However, in spite of extensive searches, no pilot and slave valves have been found which will operate satisfactorily at low pressures, e. g. pressures of less than one bar. All those valves which have been tested require operating pressures well above one bar and are relatively heavy and otherwise unsuitable (e. g. noisy in operation) for use with low pressure air bag operated equipment for supporting and lifting disabled persons, in which the relatively large volume air bags require high air flow capacity lines for supply and exhaustion of air to and from the bags for rapid inflation and deflation thereof. The problems and needs faced by the invention are for a system to operate and control such air bags, without using electrically actuated solenoid operated valves and without having large bore tubes connected to the hand control.

In order to solve the foregoing need and avoid the aforementioned problems, the present invention is based on the general concept of providing a low cost, simple to manufacture, operationally reliable, lightweight valve which is functionally effective and safe working at pressures below 1 bar (approx. lxlO5pa).

According to one aspect of the present invention there is provided a valve comprising a stiff inelastic mounting, a flexible resilient actuator mounted on one side of the mounting and a flexible resilient valve member mounted on the other side of the mounting to sealingly engage the mounting around a port in the mounting, the resilient actuator being operable to move the valve

member, via the port, out of sealing engagement to permit air to flow through the port.

The actuator may cover the port. The valve may include chambers either side of the port.

More particularly, the present invention provides a low pressure pneumatic valve control system comprising at least one manually actuable pilot valve to control a respective remote slave valve, which is characterised in that:- (a) the or each slave valve comprises a stiff inelastic mounting, a flexible resilient diaphragm actuator mounted on one side of the mounting, and a flexible resilient valve member mounted on the other side of the mounting, having an annular valve part resiliently urged into sealing contact with said other side and a central part extending through a port in the mounting to abut or be abutted by the diaphragm actuator so that a first chamber is defined between the valve part and the diaphragm; and comprising a first working air passage to said chamber, and a second working air passage from the valve to or from which said air can flow from or to the first chamber when the diaphragm is displaced to move the central part so as to lift the valve part out of sealing engagement with said other side; and in that (b) an inelastic cover is provided over the diaphragm actuator to define therewith an actuation or second chamber having an actuator air inlet to admit pilot air from the pilot valve to pressurise this chamber and drive the diaphragm actuator towards said port for opening the valve.

The present invention further provides a low

pressure pneumatic valve control system comprising at least one manually actuable pilot valve to control a respective remote slave valve, which is characterised in that:- (a) the or each pilot valve comprises a stiff inelastic mounting, a flexible resilient diaphragm actuator mounted on one side of the mounting, and a flexible resilient valve member mounted on the other side of the mounting, having an annular valve part resiliently urged into sealing contact with said other side and a central part extending through a port in the mounting to abut or be abutted by the diaphragm actuator so that a pilot pressure chamber is defined between the valve part and the diaphragm; and comprising a first passage leading to said chamber, and a second passage from the valve through which said air can flow from or to the first pressure chamber when the diaphragm actuator is displaced manually to move the central part so as to lift the valve part out of sealing engagement with the other side.

In either valve, the area bounded by the valve part is preferably less than the area of the diaphragm actuator exposed to pressure in said first chamber, and the central part is preferably attached to said diaphragm so that pressure on said diaphragm actuator tends to urge the valve part towards said mounting.

In the slave valve, the cover is preferably provided with an air bleed to slowly vent the pressure of the air in the actuation or second chamber.

The pilot and slave valves are preferably connected by narrow bore (e. g. less than 2mm bore) flexible tubing whereas the slave valve is preferably connected to an air bag or like inflatable active unit by relatively wide bore

pipe or tubing (e. g. greater than 5mm bore).

The slave valve is preferably dimensioned to provide a flow path for the working air (when the valve is open) sufficient to permit a flow of at least one order of magnitude greater than the maximum flow through the pilot valve, at the same pressure.

The diaphragm and valve member preferably have peripheral flanges by means of which they are mounted on, e. g. clamped or bonded to., the mounting.

The mounting is preferably formed from a planar sheet, board or blank of material which is apertured to provide the port.

The invention further provides pneumatic patient support apparatus comprising a remote control unit, a slave unit and an inflatable unit, wherein the remote control unit comprises at least one pair of pilot valves connected by flexible tubes to respective ones of a pair of slave valves of a remote control unit, and wherein one of the slave valves controls the supply of air under low pressure to the inflatable unit and the other controls the discharge of air under pressure from the inflatable unit.

Each pair of valves preferably comprises a common mounting with flexible resilient members bonded or clamped to both sides of the mounting around each port of a pair of ports provided in the mounting to form the valves.

Each of said units may comprise a plurality of said pairs of valves having a common mounting. The flexible tubes may be grouped together within a casing or sheath to form a flexible umbilicus between the units. The sheath may serve also as a conduit for the supply of air under pressure to the pilot valves.

The invention will be described further, by way of example, with reference to the accompanying diagrammatic drawings wherein:- FIGURE 1 shows the schematic arrangement of two pilot valves and two slave valves connected in a system for controlling the inflation and deflation of an inflatable device (now shown) all the valves being shown in vertical cross-section in which the left hand half of the view illustrates the valve in a closed condition and the right hand half illustrates the valve in an open condition; FIGURES 2A and 2B show mouldings incorporating the valve members of respectively a pair of pilot valves and a pair of slave valves; FIGURE 3 is a perspective view of a second embodiment of system of the invention; FIGURE 4 shows a slave valve unit with its housing separated of the second embodiment FIGURE 5 is a sectional view on the line A-A in FIGURE 4; FIGURE 6 is a sectional view on the line B-B in FIGURE 4.

Referring to FIGURE 1, each of the pilot air valves 1 and 2 comprises a mounting 10, an actuator 11 and a valve member 12.

The mounting 10 is a substantially rigid planar board of thermoplastics material which is apertured to provide a port 13 therein.

The actuator 11 is a moulded domed diaphragm of rubber like polymeric material which is resiliently flexible, and has an annular peripheral flange 14 which is bonded, e. g. glued or welded, to one side of the mounting so that the diaphragm provides a dome over the port. A

pilot air inlet passage 15 is provided in the diaphragm.

The valve member 12 is a moulding of an elastomeric material having a similar or greater degree of resilient strength or stiffness than the diaphragm so as to resiliently urge an annular valve portion 16 of the valve member against the other side of the mounting 10 around the port 13. An inner U-shaped portion 17 connects the portion 16 with a central upstanding portion 18 which projects upwards through the port 13. An outer U-shaped portion 19 connects the portion 16 with an annular peripheral flange 20 bounded to the other side of the mounting. A pilot air outlet passage 21 is provided in the valve member 12 leading to an annular chamber 17B.

The central upstanding portion 18 is dimensioned to connect with, e. g. abut, the actuator 11, and may, optionally, be connected thereto mechanically, e. g. by bonding or fastening, so as to be constrained to move therewith.

On the one hand, if the resilient force produced by the valve member is sufficient to hold the valve portion 16 in sealing engagement with the mounting against the oppositely directed force produced by the inlet air pressure in a pilot air chamber 17A acting on the effective piston area of the portions 17 and 18 of the valve member then the central portion 18 may merely extend to be abutted by the actuator 11 so that the valve can be opened by manual depression of the actuator. On the other hand if the resilient force is not sufficient, then the central portion 18 and actuator should be mechanically linked so that some of the force produced by the inlet air pressure in the pilot air chamber 17A acting on the larger effective piston area of the actuator is transmitted to the upstanding portion 18 to negate said oppositely directed force and supplement said resilient force.

Referring to FIGURE 1, each of the slave valves 3 and 4 comprises a mounting 22, an actuator 23, a valve member 24 and a cover 25.

The mounting 22 is a substantially rigid planar board of thermoplastics material which is apertured to provide a port 26 therein.

The actuator 23 is a moulded domed diaphragm of rubber like polymeric material which is resiliently flexible, and has an annular peripheral flange 27 which is clamped or bonded, e. g. glued or welded, to the surface of one side of the mounting so that the diaphragm provides a dome over a chamber 27A and the port 26. A pilot air inlet 28 is provided in the cover 25.

The valve member 24 is a moulding of an elastomeric material having a similar or greater degree of resilient strength or stiffness than the diaphragm so as to resiliently urge an annular valve portion 29 of the valve member against the other side of the mounting 22 around the port 26. An inner U-shaped portion 30 connects the portion 29 with a central upstanding portion 31 which projects upwards through the port 26. An outer U-shaped portion 32 connects the portion 29 with an annular peripheral flange 33 bonded to the surface of the other side of the mounting. An air passage 34 is provided in the valve member 24 leading to the annular chamber 47 enclosed by the outer U-shaped portion 32 and a further air passage 35 is provided in the actuator 23, leading to the chamber 27A.

The central upstanding portion 31 is dimensioned to connect with, e. g. abut, the actuator 23, and may, optionally, be connected thereto mechanically, e. g. by bonding or fastening, so as to be constrained to move therewith.

The cover 25 is of domed resilient but non-elastic material e. g. moulded plastics material, and has a fine or small air vent/bleed hole 36 therein to slowly depressurise a chamber 46 defined between the cover 25 and the actuator 23, when the supply of pilot air is stopped.

Referring to FIGURE 1, the system is supplied with low pressure compressed air at less than 0.5 bar, e. g.

0.35 bar (5psi) via a working air supply line 37 and is connected to a pneumatically operated unit (not shown) via a further line 38 controlled by the-system to inflate and deflate the operated unit. The system may be organised, in a simplified form of the manner illustrated in FIGURE 3, to comprise a slave valve unit 39 connected by an umbilicus 40 containing small bore flexible pipes to a pilot valve unit or pneumatic control unit 41, so that the unit 41 in its simple form based on FIGURES 1,2A and 2B comprises only the two pilot air valves, namely the"up" or inflation control valve 1 and the"down"or deflation control valve 2; and the unit 39 comprises two of the slave valves, namely the"up"or inflation valve 3 and a "down"or exhaust valve 4.

Again referring to FIGURE 1 the inlet passages 15 of the valves 1 and 2 are connected in parallel via a line 42 with the line 37 so that when the respective actuator 11 is depressed towards the mounting 10, the valve portion is moved away from the mounting 10 to open the respective valve, air can flow via the outlet passage 21 and a respective fine flexible tube 43 or 44 to the unit 39 to respectively pressurise the chamber 46 of the valve 3 or 4.

In both of the pilot valves 1 and 2, the first or pilot air chambers 17A remain pressurised and the annular chambers 17B are only actively pressurised when the valves are open to permit air to flow from chamber 17A to chamber 17B. Similarly, in the case of each of the slave valves 3

and 4 in the unit 39 the chamber 27A may be pressurised from the line 37 or 38 so that the air flows to the chamber 47 when the valve is opened, but the valve is reversible or operable with a reverse direction air flow, e. g. as illustrated by the valve 4 in FIGURE 1, in which the annular chamber 47 is pressurised from the line 38 and air is discharged'to atmosphere via a silenced vent 45 when the valve is opened by pilot air pressure in the chamber 46. In the case of the valve 3, the flow is normal, e. g. from the line 37 to the chamber 27A and when the valve is open via the chamber 47 to the line 38.

Further, in the valve 4, the valve member 24 may be arranged to perform a pressure limiting function, in that the central upstanding portion 31 may abut, but not be joined e. g. bonded, to the actuator 23 so that the valve opens automatically when the aforementioned resilient force is overcome by the pneumatic force on the portions 30 and 31 when a predetermined safety limit pressure, e. g.

0.8 bar, is exceeded in the chamber 27A, so that air is discharged via vent 45 from the pneumatically operated unit e. g. the bag or bellows of a lifting seat, e. g. in the event of an excessive load being applied to the unit/seat, or the unit/seat being left to overheat in front of a radiant heater.

Referring to FIGURES 2A and 2B, the two valve members 12 (and the two valve members 24) may be provided by parts of integral mouldings 50 and 51, so that the flanges 20 (and the flanges 23) are defined by parts of the moulding 50 or 51. FIGURE 2B also shows that the air passage 34 may be in the form of one or more apertures in the outer U-shaped portion 32 where the arrangement of the slave valve unit 39 is suitable (as exemplified in FIGURE 4).

In the second embodiment shown in FIGURES 3 to 6, the actual pilot valve unit 41 and slave valve unit 39 comprise quadruple pairs of the valves which are arranged