GB2140896A

GB2140896A - Ball valve seals

Info

Publication number: GB2140896A
Application number: GB08315269A
Authority: GB
Inventors: Rowley John Bircham
Original assignee: N H ENGINEERING Ltd
Current assignee: N H ENGINEERING Ltd
Priority date: 1983-06-03
Filing date: 1983-06-03
Publication date: 1984-12-05
Also published as: GB8315269D0

Abstract

A seal 31 for a ball valve comprises a machined piece of metal defining a first cavity 42 in which, in use, a resilient seal 43 is disposed, and a second cavity bounded on one side by an integral springy projection 40. In use the projection 40 urges the resilient seal 43 against the ball 3 to effect a seal whilst an outwardly sharp edge 41 of the projection 40 seals against an adjacent wall of the valve housing. Should the resilient seal 43 be burnt in a fire, the projection moves to take up the slack to maintain a reasonable seal between seal and valve ball. A seal 31 is disposed between the valve ball and valve housing on both the upstream and the downstream side of the valve. Pressure fluid A acting in the second cavities assists the sealing action. <IMAGE>

Description

SPECIFICATION Ball valve seals The present invention relates to ball valves and to seals therefor.

In known ball valves two seals are provided on the upstream and downstream sides respectively of the ball. These seals are disposed between the curved surface of the ball and a wall of the housing adjacent the ball. They either consist of polytetrafluoroethylene (PTFE) or other plastics type material, or rubber housed in a metal insert. The seal, which may be natural or synthetic, forms a seal with the surface of the ball. If the valve is in a fire, the seals burn away leaving gaps between the valve housing and the valve ball through which fluid can escape.

Such valves can therefore not be used satisfactorily in fire hazardous circumstances.

According to one aspect of the present invention there is provided a composite seal for a ball valve comprising a piece of metal defining a first cavity, which receives a resilient seal made of rubber or synthetic plastics material, and a second cavity bounded on one side by an integral projection which serves as a spring operative to urge the resilient seal against the ball of the valve and which also has a sealing edge operative to form a seal with an adjacent wall of the valve housing on that side of the composite seal remote from the ball.

According to another aspect of the present invention, there is provided a ball valve comprising a valve housing, a ball disposed in the housing, two composite seals disposed between the valve ball and the housing on the upstream and downstream sides of the ball respectively, each composite seal comprising a piece of metal defining a first cavity, which receives a resilient seal made of rubber or synthetic plastics material and a second cavity bounded on one side by an integral projection which serves as a spring operative to urge the resilient seal against the valve ball and which also has a sealing edge which forms a seal with an adjacent wall of the valve housing on that side of the composite seal remote from the ball.

In a preferred embodiment of the invention, the composite seal is machined from a single piece of creep resistant metal. The projection is advantageously angled away from the remainder of the seal so as to present the necessary outwardly directed sharp sealing edge. The edges of the cavity housing the resilient seal are also sharp so that a sharp sealing edge can be presented to the valve ball in the event that the resilient seal is burnt away.

A further seal, which may advantageously be an '0' ring is disposed between each composite seal and the adjacent wall of the housing. The valve ball may be supported on a trunnion and may be rotated a quarter turn between open and closed positions by means of a wrench extending through appropriate packing in the valve housing.

In orderthat the invention may be more fully understood, one embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, in which Figure 1 is a side elevational view in section of a ball valve, and Figure2 is a partial diagrammatic view to a larger scale of part of the ball valve of Figure 1, showing a seal forming part of the valve in greater detail.

Referring to the drawing, the ball valve, which is a "fixed" ball moving seat upstream sealing block and bleed type valve, comprises a valve ball 1 disposed in a valve housing 2. The ball 1, which is normally of stainless steel, but may be made of any other suitable material, defines a through bore 3 and is specially formed at its top 4 and bottom 5. The bottom formation 5 consists of a cavity which accommodates a dry bearing 6 which in turn receives a chrome nickel molybdenum trunnion 7. The top formation 4 comprises a slot which receives a complementary projection which forms part of an actuator indicated generally by the reference numeral 8. This complementary projection forms the lower part of a stem 9 which extends upwards through a part of the valve housing 2. The stem 9 is formed with a shoulder 10 on which a PTFE primary seal 11 seats.The stem extends into a dry bearing 12 corresponding to the bottom dry bearing 6. A "grafoil" secondary seal 13 is disposed around the upper part of the stem 9. This upper part also carries a disc spring 14, a tab washer 15, a gland nut 16, a wrench 17 and a wrench retaining washer and screw 18 and 19.

The valve housing 2 effectively comprises three parts respectively referenced 20,21 and 22. Part 21 is sandwiched between parts 20 and 22 which are each formed with an apertured flange for connection to other pipeline members (not shown). The parts 20 and 22 are connected to the part 21 by means of screwthreaded studs and nuts 23 and 24. Secondary seals 30 are disposed between parts 21 and 22 and a gasket is disposed between the trunnion 7 and part 21.

Two primary composite seals 31 and 32 are disposed on the upstream and on the downstream side respectively of the valve ball 1. Each of these composite seals 31 and 32 is generally ring form and is disposed in a corresponding recess formed in respective housing parts 20 and 22. Each seal 31,32 is machined from a single piece of creep resistant metal. Metal made by Firth Vickers under the designations 448B has been found to be suitable.

During the machining of each seal 31,32 a relatively slender integral projection 40 (see Figures 2 and 3) which presents an outwardly inclined sharp sealing edge 41 is formed. This projection 40 forms a spring which, in use urges the seal against the valve ball. A recess 42 is also formed. This recess houses a sealing ring 43 usually made of synthetic plastics material such as PTFE whose sealing surface is curved to fit the curved surface of the ball 1. Further 'O' ring seals 47 of natural, synthetic rubber or PTFE type materials, are disposed in corresponding recesses in respective housing parts 20 and 21. The 'O' rings sealingly engage the radially outer surfaces of the primary seals 31 and 32. Before installing the composite seals, they would normally be subjected to a settling process to limit settling in use.

In normal operation, with the valve open as shown seals 43 and 47 prevent leakage from the line by passing the ball sealing is also effective at edge 41.

Pressure fluid enters the gaps between the projections 40 of the seals 31,32 and the remainder of the seal, as shown by arrows 'A' on the upstream side of the valve in Figure 2 of the drawing thus assisting the natural inherent resilience of the metal in forcing the seal both against the surfce of the housing part recess housing it and against the valve ball 1.

Contact with the ball is through the sealing rings 43 and with the appropriate housing part 20, 22 through edge 41. The valve may be closed by turning it through a quarter turn (90 ) to the closed position, using the wrench 17. If the valve is subjected to a fire (with temperatures above 600"C) so that the sealing rings 43 burn away the slender projections 40 move further away from the remainder of the bodies of the seals under their own inherent springyness. In this way, in addition to each seal having an edge 41 in sealing engagement with the adjacent housing part, a sealing edge 45 sealingly engages the valve ball 1.

The greater the pressure, the tighter the seal at these two edges 41 and 45. Tests have shown an effective seal at pressures below 10 psi up to 2250 psi. In a fire primary seal 11 will also completely disintegrate, but leakage will be prevented or resisted by secondary seal 13. Suitable materials for the various seals are PTFE types and synthetic rubbers such as Nitrile and Viton (R.T.M.).

It will be appreciated that the above embodiment has been described by way of example only and that many variations are possible without departing from the scope of the invention.

Claims

1. A seal for a ball valve comprising a piece of metal defining a first cavity which, in use, receives a resilient seal and a second cavity bounded on one side by an integral projection which serves as a spring operative to urge the resilient seal against the ball of the valve and which also has a sealing edge operative to form a seal with an adjacent wall of the valve housing on that side of the seal remote from the ball.

2. A seal as claimed in claim 1, in which the cavities are machined from the piece of metal.

3. A seal as claimed in claim 1 or 2, in which the projection is machined from the piece of metal.

4. A seal as claimed in claim 1,2 or3, in which the projection is angled away from the remainder of the seal so as to present an outwardly directed sharp sealing edge.

5. A seal as claimed in any preceding claim, in which the edges of the first cavity are also sharp to prevent outwardly directed sealing edges.

6. A seal as claimed in any preceding claim, in which the first cavity houses a seal of resilient material.

7. A seal as claimed in claim 6, in which the resilient material is rubber or synthetic plastics material.

8. A seal as claimed in claim 6 or 7, in which the resilient material is curved to accommodate the valve ball.

9. A seal as claimed in any preceding claim, in which the piece of metal is creep resistent.

10. A seal as claimed in any preceding claim, in which a further seal is provided adapted in use to be disposed externally of the piece of metal between the piece of metal and adjacent wall of the valve housing.

11. A seal as claimed in claim 10, in which the further seal is an '0' ring.

12. A seal for a ball valve substantially as hereinbefore described with reference to the accompanying drawings.

13. A ball valve comprising a valve housing, a ball disposed in the housing, two seals each as claimed in any preceding claim disposed between the valve ball and the housing on the upstream and downstream sides of the ball respectively.

14. A ball valve as claimed in claim 13, in which the valve ball is supported on a trunnion in the valve housing and is rotatable one quarter turn between open and closed positions.

15. A ball valve as claimed in claim 14, in which a wrench which extends through packing in the valve housing is provided for rotating the valve ball.

16. A ball as claimed in any of claims 13 to 15, in which the valve housing defines two recesses which respectively accommodate the two seals.