GB2076941A

GB2076941A - Flow regulating valve

Info

Publication number: GB2076941A
Application number: GB8115693A
Authority: GB
Original assignee: Asulab AG
Current assignee: Asulab AG
Priority date: 1980-05-23
Filing date: 1981-05-21
Publication date: 1981-12-09
Also published as: IT8121922A0; GB2076941B; IT1137481B; FR2483039A1; JPS5722468A; DE3025457A1

Abstract

A valve (1) for controlled ventilation of an inflatable sleeve of blood pressure measuring equipment comprises within a housing (3) a generally cylindrical rubber-elastic flow control body (7) with an axial bore (7a) forming part of a flow path (15) through the housing (3) from an inlet (3a) to an outlet (9). The body (7) is held at its ends and has on a circumferential surface portion thereof intermediate its ends an annular recess (7b) forming part of a pressure chamber (19). The chamber (19) is connected to the flow path (15) between inlet (3a) and bore (7a) by a branch duct (17). On ventilation of the sleeve, air under pressure is exhausted from the sleeve through inlet (3a) to the pressure chamber (19) and in dependence on the pressure difference between the inlet (3a) and outlet (9), the pressure in the chamber (19) deforms the control body (7) so as to constrict bore (7a). This varies the resistance to flow along the flow path (15) and causes the pressure in the sleeve to reduce, over a certain pressure range, at an approximately constant rate. <IMAGE>

Description

SPECIFICATION Flow regulating valve The present invention relates to a valve and to blood pressure measuring equipment incorporating the valve.

Blood pressure measuring equipment disclosed in US patent specification No. 3450 131 comprises a microphone connected with a logic circuit. Also included in the equipment are an inflatable sleeve, a pressure sensor connected through an analogdigital converter, which can be switched on and off, and a gate circuit with a pressure recording device.

When carrying out blood pressure measurement, the sleeve is inflated to a pressure above systolic pressure and then slowly ventilated. In that case, Korotkoff tones are generated in a certain pressure range and converted by the microphone into electrical signals. When each Korotkoff tone occurs, the analog-digital converter and the gate circuit are controlled by the logic circuit in such a manner that the instantaneous pressure measured by the pressure sensor is recorded in the pressure recording device. The first recorded pressure valve corresponds to systolic pressure and the last recorded pressure value to diastolic pressure.

The sleeve of the equipment disclosed in US patent specification No. 3 450 131 is inflated and ventilated through a control unit which is not described in detail. It is therefore to be assumed that the air during the ventilation phase flows away independently of the instantaneous pressure through an outlet with a valve and possibly a throttle which during the entire ventilation phase have a constant passage cross-section. However, this has the consequence that the outflow speed is greater at the start of the ventilation phase, when the pressure is still high, than towards the end of the ventilation phase. Consequently, the pressure reduction per unit time is greater during the measurement of the systolic pressure than during the measurement of the diastolic pressure.This in turn has the consequence that measurement of the systolic pressure is less accurate than of the diastolic pressure. If, for example, the pressure reduction as a function of time is determined to be so small that a certain minimum accuracy is attained in measurement of the systolic pressure, the measurement of both pressures occupies a relatively long time. This is particularly so due to the fact that the outflow speed becomes even slower after falling below the diastolic pressure, so that complete emptying of the sleeve takes a long time. A further disadvantage of the equipment described in US patent specification No.

2450 131 is that there is an appreciable risk of under-inflation of the sleeve so that the pressure measured on arrival of the first Korotkoff tone and accepted as being the systolic pressure lies below the actual systolic pressure.

Also known in blood pressure measuring equipment incorporating a throttle valve which comprises a housing having an inlet and an outlet connected by a passage, and a displaceable throttle body for varying the flow resistance of the passage. The throttle body is connected to one end of a tightly sealed spring bellows, which is disposed in an ambient pressure zone and the other end of which is connected to the housing. The interior of the bellows is connected, in terms of fluid flow, with the inlet so that the bellows displaces the throttle body in dependence on the pressure at the inlet side. The passage and the throttle body are constructed in such a manner that the latter throttles the air outflow from the sleeve to a greater extent at high pressure than at low pressure.By this measure it is to be secured that the pressure reduction per unit time remains approximately constant during the entire measurement.

With this valve, the passage must include a valve seat at which the passage cross-sectional area can be varied through displacement of the throttle body.

Furthermore, as mentioned, a spring bellows is necessary for effecting displacement of the throttle body. In order for the valve to fulfil its function, the throttle body and the valve seat must be accurately matched to one another and therefore manufactured with correspondingly high precision. To enable compensation for tolerances of the bellows, in practical terms it is essential to provide at least one adjusting element. The known valve is thus relatively complicated and expensive.

In the unpublished specification of the applicant's United Kingdom patent application No. 81 04 320 Serial No. 2,069,707, it is proposed to provide blood pressure measuring equipment with a valve which has an electro-magnetically displaceable throttle body. This blood pressure measuring equipment also includes a pressure sensor, electrical circuit means connected therewith for determination of the temporal change in the pressure, and an electronic regulator for the regulation of the valve. The temporal pressure reduction can be regulated by these devices so that the mean pressure, i.e. the pressure resulting when discounting the superimposed pressure fluctuations caused by heart activity, reduces by an exactly constant value per unit time during the measuring phase.Other advantages are provided, but regulation by means of an electronic regulator is relatively expensive and therefore can be considered only for equipment in a higher price bracket.

US patent specification 2 878836 discloses a valve for water supply systems. The valve comprises a casing forming a chamber. An annular flow control body of resilient material having a central passage therethrough is arranged in the chamber. The flow control body has a large diameter rim portion and a smaller diameter portion providing a shoulder therebetween. The flow control body has a large flat end surface facing upstream so that it is subjected to the pressure of the incoming fluid. The surfaces of the rim of larger diameter portion and the smaller diameter portion are formed with a series of axial grooves that extend across the periphery.

In the operation of the valve, at low pressure the fluid will pass freely through the central passage as well as through the grooves of the flow control body.

The building up of pressure in the lower ranges will cause axial compression of the flow control body.

This axial compression results in closing of a gap connecting the grooves of the large diameter portion and those of the smaller diameter portion, so that the flow through the grooves is shut off at a predetermined pressure. Beyond this limit, any additional fluid pressure upon the resilient flow control body will also cause the elementto be compressed radially and to restrict the central passage.

The valve described in US patent specification 2 878836 is not intended for use in blood pressure measuring equipment and has several disadvantages making it unsuitable for such an application.

Firstly, it can be recognized that if an air chamber of an inflatable sleeve is to be vented through a valve according to US patent specification 2 878 836, the pressure would not be reduced at a constant rate.

The ventilation characteristic would in fact have a break at the pressure where the flow through the grooves is shut off. In the pressure ranges where flow through the grooves takes place, the pressure would almost certainly not decrease at a constant rate. In view of the fact that the length of the central passage of the resilient flow control body is considerablysmallerthanthe smallest diameter of the body, it is highly probable that the pressure would not even decrease at a constant rate in the range in which the body is also radially compressed.

The length of the control body along its central flow passage is considerably smaller than its diameter. In addition the body exposes at its periphery, at least in the low pressure range when the body is not yet strongly compressed, only the surfaces of the said grooves to the fluid. Another important feature of the known valve is that the compression and particularly the radial compression of the control body occurs only at relatively high pressures. This may be acceptable for use of the valve in water supply systems where the pressure may have a magnitude in the range of MegaPascal, but not for blood pressure measuring equipment where the pressure ranges typically from 10 to 20 kiloPascals.

German utility model specification 1 676255 discloses valves serving particularly for controlling or shutting-off the flow of salty solutions. Such a valve comprises a casing forming a chamber in which an annular resilient flow control body is arranged. The latter can be compressed by a sleeve that is axially displaceable by manually operating a nut provided with handles. The valves may be provided with a bolt extending through the central passage of the resilient flow control body. The bolt preferably has a circular cross-section and may be provided with radially protruding pins or wings. The bolt should limit the compression of the resilient flow control body in the shutting-off position for sparing the resilient material. The bolt may also be manually rotated and displaced for removing salt sediments.

The valves disclosed in German utility model specification 1 676 255 are not intended for use in blood pressure measuring equipment and would certainly not be suitable for such an application.

There is accordingly a need for a valve providing a flow resistance which varies in dependence on flow pressure, such pressure dependence of the flow resistance being determinable or determined in such a manner that the flow resistance is steadily decreasing with decreasing pressure difference across the valve at least over a certain pressure range. Desirably, such a valve should be highly sensitive to pressure differences occurring between an inlet and an outlet so that it may be used as a ventilation valve in blood pressure measuring equipmentto cause the pressure in an inflatable chamber of the equipment to decrease at an at least approximately constant rate during at least a part of the ventilation phase.

According to one aspect of the present invention there is provided a valve comprising a housing provided with fluid inlet means and fluid outlet means arranged to be in flow communication with each other by way of a flow path through the housing, and a resiliently deformable flow control body arranged in the housing and provided with passage means extending through the control body between opposite ends thereof to form at least part of the flow path, the housing including means defining with at least a portion of the external.

surface of the control body a fluid pressure chamber which is in flow communication with the flow path so as to be fillable with fluid when fluid flows through the housing and which is so arranged and dimensioned that, on flow of fluid under pressure along the flow path, the pressure exerted by fluid filling the chamber deforms the control body so as to vary the flow resistance of the passage means in dependence on the difference between the fluid pressure at the inlet means and the outlet means, at least the greater part of said external surface portion of the control body being so arranged between said ends of the control body that at least the major part of such pressure acts on the control body substan tiallytransversely of the passage means.

According to another aspect of the present invention, there is provided blood pressure measuring equipment incorporating a valve as defined above, the equipment comprising a sleeve which is adapted to be fastened to a limb of a person and which comprises pressure-displaceable wall means enclosing a pressure chamber, the inlet means of the housing of the valve being in flow communication with the chamber of the sleeve.

By the use of such a valve in this manner, it may be achieved that the flow resistance of the valve varies in such a way with the pressure difference across the valve that this pressure difference, and also the pressure in the chamber of the sleeve, decreases substantially linearly with time when the chamber is ventilated. It may be noted that also the fluid outflow rate during the ventilation will then be approximately constant.

An embodiment of the present invention will now be more particularly described byway of example and with reference to the accompanying drawings, in which: Figure 1 is a cross-section of a throttle valve according to the said embodiment, Figure 2 is a plan view, to an enlarged scale, of a setting member projecting into a throttle body of the valve of Figure 1, Figure3 is a schematic elevation of blood pressure measuring equipment incorporating the valve of Figure 1, Figure 4 is a view similar to Figure 2 of a setting member according to a first modification, Figure 5 is a view similar to Figure 2 of a setting member according to a second modification, Figure 6 is a cross-section, to an enlarged scale, of a throttle body and setting member modified to act as an electrical switch, and Figure 7 is a perspective view of the setting member of Figure 6.

Referring now to the drawings, there is shown in Figure 1 a flow regulating valve comprising a generally cylindrical housing 3 provided at its lower end with a stub pipe defining an inlet 3a. A cylindrical sleeve 5 is arranged co-axially in the housing 3 and rigidly and hermetically connected thereto at the end of the housing remote from the inlet. The sleeve 5 is provided in the centre of its end wall at the inlet side with a circularly round di aphragm opening 5a, and the cylindrical wall of the sleeve is provided approximately in its central region with openings 5b distributed uniformly around its circumference.

Retained in the sleeve 5 is a throttle body 7, which is co-axial with the axis of the housing 3 and the sleeve 5 and which consists of a rubber-elastic material having a modulus of elasticity of about 1 to 100 MegaPascals, for example silicone rubber. The throttle body 7 is provided with a continuous longitudinal passage 7a, which is of cylindrical form in the undeformed state of the throttle body. The throttle body 7 itself has a generally cylindrical shape and is provided at its ends with two support portions, the circumferential surfaces of which lie flush against and in sealing contact with the internal surface of the sleeve 5. Disposed between these portions is an annular groove 7b, which is bounded by a cylindrical base surface 7c and two annular end surfaces extending at right angles thereto.The length of the throttle body 7 measured along the passage 7a is greater, namely at least 50% greater, than the diameter of the throttle body. The length of the throttle body 7 may be for instance about twice the diameter of the throttle body.

Arranged at the end of the housing 3 remote from the inlet 3a is an outlet member 9, which comprises a stub pipe projecting out of the housing and a disc-shaped flange, which is disposed in the housing interior and which bears against an end face of the throttle body 7. A resilient tension ring 11 inserted into an annular groove of the housing 3 holds the outlet member 9, and thereby the throttle body 7, firmly in the housing. The two plane, radial end surfaces of the throttle body 7 lie flush against and in substantially gas-tight sealing contact with the adja cent surfaces of the end wall of the sleeve 5 and the radial collar of the outlet member 9, respectively.

The outlet member 9 defines an outlet passage which is formed at least in part by a threaded bore 9a.

Associated with the throttle body 7 is a setting member 13 which comprises a threaded spigot 13a threadedly engaged in the bore 9a and a thinner, cylindrical pin 13b, which projects into the passage 7a of the throttle body. The diameter of the pin 13b is smaller than that of the passage 7a so that, with the throttle body in its undeformed state, a free, annular air flow gap is present between the external surface ofthe pin 13b and the wall surface of the passage 7a.

The threaded spigot 13a is provided with a groove or a flattening 13c extending over its entire length, so that a free flow channel is provided between the spigot 13a and the internal surface of the outlet member 9. The spigot 13a is preferably provided at its end face with a slot or other means enabling engagement of a tool for effecting rotation of the setting member. The setting member 13 has a longitudinal bore 13d (Figure 2) which, starting from the end face of the pin 13b remote from the spigot 13a, extends at least to the end of the pin 13b where it adjoins the spigot or else extends continuously over the entire length of the setting member 13 and which is connected with a radial bore 13e opening out into the groove or flattening 13c.The setting member itself consists of a material which is rigid in comparison with the material of the throttle body 7, i.e. has a substantially greater modulus of elasticity.

The inlet 3a, the opening 5a, the passage 7a of the throttle body 7 and the channel present between the spigot 13a and the internal surface of the outlet member 9 together form part of a flow path 15 for air to be conducted through the valve 1. The flow cross-sectional area of the opening 5a is smaller than that of the inlet 3a and also that of the passage 7a. A space is present between the internal end surface of the housing 3 at the inlet side and the adjacent end of the sleeve 5 and this space forms the rest of the flow path 15 as well as, together with the openings 5b and a space between the housing inner circumferential wall surface and sleeve outer circumferential wall surface, a branch 17 from the flow path.The branch 17 connects the flow path with a pressure chamber 19, which is bounded partly by the surfaces of the throttle body 7 defining the groove 7b and partly by the housing 3 and sleeve 5.

In operation of the valve 1, the inlet 3a thereof is connected with a chamber which contains air standing under excess pressure with respect to the pressure of the ambient atmosphere and which is to be ventilated. Air exhausted from the chamber flows in the direction of the arrow 21 along the flow path 15, whilst a pressure gradient arises between the inlet 3a and the outlet provided by the outlet member 9. Air also flows from the flow path 15 through the branch 17 to the chamber 19, which extends annularly around a part of the outer wall surface of the throttle body 7 and thereby also around the passage 7a. The air filling the chamber 19 has a higher pressure than the air flowing through the passage 7a and exerts a pressure force on the rubber-elastic, deformable throttle body 7. As the radial end surfaces of the resilient throttle body 7 are substantially gas-tightly covered by the end wall of the sleeve 5 and the radial collar of the outlet member 9, respectively, the pressure forces exerted on the throttle body 7 are, at least to the major part, directed generally radially to the longitudinal axis of the throttle body 7. The area of the surface of the groove 7b partially bounding the chamber 19 is substantially greater than that of the surface bounding the passage 7a. In particular, the area of the cylindrical base surface 7c of the groove 7b is about five to twenty times, preferably approximately twelve times, that of the boundary surface of the passage 7a.The radially inwardly directed pressure acting on the throttle body at the groove 7b is therefore correspondingly higher than the radially outwardly directed pressure force acting in the pressure 7a. The throttle body 7 is therefore compressed when a pressure difference is present between the housing inlet and outlet and air flows through the housing via the flow path 15 and into the environment. The deformation of the throttle body is, depending on the construction of the valve 1 and particularly of the throttle body 7, noticeable even at very small pressure differences or else only when the pressure differences exceed a certain minimum value.

At the beginning of the ventilating operation, the throttle body can be so strongly compressed that it tightly encloses the pin 13b. In this case, the air can at first flow out only through the bores 13d and 13e of the setting member 13. When the pressure then reduces with progressive ventilation of the chamber, with which the inlet 3a is connected, the amount of compression of the throttle body also becomes smaller. As a result, a progressively enlarging crosssectional area of the passage 7a is provided for the flow or air therethrough. The flow resistance of the passage 7a thus reduces when the pressure on the inlet side of the valve reduces within a certain pressure range. Accordingly, the smaller the press ure, the less the throttle valve throttles the air outflow.It can be achieved through suitable dimensioning that the pressure reduction during ventilation, for example from 40 kilopascals down to 10 kiloPascals or even down to smaller pressures, takes place substantially linearly with time, i.e. by a constant magnitude per unit time. The rate of pressure decay naturally depends on the dimensioning of the valve and on the volume of the chamber to be ventilated. However, the steepness of the pressure decay curve, i.e. the magnitude of the pressure reduction per unit time, can be set within certain limits through axial displacement of the setting member 13.

The cross-sectional areas of the different sections of the branch 17 are substantially greater than those of the surfaces defining the part of the flow path 15 adjoining the branch in the flow direction. As already mentioned, the cross-sectional area of the opening 5a is smaller than that of the stub pipe bore forming the inlet 3a and of the passage 7a. This dimensional correlationship ensures that even in the event of sudden initiation of the ventilating operation, a pressure builds up in the chamber 19 before noteworthy quantities of air flow through the valve and lead to pressure decay.

In this connection it is to be noted that the pressure in the passage 7a reduces not only because of the pressure gradient produced by the opening 5a and the passage 7a, but also according to the Bernoulli equation in view of the relatively high flow speed in the passage 7a.

The valve 1 can in particular be employed as a component of blood pressure measuring equipment, as schematically illustrated in Figure 3. The blood pressure measuring equipment comprises an inflatable sleeve 31, which is fastenable to the arm of a person to be examined and which includes a pressure-tight deformable air chamber and a microphone 33. The air chamber is connected by an air duct 35, which is formed at least in part by a flexible hose, with the inlet 3a of a valve 1, with a manometer 37 and with a pump 39. The pump comprises a manually actuable pump bellows and suction and outlet non-return valves. The microphone 33 is connected by an electrical lead 41 with an electronic unit 43, which includes a battery, an amplifier and a luminescent diode 43a.The valve 1, manometer 37, pump 39 and electronic unit 43 can be integrated into a single appliance which can be held in the hand.

When the blood pressure of a person is to be measured, the sleeve 31 is fastened to the arm of the person concerned. The electronic unit 43 is then switched on by means of a switch provided on the unit and the sleeve is pumped up through actuation of the pump 39, a small amount of air simultaneously flowing out through the valve 1. When a pressure is reached which lies above the maximum blood pressure to be expected, for example, a pressure of 30 kiloPascals, the pumping operation is terminated.

The air then flows through the throttle valve into the ambient atmosphere. The throttle valve is matched to the volume of the air chamber and the setting member 13 is adjusted in such a manner that the pressure reduces at a constant rate, for example a rate in the range of 300 to 500 Pascals per second, at least in the pressure range in which the systolic pressures lie.

With regard to the definition of constant rate of pressure reduction, when the pressure in the air chamber lies within a certain range, the heart activity has the consequence that a small pressure fluctuation arises on each heartbeat. These brief pressure fluctuations, which are rapid by comparison with the ventilation, do not need to be compenstated for by the valve 1. The valve therefore holds constant only the rate of the reduction of the mean pressure, i.e.

the rate of the pressure reduction caused by the ventilation.

Within a certain pressure range, blood flowing through the arteries causes noises, the so-called Korotkoff tones, on each heartbeat. These are detected by the microphone 33 and processed in the electronic unit 43 in such a manner that the luminescent diode 43a provides a visual signal on the occurrence of each Korotkoff tone. The person performing the measurement can at the first signal read off the value of the systolic pressure and at the last signal read off the value of the diastolic pressure from the manometer 37.

In Figure 4 there is shown a modified setting member 53 which comprises a threaded spigot 53a with a flattening 53c and a pin 53b. The setting member 53 differs from the setting member 13 in that, instead of bores 13d and 13e, it has a longitudinal groove 53d, which extends at least over the entire length of the pin 53b and preferably over the entire length of the setting member 53, on the side of the flattening 53c.

In Figure 5 there is shown a setting member 73 according to a further modification, the member 73 having a threaded spigot 73a with a flattening 73c and a pin 73b. The pin is provided in the region of the flattening 73c with a flattening 73d extending over the entire length of the pin. Apart from this flattening 73d, which is defined by a plane parallel to the longitudinal axis of the setting member 73, the pin is bounded by a cylindrical surface.

When the setting member 53 or 73 is used in the valve 1 in place of the setting member 13, the groove 53d of the setting member 53 or the flattening 73d of the setting member 73 performs a similar function, in the use of the valve, as the bores 13d and 13e of the setting member 13.

Figure 6 shows a modified throttle body 87 and setting member 93, the throttle body comprising a basic member of rubber-elastic, electrically insulating material and being constructed in similar manner to the throttle body 7. In that region of a passage 87a of the throttle body that receives a pin 93b of the setting member 93, which is shown in more detail in Figure 7, the passage is provided with an annular, electrically conducting contact 89, which could, for example, be formed by a graphite coating not obstructing deformation of the throttle body. The setting member 93 comprises a basic body of electrically insulating plastics material, which is formed as a threaded spigot 93a and the abovementioned pin 93b.The pin 93b is provided with two spaced apart electrically conducting contacts 95, which extend in the longitudinal direction of the pin and which can be formed by, for example, metal coating. Two electrical conductors 97, formed by a wire or a stranded flexible conductor, each extend through a respective bore of the threaded spigot 93a and are connected to a respective one of the contacts 95. The setting member 93 is otherwise constructed in similar manner to the setting member 13 and also fastened in place in like manner. The remaining parts of the throttle valve receiving the throttle body 87 and the setting member 93 can also be constructed as for the valve 1.

When the throttle body 87 is in its undeformed state, it does not touch the pin 93b or the contacts 95 thereof. However, when the throttle body 87.is compressed to a sufficient extent by air under pressure, the contact 89 contacts the contacts 95 and produces an electrical connection therebetween. A valve equipped with the throttle body 87 and the setting member 93 thus serves to provide, in addition to pressure-dependent throttling of ventilation, pressure-dependent electrical switching.

- When this combined valve and switch is utilised as part of blood pressure measuring equipment, the valve switch can be used in place of a manually actuable switch for switching on of the electronic unit. The valve switch is preferably designed so that the electrical connection between the two contacts 95 is made only when the sleeve has been pumped up to a minimum pressure above the anticipated maximum systolic pressure. The electronic unit can include a timing generator, which is connected with the switch, is started by closing of the switch, keeps the electronic unit in operation for a predetermined period of, for example, a few minutes, and thereafter switches it off again.

The throttle valve can also be modified in other respects. For example, the setting member is not absolutely necessary and could be replaced by a non-displaceably fastened pin or otherwise completely omitted.

In addition, the shape of the throttle body could be varied. For example, in place of the groove 7b with a cylindrical base surface, a groove could be provided which is bounded by a surface having a steadily curved profile. In order that the throttle body is compressed when air is fed under pressure into the throttle body groove, the area of the boundary surface of the groove is, however, preferably larger than that of the boundary surface of the longitudinal passage of the throttle body. Of primary importance for the compression of the throttle body are the radially directed components of the forces exerted internally and externally on the throttle body by the air.If the groove is not exclusively bounded by cylindrical and radial surfaces or if the longitudinal passage of the throttle body is not cylindrical, the area acted on by pressure on the outer circumferential side ofthethrottle body by air fed through the inlet, and the area of the boundary surface of the longitudinal passage acted on by the pressure of air flowing therethrough, should be dimensioned in such a manner that the passage of the throttle body will be constricted when the air fed through the inlet has an excess pressure with respect to ambient air pressure.

The throttle body does not need to necessarily have a groove on its outer circumferential side, but could for example be cylindrical over its entire length. It would then merely need to be so retained that an annular part of its cylindrical outer surface can be acted on by pressure of air fed through the inlet.

The throttle body need not consist entirely of a rubber-elastic material. It could, for example, be constructed as compound body with a rubber-elastic middle member and, at each of the end faces thereof, a ring rigidly cemented or fastened in other manner to the middle member. The throttle body could then be sealingly retained in the housing by these rings.

It would also be possible to attach the throttle body at the end facing the inlet of the valve by an adhesive or other means to the end wall of the sleeve 5 or a different rigid holding member rigidly mounted to the casing of the valve. This holding member should preferably gas-tightly cover the radial end face of the resilient throttle body so as to protect the throttle body against axial pressure forces, but should, of course, have an opening in line with the air passage through the throttle body. The radial end surface of the throttle body adjacent to the outlet of the valve could possibly then be ieft free.It is pointed out in this regard that it is not absolutely necessary to cover the end surface of the throttle body facing the outlet of the valve, because the fluid pressure on the downstream side of the resilient throttle body is substantially equal to the pressure of the ambient atmosphere.

Moreover, the cylindrical throttle body could be replaced by a throttle body formed by a half cylinder obtained by, for example, cutting the throttle body 7 along a longitudinal plane into two halves. Athrottle body with the form of such a ha If cylinder could then be mounted in such a way that its longitudinal plane surface lies flush against and in sealing contactwith a plane surface of a rigid member attached to the housing. The passage 7a would thus be replaced by a passage defined partially by the resilient throttle body and partially by the rigid member. At least that end surface of the throttle body that is facing the inlet of the casing should be gas-tightly covered by a rigid cover to resist axial pressure force. The cover would, of course, be provided with an opening for the air passage.

It is also to be noted that the valves of the described kinds are usable not only for ventilation of the sleeve of blood pressure measuring equipment, but also for other equipment in which the flow resistance to a fluid flowing through the valve is to be varied in dependence on the fluid pressure, or stated more accurately, on the difference between fluid pressure at an inlet side and fluid pressure at an outlet side or ambient pressure.

Claims

1. Avalve comprising a housing provided with fluid inlet means and fluid outlet means arranged to be in flow communication with each other by way of a flow path through the housing, and a resiliently deformable flow control body arranged in the housing and provided with passage means extending through the control body between opposite ends thereof to form at least part of the flow path, the housing including means defining with at least a portion of the external surface of the control body a fluid pressure chamber which is in flow communication with the flow path so as to be fillable with fluid when fluid flows through the housing and which is so arranged and dimensioned that, on flow of fluid under pressure along the flow path, the pressure exerted by fluid filling the chamber deforms the control body so as to vary the flow resistance of the passage means in dependence on the difference between the fluid pressure at the inlet means and the outlet means, at least the greater part of said external surface portion of the control body being so arranged between said ends of the control body that at least the major part of such pressure acts on the control body substantially transversely of the passage means.

2. A valve as claimed in claim 1, wherein the control body is made of a rubber-elastic material.

3. A valve as claimed in either claim 1 or claim 2, wherein the control body is substantially rotationally symmetrical, the passage means extending along the axis of rotational symmetry of the control body and the pressure chamber extending annularly around the control body.

4. A valve as claimed in any one of the preceding claims, comprising means defining flow connection means connecting the pressure chamber to a section of the flow path between the inlet means and the passage means.

5. A valve as claimed in any one of the preceding claims, wherein the length of the control body in direction along the passage means is greater than the maximum dimension of the body in direction transversely of the passage means.

6. A valve as claimed in claim 5, wherein the length dimension of the control body is at least 50% greater than said maximum transverse dimension.

7. Avalve as claimed in any one of the preceding claims, wherein the control body is provided at each of said ends thereof with an end surface extending substantially transversely to the passage means, at least the major part of said external surface portion of the control body being disposed between said end surfaces.

8. A valve as claimed in claim 7, further comprising a rigid cover member rigidly mounted to the housing and fluid-tightly covering that one of said end surfaces at the upstream end of the passage means, the cover member being provided with a flow opening aligned with the passage means.

9. A valve as claimed in claim 8, wherein the flow opening is disposed downstream of a section of the flow between the inlet means and the passage means, the cross-sectional area of the flow opening being less than that of at least a portion of the passage means.

10. Avalve as claimed in any one of the preceding claims, wherein the area of said greater part of said external surface portion is at least five times that of the wall surface of the passage means.

11. Avalve as claimed in any one of the preceding claims, wherein the shape and size of said external surface portion of the control body is so related to the shape and size of the wall surface of the passage means that, when the difference between the fluid pressure at the inlet means and the outlet means increases, the fluid pressure acting on said external surface portion exceeds that acting on said wall surface by such an amount as to cause the control body to be compressed and thereby at least a portion of the passage means to be narrowed.

12. A valve as claimed in any one of the preceding claims, comprising an elongate member which projects into the passage means and so extends therein as to define an annular flow passage between the circumferential surface of the member and surrounding wall surface of the passage means, the modulus of elasticity of the member being less than that of the control body and the cross-sectional shape of the member being such that said part of the flow path through the control body is maintained even on deformation of the control body to substantially close the annular flow passage.

13. A valve as claimed in claim 12, wherein the elongate member is fastened to the housing and is arranged to be displaceable in the passage means parallel to the flow direction therethrough.

14. Avalve as claimed in either claim 12 or claim 13, wherein the wall surface of the passage means and the circumferential surface of the elongate member are each composed at least part of electrically conductive material, the control body being adapted to be so deformed by fluid pressure in the pressure chamber as to cause the electrically conductive material part of the circumferential surface of the elongate member to be placed in electrically conductive contact with the electrically conductive material part of the wall surface of the control body.

15. A valve substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

16. Avalve as claimed in claim 15 and modified substantially as hereinbefore described with reference to Figure 4, Figure 5 or Figures 6 and 7 of the accompanying drawings.

17. Blood pressure measuring equipment provided with a valve as claimed in claim 1,the equipment comprising a sleeve which is adapted to be fastened to a limb of a person and which comprises pressure-displaceable wall means enclosing a pressure chamber, the inlet means of the housing of the valve being in flow communication with the chamber of the sleeve.

18. Equipment as claimed in claim 17, wherein the valve is constructed and arranged to so control fluid outflow from the chamber of the sleeve as to cause fluid pressure in the chamber to reduce at a substantially linear rate over at least a substantial part of the outflow time.

19. Blood pressure measuring equipment as claimed in claim 17 and substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.