US3756380A

US3756380A - Conveyors

Info

Publication number: US3756380A
Application number: US00216174A
Authority: US
Inventors: R Ackroyd; C Mann
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1969-05-08
Filing date: 1972-01-07
Publication date: 1973-09-04
Anticipated expiration: 1990-09-04
Also published as: GB1291115A

Abstract

A conveyor having an air cushion supported endless belt wherein the belt is pervious to enable air to pass through and provide secondary air cushions for supporting conveyed articles on the belt. There is wall boundary means for containing the secondary air cushions. The air supply to the conveyor belt is by way of load responsive valves which open in the presence of a conveyed article. Dual air pressures enable articles to be hovered and manouvered above the belt whilst the conveyor is in operation.

Description

United States Patent 1191 Ackroyd et al. Sept. 4, 1973 54] CONVEYORS 7 3,628,673 12/1971 Lynn 302 29 17 1 2.2233 21:22: 1215:1315; 11:32:?

Pw Charles Alan 3,283,920 11 1966 Schonfelder 302/29 Mann, Annes, both of England United Kingdon Atomic Energy Authority, London, England Filed: Jan. 7, 1972 Appl. No.: 216,174

Assignee:

Foreign Application Priority Data May 8, 1969 Great Britain 23,625/69 References Cited UNITED STATES PATENTS 11/1969 Fleischauer l98/l84 Primary Examiner-Even C. Blunk Assistant ExaminerH. S. Lane Attorney-Robert B. Larson et al.

[ 57] ABSTRACT ions. The air supply to the conveyor belt is by way of load responsive valves which open in the presence of a conveyed article. Dual air pressures enable articles to be hovered and manouvered above the belt whilst the conveyor is in operation.

11 Claims, 12 Drawing Figures PATENTEDSEP 4:915 3756 380 SHEEI 1 [1F 4 CONVEYORS BACKGROUND TO THE INVENTION veyors having mechanical support means for the upper runs of the belts. Known air cushion conveyors are, however, unsuitable for conveying really heavy loads such as the containers now being used in commercial freight traffic notably in the shipping industry and on the railways, because they would require considerably increased power inputs to drive them and would also have to be provided with strengthened load carrying endless belts.

SUMMARY OF THE INVENTION According to the invention in a conveyor comprising a load carrying endless belt mounted on a pair of spaced rotary members, at least one of which is adapted to be driven and to transmit drive to the load carrying endless belt, and having the upper run of the load carrying endless belt supported by an air cushion, the load carrying endless belt is pervious in order to provide a secondary air cushion for at least partially supporting an article on its upper run, there being wall boundary means for containing the secondary air cushion and load responsive valve means which opens in the presence of a conveyed article to supply air under pressure to beneath the load thereby conserving air and permitting reduced belt tension.

The wall boundary means may be associated with the conveyed article or with a carrier therefor or may comprise an inflatable envelope associated with the belt.

The air pressure may be supplied to the belt supporting cushion by way of two sources of different pressure, air from the higher pressure source being utilised to cause air cushion supported articles to hover above the belt whilst the conveyor is operating.

The conveyor according to the invention may be arranged with the base plate disposed beneath both upper and lower runs of the belt in which case the upper run is supported on a cushion of air supplied through the lower run which is itself supported on a cushion of air from the base plate.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view, illustrating the upper run of the load carrying endless belt, of a first construction of a conveyor according to the invention,

FIG. 2 is a fragmentary longitudinal view in section of part of the load carrying endless belt shown in FIG. 1,

FIG. 3 is a plan view similar to that of FIG. 1 and illustrates a second construction of conveyor,

FIG. 4 is a fragmentary longitudinal view in section of part of the load carrying endless belt shown in FIG. 3, shown inclined to the horizontal,

FIG. 5 is a fragmentary cross sectional view of part of a third construction of conveyor,

FIG. 6 is a fragmentary perspective view of a fourth construction of conveyor,

FIG. 7 is a fragmentary sectional view of a fifth construction,

FIGS. 8 and 9 are diagrammatic views of alternative carriers for use with the construction shown in FIG. 7,

FIG. 10 is a fragmentary view of a sixth construction,

FIG. I l is a fragmentary side view in section of a base plate showing load responsive valves, and

FIG. 12 is a diagrammatic view of a seventh construction of conveyor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGS. 1, 2 and 11 there is shown a conveyor comprising a pair of horizontally spaced rotary members 3, 4 and a pervious endless belt 2. Member 3 is adapted to be driven by conventional means not shown. A base plate 7 is disposed beneath the upper run of the belt and has apertures 8. The apertures 8 house load responsive valves 1 and are connected to a common manifold 7a which is connectable to a source of pressurised air. The valves 1 comprise spherical closure members 1a which are normally urged into sealing contact with a valve seat at the mouth of the aperture by the air pressure in the manifold and which normally project above the surface of the table. Associated with the article there is wall boundary means 9 which defines an air retaining chamber 11 above the upper run of the belt for containing air passing through the pervious belt to create a cushion of air between the upper run of the belt and an article being conveyed. The boundary means 9 shown in FIG. 2 takes the form of a carrier for a con veyed article (not shown) and comprises a peripheral skirt 10 having feet 14. The defined air retaining chamber has internal walls 13 of depth co-extensive with the skirt 10 for dividing the chamber into compartments 12. The internal walls have feet 15. The conveyor belt 2 is of composite construction comprising an inner tractive layer 5, an intermediate resiliently deformable layer of foamed rubber 5a and an outer smooth protective layer 5b or skin for the deformable layer. The composite belt is perforated with slots 6. In operation the belt driven by rotary member 3 passes over the surface of the base plate 7 and displaces at least some of the valve closure members 1a from their seatings. Compressed air issuing from the apertures 8 forms an air cushion between the belt 2 and the base plate 7. Air flowing through the apertures tends to entrain the closure members In and closes the valves so that the valves are opened only by physical contact with the belt and, in general, that condition occurs only in the presence of a conveyed load. Air passes along the underside of the belt to extend the air cushion to unloaded parts of the belt; the air cushion assisted by belt tension, serving to hold the belt clear of the base plate. Air also passes from this air cushion through the slots 6 in the belt 2 into the compartments 12 beneath the boundary means 9 where the air is confined by the feet 14 and 15 sealing with the foamed rubber outer covering 5a. The article associated with the boundary means 9 is thus at least partially supported by secondary air cushions on the belt 2 which is itself supported above the base plate 7 by an air cushion. The load responsive valves improve stability by maintaining the air cushion thickness between article and base plate substantially uniform and the total load of a conveyed article is uniformly distributed over the belt. The load sensitive valves can be arranged to have slight leakage so that even at the unloaded parts of the belt there is sufficient air to provide lubrication between the base plate and belt. Furthermore, if the air pressure in the chamber 11 beneath the article is temporarily increased by increasing the air supply to the air cushion between the base plate 7 and the belt 2 supporting the article, the article will hover above the belt 2 so that it remains stationary even though the belt is still moving. Under these conditions the article is easily moved from one load carrying endless belt to another one moving either in line or at an angle.

FIGS. 3 and 4 of the drawings show another form of conveyor in which a load carrying endless belt 16 is mounted on spaced rotary members 17 and 18, one or both of which are driven. The belt 16 has a tractive portion 19, of conventional rubberised canvas construction, which is covered on its outer surface by a layer of foamed rubber 20 having a smooth slightly resilient outer covering 21. A base plate 22 beneath the upper run of the belt 16 has valved apertures in similar manner to the base plate 7 of the previous described embodiment to effect the formation of an air cushion 23 between the lower surface of the tractive portion 19 of the belt 16, and the base plate 22. The belt 16 is perforated by slots 24 which extend parallel with the longitudinal centre-line of the belt 16 and are equidistantly spaced apart from one another in the length and breadth of the belt 16. As shown in FIG. 3, this arrangement is such that the slots 24 are offset from one another and from staggered lines of slots across the breadth of the belt 16.

An article 25 located on the belt 16 has an air retaining chamber 26 enclosed by a peripheral skirt 27 associated with the base of the article 25. The chamber 26 is provided with moulded rubber or plastic inserts 28 forming an egg-box configuration of compartments beneath the article. The inserts 28 are deeper than the skirt 27.

In operation, air from the air cushion 23 is in communication via the slots 24 in the belt 16 with the compartments of the chamber 26 enclosed within the peripheral skirt 27 at the base of the article 25. Because the inserts 28 are deeper than the peripheral skirt 27 of the article 25, the walls of the compartments form effective air seals with the resilient outer covering 21 of the belt 16. The outer covering 21 in addition to being smooth and resilient is connected to the tractive portion 19 of the belt 16 by convolute canvas linkages 29 extending through the foamed rubber layer 20. The conveyor can thus be used for conveying articles 25 up inclines, the conveyor shown in FIG. 4 being shown so inclined. A heel 30 at one end of the air retaining skirt 27 of the article 25, deforms the layer 20 causing it to contract from its normally expanded position. The foamed rubber layer immediately behind the article 25 expanding to the full height of the linkages 29, thus providing a barrier to prevent the articles 25 from sliding down the incline. The air pressure in the compartments provides air support for the weight of the article 25. Furthermore, if the air pressure in the air cells beneath the article 25 is temporarily increased by increasing the air supply to the air cushion between the base plate 22 and the belt 16 supporting the article 25, the article 25 will hover above the belt 10 so that it remains stationary even though the belt is still moving. Under these conditions the article 25 is easily moved from one load carrying endless belt to another one moving either in line or at an angle.

FIG. 5 shows a cross section of part of an alternative form of load carrying endless belt according to the invention in which a load carrying endless belt 31 has an article 32 supported on it. The article 32 has a skirt 33 attached to the periphery of its base the skirt defining an air retaining chamber 34 which is divided into compartments 35 by internal walls 36. The load carrying endless belt 31 comprises an outer sheath 37 filled with a resilient material 38 such as sponge rubber and a foraminous membrane 39 extending around the outer surface of the sheath, the membrane being sealably attached to the edge regions of the belt 31. An air cushion 40 is formed between the inner surface of the belt 31 and a base plate 41. Jets located in the base plate 4] supply air by way of load responsive valve closure members la to the air cushion 40 and some of this air passes to the underside of the resilient foraminous membrane 38 by means of aligned perforations 42 in the sheath 37 and the resilient material 38.

In operation air from the air cushion 40 passes through the perforations 42 and then diffuses through the resilient foraminous membrane 39 into the chamber 34 beneath the article 32. The build-up of air pressure in the chamber 34 partially supports the article 32 on the belt 31. At the same time the pressure drop across the resilient foraminous membrane 39 forces it upwards into sealing contact with the air retaining skirt 33 and the internal walls 36. Thus a space 43 is created between the resilient foraminous membrane 39 and the sheath 37. The build-up of air pressure in the space 43 compresses the resilient material 38, extending the space 43, so that it acts as an air spring supporting the article 32. Alternatively the compartments 35 of the chamber 34 beneath the article 32 may be occupied by flexible containers filled with a relatively incompressible material, such as water, which allows the material to change shape without any change in its volume.

A temporary increase in air flowing to the air cushion 40 immediately below the article 32 will cause an increased air flow into the chamber 34 beneath the article 32. The resulting increase in air pressure in the chamber 34 will cause the container to hover above the belt 31 so that it remains stationary even though the belt 31 is still moving. Under these conditions the article 32 may be easily moved from one conveyor to another.

The conveyor shown in FIG. 6 is generally similar to the previously described conveyors in that it comprises an endless pervious conveyor belt 44 mounted on rotary members (not shown) and base plate 45 disposed beneath the upper run of the belt. The base plate has apertures 46 housing load sensitive valve members (not shown) and which are connected to a common manifold for supply of compressed air for supporting the belt and conveyed article on cushions of air. For conveyance the articles are mounted on carriers only one of which is shown and designated 47. The carrier has a flexible inflatable portion 48 comprising a light membrane peripherally sealed to a load bearing platform 49 and the membrane has four air inlet defining apertures 50 in the central region adjacent the belt. In use air passing through the belt flows through the apertures 50 to inflate the inflatable portion and creates an air supporting cushion beneath the article; inflation is achieved because static pressure within the envelope builds up to a higher value than that flowing along the outside of the membrane.

In a further embodiment of the invention illustrated in FIG. 7 the construction of conveyor is generally as described with reference to FIG. 6 except that the carrier comprises a load supporting platform having inflatable portions in the form of expansible bellows disposed between the platform and the conveyor belt. The base plate complete with load responsive valves is shown at 51, the belt at 52 and the carrier is designated 53. The carrier comprises a load bearing platform 54 having attached to its underside an annular bellows forming a seal 56 and an annular rubber pad 57. A three port control valve 58 carried at the upper side of the platform is connected to the interior of the air cushion seal 55 which is closed at its lower face. The air cushion seal 55 is selectively connectable to a vent 59 or to the central regions 60 of the lower face of the platform bounded by the annular central seal 56. The valve 58 is actuated automatically by valve actuating bellows 61 connected to the interior of the annular central seal 56. The lower face of the annular central seal 56 has penetrations 62. The rubber pad 57 has concentric grooves 63 in its lower face. In operation air passing through the conveyor belt 52 from the belt supporting air cushion enters the annular central seal 56 by way of the apertures 62 and the build up of static pressure extends the seal to abut the belt. The pressure extends to bellows 61 and actuates the valve 58 to connect the central region 60 of the underside of the platform to the air cushion seal 55 so that the seal is expanded to engage the surface of the belt. Thus an air supporting cushion is created between the rubber pad and the belt the air cushion being retained by the annular expandible seals 55, 56. When air pressure to the conveyor is cut off the annular central seal and the valve actuating bellows collapse thereby actuating the control valve 58 to vent the air cushion seal 55. FIGS. 8 and 9 show further alternative constructions of inflatable carrier. The carrier shown in FIG. 8 is a simple polythene envelope 69 having an aperture 70 in the face adjacent the belt. Air passing from the belt can enter the envelope through the aperture 70 and inflate it. The carrier shown in FIG. 9 is a similar envelope but it contains an annular hard rubber base 71 and is vented to atmosphere by way of a valve 72. When used to carry an article on the conveyor belt the valve 72 is closed so that the envelope is inflated by air passing through the belt; when the valve is opened the article is supported on the belt simply by resting on the rubber base 71. The inflatable carriers shown in FIGS. 8 and 9 are of simple inexpensive construction and adapt themselves to irregular bases of conveyed articles. They are readily used by slipping them under articles which are being lowered on to the conveyor belt.

In the construction of conveyor shown in FIG. the apertures in the base plate 64 are arranged in two

groups

65, 66. The group 65 of apertures is connected to a manifold 67 which has a source of pressure sufficient normally to provide continuous air cushions for the belt (not shown) and articles being conveyed and air cushion supported on the belt. The group 66 of apertures is connected to a manifold 68 which is connectable to a source of pressurised air of higher pressure than the first source the second source pressure being sufficient to cause articles on the belt to hover. Although only two groups 68 of apertures are shown, the air table may have a greater number of such groups thus making the conveyor particularly useful where it is required selectively to cause articles to hover at prearranged stations prior to their sideways transference to other conveyors or spaced vehicles, for example, rail wagons.

The construction of conveyor shown in FIG. 12 has the base plate 73 disposed beneath both upper and

lower runs

74, 75, of the conveyor belt. In use, the upper and lower belt runs and a conveyed article designated 76 are spaced apart by air cushions. This conveyor has particular advantage where space to accommodate the conveyor is restricted, for example, on board ship the air table can be disposed at deck level and both runs of the belt disposed above the deck.

Possible applications of conveyors according to the invention in the container shipping industry and in rail transport will now be described.

The loading and unloading system of a container ship may employ conventional conveyors, but there is a practical objection to this type of system in that a container ship must operate with a high utilisation factor in order to be economic. Maintenance of such a system with its multitude of moving parts is only practicable when the ship is in port and is empty. Thus reducing the utilisation factor of the ship. This consideration is particularly pertinent when the ship is nuclear powered. The conveyor of the invention is particularly suitable for such a system in that each deck would be provided with fore and aft conveyors and transverse conveyors all of which are on the same horizontal level so that containers can be moved by the conveyors and between the conveyors. In addition the air supply and power requirements for the rotary members can be generated economically on board ship and maintenance of the moving parts (i.e., the rotary members and the load carrying endless belts) or replacement of any of these parts may be accomplished whilst the ship is at sea, thus giving it a very high utilisation factor.

The ship will thus hve a short turn round time when in port, as the containers are simultaneously loaded and unloaded, and all decks may be worked simultaneously.

At present container traffic on the railway system in the form of liner trains and their associated terminals is confined to large flows of freight traffic between major centres of population. Utilising conveyors of the invention it is possible to extend this container rail traffic to include freight traffic between minor centres of population and between major and minor centres of population.

Two kinds of container wagon would be used, one being provided with short conveyors or air table extending across the width of the wagon, whilst the other kind would have one conveyor extending the length of the wagon. These conveyors having the capacity to cause containers located on them to hover above the conveyor belt allows the container to be easily moved from a wagon on to another conveyor or in the reverse direction.

The wagons equipped with conveyors or air tables extending across their widths enable loading of containers on and off station platforms and could be used for services where there is need for rapid interchange of goods; they could be attached to trains operating on ordinary passenger services providing a fast and regular service. Unloading and loading of containers at stations would be rapid and would not extend the stopping time of the trains. The station platfonns would also be equipped with conveyors according to the invention in order to give rapid movement of containers to and from the trains.

Wagons equipped with longitudinal conveyors could be used for liner trains. By equipping the liner train terminals with similar conveyors very rapid handling of containers would occur and consequently would greatly improve the utilisation of rolling stock by comparison with the present use of cranes. In addition suitable combinations of conveyors according to the invention would also provide shunting facilities for the station platforms and terminals. Two longitudinal conveyors arranged side-by-side down a station platform enable rapid sorting and marshalling of goods. For example, it is a relatively simple operation to sort a specific group of goods from a random array on a train having air tables and to re-arrange them in a desired order. Typically, the specified goods and non-specified goods are transferred sideways to the two conveyors to form sub-groups and by a combination of longitudinal movement of the conveyors, hovering and sideways transfer, the goods are re-arranged in the desired order on the conveyors and then returned to the train.

We claim:

1. A conveyor comprising:

a pair of horizontally spaced rotary members,

an endless pervious conveyor belt mounted on the members,

means for transmitting drive to at least one of the rotary members,

a base plate disposed beneath the upper run of the belt, the base plate having apertures therein,

a load responsive valve in each of at least some of the apertures, the load responsive valves being adapted to open to allow fluid flow through the apertures in response to the presence of a conveyed load,

at least one common manifold connected to the apertures for directing a pressurised air flow therethrough to form an air cushion support for the upper run of the belt, and a carrier for an article, the carrier having a rigid peripheral skirt scalable with the belt and bounding an air retaining chamber above the upper run of the belt for containing air passing through the pervious belt to create at least one cushion of air between the upper surface of the upper run of the belt and the carrier being conveyed.

2. A conveyor according to claim 1 wherein the carrier has internal walls of depth at least co-extensive with the skirt for dividing the chamber into compartments.

3. A conveyor according to claim 2 wherein the pervious endless belt is perforated and is of composite construction comprising an inner tractive layer, an intermediate resiliently deformable layer and an outer smooth protective layer for the deformable layer.

4. A conveyor according to claim 3 wherein the perforated load carrying endless belt has convolute linkages extending through the perforated resiliently deformable material connecting the smooth protective layer to the inner tractive layer.

5. A conveyor according to claim 1 wherein the apertures in the base plate are arranged in two groups, the

apertures in one group being connected to a first manifold and connectable to a first source of pressurised air and the apertures of the second group being connected to a second manifold and connectable to a second source of pressurised air of higher pressure than the first source, at least the second group of apertures having a load responsive valve in each aperture.

6. A conveyor comprising:

a pair of horizontally spaced rotary members, an endless pervious conveyor belt mounted on the members, means for transmitting drive to at least one of the rotary members,

a base plate disposed beneath the upper run of the belt, the base plate having apertures therein, a load responsive valve in each of at least some of the apertures,

the load responsive valves being adapted to open to allow fluid flow through the apertures in the presence of a conveyed article, at least one common manifold connected to the apertures for directing a pressurised air flow therethrough to form an air cushion support for the upper run of the belt, and

a carrier for an article supported by the belt, the carrier having at least one flexible inflatable portion disposed above the upper surface of the upper run of the belt and at least one air inlet for receiving air passing through the belt thereby to inflate the inflatable portion and create an air supporting cushion beneath the article.

7. A con'veyor according to claim 6 wherein the carrier comprises a membrane peripherally sealed to a load supporting platform, the membrane having at least one air inlet defining aperture in the central region and adjacent the belt.

8. A conveyor according to claim 6 wherein the carrier comprises,

a load bearing platform,

an outer annular expansible bellows,

an inner annular expansible bellows,

an intermediate annular resilient pad, the annular expansible bellows and pad being attached to the underside of the platfonn, the outer annular expansible bellows having a closed end wall adjacent the conveyor belt, the inner expansible bellows having a perforated end wall adjacent the conveyor belt,

means defining a duct extending from the central regions of the lower face to the platform to the interior of the outer annular expansible bellows, a three port control valve included in said duct and operable to connect the interior of the outer expansible bellows with, selectively, said central regions and to atmosphere,

a control bellows having the interior in communication with the interior of the inner expansible bellows, and actuating linkage connecting the control bellows with the control valve.

9. A conveyor comprising: a pair of horizontally spaced rotary members, an endless pervious conveyor belt mounted on the members, means for transmitting drive to at least one of the rotary members,

a load responsive valve in each of at least some of the apertures, the load sensing valves being adapted to open to allow fluid flow through the apertures in the presence of a conveyed article at least one common manifold connected to the apertures for directing a pressurised air flow therethrough to form an air cushion support for the upper run of the belt, and a foraminous membrane extending around the outer surface of the endless belt, the membrane being sealably attached to the edge regions of the outer surface.

10. A conveyor according to claim 9 wherein the pervious conveyor belt is perforated and comprises a resiliently deformable layer sheathed by a tubular tractive layer.

11. A conveyor comprising:

a pair of horizontally spaced rotary members,

an endless conveyor belt mounted on the members,

means for transmitting drive to at least one of the rotary members,

a base plate disposed beneath the lower run of the belt, the base plate having apertures therein,

a load responsive valve in each of at least some of the apertures, the load responsive valves being adapted to open to allow fluid flow through the apertures in the presence of a conveyed load on the belt, at least one common manifold connected to the apertures for directing a pressurised air flow therethrough to form a supporting air cushion between the base plate and the lower run of the belt, the upper run of the belt being arranged in sliding contact with the lower run of the belt and the belt having perforations to enable air to pass through the belt to form a lubricating air cushion between the lower and upper runs of the belt and to form a load supporting air cushion disposed between the upper run of the belt and a conveyed load.

Claims

1. A conveyor comprising: a pair of horizontally spaced rotary members, an endless pervious conveyor belt mounted on the members, means for transmitting drive to at least one of the rotary members, a base plate disposed beneath the upper run of the belt, the base plate having apertures therein, a load responsive valve in each of at least some of the apertures, the load responsive valves being adapted to open to allow fluid flow through the apertures in response to the presence of a conveyed load, at least one common manifold connected to the apertures for directing a pressurised air flow therethrough to form an air cushion support for the upper run of the belt, and a carrier for an article, the carrier having a rigid peripheral skirt sealable with the belt and bounding an air retainIng chamber above the upper run of the belt for containing air passing through the pervious belt to create at least one cushion of air between the upper surface of the upper run of the belt and the carrier being conveyed.

5. A conveyor according to claim 1 wherein the apertures in the base plate are arranged in two groups, the apertures in one group being connected to a first manifold and connectable to a first source of pressurised air and the apertures of the second group being connected to a second manifold and connectable to a second source of pressurised air of higher pressure than the first source, at least the second group of apertures having a load responsive valve in each aperture.

6. A conveyor comprising: a pair of horizontally spaced rotary members, an endless pervious conveyor belt mounted on the members, means for transmitting drive to at least one of the rotary members, a base plate disposed beneath the upper run of the belt, the base plate having apertures therein, a load responsive valve in each of at least some of the apertures, the load responsive valves being adapted to open to allow fluid flow through the apertures in the presence of a conveyed article, at least one common manifold connected to the apertures for directing a pressurised air flow therethrough to form an air cushion support for the upper run of the belt, and a carrier for an article supported by the belt, the carrier having at least one flexible inflatable portion disposed above the upper surface of the upper run of the belt and at least one air inlet for receiving air passing through the belt thereby to inflate the inflatable portion and create an air supporting cushion beneath the article.

7. A conveyor according to claim 6 wherein the carrier comprises a membrane peripherally sealed to a load supporting platform, the membrane having at least one air inlet defining aperture in the central region and adjacent the belt.

8. A conveyor according to claim 6 wherein the carrier comprises, a load bearing platform, an outer annular expansible bellows, an inner annular expansible bellows, an intermediate annular resilient pad, the annular expansible bellows and pad being attached to the underside of the platform, the outer annular expansible bellows having a closed end wall adjacent the conveyor belt, the inner expansible bellows having a perforated end wall adjacent the conveyor belt, means defining a duct extending from the central regions of the lower face to the platform to the interior of the outer annular expansible bellows, a three port control valve included in said duct and operable to connect the interior of the outer expansible bellows with, selectively, said central regions and to atmosphere, a control bellows having the interior in communication with the interior of the inner expansible bellows, and actuating linkage connecting the control bellows with the control valve.

9. A conveyor comprising: a pair of horizontally spaced rotary members, an endless pervious conveyor belt mounted on the members, means for transmitting drive to at least one of the rotary members, a base plate disposed beneath the upper run of the belt, the base plate having apertures therein, a load responsive valve in each of at least some of the apertures, the load sensing valves being adapted to open to allow fluid flow through the apertures in the presence of a conveyed article at least one common manifold connected to the apertures for directing a pressurised air flow therethrough to form an air cushion support for the upper run of the belt, and a foraminous membrane extending around the outer surface of the endless belt, the membrane being sealably attached to the edge regions of the outer surface.

11. A conveyor comprising: a pair of horizontally spaced rotary members, an endless conveyor belt mounted on the members, means for transmitting drive to at least one of the rotary members, a base plate disposed beneath the lower run of the belt, the base plate having apertures therein, a load responsive valve in each of at least some of the apertures, the load responsive valves being adapted to open to allow fluid flow through the apertures in the presence of a conveyed load on the belt, at least one common manifold connected to the apertures for directing a pressurised air flow therethrough to form a supporting air cushion between the base plate and the lower run of the belt, the upper run of the belt being arranged in sliding contact with the lower run of the belt and the belt having perforations to enable air to pass through the belt to form a lubricating air cushion between the lower and upper runs of the belt and to form a load supporting air cushion disposed between the upper run of the belt and a conveyed load.