inflated at the same time as the tent above it. However if the differential pressure mattress/groundsheet has the provision of a separate differential pressure valve (with low and high pressure valves 15 and 16 respectively) to that of the inflatable tent, it can be deflated converting the night-time air mattress to a day-time groundsheet with the tent covering remaining inflated and erect. In the detail of Fig. 100 the low and high pressure valves 15, 16, diaphragm 20, segment ports 14, and segments 17 are shown.

The cross-section of a hoop 120 of an inflatable tunnel tent, with multiport dpv incorporated into the base of the tent's hoops is shown in Figs. 101 and 104. The lowest pressure hoops 120 are inflated via the low pressure compartment 13 and the ports 14 as shown in Fig. 102 (the high pressure compartment 11 is shown not pressurised in Fig. 102). The inflation of the high pressure compartment 11 isolates the port 14 and hoop 120 as shown in Fig. 103. The multiport dpv with a diaphragm 20 is shown in Fig. 104 with inflation and isolation by low and high pressure valves 15 and 16 respectively. Alternatively the hoops can each have an uniport dpv connected by tubing and inflated and isolated by low and high pressure valves as shown earlier in Figs. 94 and 95.

A tent with air-filled hoops 120 attached to a multiport or several uniport dpvs 121 and with an in-fill cover 131, of for example canvas or coated nylon, is shown in Figs. 105 and 106 (outer tent not shown in Fig. 105). The dpv with low and high pressure valves 15 and 16 is shown in Fig. 105 with ports 14 in the bases of the hoops 120 between the inner and outer tents 132 and 133. An air-inflated building can be made with walls and the two slanting sides of a roof each composed of adjoining segments attached to a dpv in a similar manner to an air mattress.

Fat pneumatic cushions may form structural shapes of virtually any kind. A dome is shown in Fig. 107. The inflation and isolation of the polyhedron cushions 140 is by a uniport dpv 141 connected by low pressure and high pressure tubing 142 and 'T* pieces 143 to the low and high pressure valves 15 and 16. An entrance 144 is shown.

The designs for domes or geodesic structures can be utilised as a liferaft canopy, inflatable tent or inflatable dome as in the examples given above. Liferaft canopies may have inflatable guttering at the base of the canopy which is not illustrated. The liferaft canopies may be inflated via the buoyancy tubes rather than have a separate inflation point or dpv.

Domes with adjoining vertical segments can be based on the principles of domes with in-fill cover described above. Another type of inflatable dome with circular segments (complete or in sections) of progressively smaller diameter placed one upon the other is shown in Fig. 108 with a multiport dpv. Differential pressure domes may be used to cover radar antennae, radio and optical telescopes.

E. Hiking and/or Disposable Differential Pressure Mattresses.

The dpv lends itself to the design of a low cost, low weight and, perhaps disposable, mattress which can be used for hiking or other leisure activities.

Suitable designs are similar to inflatable bed/mattresses described in Figs. 76 to 86, or Fig. 113, or of multicellular packing material described in Figs. 145 to 150.

The hiking mattress can be stored deflated in a small volume and rolled up if that is required. Once inflated it provides, a multisegmented thin-layer differential pressure mattress which has a comfortable, relatively even surface providing good thermal insulation between the user and the ground.

F. Amusement Inflatables; Therapy Aids for the Handicapped; Dummy Targets and Decoys.

Amusement inflatables are large fluid (generally air) inflatable toys for children's amusement in the shape of animals, castles or other forms. An example of such an inflatable embodying the invention is shown in Fig. 108 with the front half of a plurality of superimposed ring segments 150 and the entrance 151 cut away. A variety of different dpvs are shown including a multiport dpv 152 with low and high pressure valves 15, 16 incorporated in some of the dome's segments. A uniport dpv 153 is connected by T pieces 154 and low (thin line) and high (thick line) pressure tubing 155, 156 to .the multiport dpv 152. A serial dpv 157 is shown between an arm of the inflatable and a bottle. The low pressure supply for the dpv 157 is from the inflated arm and the high pressure supply via tubing 156. An air bed 158 forming the base of the inflatable may have a continuous air supply or incorporate a dpv as described earlier (see Application A). Similar inflatable applications where one or more dpvs may be used include pool structures, ball crawls, therapy aids for the handicapped, dummy military targets and decoys (such as tanks and aircraft). The use of dpvs allows for many segments to be inflated and the shape retained by a minimum of two compartment valves, which increases the scope and intricacy of possible shapes and designs. G. Inflatable Boats and Hovercrafts; Immersion Suits, Casualty Bags, Liferafts, Buoyancy Devices, Lifejackets and Other Lifesaving Equipment.

For inflatable boats, hovercrafts, immersion suits, casualty bags, liferafts, buoyancy devices, lifejackets and other lifesaving equipment, the use of differential pressure valve(s) gives the advantages of having many segments or chambers, inflated and isolated together, which enhances their safety aspects in many respects. The puncture of one or more load compartments, due to an explosion, military conflict, floating debris or other reasons would still leave the devices partially inflated. The high pressure compartment can be situated for protection between, or within, the segments of the low presssure compartment. The high pressure compartment can be made, if required, or a reinforced or rigid material to further prevent its accidental puncture. By pressurising the small volume, high pressure compartment with fluid that sets into a gel or solid by chemical or other means, the isolation and sealing of the low pressure segments may be made permanent. The liferaft, inflatable boats and hovercrafts with many sealed segments would have greater stability and rigidity. Liferaft canopies etc., can be double-skinned, inflated and the segments sealed by the high pressure compartment giving a relatively rigid enclosed structure with good thermal insulation.

Segmented or separate buoyancy devices for helicopters, spacecraft, oil rigs, oil development and production platforms, and other items can be inflated and isolated by dpvs. Buoyancy aids for canoeists etc. can be in the form of a waistcoat with many parallel, longitudinal segments that are inflated and isolated by a dpv incorporated into the buoyancy jacket. Inflatable hovercraft with cylindrical tubes subdivided into several buoyancy chambers which are connected to uniport dpvs or a multiport dpv can be inflated from, for example, the hovercraft's thrust fan or bottled gas. Conventional designs of inflatable boats, hovercrafts, liferafts etc., can be fitted with uniport dpvs at each of their conventional points of inflation and then connected by tubing. Designs illustrated below where multiport dpvs are shown attached to spaced points of inflation such as buoyancy tubes may instead have several uniport dpvs connected by tubing. Multiport, uniport or combinations of any sort of dpv can be inflated from a single gas supply, such as an airline or bottled gas as described earlier. This technique is useful for emergency or military equipment. Where extra security is required (e.g. liferafts), dpvs with security screws or automatic locking devices may be preferred.

Differential Pressure Off-shore Survival and Immersion Suit.

The inflatable suit shown in Figs. 109 to 111 is for emergency use for floating and thermal insulation in cold water and to escape from submarines (rubber seals and other accessories are not shown). The life preserver worn by submariners has a buoyancy stole 160 which is inflated from the submarine (valves not shown). This form of buoyancy stole is, of course, not necessary on immersion or survival suits for personnel such as oilrig workers, pilots, helicopter personnel and coastguards. The suit incorporates a multiport dpv 161 which in this version is inflated by gas from a bottle 162, although oral inflation is an alternative. In practice one gas bottle or mouth piece is sufficient: the low pressure segments 163 are inflated first and the supply then switched over automatically or manually so that the high pressure compartment is inflated. Low and high pressure oral inflation valves 164 and 165 respectively for topping up are shown located at the wrists. Different sections of the multiport dpv 161 are connected by tubing 164 as shown in Fig. 110. The dpv 161 with a bladder 12 allows the many ports 14 and their segments 163 to be isolated giving better thermal insulation. A simpler version of the suit would have fewer segments and/or the omission of the dpv to the arms, for example. The suit can be made to be close fitting and dry to the user. The suit can be of lighter material which packs into smaller bulk than conventional designs (with one inflatable quilted chamber) because any puncture is isolated to one segment and does not cause deflation of the entire suit.

Differential Pressure Casualty Bag

The casualty bag shown in Figs. 112 and 113 is inflated in two parts: one part comprises an inflatable mattress 170, including a pillow 171, and a cover 172, including a hood. The mattress and cover are both shown with individual integral multiport dpvs. The segments 17 of the cover 172 are inflated via low and high pressure valves 15 and 16 in a multiport dpv 174 with diaphragm 20 running either side of a central zip 175. with a zip placed laterally a single length dpv on one side of the zip only is required for the cover. As the cover is not load bearing a single chamber quilted design rather than a multi-segment design may be adequate, but with a differential pressure mattress. A lower dpv 176 with low and high pressure valves 15A and 16A allows for the air mattress 170 and pillow 171 to have many isolated segments 17 as shown in Fig. 113. This provides a comfortable surface and good thermal insulation (useful also under a sleeping bag). The mattress can be made of a lighter material than single chamber ribbed or quilted air mattresses. A thinner, lighter material may have more risk of puncture but the isolation of each segment allows for continued use if punctured. There is also less risk of "bottoming out" due to the restricted movement of air in the mattress. Differential Pressure Single-seat Liferaft

Differential pressure valves can be incorporated into the design of a single-seat liferaft as shown is Figs. 114 to 117 to provide: i) a multisegmented buoyancy chamber 180 (dpv not shown), ii) a multisegmented canopy and hood 181, and iii) a multisegmented seat and floor area 182. The buoyancy chamber is inflated from gas bottles 187. The canopy and hood 181 has segments 17 which are shown as orally inflatable via a dpv 183 with low and high pressure valves 15 and 16. This integral multiport dpv 183 with a bladder 12 inflates the canopy segments 17 via the ports 14 as shown in the detail in Fig. 115. The canopy and floor/seat have improved thermal insulation due to isolated air-cells than if made from a ribbed or quilted single chamber. The materials for this design of single-seat liferaft can be of a lighter material than conventional designs, as already described in respect of the immersion suit. The area of floor which may be orally inflated through valves 15A, 16A, may include a seat area 185 only or the entire floor as shown in Fig. 116. A higher seat than the floor can be created by having wider segments for the seat area. Each segment of the inflated floor can have its port 14 isolated by a dpv 186 shown with a diaphragm 20 in Fig. 117.

Differential Pressure Liferafts

A liferaft is shown in Figs. 118 and 119. In Fig. 118 the canopy, gas cylinders to bladder dpvs, topping-up/deflation valves and accessories such as lifelines are not shown. Canopy support tubes 190 are shown schematically only. Practical support tubes can be angular in shape giving more room in the interior and to allow rainwater collection on the canopy. Support tubes and canopies of geodesic and other domed designs are shown in Figs. 92 to 98. Double membrane canopy panels can have their own dpv independent of the support tubes. A multiport dpv 191 with low and high pressure valves 15 and 16 allows inflation and isolation of tubular flooring 192 and the segmented seat-ring 193. Uniport dpvs 194 are connected by low (solid line) and high

(dashed line) pressure tubing 195, 196 and T pieces 197 to a gas cylinder 198 with sliding valve as described earlier. The uniport dpvs are shown attached to the upper and lower buoyancy chambers 199 and 200, boarding stub 201, and a canopy arch 190. The dpv allows for the use of lighter material packing into small bulk; reduces the consequences of a puncture; and increases the stability and rigidity of the liferaft.

Differential Pressure Inflatable Boats Inflatable boats with differential pressure valves are suitable for use as a dinghy, tender, sports boat, sailing boat or rescue boat with accessories and minor design modifications to suit a particular purpose. Materials, for example, which are suitable include cloths coated with natural rubber or the more modern nylon fabrics with synthetic rubber coatings, such as neoprene, hypalon and butyl. The seams of these materials are usually glued and/or sewn. Other, usually cheaper and less durable materials include various kinds of plastic sheeting (e.g. polyvinyl chloride, polyurethane) which can also be high frequency welded in some cases (the sheeting may incorporate supporting fabric) .

Figs. 120 to 122 show an inflatable boat in which uniport dpvs 210, connected to low and high pressure valves 15, 16 by tubing 211, allow inflation and isolation of eleven low pressure chambers 212 in the main buoyancy tubes 213 which are subdivided by bulkheads 214. The inflatable buoyancy tubes 213 may be attached in the conventional manner to a rigid hull; or to a stretched fabric keel (with or without an inflatable keel) and wooden/aluminium flooring; or an inflatable floor 215 as shown in Figs. 121 and 122. Rigid and hollow hulls, made for example from glass fibre can be filled with differential pressure airsacs which provides fail-safe buoyancy in the event of a damaged hull. Instead of providing two main buoyancy tubes as shown in Fig. 120 the height of the sides can be increased by one or more tubes superimposed upon the buoyancy tubes shown. Alternatively, extra height for the sides can be gained by subdividing the main buoyancy tubes so as to. provide an oval (vertical long axis) rather than a circular cross-section. Differential pressure valves can be incorporated in each of these designs.

The inflatable floor 215 shown in Figs. 121 to 124 is inflatable via an integral multiport dpv 216. The floor is fluted longitudinally and the many inflated and isolated segments 17 provide increased rigidity over a single compartment floor. Alternatively, the longitudinal segments may be shortened as indicated by the dotted line in Fig. 121, rather than extending the full length of the boat, with separate lateral flutes across the high-rise canoe-shaped bow.

The inflatable floor 215 between the buoyancy tubes may be provided with wall-dividers and/or may be of ribbed construction as shown in cross-section in Fig. 122 or in the alternative cross-section shown in Fig. 123. The former has less surface area and resistance to the water and also allows the floor to be shaped as an inflatable keel. Fig. 124 shows an inflatable keel/floor 218 with a stretch-fabric keel 219. Further rigidity can be provided by flooring of slats or boards 217.

Inflatable boats most suitably propelled by paddles or oars are shown in Figs. 125 to 127. No seats, buoyancy tube valves and other accessories are shown. The inflatable boat shown in Fig. 125 has two main buoyancy tubes 220 which come together at the bow and the stern. An inflatable floor 221 has an integral bladder multiport dpv 222 with low and high pressure valves 15 and 16 respectively. A stern cover/aft deck 223 (the bowcover/foredeck is not shown but its boundary is marked by a dashed line) has its own diaphragm multiport dpv 224 with low and high pressure valves 15A and 16A respectively, giving the cover added rigidity over that of a single chambered ribbed or quilted construction.

Figs. 126 and 127 show an inflatable boat with tapered buoyancy tubes 230 which do not meet at the stern or bow. Continuous longitudinal tubes 231 of the inflated floor 232 curve upwards at the ends to form the bow and the stern. An integral diaphragm multiport dpv 233 with ports 14 into the inflatable floor lends extra rigidity and security to the design. An inflatable canoe with an integral multiport dpv 240 is shown in Figs. 128 and 129. Topside tubes 241 of the canoe are brought together at the midline of the canoe and a dpv 240 with bladder at the stern inflates and isolates these tubes. An inflatable floor/keel 242 comprises longitudinal tubes which have an independent dpv (not shown) .

H. Medical Applications including Anti-decubitus Mattresses, Wheelchair Cushions and Inflatable Splints

Differential Pressure Mattress and Wheelchair Cushion for the prevention of Bed Sores

Multisegmented fluid or gel-filled mattresses with dpv(s) can be used to prevent and treat pressure sores (anti-decubitus mattresses). One version consists of many small low pressure segments 17, along the length (and/or breadth) of the patient, as shown in Fig. 130. These are inflated when the patient is already on the mattress; with instructions to lie in a manner that distributes their weight as evenly as possible. The load-bearing segments are connected to the ports 14 of one or more dpvs. The mattress can either by manufactured as a whole or with replacement segments. Pressurisation of the low pressure compartment 13 results in the segments acquiring the same pressure. The high pressure sealing compartment(s) 11 are then pressurised resulting in the degree of inflation, that is the volume of each individual segment, being retained. This retention by the mattress of an impression of the body's form that is in contact with the mattress, provides support and helps hold the patient in a position that gives the best weight distribution. The stability and reduction in fluid bulk flow also allows for greater ease in lifting patients in and out of bed, turning them over or sitting them up when necessary. A convenient arrangement is to have alternate load segments connected to one of two dpvs 250 and 251 so that interdigitated segments form a continuous surface. In the arrangement shown in Fig. 130 the dpvs 250 and 251 have a common low pressure compartment with valve 15 but separate high pressure compartments with valves 16. A possible modification, shown in Fig. 131, is to provide two separate, double compartment, dpvs 252 and 253 again with alternate, interdigitated segments. To accommodate for patient movement, with the patient temporarily adopting a posture with localised high pressure points, high pressure compartments are in turn depressurised then repressurised by an electrically controlled pump, allowing for the redistribution of fluid in alternate low pressure segments. Gaps can be left between segments so as to provide ventilation and prevent pooling on the surface of the mattress due to patient incontinence.

Application of the contouring properties of the differential pressure mattress to fluid-filled segments which are attached or adhered to a chair or wheelchair will help support disabled patients with the advantage of preventing sores by achieving equalised load distribution. A design of an anti-decubitus waterbed can be similar to that of Figs. 76 to 82 with the isolated segments helping inhibit wave motion. The high pressure compartment can contain either water or air and can, if required, be manually or electrically deflated and inflated to redistribute the water.

An air-inflated mattress with a dpv is suitable for use in ambulances and hospitals. Quick release valves on the high and low pressure compartment allow effective action on a hard base such as on a trolley to be taken in case of cardiac arrest.

A simple design of wheelchair cushion with a dpv has parallel, adjacent longitudinal segments connected to the dpv and is similar to the fluid-filled mattress shown in Figs. 76 to 82; a more complex design with a precontoured surface is shown in Figs. 132 to 133. Tie holes 260 in the margin 261 enable the cushion to be tied with tapes to a wheelchair with either a hard base or a sling bottom. The low and high pressure valves 15, 16 of a dpv with diaphragm 20 inflate via the ports 14 and then isolate the six segments 17 of the cushion. Segment walls 262 are welded to top and bottom continuous sheets 263, 264 to provide a relatively even surface in contact with the user, as shown in cross-section in Fig. 133. The cushion can be partially precontoured by having segment walls of different heights. It is important to relieve the pressure on the ischial tuberosities and coccyx (the area outlined by a dotted line in Fig. 132) as this is where pressure sores mainly develop. For this reason the outermost segment 17A, which has the highest profile, does not continue around the back of the cushion. The lower profile segments 17B, 17C and 17D are wider in this area. The segment walls are lowest in the dashed area. Segment 17E has slightly raised walls to separate the legs. The division of segments 17B to 17D midway into two separate segments each would give a more suitable design for those with a tilted posture due to scoliosis, a stiff hip or an amputated leg and provide nine segments connected by nine ports to the dpv.

The high pressure compartment 11 when inflated should be of a smaller diameter than any of the low pressure segments to create a space for relief behind the knees. The cushion is made from heavy duty medical grade pvc with bacteriostat. The bungs are non-protruding and laterally placed. Instructions for inflation may be written on the cushion. A two-way stretch, vapour permeable cover, handpump, pressure gauge and puncture repair kits may be accessories.

An inflatable splint is shown in Figs. 134 and 135. The ribbed segments 17 with wide welded joints 270 are inflated via a low pressure valve 15. The high pressure compartment 13 designed with as small a diameter as practical, is then inflated by a squeeze ball 271 and the valve 16. In Fig. 135, the splint is shown secured around a patient's limb 272 by tapes or VELCRO 273 on the ribbed segments 17. Many air tubes joined up as a hollow cylinder form a good pneumatically-stressed structure suitable for other uses such as inflatable pipes, cylinders (as described earlier in Fig. 34), and goal post anti-impact cushions. The exact form .of the splint depends on the limb or other part of the body it is required for. The use of transparent plastic allows the limb to be observed when the splint is in use.

I. Flotation Devices

Low pressure buoyancy segments connected to differential pressure valve(s) with extended ports or compartmental valves (see Figs. 33A and 33B) or otherwise, are submerged beneath an object which is to be raised from beneath the water. The inflation of the buoyancy segments is via the low pressure valve(s). The inflation of the high pressure compartment seals the segments and stabilises the buoyancy device. To increase the buoyancy, the sealing compartment's valve is opened and the low pressure segments are further inflated. To prevent the submerged object rising too fast, air is released from the low pressure segments. If the object upon the flotation mattress has moved and redistributed its load resulting in unacceptable variations in the pressure between points of contact between the load and flotation device, the pressure in the high pressure compartment may be released and reapplied in a short time, redistributing the air among the low pressure segments.

J. Differential Pressure Moulding and Form Work

The containing properties can be utilized for moulding. The negative impression of an object can be taken when it is laid upon or surrounded by inflated segments connected to a dpv. The shape or contour is retained and can be used as a mould after the high pressure compartment is inflated and the segments isolated.

The use of dpvs with inflatable structures, such as domes gives rigidity by isolating many segments. The inflated structure can be employed as form work for shell construction with materials such as concrete and urethane foam.

K. Tank-filling Valve, Inflatable Storage Tanks, Swimming Pools and Paddling Pools

The differential pressure valve when connected to container segments (for example, the many separate sections or chambers of a tank) allows them to be filled through the low pressure compartment and then for the individual fluid-filled segments to be isolated by the high pressure compartment. The differential pressure valve can be attached to portable tanks, the container part of transportation tankers and permanent land or sea-based (submerged or floating) tanks. This includes tanks and other containers manufactured from rubber or plastic, for example, for use for temporary, emergency, or military purposes or, on the other hand, rigid permanent structures. Fluid separated in isolated chambers reduces the volume of spillage in the event of a leak by accident or when under military attack and limits the inertial bulk flow when undergoing transportation. Fig. 136 shows a tank that is divided into chamber or segments 17 that can be emptied or filled to the same level in each chamber via the ports 14 in a dpv 280 and main valve and nozzle 281 as illustrated. A filling port 282 is shown at the top of the tank. The high pressure compartment 11 of the dpv is pressurised by a hand pump 283, in this instance as shown in the detail in Fig. 137. The high pressure in compartment 11 is released by a valve 284 into the low pressure compartment 13 which is on the other side of the dpv diaphragm 20 as shown in cross-section in Fig. 138. Alternatively the high pressure compartment may be pressurised by air and released to the atmosphere.

Inflatable and portable water (or other liquids) storage tanks can be made up of circular or polygon shaped air tubes one upon the other (with a fabric base) connected by a dpv. An alternative is to provide adjoining vertical longitudinal segments arranged in a circle (with a base) and a dpv connected in similar manner to that illustrated in Fig. 34. Designs similar to storage tanks can be applied to inflatable swimming pools and paddling pools. L. Differential Pressure Tyre Inner Tube

Several low pressure segments take the place of a conventional tyre's pneumatic inner tube. The segments are made from a similar material to that of an inner tube and connected to a dpv. The low and high pressure compartment valves protrude through one or more holes in the metal rim of the wheel so as to allow external inflation and deflation. A puncture of the tyre would result in the deflation of one segment and the partial deflation of the tyre. Travel could continue until there is a convenient time and place for repair. To repair the puncture, the punctured segment can be patched or replaced.

M. Airships and Gas-filled Balloons The use of a dpv would allow all the buoyancy gas-filled cells or segments to be filled or emptied rapidly and simultaneously, and with equal pressure in ^• all segments. The segments, once full or inflated, can then be isolated from each other by the high pressure compartment of the dpv. The use of isolated buoyancy chambers or segments reduces any loss in volume and shape in the event of a gas leak. The bulk movement of gas is reduced helping to retain the airship/balloons shape and stability. If leakage does occur the remaining gas can e redistributed with equal pressure in all segments by releasing and reapplying the high pressure compartment valve.

N. Aircraft, and other emergency escape slides

The use of the dpvs in the design of aircraft, boat, building and other emergency slides or gangways would allow for the rapid inflation of all their structural segments. The isolation of the segments by the high pressure compartment would give a more rigid structure and minimize leakage if punctured by flying debris. 0. Differential Pressure - Sail Board and Ski Board

Inflatable sail boards and surf ski boards can be composed of several or many longitudinal segments running from bow to stern. Inflatable segments with segment walls as shown for a mattress in Figs. 76 and 82 give a smoother topside and underside. The segment walls can be varied in height (as shown in Fig. 133) to give different sail board shapes such as flatboards and displacement boards. A multiport dpv with as small a radius as possible is attached transversely upon or within the segments. Mast foot, footstraps, etc., can be attached to the sailboard. A daggerboard can be inserted between a partially omitted longitudinal segment. A similar design applies to the surf ski (with . toestrap and fin). A dagger board aperture is not required. The use of pneumatic sandwich plates with nylon threads between the top and bottom surfaces is suitable for sail boards and surf skis. Contoured depressions on the surf ski for the seat and feet can be produced by reduced segment walls and/or shorter nylon threads.

P. Differential Pressure Transit, -Contouring, or Thermal Insulation Packaging. Different properties of differential pressure devices, such as many isolated segments, contouring and thermal insulation can be utilised in the design of novel forms of packaging material; insulating material and load transit mattresses. As well as being light in weight and shock absorbing, the added advantages of fluid-filled, usually air-filled, differential pressure packaging and insulating materials, mattresses, bags or containers, is that they can be deflated and stored away for re-use taking much less space than when in use. Thermal insulation can be provided by many isolated air cells in the form of low pressure segments. By the use of add-on versions of the differential pressure valve or mattress as described earlier it is possible for packaging or insulating material such as a transit mattress to be enlarged to any required size. All designs of fluid-filled differential pressure packaging and transit material if used in the manner described earlier can be used for contouring to the shape of the article within or upon the differential pressure material. Any load upon the contoured differential pressure material is well distributed and has good stability. For example, a fragile article can be placed in a box or container surrounded by differential pressure material. The box is closed and the low then high pressure valves inflated causing the differential pressure material to contour to the article's shape and holding it steady.

If desired, differential pessure packaging or insulating material can be made from the same materials, plastic film or sheeting (transparent or translucent if required), as conventional sealed air-bubble or air-cell packaging used to protect delicate goods while undergoing transit. If plastic sheet is used then it may be pre-shaped to the shape of the air-cells, connecting channels or tubing. Air cells are stronger if corners are well rounded. The dpv between air-cells can be of lower profile so as not to take loading. Thicker plastic film over the dpv (especially the high pressure compartment), or two separate dpvs for alternating air-cells provides additional security against puncture. For packaging and insulating material in general and mattresses for resting loads upon in transit in particular the designs may be similar to the fluid-filled mattresses described earlier under application A. All designs whether described earlier or given below are examples only as their exact form, shape, size and other modifications depends on the objects being transported stored or thermally insulated; or the use for which differential pressure bags or containers are required. Differential pressure packaging for protecting a cubic package is shown in Fig. 139. A bladder (or coaxial chamber) dpv 290 with low pressure and high pressure valves 15, 16 allows for ports 14 and segments in Fig. 140. Tapes or VELCRO 291 (not shown in Fig. 139), for example, secure the packaging.

Fig. 141 shows a packaging in which two dpvs 291 and 292 with diaphragms 20 allow the alternating low pressure segments or air-cells 17 to be supplied, isolated and emptied by different dpvs. Even if one dpv failed alternate segments would still be isolated. The use of bladder dpvs would allow for differential pressure packaging for the top and bottom panels 293 and 294 (see segment 17 in dashed lines) but with no provision of alternating segment fail-safe.

A mat is shown in Figs. 142 to 144. The mat has fluid cells connected via ports 14 to a cushion-shaped multiport .dpv which is pressurised and depressurised via interconnections 300 between adjacent low pressure compartments 13 and interconnections 301 between adjacent high pressure compartments 13 by low and high pressure valves 15, 16. The cushion shaped dpv is shown in Fig. 143 and has a flexible diaphragm 20 between the low and high pressure compartments 13, 11. The softer low pressure segments 17, which are not directly connected, are preferably placed towards the article being packaged (it is also less important if a segment 17 is punctured). Fig. 144 shows the low pressure valve 15 supplying all segments via interconnections 300 and ports 14. Pressurisation of the whole of the high pressure compartment 11 via the interconnections 301 (shown only partially pressurised) allows the diaphragm 20 to seal off the ports thereby isolating the segments 17. The design is suitable for gymnasium, sports and leisure mats where the softer segments are uppermost and the harder and high pressure compartment in the base of the mat prevents bottoming-out occurring. Differential pressure packaging may have many of the properties of conventional sealed air-cell packaging as will be described with reference to Figs. 145 to 150. Referring first to Fig. 145, air cells 310 arranged in a matrix are inflated via a low pressure valve 15 and compartment 13 and the ports 14 of the dpv and are isolated by pressurisation through the high pressure valve 16 and compartment 11. A design using two whole sheets 311 and one partial sheet 312 is shown is cross-section in Fig. 146. The sheets or film are for example made from translucent plastic and welded or joined together. Single cells 313 and double depth cells 314 are shown although usually one or the other would be used exclusively. The high pressure compartment 11 is welded 315 above the low pressure compartment 13 with a diaphragm 20 in between as shown in the detail of Fig. 147. The cross-section shown in Fig. 148 shows the high pressure compartment 13 welded above and to one side of the ports 14. An alternate version with the low pressure compartment above the high pressure compartment and comprising three complete sheets 311 of plastic sheeting or film welded or joined together is shown in Fig. 149. The low and high pressure compartments 13, 11, welding 315 and diaphragm 20 are shown in more detail in Fig. 150.

Q. Miscellaneous including Inflatable Load Restraint System and Inflatable Oil-slick Boom

a) Inflatable Load Restraint System

This employs inflatable segments connected to dpv(s) that restrain a load inside a load-carrying vehicle, boat, aircraft, etc. The principles of such a system are shown in Fig. 74, where folded flat segments attached to serial segment dpv(s) are hung on rails, deflated until required for use, at the end or side of a lorry for example. When the lorry is partially loaded the segments are inflated pneumatically, stressing them one after the other until the end segment presses up against the load. An electronic pressure-measuring device in the last dpv would facilitate knowing when to stop the low pressure inflation. Every second segment, in the arrangement shown in Fig. 74, is then isolated by the high pressure valve preventing undue mass movement of the fluid in the segments or of the segments under inertial or other forces from the vehicle and/or load.

b) Inflatable Oil-slick Boom

This employs long inflatable cylinders that are connected end to end in a continuous manner, with serial segment dpvs between each cylinder as indicated in Fig. 67. When the continuous cylinder is inflated with gas it is deployed to float around the oil-slick or other floating contamination on water. The cylinders are isolated by inflation of the high pressure compartment which reduces movement of gas in the cylinders by waves or leakage due to a puncture.

c) Inflatable bridges, fascines for bridging ditches, bags for righting vehicles and aircraft, and inflatable structures for use in space although not specifically described may benefit with designs incorporating dpvs.

Claims

What we claim is:

1. A differential pressure valve comprising a low pressure compartment bounded by flexible material and having a first port and one or more further ports, and a high pressure compartment having an inlet port, the low and high pressure compartments being arranged such that filling of the high pressure compartment with fluid to a pressure higher than that in the low pressure compartment is operative to close the one or more further ports in the low pressure compartment.

2. A valve as claimed in claim 1 in which the low pressure compartment has a plurality of further ports.

3. A valve as claimed in claim 1 or 2 in which at least the port of the high pressure compartment which is operative to effect closure of the one or more further ports is bounded by a membrane of flexible material.

4. A valve as claimed in any preceding claim in which the high pressure compartment is contained substantially wholly within the low pressure compartment.

5. A valve as claimed in any of claims 1 to 3 in which the high pressure compartment is adjacent the low pressure compartment and the two compartments share a common flexible boundary wall. ,•

6. A valve as claimed in any preceding claim in which the high pressure compartment is of elongate form.

7. A valve as claimed in claim 6 in which the first port of the high pressure compartment is at one end thereof and the first port of the low pressure compartment is in the vicinity of the other end of the high pressure compartment.

8. A valve as claimed in claim 6 or 7 in which the one or more further ports in the low pressure compartment are located adjacent a side of the high pressure compartment.

9. A valve as claimed in any preceding claim in which the one or more further ports on the low pressure compartment are arranged to be closed as a result of expansion of the boundary walls of the high pressure compartment.

10. A valve as claimed in any preceding claim in which the first port of the low pressure compartment and the inlet port of the high pressure compartment are connected to a common conduit and valve means are provided for closing the fluid path between the low pressure compartment and the conduit.

11. A valve as claimed in any preceding claim in which closure means for the first port of the low pressure compartment and/or the inlet port of the high pressure compartment is provided at a location remote from the associated compartment.

12. A valve as claimed in any preceding claim, in combination with another valve as claimed in any preceding claim, the low pressure compartment of one valve being connected directly or indirectly to the high pressure compartment of the other valve.

13. A valve as claimed in any preceding claim in which locking means are provided for maintaining the one or more further ports in the low pressure compartment closed, even if pressure in the high pressure compartment is reduced.

14. A device to be filled under pressure, the device including a valve as claimed in any preceding claim and respective low pressure segments communicating with each of the one or more further ports of the low pressure compartment whereby the low pressure segments can be filled with fluid through the first port of the valve and filling of the high pressure compartment to a pressure higher than that in the low pressure compartment and the segments is operative to close the one or more further ports in the low pressure compartment thereby isolating the segments from one another.

15. A device to be filled with fluid under pressure. the device including a plurality of low pressure segments, ports and a low pressure compartment interconnecting the segments, and a high pressure compartment arranged such that filling of the high pressure compartment with a fluid to a pressure higher than that in the low pressure compartment is operative to close the ports interconnecting the low pressure segments thereby isolating the segments from one another.

16. A differential pressure valve comprising a low pressure compartment and having a first port and one or more further ports, for connection to or connected to segments, and a high pressure compartment having an inlet port, the low and high pressure compartments being arranged such that filling of the high pressure compartment with fluid to a pressure higher than that in the low pressure compartment is operative to close the one or more further ports in the low pressure compartment to isolate respective segments connected thereto.