Pilot operated valves

Abstract: There is disclosed a pilot operated valve which includes a valve body (1), a main valve having a main valve member (13) controlling fluid communication between an inlet port (14) and an outlet port (3), a pilot valve (2) including a vent passage sensing downstream pressure to open and close the main vlave member (13) as the sensed pressure is above or below a predetermined pressure, and selectively operable override means (16) to suspend pilot operation of the valve. The override means may be means to occlude the vent passage (10) and thus close the main valve, means to open the vent passage (10) to atmosphere and thus open the main valve, or means to bypass the main valve.

Description: This invention relates to pilot operated valves in general where downstream pressure is sensed and a valve opened or closed in accordance with the sensed pressure. The invention relates particularly to demand valves for breathing apparatus, whereby breathable gas is supplied automatically to the wearer in accordance with his respiratory requirements. A first aspect of the invention is concerned with demand valves of the positive pressure type which continually maintain a pressure within a facepiece or helmet which is slightly greater than that of the surrounding atmosphere, so as to prevent inward leakage. In such demand valves, flow of gas to the wearer is controlled by movement of a sensitive diaphragm having one face exposed to atmospheric pressure, and the other face to pressure within the facepiece. The present invention provides control means for such valves allowing manual override and automatic shut-off of the supply of gas. Valves of the Pilot or Two Stage type are sometimes used, wherein mechanical advantage is obtained by gas pressures. Such valves generally employ pivoted levers as a means of transmitting diaphragm movement to the valve, often because the direction of diaphragm movement is inconvenient and has to be reversed. In known demand valves, the positive pressure is usually established by biassing the diaphragm with a spring. In US-A-3 805 823, there is described a pressure regulator wherein a main valve is opened and closed by a pressure difference across a main diaphragm, the pressure difference being controlled by a pilot valve having a variable restriction operated by a pressure difference sensed between the inlet and outlet ends of the main valve. A first aspect of the present invention concerns a demand valve described in UK Patent application number 2 190 001, the demand valve comprising a housing defining first and second chambers separated by a diaphragm, the first chamber being vented to atmosphere and including fulcrum means to define an eccentric pivot axis for a rigid central part of the diaphragm, the second chamber including a pilot jet facing the diaphragm and closeable thereby at a position on the side of the pivot axis remote from the centroid of the rigid portion of the diaphragm, and a vent passage having an outlet at the outlet of the demand valve, the housing further defining a third chamber communicating with the pilot jet and partially defined by a valve member adapted to deny access from a high pressure supply port to an outlet port, high pressure being supplied to the third chamber via an orifice, such that while a predetermined back pressure is applied to the outlet of the vent passage, the rigid portion of the diaphragm is held in a position to close the pilot jet and the valve member is held in its closed position by the high pressure supplied to the third chamber via the orifice, and that when the back pressure is reduced the pilot jet is opened, the pressure in the third chamber reduces and the valve member moves to permit access from the supply port to the outlet. It is advantageous for demand valves of breathing apparatus to be detachable from the facepiece, for procedural and testing purposes. To this end, the invention provides an automatic shut-off of the demand valve when the demand valve is removed from the facepiece. According to the invention, a pilot operated demand valve for mounting to a facepiece of a breathing apparatus has a housing including an inlet port and an outlet port, and a valve member which selectively allows or prevents fluid communication between the inlet and outlet ports in response to predetermined pressure levels sensed at a vent passage, and further includes means operable selectively to override the pilot operation of the valve by occluding the vent passage, the vent passage including an occluding member movable between a first position in which it occludes the vent passage, and a second position wherein the vent passage is unobstructed, the occluding member including means cooperable with the facepiece to move the occluding member from the second to the first position. In a first embodiment, the occluding member is biassed towards its first position and the occluding member has abutment means cooperating with complementary abutment means on the facepiece so that when the demand valve is mounted to the facepiece the occluding member is urged out of its first position and the vent passage communicates with the interior of the facepiece. In an alternative embodiment, an occluding arrangement may be provided in which the vent passage is occluded by means sensitive to a reduced downstream pressure and acting to open the vent passage when such a pressure is sensed. In such a device, the vent passage is manually occluded, remaining thus until reduced pressure in the facepiece, caused by the commencement of respiration of the wearer, automatically re-opens said passage. Examples of pilot valves, illustrating the invention will now be described in detail with reference to the accompanying drawings, in which: Figures 1 and 2 show first and second embodiments of the invention, in sectioned elevation in Figure 1 and in part-section in Figure 2; and Figures 3 and 4 show another override arrangement for the pilot valve, with the vent passage occluded and open, respectively. Referring now to Figures 1 and 2, there is provided a pilot operated valve, suitable for use as a demand valve, which is of small size and wherein a diaphragm regulates the flow of gas from a small pilot jet which in turn regulates the flow of gas from a larger jet to a facepiece. The demand valve comprises a housing 1 which incorporates a pilot jet 2 and an outlet port 3 for connection to a facepiece 4. A diaphragm 5 of flexible and resilient material, supported over the greater part of its area by a rigid backing plate 6, is clamped in a leak-tight manner to the housing by a cover 7 secured to the housing 1 by means of screws or a suitable clip arrangement. The cover is vented to atmosphere by one or more ports 8 and bears two internal projections 9 which act as fulcrum points about which the diaphragm 5 can tilt. A vent passage 10 connects the area under the diaphragm to the interior of the facepiece 4, by which means not only is pressure within the facepiece 4 transmitted to the diaphragm 5, but also the small flow of gas from the pilot jet 2 when open is freely allowed to escape to the interior of the facepiece. Movement of the diaphragm 5 towards or away from the pilot jet 2, in response to pressure changes within the facepiece, regulates the escape of gas from a control pressure chamber 11 respectively raising or lowering the pressure in said chamber. This control pressure results from a small flow of gas into the chamber 11 through a metering orifice 12 in a resilient disc 13. The relative proportions of the metering orifice 12 and the pilot jet 2 are so arranged that when the diaphragm 5 is almost touching the pilot jet 2 there will be sufficient pressure in the control chamber 11 to force the resilient disc 13 against the face of main jet 14, obstructing a plurality of ports 15 in said face such that escape of gas from the main jet 14 to the outlet 3 is prevented. Movement of the diaphragm away from the pilot jet 2 will cause pressure in the control pressure chamber 11 to fall, such that the resilient disc 13 will bow away from the face of the main jet 14 under the influence of gas supply pressure, whereupon gas can escape through the ports 15 thus uncovered and pass to the facepiece via the outlet port 3. To provide such a demand valve with an automatic cut-off when it is detached from the facepiece 4, there is provided a closure 16 preferably of resilient material, mounted on a lever 17 and biased by a spring 18 into a position to close the vent passage 10. The lever 17 includes a finger 19 which extends toward an abutment 20 on the facepiece, so that when locking ring 21 is tightened the closure 16 is held away from the vent passage 10, and the diaphragm 5 experiences on its underside the pressure within the facepiece, opening the main valve 13 when the facepiece pressure falls. When the demand valve is removed from facepiece 4, the closure 16 blocks vent passage 10, and the pressure built up beneath the diaphragm closes the pilot jet 2, thus closing the main valve 13 as described. Figure 2 shows a part section of a demand valve such as that of Figure 1, with an alternative arrangement for closing the vent passage 10 when the valve is disconnected from a facepiece 4. Spring 22 urges the head 23 of the rod 24 to close the upper end of vent passage 10 when the heel 25 of the rod is not urged upward by engagement with an abutment such as 20 on the facepiece 4. In Figures 3 and 4, the vent passage 10 passes through a chamber 37 closed at one end by a small resilient diaphragm 38 in which a port 39 permits communication between the vent passage outlet and the area under the main diaphragm 5. A plunger 40 projecting through the wall of the housing 1 and biased outwards by a spring 41 has a circumferential groove 42 in which a forked saddle 43 is free to slide vertically as seen in Figures 6 and 7 up and down. A spring latch 44 engages in the plunger groove 42 when the plunger is pushed into the housing, preventing its outward return. When thus engaged in the plunger groove 42, the spring latch 44 pushes the saddle 43 upwardly, so that its upper surface touches the diaphragm 38 and occludes the port 39 therein. Communication between the area under the main diaphragm 5 and the vent passage 10 is thus cut off, and pressure built up under the main diaphragm 5 closes the pilot jet 2 thus closing the main valve 14. Inhalation by the wearer creates a marked reduction of pressure within the facepiece, causing the diaphragm 38 to be drawn downwardly, pressing the saddle 43 against the spring latch 44 and disengaging the latter from the groove 42 in the plunger 40. The plunger then moves outwardly under the influence of the spring 41. The saddle 43, being located in the plunger groove 42, moves outwards with the plunger, thus exposing the port 39 in the diaphragm 38 and restoring communication between the vent passage 10 and the area under the main diaphragm 5. It should be understood that although the various embodiments described concern demand valves for breathing apparatus, it is possible to control any type of valve having a pilot vent passage by selective opening or closing of the vent passage to vary the sensed controlling pressure. The invention is thus applicable to pilot operated valves in general, and is not restricted to the exemplary configurations shown.

Claims: A pilot operated demand valve for mounting to a facepiece (4, 20), the demand valve having a housing (1) including an inlet port (14) and an outlet port (15), and a valve member (13) which selectively allows or prevents fluid communication between the inlet (14) and outlet (15) ports in response to predetermined pressure levels sensed at a vent passage (10), and further including means (16, 23) operable selectively to override the pilot operation of the valve by occluding the vent passage (10), characterised in that an occluding member (16, 23) is movable between a first position in which it occludes the vent passage (10), and a second position wherein the vent passage (10) is unobstructed, the occluding member (16, 23) including means (19, 25) cooperable with the facepiece (4, 20) to move the occluding member (16, 23) from the second to the first position. A valve according to Claim 1, wherein the occluding member (16, 23) is mounted to the housing (1) for movement between its first and second positions, the occluding member (16, 23) being biassed toward its first position, and characterised in that cooperating abutment surfaces (19, 20; 25, 20) on the occluding member (16, 23) and the facepiece (4, 20) engage to displace the occluding member (16, 23) from its first position when the demand valve is attached to the facepiece (4, 20). A valve according to Claim 2 wherein the occluding member (16, 23) is a lever (17) pivotally mounted to the valve body (1) and biassed toward its first position by a spring (18). A valve according to Claim 2 wherein the occluding member (23) includes an elongate stem (24) having an enlarged head (23) at one end adapted to occlude the vent (10), and at its other end an abutment surface (25), axial pressure on the abutment surface (25) causing the head (23) to be moved axially away from the vent (10) against the action of a spring (22). A valve according to Claim 1, characterised in that the vent passage (10) passes through a chamber (37) comprising an entry portion and an exit portion (10), a flexible diaphragm (38) extending across the chamber (37) to separate the entry and exit portions, and having an aperture (39) to provide fluid communication therebetween, closure means (43) being selectively engageable with the aperture (39) to occlude the vent passage (10), said closure means (43) being resiliently biassed away from its aperture-closing position and being maintained in that position by a latch means (44), the latch means (44) being releasable by a movement of the flexible diaphragm (38) in the direction towards the exit portion of the chamber (37). A valve according to Claim 5, wherein the closure means (43) comprises a first sliding member (40) mounted to the housing (1) for movement in a plane parallel to that of the flexible diaphragm (38) and a second sliding member (43) carried by the first sliding member (40) for movement in directions perpendicular to the plane of the flexible diaphragm (38), latch means (44) engaging the first sliding member (40) in the aperture-closing position being released by movement of the second sliding member (43) in a direction away from the flexible diaphragm (38).

Inventors: JACKSON PETER JOSEPH, JACKSON, PETER JOSEPH
Applicants: JACKSON PETER JOSEPH, JACKSON, PETER JOSEPH
Application year: 1987
Main classification: A62B9
IPC codes: A62B9