GB2096745A

GB2096745A - Safety valve

Info

Publication number: GB2096745A
Application number: GB8207224A
Authority: GB
Original assignee: Bendix Ltd
Current assignee: Honeywell UK Ltd
Priority date: 1981-04-15
Filing date: 1982-03-12
Publication date: 1982-10-20

Abstract

In an air pressure safety valve a spring loaded spherical valve closure member 4 engages a main hard metallic valve seat 8 after compressing a relatively soft resilient seat 8a concentric with the main seat to provide reduced risk of air pressure leakage, and between the main seat and a vent port the closure member rests in close proximity to a further seat 14 to provide effective area enhancement for snap action during opening of the valve. <IMAGE>

Description

SPECIFICATION Biassed check valves This invention relates to biassed check valves and relates especially but not exclusively to safety valves.

Safety valves in fluid pressure braking systems have previously been proposed with hard valve seats to withstand the heavy loadings of associated closure springs. Such valves have had an undesirable tendency to leak if only slightly and the object of the present invention is to reduce such tendency.

According to the invention, there is provided a biassed check valve having a housing including a pressure input port and a relief port and a valve closure member biassed towards a relatively hard main valve seat to close a passage between said ports and characterised by said valve seat having a relatively soft ancillary seat which deforms to afford a seal with the valve member before closure thereof against the main seat.

Preferably the ancillary seat is formed by a tubular member located within the confines of the main seat.

In order that the invention may be more clearly understood and readily carried into effect the same will be further described by way of example with reference to the accompanying drawings of which: Fig. 1 illustrates in diagrammatical form a safety valve embodying a check valve according to the invention, and Fig. 2 illustrates an enlargement of a portion of the valve member and valve seats of the safety valve of Fig. 1.

Referring to Fig. 1, the safety valve shown therein is outwardly a generally fairly typical form of safety valve for use in fluid pressure systems such as fluid pressure braking systems and comprises a screw-in housing 1 having a threaded spigot 2 and a suitable hexagon 3 for enabling screwing into a suitable pressure relief port. The valve includes a valve closure member which in this case comprises a steel ball 4 resiliently biassed by a biassing spring 5 captive between the ball 4 and a plug member 6 retained in the housing by a through-pin 7. The ball 4 seats against a relatively small diameter relatively resilient ancillary valve seat 8a formed on the upper end of a resilient tubular member 9 bonded into the input bore 10 of the body 1.The resilience of the seat 8 also enables the ball 4 in the limit to seat against a surrounding chamfered main valve seat 8 leaving a slight clearance between ball 4 and a further relatively larger diameter valve seat provided by a chamfer 14 formed on a shoulder within the housing. A relief port 12 is provided downstream of the two valve seats having regard to the input bore 10.

Considering the operation of the safety valve of Fig. 1, the bore 10 constitutes a pressure input port. The safety valve is screwed into a relief port of an air pressure system. If the air pressure within the bore 10 attains a predetermined value acting on the area enclosed by the valve seat 8 and the valve member 4, this value being such as to just counterbalance the force of the spring 5, the valve member 4 will unseat from the valve seat 8. The air pressure will now reach the annular region 13 between the valve seat 8 and the valve seat 14.

There is, therefore, an abrupt enhancement of the area of the valve member 4 which is subject to the pressure in the bore 10, with the result that a snap action occurs whereby the valve member 4 is lifted well clear of both valve seats and air pressure is thereby rapidly vented from the system via the bore 10, valve seats 8 and 14 and the port 12 until the air pressure descends to a value at which the spring 5 is again able to reclose the valve member 4 towards the valve seats 8 and 11.

Referring to the enlarged view of the two valve seats as shown in Fig. 2, the chamfered main valve seat 8 and the chamfered seat 11 are more clearly shown. The seat 8a is shown not depressed by the action of the ball 4, namely as it would be at a point in time just before the air pressure acting beneath the valve member lifts it out of contact with the resiliently deformable seat 8a.

By virtue of the ancillary valve seat 8a being provided of relatively soft material such as neoprene, a good seal is achieved by the closure member 4. At the same time the loading of spring 5 is supported by the main valve seat 8 which may therefore not be of particularly high standard of sealing.

Since moreover a slight clearance is provided between the closure member 4 and the larger diameter seat 14 any slight air leakage past the seats 8 and 8a does not result in an accumulation of air pressure in the annular region 13 which could result in unwanted lifting of the safety valve at a less than critical air pressure in passage 10.

1. A biassed check valve having a housing including a pressure input port and a relief port and a valve closure member biassed towards a relatively hard main valve seat to close a passage between said ports and characterised by said valve seat having a relatively soft ancillary seat which deforms to afford a seal with the valve member before closure thereof against the main seat.

2. A biassed check valve as claimed in claim 1 characterised by the ancillary valve seat being provided by a tubular member located within the main valve seat.

3. A biassed check valve as claimed in claims 1 or 2 characterised by said valve closure member having a close fitting within the housing whereby upon unseating of the closure member from the main valve seat an enhanced area of the closure member is presented to the pressure at the pressure port.

4. A biassed check valve as claimed in claim 3 characterised by said close fitting being provided by a further valve seat into close proximity of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Biassed check valves This invention relates to biassed check valves and relates especially but not exclusively to safety valves. Safety valves in fluid pressure braking systems have previously been proposed with hard valve seats to withstand the heavy loadings of associated closure springs. Such valves have had an undesirable tendency to leak if only slightly and the object of the present invention is to reduce such tendency. According to the invention, there is provided a biassed check valve having a housing including a pressure input port and a relief port and a valve closure member biassed towards a relatively hard main valve seat to close a passage between said ports and characterised by said valve seat having a relatively soft ancillary seat which deforms to afford a seal with the valve member before closure thereof against the main seat. Preferably the ancillary seat is formed by a tubular member located within the confines of the main seat. In order that the invention may be more clearly understood and readily carried into effect the same will be further described by way of example with reference to the accompanying drawings of which: Fig. 1 illustrates in diagrammatical form a safety valve embodying a check valve according to the invention, and Fig. 2 illustrates an enlargement of a portion of the valve member and valve seats of the safety valve of Fig. 1. Referring to Fig. 1, the safety valve shown therein is outwardly a generally fairly typical form of safety valve for use in fluid pressure systems such as fluid pressure braking systems and comprises a screw-in housing 1 having a threaded spigot 2 and a suitable hexagon 3 for enabling screwing into a suitable pressure relief port. The valve includes a valve closure member which in this case comprises a steel ball 4 resiliently biassed by a biassing spring 5 captive between the ball 4 and a plug member 6 retained in the housing by a through-pin 7. The ball 4 seats against a relatively small diameter relatively resilient ancillary valve seat 8a formed on the upper end of a resilient tubular member 9 bonded into the input bore 10 of the body 1.The resilience of the seat 8 also enables the ball 4 in the limit to seat against a surrounding chamfered main valve seat 8 leaving a slight clearance between ball 4 and a further relatively larger diameter valve seat provided by a chamfer 14 formed on a shoulder within the housing. A relief port 12 is provided downstream of the two valve seats having regard to the input bore 10. Considering the operation of the safety valve of Fig. 1, the bore 10 constitutes a pressure input port. The safety valve is screwed into a relief port of an air pressure system. If the air pressure within the bore 10 attains a predetermined value acting on the area enclosed by the valve seat 8 and the valve member 4, this value being such as to just counterbalance the force of the spring 5, the valve member 4 will unseat from the valve seat 8. The air pressure will now reach the annular region 13 between the valve seat 8 and the valve seat 14. There is, therefore, an abrupt enhancement of the area of the valve member 4 which is subject to the pressure in the bore 10, with the result that a snap action occurs whereby the valve member 4 is lifted well clear of both valve seats and air pressure is thereby rapidly vented from the system via the bore 10, valve seats 8 and 14 and the port 12 until the air pressure descends to a value at which the spring 5 is again able to reclose the valve member 4 towards the valve seats 8 and 11. Referring to the enlarged view of the two valve seats as shown in Fig. 2, the chamfered main valve seat 8 and the chamfered seat 11 are more clearly shown. The seat 8a is shown not depressed by the action of the ball 4, namely as it would be at a point in time just before the air pressure acting beneath the valve member lifts it out of contact with the resiliently deformable seat 8a. By virtue of the ancillary valve seat 8a being provided of relatively soft material such as neoprene, a good seal is achieved by the closure member 4. At the same time the loading of spring 5 is supported by the main valve seat 8 which may therefore not be of particularly high standard of sealing. Since moreover a slight clearance is provided between the closure member 4 and the larger diameter seat 14 any slight air leakage past the seats 8 and 8a does not result in an accumulation of air pressure in the annular region 13 which could result in unwanted lifting of the safety valve at a less than critical air pressure in passage 10. CLAIMS

4. A biassed check valve as claimed in claim 3 characterised by said close fitting being provided by a further valve seat into close proximity of which the valve closure member rests when engaging the main valve seat.

5. A biassed check valve as claimed in claims 3 or 4 characterised by a leakage path being provided to prevent build up of leakage air pressure over the enhanced area when the closure member is against the main seat.

6. A biassed check valve substantively as described herein with reference to the accompanying drawings.