GB2416382A

GB2416382A - Combined pressure regulation and relief valve

Info

Publication number: GB2416382A
Application number: GB0416047A
Authority: GB
Inventors: Nicholas Bridge
Original assignee: Polyflex Aerospace Ltd
Current assignee: Polyflex Aerospace Ltd
Priority date: 2004-07-17
Filing date: 2004-07-17
Publication date: 2006-01-25
Also published as: GB0416047D0

Abstract

This valve combines downstream pressure regulation, to an absolute pressure reference, and downstream pressure relief, to a near absolute pressure reference, using a single sealed and evacuated bellows sensing element. The regulation pressure therefore remains constant and the relief pressure remains almost constant regardless of the external/ambient pressure. At normal downstream pressures valve operates just like a normal absolute pressure regulator but once the regulator seal (7) has closed against the regulator seat (10) should the downstream pressure continue to rise the bellows assembly (3) will continue to shorten by moving at the bottom end under the influence of the relief valve return spring (12) until arrested by the circlip (5) earthing against the adjuster body (6). Further downstream pressure increases will reduce the length of the Bellows (3) further but the movement is now forced to be at the top thus moving the relief valve seal (2) away from the Relief Valve Port (1) and opening a relief flow.

Description

-1- 2416382

COMBINED PRESSURE REGULATION AND RELIEF VALVE

This invention relates to a single valve that provides both downstream pressure regulation and downstream pressure relief functions, to an absolute pressure reference, with a single control element.

Pressure regulation and pressure relief valves are well known and sometimes both the functions are provided in one housing but are essentially 2 separate valves in one body.

Genuine combined valves using a single control element (e.g. a spring) do exist but they control both the regulation and relief pressures to a gauge or ambient reference. If a regulation pressure is required to an absolute pressure reference (i.e. referenced to absolute zero pressure instead of the ambient or the environment pressure) then the relief valve, whether in the same body or not, will be a separate valve with a separate control element (usually a spring) controlling to a gauge reference (i.e. ambient pressure reference). This requires the relief pressure to be significantly higher than the regulation pressure, especially if the valve is to be used in an environment with a variable ambient pressure (i. e. an aircraft or any other variable altitude environment). In absolute terms the regulation pressure will remain constant but in gauge terms, as the ambient pressure reduces, it will increase while the relief pressure remains constant in gauge terms. Therefore the relief pressure has to be higher than the regulation pressure by at least the variation in ambient, or environment, pressure to prevent both sections of the valve being open at the same time and the fluid under control just continuously venting to ambient, or the environment, through the relief valve. Sometimes it would be beneficial to control both the regulation and relief pressure to an absolute pressure reference.

Typical applications for this valve are found in Aerospace applications where the altitude range of the aircraft causes significant variations in the ambienVenvironment pressure and the device receiving the regulated fluid requires a constant pressure in absolute terms. For example the performance of an air compressor is very dependent upon the density, and therefore the absolute pressure, of the inlet gas. The minimum compressor size, for a given performance, over the aircraft altitude range is achieved by taking pressurised air from the engine bleed or ECS system and accurately controlling this air to a known absolute pressure at the inlet to the compressor. Also to properly protect the compressor from excessive torque, in the event that the regulation pressure is exceeded, the maximum inlet pressure must also be relieved to an absolute pressure that is as close as possible to the regulation pressure.

The present invention combines downstream pressure regulation, to an absolute pressure reference, and downstream pressure relief, to a near absolute pressure reference, in one unit using a single sealed and evacuated bellows sensing element. The device also provides means of adjusting the regulating pressure and adjusting the difference between the regulation and relief pressures. Modifications of the design can be incorporated to provide guided and friction damped movement of the evacuated bellows assembly, should it be required to eliminate vibration or shock induced performance variations for example.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying Figure 1 in which: 1. Relief Valve OutleVExhaust Port 2. Relief Valve Soft Seal (in this case rubber but could be another soft material) 3. Bellows Assembly, hermetically sealed with a vacuum in its internal volume (in this case the bellows are of a welded edge construction but could equally be of the hydra formed construction) 4. Valve Housing 5. Circlip (to arrest the movement of the lower end of the bellows at pressures above the regulating pressure) 6. Adjuster body

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7. The Regulator Valve Soft Seal (in this case rubber but could be another soft material) 8. Regulator Valve Return Spring 9. Fluid Inlet Port 10. Seat, Regulator Valve 11. Operating Pin, Regulator Valve 12. Relief Valve Return Spring 13. Regulator Valve Outlet Port The evacuated and hermetically sealed bellows assembly (3) provides the single sensing element for this valve. The free length of the bellows assembly is inversely proportionally to the absolute pressure of the environment in which it lies. The force exerted by the bellows assembly is also proportional to the difference between its free length and its actual length (as it is with a spring). Therefore the bellows force is also inversely proportional to the difference between the actual downstream pressure and the set downstream pressure, where it equals the pressure difference multiplied by the area over which the vacuum in the bellows acts.

With the downstream pressure below the set pressure of the valve the force of the Bellows Assembly (3) is greater than the sum of the forces from the Regulator Valve Return Spring (8), Relief Valve Return Spring (12) and the small Inlet Pressure force acting over the open area of the Seat (10). Therefore the Bellows Assembly is extended as far as it can onto the Adjuster Body (6) and the Regulator Valve Soft Seal (7) is pushed down off the Seat, Regulator Valve (10) by the Operating Pin (11). Under these conditions, provided the inlet pressure is greater than the downstream pressure, fluid will flow from inlet to outlet. If the outlet flow demand is less than the inlet flow the downstream pressure will increase. The downstream pressure will rise, reducing the bellows assembly force, until the bellows assembly force is balanced with the forces from the 2 springs (8) & (12) and the inlet pressure force. Any further increase in downstream pressure will reduce/counter the bellows assembly force further and the bellows assembly will start to reduce in length. Under the influence of the Relief Valve Return Spring (12) the bottom, or regulator, end of the bellows assembly will move away from the Adjuster Body (6). Under the influence of the Regulator Return Spring (8) the Regulator Seal (7) will start to move towards the Regulator Seat (10) thus closing the regulator flow area and reducing the flow from inlet to outlet. This will continue until the flow from inlet to outlet matches the demand flow and therefore the downstream or outlet pressure will remain constant. If the demand flow further reduces, the outlet pressure will start to rise again and the process will continue again. In the limit the demand flow is zero and the Regulator Seal (7) has closed against the Regulator Seat (10) and the flow from inlet to outlet has reduced to zero. When the demand flow increases again the process will occur in reverse.

From the position where the Regulator Seal (7) has closed against the Regulator Seat (10) and the flow from inlet to outlet is zero. Should, for whatever reason (e.g. the Regulator Seal (7) leaks, there is an inflow to the downstream side from an external source or the temperature has risen a lot) the outlet pressure continue to rise, the bellows assembly force will be further reduced and under the influence of the Relief Valve Return Spring (12) the bottom, or regulator, end of the bellows assembly will move further away from the Adjuster Body (6) until that movement is arrested by the Circlip (5) coming against the Adjuster Body (6). If the outlet pressure continues to rise the bellows assembly force will be reduced further and the bellows assembly will further reduce in length. This time, because movement of the lower, or regulator end, has been arrested, movement at the upper end will achieve the reduction in Bellows Assembly length. This will move the Relief Valve Seal (2) away from the Relief Valve Port (1) opening up the port so that fluid exhausts from the outleVdownstream volume to the environmenVambient. The Bellows Assembly (3) will continue to reduce in length and open the Outlet Port (1) until the exhausVrelief flow increases to equal to the inflow and thus maintain the outleVdownstream pressure constant. If the inflow should reduce the outleVdownstream pressure will start to reduce, the Bellows Assembly (3) will increase in length, the Outlet Port (1) will start to close and the exhaust flow will reduce until it matches the inflow to the downstream side of the valve.

By introducing a thread to the outside diameter of the Adjuster Body (6) so that it may be screwed into the Valve Housing (4) the valve can be set to different pressures by inserting a tool through the Inlet Port (9) to rotate the Adjuster Body and therefore adjust the length of the Bellows Assemble (3) thereby altering the set pressure of the valve.

The difference or separation between the regulation and relief pressures can be adjusted by altering the spring force exerted by the Relief Valve Return Spring (12). The difference between the regulation and relief pressures is proportional to the force exerted by the Relief Valve Return Spring (12).

A modification can be added to the design to incorporate guide pistons to each end of the Bellows Assembly (3) that have a running fit in the bore of the Valve Housing (4) to guide the axial movement of the Bellows Assembly and restrict all non axial movement. Once guide pistons are fitted then piston rings can be fitted to the guide pistons to provide friction damping of the Bellows movement.

Claims

1. A combined downstream pressure regulating valve and downstream pressure relief valve using a single, hermetically sealed and evacuated, bellows sensing element to control both valves to an absolute pressure reference, i.e. operating pressures not effected by the ambient pressure.

2. A combined pressure regulating and pressure relief valve as claimed in claim 1 wherein a means of adjustment is provided to enable the set pressures to be raised or lowered to different pressures.

3. A combined pressure regulating and pressure relief valve as claimed in claim 1 or claim 2 wherein a means of setting the pressure between the regulation pressure and the relief pressure is provided.

4. A combined pressure regulating and pressure relief valve as claimed in any previous claim wherein the hermetically sealed and evacuated bellows assembly is provided with guides to restrict non-axial movement whilst permitting axial movement.

5. A combined pressure regulating and pressure relief valve as claimed in claim 4 wherein friction damping is provided to damp the axial movement.

6. A combined pressure regulating and pressure relief valve substantially as described herein with reference to the accompanying drawing (Figure 1).