GB2205631A - Improvements in or relating to valves - Google Patents

Abstract

In a ball valve, the annular seals 4, (42) sealing the ball 1 with respect to the flow passages in the valve body are formed of a hard ceramic material, such as transformation toughened partially stabilized zirconia. Accordingly, abrasive particles in the flow medium cannot become embedded in the seal surfaces, so that damage to the ball surface by the seals is diminished, and operating torque can be kept low. <IMAGE>

Description

DESCRIPTION OF INVENTION Title: "Improvements in or relating to valves" THIS INVENTION relates to valves and more partiularly, but not exclusively, to ball valves for use in controlling fluids carrying abrasive particles.

Ball valves are known which comprise a valve member in the form of a ball having a diametral passage therethrough, the ball being mounted in a housing defining fluid passage portions on either side of the ball which, in the open position of the valve, define, with the passage through the ball, a fluid passage through the valve, said fluid passage portions being blocked off by the ball in the closed position of the valve. Such ball valves are known in which the ball surface is sealed with respect to the fluid passage portions in the housing by means of annular seals carried by annular seal carriers which are received in enlarged inner end parts of the fluid passage portions provided in the housing and are resiliently urged towards the ball to thrust the seals sealingly against the ball surface.

Such annular seals are commonly of relatively soft plastics or elastomeric materials which are able to adapt themselves to the ball surface to achieve reliable sealing. However, when ball valves of this character are used to control fluids carrying abrasive particles, such particles become embedded in the sealing surfaces of the sealing rings thereby increasing the friction between the sealing rings and the ball surface and thus increasing the operating torque required for the valve and, furthermore, leading to scratching or scoring of the surface of the ball and eventual impairment of sealing.

It is among the objects of the present invention to provide an improved valve which is suitable for use in controlling the flow of fluids carrying abrasive particles and which is less subject than known valves to the defects noted above.

According to one aspect of the present invention there is provided a valve having a valve member which, in operation of the valve, carries out a sliding movement relative to, and in engagement with a seat member, wherein the cooperating surfaces of said members are smooth to afford a seal with respect to each other and to minimise friction between said members, and wherein one of said members comprises a hard ceramic material.

An embodiment of the invention is described below by way of example with reference to the accompanying drawings in which: FIGURE 1 is a sectional view of a ball valve embodying the invention, FIGURE 2 is a partial sectional view to an enlarged scale as compared with Figure 1 showing a detail of the valve, and FIGURE 3 is a view, similar to Figure 2, of a variant valve embodying the invention.

The ball valve of Figure 1 comprises, in known manner, a valve body including a middle section 20 which houses a valve member in the form of a ball 1, and end portions 24 for connection with respective parts of a pipe line in which, in use, the valve is fitted. The ball 1 has a through passage 25 which, in the open position of the valve, as illustrated, is aligned with respective internal passage portions 26 in the end fittings 24 to define a straight passage for fluid flow through the valve, such passage extending diametrally through the ball 1.The ball 1 is mounted, in known manner, for rotation in the valve body about an axis perpendicular to and intersecting the axis of the fluid passage portions 26 through the end fittings 24 so that when the ball is rotated, about its axis, through 900 from the position shown in Figure 1, the fluid passage through the valve is blocked by the ball. Also in known manner, the surface of the ball is engaged by seals 4 carried by respective annular seal carriers 3 each located at the inner end of the passage portion in a respective end fitting 24, each seal carrier being resiliently biased towards the ball 1 by means of springs 6, in order to maintain sealing contact between the respective seals 4 and the outer surface of the ball 1.

Figure 2 is a view to an enlarged scale of the portion of Figure 1 shown encircled by the dotted line at 35. It will be noted that the seal carrier 3 is located in an enlarged recess at the inner end of the respective fluid passageway 26 such recess including a smaller diameter counterbore 28 further from the ball and a larger diameter counterbore 29 nearer to the ball. The seal carrier 3 includes a first portion 30, further from the ball 1, which, on its outer periphery, is a close sliding fit within the counterbore 28 in the end fitting 24, and a further part 32, of greater outer diameter, which is received with clearance in the larger counterbore 29 at the extreme inner end of the respective end fitting 24.An O-ring 7 and associated packing rings are received in an annular groove formed in the outer periphery of the portion 30 of the seal carrier 3 to seal the seal carrier with respect to the wall of the bore 28.

The seal 4 is received in, and projects from, an annular recess formed in the forward end of the seal carrier 3.

An emergency seal 8, in the form of a graphite ring, is located in a rebate formed between a rearwardly facing surface 16 of part 32 and the outer peripheral surface of the part 32 of the seal carrier 3. An annular pressure plate 40 acts upon the rearwardly presented surface 16 by way of a heat-destructible ring 10, the annular pressure plate 40 being in turn acted on by the springs 6. The pressure plate 40 has, around its outer edge, an annular flange directed towards the emergency seal 8. In normal use, the emergency seal 8 is substantially clear of the counterbore 29 and the pressure plate 40 is held out of contact with the emergency seal 8 by the ring 10.

Destruction of the ring 10 by fire, however, allows the springs 6 to urge the plate 10 closer to the seal 8, compressing the latter and causing it to engage sealingly the surface of the counterbore 29. The mounting arrangement for the other seal is, of course, identical.

The above-described features do not, in themselves, form part of the present invention.

In conventional valves of this general type, the seal 4 is made of a relatively soft plastics or elastomeric material such as nylon, PTFE or the like on the basis that such material will be forced by the pressure of the biasing springs 6 to conform closely and sealingly with the ball surface. Such materials also have the advantage of having low coefficients of friction with respect to the material (usually metal) of the ball and thus allow desirably low operating torques to be achieved. However, where the valve is required to carry fluid in which abrasive particles are suspended, such particles tend to become jammed between the surface of the ball and the cooperating surface of the seal 4 during opening and closing of the valve and become embedded in the sealing surface of the seal. Consequently, during subsequent operation of the valve, such particles bite into the peripheral surface of the ball and substantially increase the friction between the ball and the seal and thus substantially increase the operating torque required for the valve. Furthermore, each time the valve is opened or closed, the embedded particles score the surface of the ball so that ultimately sealing of the valve is impaired.

In order to avoid these disadvantages, in accordance with the present invention, the seal 4 is manufactured from a hard ceramic material which is resistant to penetration by abrasive particles in the fluid medium conveyed through the valve and is thus much less prone to become embedded with such abrasive particles than conventional seals, thereby avoiding the increase in operating torque arising in the manner noted above in conventional valves and substantially reducing the rate of deterioration of the sealing surface of the ball.

The sealing surface of the ceramic seal is lapped to provide a smooth polished surface which will conform closely with the surface of the ball. The ball, in turn, is preferably of a hard-based material, e.g. a ceramic material of the same type as the seal, or alternatively of a soft material, such as stainless steel, with a hardened peripheral surface, e.g. hardened nickel, cooperating with the seals.

The material for the seal 4 is a ceramic, preferably of the tougher magnesia-partially stabilised zirconia (Mg-PSZ) type. This seal material has a low coefficient of friction with respect to the metallic ball surface and there is no tendency to galling between the surface of the ceramic seal and the surface of the ball, which would be likely to occur if both the seal and the ball were made of metal, for example. Furthermore, the preferred material is, o,f course, highly resistant to wear. The preferred seal material has high strength and exceptional toughness derived from the transformation toughening characteristic of its microstructure. In particular, this material is resistant to fracture under shock mechanical and/or thermal loads and has thermal expansion and elasticity characteristics similar to steel.Accordingly, the seal 4 may be fitted securely and sealingly in the seal carrier 3 simply by, for example, making it an interference fit. The characteristics of the ceramic material would, however, allow the ceramic seal to be formed with a screw thread whereby the seal may be screwed into a correspondingly screw threaded recess in the seal carrier. Alternatively the seal might be clamped in position by a metallic screw-threaded clamping ring, or held in place by screws or in any other convenient way.

Despite the low friction between the ball 1 and the seal 4, and because of the rigidity of the seal 4, coupled with the configuration of the ball valve, there is a tendency, when the ball is turned, for the seal and seal carrier to be entrained with the ball, resulting in the seal carrier 3 being thrust against one side of the respective recess in the respective end fitting. This can lead to a temporary binding of the seal carrier in its recess, but in conventional valves the temporary immobility of the seal carrier is compensated for by resilient displacement of the resilient material of the seal itself, which in turn limits the force with which the seal carrier is thrust against the side of its recess and the corresponding reactive force with which the seal is thrust against the ball.However, in the valve embodying the invention under discussion, in which the seal is substantially rigid, it is more important to ensure freedom of movement of the seal carrier towards and away from the ball at all times, and, accordingly, the peripheral surface of the part 32 of the seal carrier is provided with a bearing ring 5 of low-friction material such as nylon, PTFE or graphite, accommodated in an appropriate peripheral channel in the seal carrier and projecting radially from the seal carrier to engage the opposing surface of the counterbore 29.Accordingly, any lateral thrust applied to the seal carrier 3 during opening of closing of the valve is received by the bearing ring 5 engaging the wall of the counterbore 29, and because of the low-friction characteristics of the bearing ring 5, the seal carrier 3 can still slide freely along the counterbores 28 and 29 without jamming.

Figure 3 is a view corresponding to Figure 2 but illustrating a variant embodying the invention. In Figure 3, parts corresponding to parts in Figure 2 have the same references as in Figures 1 and 2.

In the variant illustrated in Figure 3, the seal 4 and seal carrier 3 of Figures 1 and 2 are dispensed with and a unitary annular seal 42, of the ceramic material referred to above, is utilised which affords, in addition to the concave part-spherical sealing surface which bears directly on the ball 1, a cylindrical outer peripheral surface 44 cooperating closely with the larger diameter counterbore 29. The seal 42 terminates, at its axial end remote from the ball 1, in a flat end face, normal to the axis of the ring and which opposes an annular shoulder 46 formed at the end of the counterbore 29. The springs 6, pressure plate 40, ring 10 and emergency seal 8 of Figures 1 and 2 are likewise dispensed with in the variant of Figure 3.Furthermore, the seal 42 lacks any structure corresponding with the first portion 30 in Figure 2 extending within the smaller diameter counterbore 28 and the O-ring 7 and associated packing ring are likewise dispensed with. Instead, sealing of the seal 42 with respect to the valve body is provided by a metal sealing ring 50 which also applies a resilient bias to the ring 40 to urge the latter axially into sealing engagement with the ball 1. The sealing ring 50, shown in axial section in Figure 3, is generally C-shaped in half-section, having a continuous slot running all around its entire inner periphery.The counterbore 28 is substantially shorter axially than that in Figure 2 and the sealing ring 50 bears sealingly against, on the one hand, the rearwardly presented face of the ring 40 and, on the other hand, the opposing shoulder 46 at the end, furthest from the ball 1, of the counterbore 28. The ring 50 is made of an appropriate material, for example the alloy designated Inconel X-750, which is corrosionresistant and retains its resilience and sealing properties at temperatures in excess of the limits at which the valve is required, in the case of fire, to be capable of sealing off the pipeline in which it is installed.

The construction illustrated in Figure 3 is rendered possible because, it has been discovered, the ceramic material of the annular seal 42 presents a low frictional resistance to sliding with respect to the valve body and consequently, with the construction illustrated in Figure 3, the difficulties which might be encountered with a metal seal carrier binding in the counterbore 29 are not encountered. Furthermore, the resilience, in the axial direction, of the sealing ring 50 allows the springs 6 of the embodiment of Figures 1 and 2 to be dispensed with, whilst, because the ring 50 is itself fire-resistant, there is no need to provide the emergency sealing arrangement 8, 40, etc., of the embodiment of Figure 1 and 2. Thus, the construction of Figure 3 simplifies the manufacture of the valve considerably and allows the valve to be made more cheaply, without sacrificing any of the desirable characteristics of the valve of Figures 1 and 2.

It has been found that, because the ceramic material utilised for the seals 4, 42, is not significantly prone to wear, nor is it significantly subject to plastic deformation under pressure, the range of axial movement required for the seal 42 in the arrangement of Figure 3, or, for that matter, for the seal carrier 3 in the arrangement of Figure 2, is substantially less than with conventional arrangeents utilising seals of PTFE or the like and is well within the range of axial adjustment which can be accommodated by a metal sealing ring of the form indicated at 50. Indeed, the amount of axial compressibility required for the seal 50 is merely that dictated by production tolerances.

Claims (13)

1. A valve having a valve member which, in operation of the valve, carries out a sliding movement relative to, and in engagement with a seat member, wherein the cooperating surfaces of said members are smooth to afford a seal with respect to each other and to minimise friction between said members, and wherein one of said members comprises a hard ceramic material.

2. A valve according to claim 1 wherein one of said members is of metal and the other is of said hard ceramic material.

3. A valve according to claim 1 or claim 2 wherein said ceramic material comprises transformation toughened partially stabilised zirconia.

4. A valve according to any preceding claim, which is a ball valve wherein said valve member is a ball rotatably mounted in a housing and said seat member comprises an annular seal carried by a seal carrier mounted in said housing for movement along a valve passage towards and away from the ball, the seal carrier being energised towards the ball to hold said annular seal against the ball and said annular seal being of said hard ceramic material.

5. A valve according to claim 4 wherein at least one bearing member of low-friction material is located between the wall of said valve passage in which said seal carrier is mounted, and the opposing surface of the seal carrier.

6. A valve according to claim 5 wherein said bearing member takes the form of a ring of said low-friction material encircling the seat carrier.

7. A valve according to claim 5 or claim 6 wherein said bearing member is of nylon or PTFE.

8. A valve according to claim 5 or claim 6 wherein said bearing member is of graphite.

9. A valve according to any of claims 1 to 3, which is a ball valve wherein said valve member is a ball rotatably mounted in a housing and said seal member is an annular seal of said hard ceramic material mounted as a close sliding fit in a valve passage for movement along said valve passage towards and away from the ball, the annular seal being energised towards the ball to hold said annular seal against the ball.

10. A valve according to claim 9 wherein said annular seal is energised towards the ball by means of a resilient annular metal element which also provides a seal between said annular seal and the valve body.

11. A valve substantially as hereinbefore described with reference to, and as shown in, Figures 1 and 2 of the accompanying drawings.

12. A valve substantially as hereinbefore described with reference to, and as shown in Figure 3 of the accompanying drawings.

13. Any novel feature or combination of features described herein.