GB2077859A

GB2077859A - Pneumatic Systems

Info

Publication number: GB2077859A
Application number: GB8110420A
Authority: GB
Original assignee: Watkins and Watson Ltd
Current assignee: Watkins and Watson Ltd
Priority date: 1980-04-03
Filing date: 1981-04-02
Publication date: 1981-12-23
Also published as: GB2077859B

Abstract

The invention relates to pneumatic systems in which a bellows 5 is inflated by a source of pressurised air and a control valve 9 is arranged between the bellows and the source, the control valve being arranged to feed air as required to maintain the bellows in a predetermined inflated condition. The system is particularly applicable to articulated beds and includes a solenoid operated actuating valve 17 for inflating the bellows. <IMAGE>

Description

SPECIFICATION Pneumatic Systems This invention relates to pneumatic systems and in particular to control and actuating valves for such systems.

In our British Patent No. 1,474,018 there is described a pneumatic system which is particularly intended for raising and lowering the articulated sections of a bed. In the particular embodiment described in our prior British Patent Specification, the head and foot sections of the bed are each articulated to the main frame of the bed and are hingedly movable by means of pneumatically actuated bellows. This is a very convenient system for powering a hospital bed, particularly so-called "low air loss beds" of the kind described in "Bed Sore Biomechanics", pages 259-299, edited by Kenedi, Cowden s Scales, published by Macmillan, 1976, which utilize low pressure air for inflation of groups of sacs for supporting a patient. British Patent No.

1,442,994 also describes beds of this kind.

In the bed described in our Specification No.

1,474,018 the head section, for example, is raised pneumatically by operating a hand control valve which is then switched to an 'off' position, thereby maintaining the head section in the desired raised position by means of the volume of air trapped in the actuating bellows. A similar arrangement may be provided for the foot section.

A particular problem arises with this simple system however, as a result of the great difficulty in producing, on a production basis, a bellows system which is 100% airtight. Even a very small leak in the bellows or its air supply system will result in the hinged head or foot section of the bed collapsing after a few hours. It is to the solution of this problem that the present invention in one of its aspects is specifically directed, although the invention will also find application in other pneumatic systems in which low pressure air is used as an operating field.

Another problem associated with the practical design of beds of the kind described above is to provide suitable means for actuating the articulation of the bed. Such means should preferably be capable of remote actuation by the patient who may be very weak and unable to operate a conventional air valve. The present invention provides in another of its aspects an actuating valve which can be operated remotely merely by touch pressure.

According to the present invention there is provided a pneumatic actuating system which comprises a bellows that is inflated by a source of air under pressure and a control valve disposed between the bellows and said source, said valve being arranged to feed air intermittently and automatically to said bellows as required to maintain the bellows in a predetermined inflated condition.

Various means may be provided to enable the valve to sense deflation of the bellows and thereby actuate the valve to feed the necessary volume of air to the bellows. For the particular use discussed above, namely in bed construction, it has been found that one convenient way of achieving this is to connect the valve to the hinged portion of the bed by a mechanical connection, such as a lever or a line and pulley system.

Various embodiments in accordance with the present invention will now be described by way of illustration with reference to the accompanying drawings in which: Figure 1 is a partial elevation of a bed of the general type described in our prior Patent Specification No. 1,474,018 fitted with a control valve in accordance with the invention; Figure 2 shows diagrammatically the air connections for feeding air to the bellows of the bed shown in Figure 1; Figure 3 is a sectional elevation of the control valve, and Figure 4 is a sectional elevation of the actuating valve for the bellows.

Referring to the accompanying drawings and particularly Figures 1 and 2, the bed comprises a head section 1 which is hingedly connected to the main section of the bed 2 by means of a pivot 3 which is free to move along a track 4 in the direction shown by the arrow Z when the part 1 is hinged upwardly. Upward movement of the head section 1 is effected by supplying air under pressure to bellows 5 disposed between head section 1 and the main section 2. The air circuit diagram is shown in Figure 2 from which it will be seen that the bellows 5 are supplied with air under pressure from an air supply conduit 16 via a bellows actuating valve 1 7 and an inlet tube 18.

An automatic control valve 9 is connected across the actuating valve 1 7 for a purpose which will be described later.

In normal operation of the bellows 5, the actuating valve 1 7 is opened to supply air to the bellows 5. Once the head section 1 of the bed has been raised to the desired position, valve 17 is closed so as to maintain air in the bellows 5.

Valve 1 7 is a three-port valve, the third port being to atmosphere so that when it is desired to lower the head section 1 , valve 1 7 is opened to atmosphere to allow air to escape. The construction of valve 1 7 is shown in detail in Figure 4. Valve 9 is provided to maintain air in the bellows 5 when in its inflated condition and to compensate for any leakages occurring in the system between the valve 1 7 and the bellows 5.

The automatic control valve 9 is located beneath the main section 2 of the bed and linked by levers 7 and 8 to the head section 1 of the bed.

Lever 7 is pivotally connected at one end to the head section 1 and at the other to a wheel forming one plate of a friction clutch 10. The other plate of friction clutch 10 is connected to one end of lever 8, the other end being linked to a push rod 11 which is attached to the moving part of the valve 9.

In an alternative arrangement the movement of the head section 1 can be transmitted to the control valve 9 by means of a cable attached at one end to the head section and passing around a pulley which is connected to one plate of the clutch 10. If the cable is kept under tension by a suitable spring means, pivoting movement of the head section will cause the pulley to rotate and this movement will be transmitted through the clutch to the valve 9.

Referring to Figure 3, the valve 9 is a spool valve having a body 21 which is bored to receive 3 valve spool 22. Spool 22 is connected at its right hand and, as shown in Figure 3, to push rod 11 by means of a threaded stud portion and nut 23. The other end of spool 22 is connected to a threaded rod 24 which is slidable in a guide 25 projecting from body 21. Nuts 26 and 27, which are adjustably mounted on rod 24, provide stops limiting the linear travel of the valve spool 22. The valve body 21 is apertured to provide an inlet port 28 and an outlet port 29. It will be appreciated that the valve 9 is shown in its closed position in Figure 3, that movement of the rod 11 in the direction indicated by the arrow will result in the groove 30 in the valve spool to align with the ports 28 and 29, whereupon pressurised air will flow along air lines 12 and 1 3 into the bellows 5.

'0' ring seals are provided between the valve spool and valve body.

The control valve 9 operates as follows. If the head section 1 of the bed begins to fall e.g.

because of a slight leak in the system, this movement causes the lever 7 to move in an anticlockwise direction as shown in Figure 3 and this movement is transmitted to the clutch plate of the clutch 10 to which it is connected. This rotation is transmitted by the clutch to lever 8 thus causing the lever 8 to move rod 11 if the direction of arrow X in Figure 1. This movement causes the valve spool 22 to move towards the right as shown in Figure 3 so that air is allowed to pass from port 28 through the valve and into airline 13.

Airline 1 3 is connected to the bellows 5 so that air is fed to the bellows to compensate for that lost as a result of the leakage. As bellows 5 reinflates to its former condition lever 7 moves in the opposite direction and this movement is transmitted via clutch 10 to lever 8 so as to close the valve once more. When the valve 9 reaches its closed position, the friction clutch 10 slips. A further adjustable port (not shown) may be provided in the control valve or in another part of the system in order to produce a controlled small leak in cases where the natural leak is too small to actuate the valve 9.

Where the bed includes a pneumatically raisable foot section a further control valve 9 may be provided to ensure an automatic supply of air to the foot section actuating bellows. In general however, it has been found that this is not normally necessary because the weight which the raised foot section is required to support is usually much less than the head section.

The construction of the actuating valve 1 7 is shown in Figure 4. Valve 17 comprises a chamber 41 having an inlet port 42 connected to a source of pressurised air, such as conduit 1 6 (see Figure 2) connected to a blower. A second port 43 provides an exhaust to atmosphere and an outlet tube 44 is connected to the bellows 5. Flow of air into the chamber 41 from the conduit 16 is controlled by a valve head 45 which comprises a steel washer 46 attached to a plunger 47 by a countersunk bolt and spacer nut 48. Bonded to the surface of the washer 46 is a flexible cylindrical pad 49 formed from noninterconnecting, cellular natural rubber or neoprene (available under the Trade Mark "Ruberzote"). Port 42 is fitted with an insert 50 having an upstanding rim 51 which provides an edge onto which the pad 49 can form an airtight seal.Plunger 47 is biased outwardly into its closed position by a spring 52, acting between the back surface of washer 46 and a housing 53 for a solenoid coil. Plunger 47 is formed at least partly from ferromagnetic material and the solenoid coil is so arranged that on passage of a current therethrough, plunger 47 is attacked into housing 53 against the action of the spring thereby lifting the valve head 45 of its seat.

As can be seen, opening and closing of port 43 is effected by a solenoid controlled valve 54 whose construction is the same as the valve described above. All joints in the valve chamber 41 are sealed with a room temperature curing silicone resin such as 'RTV 732' available from Dow Corning. The housing 53 and the housing of the adjacent valve 54 are attached to the chamber 41 by yoke 55 and bolts 56 and 57, the latter being capable of adjusting the compression of the solenoid housings into chamber 41.

Electrical wires for the solenoids are sealed into the housings with silicone resin.

The solenoids are wired to control buttons in a control panel adjacent to the occupant of the bed and the wiring is arranged so that when one solenoid in housing 53 is energised to open its associated valve, the other is not energised thus remaining closed under the influence of its biasing spring. In this condition the bellows will be inflated. In the position shown in Figure 4, the solenoid in housing 53 is de-energised and the other solenoid is energised, thus exhausting the bellows to atmosphere and allowing the head section to sink. A third position requires both solenoids to be de-energised and in this condition both of ports 42 and 43 are closed and the bellows is maintained in an inflated condition, subject to any leaks in the system. As already described, any leaks are automatically compensated by the control valve 9.

instead of using solenoids to power the valves 45 and 54, hydraulic or pneumatic means could be provided to actuate the valve heads and such means could be actuated remotely from the valve.

While the invention has been described with particular reference to a bed having articulated sections, it will be appreciated that the invention is equally applicable to any pneumatic system in which low pressure air is used as an operating fluid.

Claims

1. A pneumatic system which comprises a bellows that is inflated by a source of air under pressure and a control valve disposed between the bellows and said source, said valve being arranged to feed air from said source automatically to said bellows as required to maintain the bellows in a predetermined inflated condition.

2. A bed having a section which is raisable and lowerable with respect to an adjacent section by means of a bellows which is inflatable with pressurised air from a source, the bed including a control valve disposed between the bellows and the source and arranged to feed air from said source automatically to said bellows as required to maintain the bellows in a predetermined inflated condition.

3. A bed according to claim 2 in which the control valve is provided with means for sensing relative movement of the raisable section in a downward direction and is arranged to supply air to the actuating bellows in response thereto in an amount sufficient to restore the raisable section to a predetermined raised altitude.

4. A bed according to claim 3 in which the means for sensing relative movement is a lever connected at one end to the raisable section.

5. A bed according to claim 4 in which the lever is drivably connected to the control valve via a friction clutch.

6. A bed according to any one of claims 2 to 5 in which the control valve comprises a spool valve.

7. A pneumatic system which comprises a bellows which is inflated by a source of air under pressure and an actuating valve for admitting air from said source to the bellows, said actuating valve comprising a chamber having an inlet port connected to the source and a conduit connecting the chamber to the bellows, a valve head carried by a plunger and arranged to move between a position wherein the inlet port is open and a second position in which the port is closed, and remotely operable means for moving the valve head between said open and said closed positions.

8. A system according to claim 7 wherein the valve head is flexibly mounted on the plunger.

9. A system according to claim 7 or claim 8 wherein the valve head comprises a flexible pad which is arranged to seal onto an upstanding surround of the inlet port.

1 0. A system according to any one of the preceding claims wherein the means for moving the valve head between said open and said closed positions includes a solenoid.

11. A system according to any one of the preceding claims wherein the actuating valve comprises twin valve heads, one of said valve heads being operable to open or close said inlet port and the other valve head being operable to open or close an outlet port from said chamber to atmosphere.

12. A pneumatic system according to any one of claims 7 to 11 which includes a control valve for automatically maintaining the bellows in a predetermined inflated condition, said control valve having the features claimed in any one of claims 1 to 6.