GB2109506A - An obturator and seat arrangement for a valve - Google Patents

Abstract

The present invention relates to an obturator (20) and seat (21) arrangement for a valve (10) wherein the obturator (20) cooperates with the seat (21) to regulate fluid flow through the valve (10). Closure of the valve (10) is achieved by the mating of complimentary formations (70, 84) on the obturator (20) and seat (21). One of the formations (84) is provided with a seal (88) which is brought into contact with the other formations (70) to close the valve (10). One of the formations (70) is in the form of an annular projection and this cooperates with an annular recess which constitutes the other formation (84). Preferably, an insert (88) is provided in the annular recess (84). Advantageously, the obturator (20) and seat (21) are each provided with an additional formation (72, 86) which contact each other when the valve (10) is fully closed. <IMAGE>

Description

SPECIFICATION An obturator and seat arrangement for a valve The present invention relates to an obturator and seat arrangement for a valve wherein the obturator cooperates with the seat to regulate fluid flow through the valve.

Many forms of obturator and seat arrangements are known but the characteristics of the known arrangements often do not reach the desired standards.

The present invention seeks to provide an improved obturator and seat arrangement which is capable of a wide range of applications and which has special advantages for particular applications.

According to the present invention there is provided an obturator and seat arrangement for a valve wherein the obturator cooperates with the seat to regulate fluid flow through the valve and closure of the valve is achieved by the mating of complementary formations on the obturator and seat, one of which is provided with a seal which is brought into contact with the other formation to close the valve, one of the formations being in the form of an annular projection which cooperates with an annular recess which constitutes the other formation.

Advantageously the seal is in the form of an insert is provided in the annular recess, the insert being contacted by the annular projection when the valve is fully closed. Preferably, the insert is formed of a relatively soft material compared with the materials of the seat and obturator. The recess may be beneficially provided with an undercut shoulder by which the insert is retained.

Preferably, the obturator and seat are each provided with an additional formation, the additional formations contacting each other when the valve is fully closed.

Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which; Figure 1 illustrates a vertical section through a valve, the section being taken in a direction orthogonal to fluid flow through the valve, and Figure 2 shows, to an enlarged scale, the seat and obturator arrangement shown in Figure 1.

Figure 1 shows a valve 10. The valve 10 comprises a housing 12 having a hollow and open-ended cylindrical portion 14, an inlet port and an outlet port. The ports are interconnected by a flow space 1 6 which extends within the cylindrical portion 14 of the housing 12. A head in the form of a hollow piston 1 8 is located co-axially with and movable along the axis of the cylindrical portion 14. An obturator, designed generally by the reference numeral 20, is provided within the flow space 1 6 and is attached to the piston 1 8 by a stem 22. The obturator 20 cooperates with a seat 21 in order to regulate the fluid flow through the valve 10.

The head 1 8 has a boss 34 projecting centrally from its inner surface. Threadedly engaged with the boss 34 is a cap 36. The top of the cap 36 is provided with a circumferential flange or lip 38 which engages a seal 30. The seal 30 is compressed against the inner surface of the head 18 by the lip 38 of the cap 36 and bears upon the inner surface of the cylindrical portion 14 of the housing 12. The seal 30 is generally in the form of a hollow and open-ended cylinder in which the hollow is frusto conical in shape. That part of the cap 36 which engages the boss 34 of the head 1 8 has an external configuration which corresponds to the inclined inner surface of the seal 30.

Therefore, as the cap 36 is tightened onto the boss 34 not only is the seal 30 compressed against the head 1 8 but a radially outward force is also applied to the seal 30. The seal may be formed of a material such as PTFE. A spring 31 is located between the inner surface of the head 1 8 and the upper surface of the valve 30 so as to maintain a compressive force upon the seal 30 and this is particularly advantageous if the seal 30 is manufactured from a material exhibiting a "flow" characteristic, such as PTFE.

A bellows 24 is provided co-axially with and surrounding the cylindrical portion 14 of the housing 1 2. One end of the bellows 24 is secured to the periphery of the head 1 8 and the other end of the bellows 24 is secured to the housing 12.

The bellows 24 is secured to the housing 1 2 by means of a retaining ring 38 welded to the end of the bellows 24 and clamped to the housing 12 by a collar 40.

An external cover 26 is provided which fits over and encloses the head 18 and the bellows 24. The cover 26 is threadedly engaged with the housing 12. The head 1 8 is axially slidable within the cover 26 and seals 28 provided on the circumference of the head 1 8 ensure a fluid tight seal with the cover 26.

Seal 30 forms the primary seal for preventing leakage of fluid from the flow space 1 6. The bellows 24 provide a secondary seal 30, direct leakage from the valve 10 does not ensue. Seals 28 form a third barrier inhibiting leakage from the flow space 1 6 to the exterior of the valve 10.

The space 23 between the bellows 24 and the cylindrical portion 14 of the housing 12 is connected to a leak detector 42 by a bore 41. The ring 38 is not a tight fit on the exterior of the cylindrical portion 14 and therefore communication between the space 23 and bore 41 is ensured. Preferably, the space 23 is partially evacuated via a valve 44 provided in the housing 12 and connected to the space 23 via a bore 43.

The leak detector 42 comprises a bellows 46 having an indicator 48. If leakage occurs past the seal 30, pressure within the space 23 increases and consequently the bellows 46 tends to collapse. Collapse of the bellows 46 urges an indicator 48 carried by the bellows 46 towards a window 50 provided in the outer surface of the housing 12.

Cooperation between the obturator 20 and the seat 21 is controlled by the axial position of the head 1 8. The axial position of the head 1 8 is controlled by a hand wheel 52 which has a stem 54 which acts upon the top surface of the control head 1 8. The hand wheel 52 has a hub 54 which is free to rotate in the cover 26 and which has a threaded central recess which opens to the inside of the valve. A threaded stem 56 is engaged in the threaded recess of the hub 54 and rotation of the hand wheel 52 results in axial movement of the stem 56. The stem 56 is secured to the top of the head 18 by a collar 58 and axial movement of the stem 56 therefore results in axial movement of the head 18.

The stem 22 is attached to the head 1 8 via the cap 36. The cap 36 includes a structure 60 with a generally U-shaped vertical cross-section which extends from the cap 36 towards the obturator 20. An aperture 62 is provided centrally through to the base of the U-shaped extension 60 of the cap 36. The upper end of the stem 22 passes through the aperture 62 and is threadedly engaged with a locknut 64 which is positioned between and prevented from rotating by the uprights of the U-shaped extension 60 of the cap 36. Once the stem 22 has been secured in the locknut 64 a retaining pin 66 is inserted into the locknut 64 and stem 22 so as to prevent the components from unscrewing. The sides of the aperture 62 are inclined to the central axis of the valve 10 and diverge towards the obturator 20.

Thus, lateral displacement of the obturator 20 with respect to the seat 21 during closure of the valve is permitted.

The details of the obturator 20 and seat 21 arrangement are illustrated to an enlarged scale in Figure 2. The seat 21 is in the form of an insert which is threadedly secured to the valve housing 12. The seat 21 is generally tubular in shape with the thread for engagement with the housing 12 being provided on the external surface of the seat 21. Towards the upper extreme of the seat 21, 1 the external surface is stepped so as to provide a portion 68 having a reduced external diameter.

This stepped portion 68 of the seat 21 mates with a complementarily shaped formation on the housing 12. The lower end of the seat 21 is also stepped so as to provide a portion having a reduced ex.erna] diameter, portion 70. The portion 70 presents a downwardly extending annular projection and it is with this projection that the obturator 20 cooperates in order to regulate fluid flow through the valve 10. The internal diameter of the seat 21 is constant except at its lower extreme where it forms the rree end of the projection 70. At the free end of the projection 70 the internal diameter of the seat 21 increases at a uniform rate.The inclined surface 72 which is produced by the increase in internal diameter of the seat 21 does not meet the external surface of the seat 21 and the lower surface of the seat 21 is therefore in the form of an annulus with its plane perpendicular to the external surface of the seat 21. The seat 21 is located in the housing 12 coaxially with the cylindrical portion 14.

The obturator 20 comprises a body 74 which is secured to the lower end of the stem 22. The body 74 of the obturator 20 has a domed central portion 76 which encloses the end of the stem 22.

The end of the stem 22 is threaded and engages a threaded recess which projects into the domed portion 76. The sides 78 of the domed portion 76 are parallel to the axis of the stem 22 and provide a hexagonal external configuration which can be engaged by a spanner of the like so as to secure the obturator body 70 with the end of the stem 22 by providing relative rotation between those components.

The stem 22 is prevented from rotating by virtue of the retaining pin 66 and locknut 64 which is rotationally constrained by the walls of the U-shaped extension 60 of the cap 36. Above the side walls 78 the obturator body 74 extends radially outwards so as to form a cylindrical portion 80. The cylindrical portion 80 has an external diameter approximately equal to the full external diameter of the seat 21.

The stem 22 passes through an axial recess 82 in the cylindrical portion 80 of the obturator body 74 so that the end of the stem 22 can engage with the threaded recess inside the domed portion 76 of the obturator body 74. The axial recess 82 has a circular cross-section which creases towards the domed portion 76 of the obturator body 74.

The lower portion of the stem 22 has a decreasing diameter towards its threaded end which provides a configuration complementary to that of the recess 82. Consequently, as the obturator body 74 is tightened onto the stem 22, the stem 22 acts as a wedge in the cylindrical portion 80 of the obturator body 74 and a very tight seal results between the stem 22 and the obturator body 74.

This tight seal inhibits the ingress of fluid and therefore reduces the possibility of the threaded engagement of the obturator 20 and stem 22 becoming ceased.

An annular recess 84 is provided in the upper surface of the cylindrical portion 80 of the obturator body 74. The depth of the recess extends parallel with the axis of the valve. The recess 84 in the obturator 20 cooperates with the projection 70 of the seat 21 in order to regulate fluid flow through the valve. The outer wal of the recess 84 is perpendicular but te inner surface of the recess is formed by two inclined surfaces 86 and 88. The surfaces 86 and 88 are both inclined to the axis of the valve 10 but in opposite directions and at different angles. The inner of the two surfaces, 88, diverges away from the obturator 20 and the surfaces 86 and 88 therefore form an undercut shoulder. The surface 86 is inclined at the same angle as and mates with the inclined surface 72 which terminates the internal surface of the seat 21. When the valve to is fully closed the surface 86 of the obturator body 74 is in contact with the surface 72 of the seat 21.

A seal 90 is seated in the recess 84 in the obturator body 74 and in particular is retained by the undercut shoulder formed by the surfaces 86 and 88. The flat annular surface of the lower end of the seat 21 contacts the seal 90 when the valve 10 is fully closed. As the valve 10 closes the projection 70 of the seat 21 will first contact the seal 90 which will be compressed until the surfaces 86 and 72 are brought into contact and the valve is then fully closed. The obturator 20 and seat 21 arrangement of the present invention forms a very efficient seal when the valve is fully closed and also provides a number of other advantages. The obturator body 74 and seat 21 will typically be formed of metal.

The obturator 20 and seat 21 arrangement can permit a fire proof valve to be constructed. If the seat 21 and obturator 20 are manufactured of metal then, with the valve 10 closed, a fire proof seal will exist due to the contact of the surfaces 72 and 86. Hence if the seal 90 is manufactured of a material such as PTFE and a fire occurs within the valve 10 and the ring 90 is destroyed, the valve 10 will isolate the fire due to the contact between the surfaces 72 ancl 86. In addition, the residue of the burnt PTFE ring 90 will tend to be retained within the recess 84 therefore reducing contamination of the system in which the valve 10 is located and in particular of the seal between the surfaces 72 and 86.For applications in which a fire proof valve is required the material from which the seal 90 is formed is selected so as to reduce the possibility of the ring 90 being destroyed.

Examples are; a ring formed of carbon granules or a ring formed of asbestos material.

The seat 21 may be secured to or removed from the housing 12 and the obturator 20 secured to or removed from the stem 22 by removing the base 92 from the valve 10. The base 92 is secured to the housing 12 by bolts 94 which engage with threaded recesses in the housing 1 2. The base 92 has a hollow boss 96 which projects into the flow space 1 6 and the external configuration of the boss 96 is stepped so as to correspond with a step provided in the housing 12. For applications in which maximum leak proof characteristics are required, the removal base 92 may be enclosed by a cover as shown by the phantom line 98 in Figure 1. The cover would be welded to the housing 1 2 and the weld subsequently ground off when it is desired to dismantle the valve or service the obturator and seat.

Claims (10)

1. An obturator and seat arrangement for a valve wherein the obturator cooperates with the seat to regulate fluid flow through the valve and closure of the valve is achieved by the mating of complementary formations on the obturator and seat, one of which is provided with a seal which is brought into contact with the other formation so as to close the valve, One of the formations being in the form of an annular projection which cooperates with an annular recess which constitutes the other formations.

2. An obturator and seat arrangement as claimed in claim 1 wherein the seal is in the form of an insert and is located in the annular recess, the insert being contacted by the annular projection when the valve is fully closed.

3. An obturator and seat arrangement as claimed in claim 2, wherein the insert is formed of a relatively soft material as compared with the materials of the seat and obturator.

4. An obturator and seat arrangement as claimed in claim 2 or 3, wherein the recess is provided with an undercut shoulder by which the insert is retained.

5. An obturator and seat arrangement as claimed in any preceding claim wherein the obturator and seat are each provided with an additional formation, the additional formations contacting each other when the valve is fully closed.

6. An obturator and seat arrangement as claimed in any preceding claim, wherein the seat and obturator are formed of metal.

7. An obturator and seat arrangement as claimed in claims 3 and 6, wherein the insert is formed of PTFE.

8. An obturator and seat arrangement as claimed in claims 3 and 6, wherein the insert is formed of carbon granules or asbestos.

9. An obturator and seat arrangement substantially as hereinbefore described with reference to the accompanying drawings.

10. An obturator and seat arrangement in combination with a valve, substantially as hereinbefore described with reference to the accompanying drawings.