GB2157810A

GB2157810A - Fluid control valve

Info

Publication number: GB2157810A
Application number: GB08509953A
Authority: GB
Inventors: Neil David Auld Graham
Original assignee: DAVID AULD VALVES Ltd
Current assignee: DAVID AULD VALVES Ltd
Priority date: 1984-04-19
Filing date: 1985-04-18
Publication date: 1985-10-30
Also published as: GB8509953D0; GB8410327D0

Abstract

A fluid control valve of the type having a valve member 4 which is movable relative to a seat member 3 for varying the fluid flow is provided with a sealing member 7 which seals against the seat member to prevent fluid flow in one position of the valve member. The sealing member is in the form of an 'O' ring seal which has an elastic material core portion, to provide the seal with resilience, and a plastic material casing portion to allow the seal to deform to seal against adjacent sealing surfaces on the valve member and the seat member. A pilot valve 10 is moved to close the seat 11 by downstream pressure to close the main valve 4. <IMAGE>

Description

SPECIFICATION Fluid control valve This invention relates to an improved fluid control valve.

Fluid control valves are generally provided with a sealing member between the actual valve member and a valve seat in the valve body. These sealing members require to be made of a material soft enough to deform and mould to the shape of the adjacent sealing surfaces to provide a good seal when the valve is closed. At the same time the material must be able to withstand repeated opening and closing of the valve member. It has not always previously been possible to provide a sealing member which is capable of providing a good seal and also has a long life.

According to the present invention there is provided a fluid control valve having a valve member which is movable relative to a seat member for varying the fluid flow, the valve member having a sealing member which seals against the seat member to prevent fluid flow in one position of the valve member, wherein the sealing member has an elastic material core portion and a plastic material casing portion, the elastic material core portion providing the sealing member with resilience and the plastic material casing portion allowing the sealing member to deform to seal against adjacent sealing surfaces on the valve member and on the seat member.

Preferably, the casing portion is bonded to and forms a composite construction with the core portion.

Further according to the present invention there is provided a fluid control valve comprising a valve body having a first, upstream, chamber; a second, intermediate, chamber; and a third, downstream, chamber; a main valve member between the first and third chambers and a pilot valve between the second and third chambers; a passage in the main valve member allowing fluid to flow into the second chamber from the first chamber to equalise the pressure in the first and second chambers; said pressure in the second chamber acting on the main valve member causing it to remain closed, wherein a drop in pressure in the third chamber causes the pilot valve to open between the second and third chambers allowing the pressure in the second chamber to drop and allowing the main valve to open to allow fluid flow from the first to the third chambers, the main valve member being fitted with at least one sealing member to prevent fluid leakage around the main valve member, said sealing member comprising an '0' ring seal having an elastic material core portion and a plastic material casing portion, the elastic material core portion providing the sealing member with resilience and the plastic material casing portion allowing the seal to deform to seal against adjacent sealing surfaces on the main valve member and on the valve body.

Preferably, the casing portion of the sealing member is bonded to and forms a composite construction with the core portion.

Preferably also, the main valve member and the pilot valve member are normally biased towards the closed portion by spring means.

Preferably also, further spring means are provided which bias the pilot valve towards the open position against the fluid pressure in the third chamber.

Preferably also, means are provided for varying the tension said further spring means being such that the pressure drop in the third chamber required to cause said pilot valve to open is variable.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a sectional side view of one embodiment of a fluid control valve made in accordance with the present invention; and Figure 2 is an end view of the fluid control valve taken along the line A-A of Fig. 1.

Referring to the drawings, a fluid control valve comprises a valve body 1 having an upstream chamber 1 a, a downstream chamber 1 b and an orifice 2 defining a valve seat 3. A piston valve 4 is slidably mounted in a guide tube 5 and is biased towards the valve seat 3 by a spring 6. Seals 7 and 8 allow the piston valve 4 to seal against the valve seat 3 and the guide tube 5 respectively. The piston valve 4 is also fitted with a stud 1 7 having a bore 1 7a which extends through the piston valve 4.

A pilot valve assembly 9 controls a valve member 10, which seats in a valve seat 11, by way of a spring 1 2. The valve member is normally biased towards the valve seat 11 by the spring 6.

A pressure chamber 1 3 is provided below the pilot valve assembly 9 and is connected to the downstream side 1 b of the valve body 1 by fluid passages 1 4 and 1 5. An adjustment mechanism 1 6 is provided to vary the tension in the spring 12.

The fluid control valve is seif-contained and obtains its operating energy from the fluid which it is designed to regulate. The fluid, which may, for example, be steam, air or water, enters the valve body 1 by way of the upstream chamber 1 a and flows up through the orifice 2 under the piston valve 4. A restricted flow passes up the bore 1 7a of the stud 1 7 and enters the space formed by the piston valve 4 and guide tube 5.

Under "dead end" (no flow) conditions the pilot valve member 10 is closed resulting in the fluid pressure being the same above and below the piston valve 4. Since the area of the upper surface of the piston valve 4 is greater than the area of the orifice 2, a downward force assisted by the spring 6 clamps the piston valve 4 shut against the valve seat 3.

On flow demand to the control valve the pressure in the downstream chamber 1 b tends to fall slightly. The pressure drop is transmitted by the passage 14 and 1 5 to the pressure chamber 1 3. The decrease in pressure in the pressure chamber 1 3 results in a decrease in the upward force against the spring 12 of the pilot valve assembly 9. This alters the balance of forces acting on the valve member 11 from the springs 6 and 1 2 such that the valve member 11 is now forced open away from the valve seat 11. This allows the fluid above the piston valve 4 to escape through the valve member 10, passage 14 and passage 1 5 to the downstream chamber 1 b.

The escape of fluid lowers the pressure above the piston 4 thus allowing the pressure in the upstream chamber 1 a to open the piston valve 4 to allow sufficient fluid to flow through an opening 1 9 in the side of the guide tube 5 to maintain the required pressure in the downstream chamber 1 b.

An increase in pressure in the downstream chamber 1 b will produce an increase in pressure above the piston valve 4 tending to close the piston valve 4 and hence reducing the flow through the opening 1 9 and the pressure in the downstream chamber 1 b.

The adjuster mechanism 1 6 allows the tension in the spring 1 2 to be varied so as to vary the pressure values at which the control valve operates.

The seals 7 and 8 are required to maintain the pressure differential across the piston valve 4 which allows the control valve to operate efficiently. The seal 7 seals the piston valve 4 against the valve seat 3 and the seals 8 seal the piston valve 4 against the guide tube 5. These seals have a concentric composite construction. Each seal comprises an elastic core, completely surrounded by a plastic jacket or outer casing. The elastic core provides each seal with an ability to maintain or recover shape, while the plastic outer casing moulds to the adjacent surfaces to produce the fluid seal.

Although this type of composite construction seal is particularly useful in the type of fluid control valve described above it can also be used effectively in many other types of valves.

Modifications and improvements may be incorporated without departing from the scope of the invention.

Claims

t. A fluid control valve having a valve member which is movable relative to a seat member for varying the fluid flow, the valve member having a sealing member which seals against the seat member to prevent fluid flow in one position of the valve member, wherein the sealing member has an elastic material core portion and a plastic material casing portion, the elastic material core portion providing the sealing member with resilience and the plastic material casing portion allowing the sealing member to deform to seal against adjacent sealing surfaces on the valve member and on the seat member.
2. A fluid control valve according to Claim 1, wherein the casing portion of the sealing member is bonded to and forms a composite construction with the core portion.
3. A a fluid control valve comprising a valve body having a first, upstream, chamber; a second, intermediate, chamber; and a third, downstream, chamber; a main valve member between the first and third chambers and a pilot valve between the second and third chambers; a passage in the main valve member allowing fluid to flow into the second chamber from the first chamber to equalise the pressure in the first and second chambers; said pressure in the second chamber acting on the main valve member causing it to remain closed, wherein a drop in pressure in the third chamber causes the pilot valve to open between the second and third chambers allowing the pressure in the second chamber to drop and allowing the main valve to open to allow fluid flow from the first to the third chambers, the main valve member being fitted with at least one sealing member to prevent fluid leakage around the main valve member, said sealing member comprising an '0' ring seal having an elastic material core portion and a plastic material casing portion, the elastic material core portion providing the sealing member with resilience and the plastic material casing portion allowing the seal to deform to seal against adjacent sealing surfaces on the main valve member and on the valve body.
4. A fluid control valve according to Claim 3, wherein the casing portion of the sealing member is bonded to and forms a composite construction with the core portion.
5. A fluid control valve according to either Claim 3 or 4, wherein the main valve member and the pilot valve member are normally biased towards the closed position by spring means.
6. A fluid control valve according to Claim 5, wherein further spring means are provided which bias the pilot valve towards the open position against the fluid pressure in the third chamber.
7. A fluid control valve according to Claim 6, wherein means are provided for varying the tension said further spring means being such that the pressure drop in the third chamber required to cause said pilot valve to open is variable.
8. A fluid control valve substantially as hereinbefore described with reference to the accompanying drawings.
9. A sealing member for a fluid control valve having an elastic material core portion and a plastic material casing portion, the elastic material core portion providing the sealing member with resilience and the plastic material casing portion allowing the sealing member to deform to seal against adjacent sealing surfaces on the valve member and on the seat member.
10. A sealing member for a fluid control valve substantially as hereinbefore described with reference to the accompanying drawings.