PRESSURE-RESPONSIVE VALVE

Abstract: A pressure regulator comprises a housing (1) defining first and second chambers separated by a movable partition (4,5), the first chamber being provided with an inlet port (2) facing towards and sealingly closeable by a rigid central portion (5) of the partition at a position remote from its centroid and an outlet port (3), and the second chamber being vented (7) to a reference pressure, the regulator including means (8) extending between the housing and the central portion (5) of the partition to define a pivot axis for the partition extending between its centroid and the position of the inlet port (2). The partition (4,5) may be a tilting diaphragm or a piston (D) with a peripheral sealing element (S). The pivot axis for the partition may be defined by a fixed pivot pin (20), or by projections (8) extending across the first chamber to abut the partition (4,5). A two-stage device is also described in which the tilting partition (35) controls a pilot jet (32) which in turn controls a valve member (43) adapted to permit or deny access from a supply port (44) to an outlet port (33).

Description: This invention relates to pressure regulators, and is particularly concerned with demand valves for breathing apparatus, whereby breathable gas is supplied automatically to a facepiece or mask in accordance with the wearer's respiratory requirements. Most particularly, the present invention relates to demand valves of the positive pressure type which continually maintain a pressure slightly greater than that of the surrounding atmosphere within a facepiece or helmet, 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. Such a valve is disclosed in GB 2,116,852, where a main valve controlling gas supply is operated in response to a pressure drop in a pilot chamber to which pressurised gas is fed via a first orifice and exhausted by a second, larger orifice. A lever adjacent the second, outlet orifice is moved by a diaphragm towards and away from the outlet orifice to exert a throttling effect without coming into sealing contact with the second orifice. In practice, very small changes in pressure across the diaphragm, of the order of 1 millibar or less, may be required to regulate the flow of gas entering the valve at a supply pressure of typically 7 bar or greater, and in order to gain the necessary mechanical advantage, known valves generally employ various lever and spring arrangements. Alternatively, valves of the Pilot or two-stage type are sometimes used, wherein the mechanical advantage is obtained by gas pressures. However, such valves still 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 biasing the diaphragm with a spring. One such device is described in GB-A-2075848, wherein a diaphragm is continually urged into sealing engagement with a valve seat by means of a spring so that the valve normally remains closed, the diaphragm being tilted about an edge of the valve port when a pressure differential is applied so that the port is opened. The reliability of breathing apparatus is of the utmost importance, and to this end it is desirable for its construction to be very simple. In accordance with the invention, a two-stage pressure regulator comprises a pilot valve and a main valve, the main valve comprising an inlet port for high-pressure gas, a movable valve member adapted for movement between an open and a closed position to respectively allow or deny access from the inlet port to an outlet port of the pressure regulator, the valve member being urged toward its closed position by the fluid pressure in a pilot chamber of the pressure regulator, pressurised fluid being supplied to the pilot chamber via a flow restricting orifice from the high-pressure gas supply, the pilot chamber having a vent opening, with the pressure regulator being characterised in that the vent opening discharges into a control chamber bounded on one side by a partition having a rigid central portion capable of engaging the vent opening at a point remote from the centroid of the rigid central portion of the partition to seal the vent opening, the control chamber being in fluid communication with the outlet of the pressure regulator via a passage, and the face of the partition remote from the control chamber being exposed to a reference pressure and being engaged at a point between the vent opening and the centroid of the partition by a fulcrum defining a pivot axis for the partition, the arrangement being such that while a predetermined excess pressure exists in the control chamber, the gas pressure applied to the partition causes the rigid central portion of the partition to be held in a position to close the vent opening ensuring that the valve member is held in its closed position by fluid pressure in the pilot chamber, and when the excess pressure in the control chamber is reduced the vent opening is opened by a pivoting movement of the partition to release the pressure in the pilot chamber, and the valve member moves towards its open position. The partition may comprise a diaphragm having a rigid central portion and a flexible peripheral portion sealingly secured to isolate the first and second chambers, or may comprise a piston having a rigid central disc and a peripheral sealing element capable of sealing against the inner surface of the housing as the piston is tilted. The means defining the fulcrum comprises one or more projections contacting the central portion of the diaphragm on its side remote from the inlet port. Two projections may be provided, one on either side of a line joining the inlet port to the centroid of the central portion of the diaphragm. Most preferably, the diaphragm is circular and the rigid central portion is formed by a rigid circular backing plate fixed concentrically to the diaphragm on its side remote from the inlet port. An exemplary embodiment of the invention will now be described in detail with reference to the accompanying drawings, in which:- Figure 1 illustrates, in plan view, a pressure regulator wherein a tilting diaphragm valve operates as a pilot valve; Figure 2 shows the pressure regulator of Figure 1 in sectional elevation in its closed state; and Figure 3 shows the pressure regulator of Figures 1 and 2 in sectional elevation in its open state. Referring now to Figures 1 to 3, there is provided a demand valve of much reduced proportions, wherein a diaphragm arrangement 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 31 which incorporates a pilot jet 32 and an outlet port 33 for connection to a facepiece. A diaphragm 34 of flexible and resilient material, supported over the greater part of its area by a rigid backing plate 35, is clamped in a leak-tight manner to the housing 31 to form a control chamber therewith by a cover 36 secured to the housing by means of screws or a suitable clip arrangement. The cover is vented to atmosphere by one or more ports 37 and bears two internal projections 38 which act as fulcrum points about which the diaphragm 34 can tilt. A port 39 connects the control chamber under the diaphragm 34 to a facepiece, by which means pressure in the facepiece is transmitted to the control chamber and diaphragm 34, and the small flow of gas from the pilot jet 32 is freely allowed to escape to the facepiece when the pilot jet 32 is open. The relative dispositions of the inlet port 32 and the fulcrum points 38 with respect to the diaphragm centre are clearly shown in Figure 1 and it may be seen that the greater part of the diaphragm area lies to one side of the fulcrum axis z-z whilst the inlet port 32 lies to the other side. The diaphragm arrangement may be likened to a simple beam balance in which the diaphragm plate 35 represents the beam, pivoting about the fulcrum points 38 according to the moments applied on the one hand by pressure at the inlet port 32 and on the other hand by pressure within the control chamber. When the pressure in the control chamber exerts a moment greater than that of the inlet port pressure, the diaphragm will close the inlet port. Thus it may be seen that without pressure in the housing the valve cannot close. For a clearer understanding, there follows a description of the way in which the pilot valve operates in practice. When gas, at a substantially constant supply pressure, is admitted to the inlet port 32 the resultant force applied locally to the diaphragm 34 pushes the diaphragm away from the port 32 by tilting it on the fulcrum points 38 in the cover 36, and gas can freely escape from the port 32 into the control chamber. The outlet port 29 allows the incoming gas to pass freely from the control chamber to a facepiece. A spring-loaded exhalation valve in the facepiece (not shown) prevents free escape of the gas to atmosphere, causing pressure to rise in the facepiece and consequently in the control chamber. The resultant force acting on the greater part of the diaphragm area urges the diaphragm to rotate anticlockwise as seen in Figure 3 to a position where the resilient material of the diaphragm 34 seats against the inlet port 32 and the passage of gas is prevented. For any given supply pressure, the proportions of the inlet port and diaphragm, and the relative positions of the fulcrum axis and the inlet port 32 with respect to the diaphragm centre, may be arranged so as to achieve closing of the valve at virtually any desired pressure difference between the control chamber and the reference pressure at vent 37. This closing pressure will always be greater than ambient pressure and this excess might, for example, be of the order of 2 millibars, whilst the exhalation valve on the facepiece might conveniently be arranged to open at an excess pressure of 4 millibars so that the superatmospheric pressure in the facepiece will automatically be maintained at a level between these two Figures. On inhalation, pressure in the facepiece will fall slightly, causing the demand valve to open, admitting gas to restore the closing pressure. On exhalation, pressure in the facepiece will rise, causing the exhalation valve to open, allowing the exhaled breath to escape to atmosphere. If the force applied to the diaphragm by gas pressure at the small pilot jet 32 is not sufficient to bias the diaphragm adequately, then one or more springs 40 concentric with or adjacent to the pilot jet may be used to establish the required closing pressure of the valve. Movement of the diaphragm 34 towards or away from the pilot jet 32, in response to pressure changes within the facepiece, regulates the escape of gas from a pilot chamber 41 respectively raising or lowering the pressure in said chamber. This control pressure results from a small flow of gas into the pilot chamber 41 through a metering orifice 42 in a resilient disc 43. The relative proportions of the metering orifice 42 and the pilot jet 32 are so arranged that when the diaphragm 34 is almost touching the pilot jet there will be sufficient pressure in the pilot chamber 41 to force the resilient disc 43 against the face of the main jet 44 obstructing a plurality of ports 45 in said face such that escape of gas from the main jet 44 to the outlet 33 is prevented. Movement of the diaphragm away from the pilot jet 32 will cause pressure in the pilot chamber 41 to fall, such that the resilient disc will bow away from the face of the main jet 44 under the influence of gas supply pressure, whereupon gas can escape through the ports 45 thus uncovered and pass to the facepiece via the outlet port 33 as indicated in Figure 3. This embodiment of the invention is virtually unaffected by quite wide variations in supply pressure and, if required, the closing pressure may be readily changed by altering the biasing spring 40. For certain applications, the cover 36 may be vented not to atmosphere but to some other reference pressure and, if required, the two fulcrum points 38 may be replaced with a single ridge without affecting the principle of operation. Manual override means, such as an aperture in cover 36 to allow manual tilting of the diaphragm from its closed position, may also be provided. The advantages of this invention over other known demand valves lie in its extremely simple and reliable construction, requiring virtually no maintenance and no adjustment. It is frictionless and free from backlash and, having only two moving parts, the response can be very fast due to the low moving masses. Further, when the valve is in use, continual contact between the diaphragm and the fulcrum points and the tilting motion of the diaphragm allow a smoother operation and less susceptibility to vibration than known valves in which the diaphragm moves with a piston-like motion. The valve may be further protected from the effects of external vibration or acceleration by counterweighting the diaphragm plate 35 so as to obtain a balanced mass on either side of the fulcrum axis. As the resilient material of the diaphragm itself is used as the valve seating, the diaphragm may be rotated slightly to present a new surface to the inlet port, should wear occur. The absence of any load between the diaphragm plate 35 and the port 32 when the valve is not in use prevents any permanent deformation of the resilient material. A further advantage is that, should supply pressure rise due, say, to pressure regulator malfunction, the valve will tend to open, venting the excess gas into the facepiece and hence to atmosphere, thus acting as a relief valve. In an alternative embodiment, not illustrated, the diaphragm 34 may be replaced by a piston comprising a central rigid disc and a peripheral sealing element. The disc will, in operation, pivot about the pivot axis defined by projections 38 to occlude the inlet port 32 when the pressure within the control chamber reaches the required level above that in the chamber vented by port 37. The operation of the regulator is in all other respects as described above. While the valve has been described principally as a demand valve for breathable gas, it should be understood that the valve may be used with other fluids in other applications than as a demand valve.

Claims: A two-stage pressure regulator comprising a pilot valve and a main valve, the main valve comprising an inlet port (44) for high-pressure gas, a movable valve member (43) adapted for movement between an open and a closed position to respectively allow or deny access from the inlet port (44) to an outlet port (45, 33) of the pressure regulator, the valve member (43) being urged toward its closed position by the fluid pressure in a pilot chamber (41) of the pressure regulator, pressurised fluid being supplied to the pilot chamber via a flow restricting orifice (42) from the high-pressure gas supply, the pilot chamber having a vent opening (32), with the pressure regulator being characterised in that the vent opening (32) discharges into a control chamber bounded on one side by a partition (34) having a rigid central portion (35) capable of engaging the vent opening (32) at a point remote from the centroid of the rigid central portion (35) of the partition (34) to seal the vent opening (32), the control chamber being in fluid communication with the outlet of the pressure regulator via a passage (39), and the face of the partition (34) remote from the control chamber being exposed to a reference pressure and being engaged at a point between the vent opening (32) and the centroid of the partition (34) by a fulcrum (38) defining a pivot axis for the partition, the arrangement being such that while a predetermined excess pressure exists in the control chamber, the gas pressure applied to the partition (34) causes the rigid central portion (35) of the partition (34) to be held in a position to close the vent opening (32) ensuring that the valve member (43) is held in its closed position by fluid pressure in the pilot chamber, and when the excess pressure in the control chamber is reduced the vent opening (32) is opened by a pivoting movement of the partition (34) to release the pressure in the pilot chamber (41), and the valve member (43) moves towards its open position. A pressure regulator according to Claim 1, wherein the valve member (43) is a resilient element which is unstressed in its closed position, and is resiliently deformed in its open position. A pressure regulator according to Claim 2, wherein the orifice (42) connecting the pilot chamber (41) to the high pressure supply port (44) comprises a passage of small diameter passing through the valve member (43). A pressure regulator according to Claims 1, 2 or 3, wherein the partition comprises a diaphragm (34) having a rigid central area (35) and a flexible peripheral area. A pressure regulator according to Claims 1, 2 or 3, wherein the partition comprises a tilting piston having a rigid central area and a peripheral sealing element. A pressure regulator according to any preceding Claim, wherein the fulcrum means (38) comprises a single elongate projection engaging the central portion (35) of the partition along the pivot axis. A pressure regulator according to Claim 1, wherein the fulcrum means (38) comprises two or more substantially axisymmetric projections (38) extending from the housing (36) towards the central portion (35) of the partition (34), the pivot axis for the partition (34) extending along a line joining the free ends of the projections (38). A pressure regulator according to Claim 1, wherein the partition (34, 35) has its centre of mass situated on the pivot axis. A pressure regulator according to Claim 8, wherein one or more weights are attached to the central portion (35) of the partition (34) to adjust the centre of mass of the partition (34) and weight or weights so that it lies on the pivot axis. A breathing apparatus characterised by including a pressure regulator according to any preceding Claim.

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