GB2143930A - Plug valves - Google Patents

Abstract

A plug valve having a conical or cylindrical plug 8 which is rotatably mounted in the valve body by means of a self-supporting sleeve 6 held within the body and having a coating of gasket material on either side to form a seal between the sleeve and the body and between the plug and the sleeve, the plug being allowed to "float" in the valve closed position so that sealing of the valve is enhanced. The sleeve 6 is metallic with a ptfe gasket coating. <IMAGE>

Description

SPECIFICATION Valves and mechanisms therefor This invention relates to plug valves having a conical or cylindrical plug and more particularly to such plug valves which employ liners to form a seal between the plug and the valve body and which can be subjected to high operating pressures.

Plug valves of this type are well known and the invention is concerned with overcoming problems commonly associated with the sealing of such valves across a wide pressure range and across a high temperature range, whilst maintaining a low operating torque, even after protracted periods of non-use, and obviating the need in general for lubrication.

In accordance with the invention, there is.

provided a plug valve comprising a body having an inlet and an outlet linked by a body cavity, a conical or cylindrical plug rotatably mounted in the cavity and having a passageway therethrough and adapted to be selectively turned by means of a spindle from an open position in which the passageway communicates the inlet with the outlet and a closed position in which such communication is prevented, the plug being able, in the closed position, to float within the cavity relative to the spindle along a line linking the inlet and the outlet, and a self-supporting liner member located between the body cavity and the plug, the liner member having an inlet and an outlet aligned with the inlet and outlet respectively of the body and having a gasket material across substantially the whole of both its interior and exterior surfaces to enable a seal to be formed in the area of at least the body outlet firstly between the body and the liner member and secondly between the liner member and the plug.

Rotation of the plug through 90" or a 1/4turn will generally move the valve from its open position to its closed position and means may be provided to limit rotation of the plug with the cavity to this amount.

The ability of the plug to move within the cavity independently of the valve spindle, ie float, along a line between the valve inlet and outlet in the valve closed position means that sealing between the body and the liner member and between the liner member and the plug can be ensured because the pressure of the fluid in a system to which a valve is attached will be exerted on the plug at the upstream end of the valve. It should be appreciated, however, that in general the amount of movement of the plug within the cavity when it "floats" is relatively small.

The liner member is generally in the form of a sleeve, the dimensions of which allow it to be fitted in close contact with the wall of the valve cavity and with the exterior surface of a plug. The plug is either cylindrical or conical, usually frusto-conical, and the body cavity can therefore usefully be cylindrical or conical.

Also in such cases, the liner member can be: i) cylindrical on the exterior and conical on the interior, ie for a cylindrical cavity and conical plug, ii) cylindrical on both the exterior and interior, ie for a cylindrical cavity and plug, iii) conical on the exterior and the interior, ie for a conical cavity and plug.

The liner member must be self supporting and this can readily be effected by forming this member from a strong, commonly metal, substrate and cladding it with the gasket material. This cladding can be any type of plastic or elastomeric material and the choice for any specific valve will depend on the nature of the fluid which will pass through the valve and the conditions of use of the valve.

Both surfaces of the liner member will generally, although not necessarily, be clad with the same gasket material.

The internal cladding in the liner member must have a sufficiently low coefficient of friction to allow ready rotation of the plug within the liner member. A preferred cladding material for the liner member is a fluorocarbon resin, especially polytetrafluroethylene (PTFE), which may be reinforced by the inclusion of fibres, metal particles or other known reinforcing substances; an example of such a reinforced gasket material is nickel-loaded PTFE. Typically, the thickness of cladding on each side of the liner member will be from 0.004 to 2 mm, for example 0.5 mm.

Means are preferably provided to prevent rotation of the liner member within the body.

This can be effected, for example, by providing female bores in the lower section of the member which can receive studs or other protrusions fixed to the body. Alternatively the bores may be in the body and the studs/protrusions may be in the liner member.

To allow the plug to float, the valve spindle must be independent of the plug. To allow the spindle to rotate the plug, however, the plug can usefully be provided with means, for example a substantially rectangular slot in its surface adjacent the spindle i.e. normally its upper surface, which can receive and cooperate with an extension of the spindle, for example a square or rectangular extension lid can engage the smaller dimension of the rectangular slot in the plug, to enable rotation to be effected and in the valve closed position, to allow the plug to float. In the exemplified arrangement, the longer dimension of the slot is, however, perpendicular to the longitudinal axis of the plug passageway and the spindle therefore allows the plug to move along the slot only when the valve is in the closed position.

In a preferred embodiment of the valve of the invention, the plug has an insert contained within a cavity on the surface of the plug and biassed, in the valve closed position, away from the centre of the plug and towards the valve outlet, thereby aiding valve sealing.

The insert will generally be of a size and shape which allows it completely to cover the valve outlet in the closed position. Typically, therefore, the valve outlet will be a circular outlet leading from the valve body cavity and the insert will also be circular with a diameter larger than that of the outlet and positioned so that, when the plug is turned to the closed position, the insert completely covers the outlet.

The biassing means which urges the insert into close contact with the outlet can be any suitable type of spring means including Belville washers.

Overall, the shape and size of the insert should not detract from the overall outer surface of the plug and in general the insert should not protrude from the surface of the plug to any great extent because contact between the insert and body cavity will prevent this in both the "open" and "closed" position.

The valve insert will generally be made from the same type of material as the remainder of the valve, commonly metal, although it may differ from time to time. However, it may in certain circumstances be necessary to use gasket material in conjunction with the insert to ensure full sealing of the valve. For example, an annular ring of such material, commonly PTFE, can be present in a groove around the periphery of the insert and which can therefore contact the wall of the body cavity. Such a ring can also usefully be in contact with the wall of the plug cavity also.

The surface of the insert adjacent the liner member may also be coated with gasket material, for example PTFE, if required and especially at high temperatures.

For a better understanding of the invention, reference will now be made, by way of example only, to the accompanying drawings of which: Figure 1 shows a vertical section through a plug valve of invention, the valve being in the closed position.

Figure 2 shows a plan view of the upper end of the plug of the valve shown in Figure 1.

Figure 3 shows a plan view of the lower end of the plug of the valve shown in Figures 1 and 2 showing the means by which a 1/4turn restriction of the plug is effected.

Figure 4 shows a partial vertical section of a modified valve of the invention to that of Figure 1.

Figure 5 shows a partial horizontal section of a further valve of the invention.

The valve shown in Figure 1, comprises a body 1 having flanges 2 at either side for connection to a pipeline (or whatever). Cylindrical bores 3 and 4 in the valve body define the inlet and outlet respectively and the direction of flow is depicted by A.

The body also has a cylindrical bore 5 which defines a body cavity linking the valve inlet 3 and outlet 4. Mounted in the cavity is a liner member in the form of a sleeve 6 of generally cylindrical shape on both outside and inside. The size of the sleeve 6 is such that it is in close contact with the body cavity across substantially all its exterior surface. The sleeve has apertures at either side which correspond in shape and size with the valve inlet and valve outlet. The sleeve is prevented from rotating within the cavity by means not shown.

The central core of the sleeve 6 is metallic and both sides are coated with a layer 7. 7' of gasket material and of PTFE in particular which is approximately 0.5 mm thick (although this thickness may vary from valve to valve as described above).

A plug 8 having a cylindrical outer surface is positioned within the sleeve and this contacts the sleeve across its exterior surface.

The plug 8 is rotatably mounted in the body cavity within the sleeve 6. The exterior surface of the plug is of a size which can be accommodated in close contact with the interior surface of the sleeve across substantially the whole of the surfaces. Because of the low coefficient of friction of the PTFE which forms the internal coating of the sleeve 6, the plug is freeiy rotatable within the body cavity of the valve.

The plug 8 has a circular cross-section passageway 11 which, in the valve open position, is aligned with the body inlet 3 and outlet 4. Figure 1 shows the valve in the closed position. The valves of the invention are particularly useful for providing a "full bore" and it can be seen from Figure 1 that the particular embodiment of the invention does show such a "full-bore".

The plug has an annular cavity 9 which receives an annular insert 10 of a diameter corresponding to that of the cavity but allows the insert to slide within the cavity. The insert is biassed outwards from the centre of the plug by means of a spring washer 1 2 but is prevented from protruding from the surface of the plug by its contact with the inner surface of the sleeve 6. Because the diameter of the insert 10 is larger than the diameter of the outlet 4 and the corresponding aperture in the sleeve 6, the insert 10 is firmly urged againstthe outlet 4 about the whole of the circumference of the outlet.

A similar plug cavity 13, plug insert 14 and spring washer 1 5 is provided on the outer side of the plug so that the valve is reversible.

Rotation of the plug is effected by means of a spindle 16. The spindle is rotatably mounted in a cap 1 7 of the body 1, the cap 1 7 being securely fixed to the body by means of a bolt 18. The spindle 16 is thus firmly held by the cap 1 7 but the plug 8 is allowed to "float" within the body cavity 5 by the presence of see Figure 2 in particular an elongated slot 1 9 in the upper surface of the plug 8 which receives an essentially rectangular cross-section extension of spindle 16.Independent movement of the spindle relative to the plug 8 is therefore allowed only in a line dictated by the slot 1 9 in the plug which is perpendicular to the longitudinal axis of the plug passageway 11 and, as the plug will "float" by virtue of upstream fluid pressure A, the movement of the plug relative to the spindle can occur only when the valve is in the closed position. Relevant parts of the spindle can usefully be coated with PTFE or similar material to aid rotation.

The spring 20, centred in the upper shaft, provides a certain pressure on the plug 8 within the sleeve 1 and also ensures an electrical connection between the plug and the body via the shaft; in this way the spring 20 acts as an antistatic device.

The valve clearly operates by virtue of a 1 /4-turn of the spindle 1 6 and hence of the plug 8 and it is useful to limit the possible rotation of the plug to a 1 /4-turn. This is achieved in the particular valve shown in Figure 1 by arranging for a circular machined portion 8' on the lower end of the plug 8-see Figure 3 also--to engage with a pin 21 fixed in the body 1.

The plug 8 has a further passageway 22 linking the cavities 9 and 1 3 so that, in the "closed" position, the fluid pressure in the inlet 3 is communicated via this further passageway and plug passageway 11 to the inside surface of insert 10 so as to aid sealing of the valve.

In the valve embodiment shown in Figure 1, optional annular gaskets 23, 24 are received in annular grooves present in the outer surface of the inserts 10 and 1 4. These gaskets are present in the specific embodiment shown in Figure 1 to aid sealing of the valve in the closed position by ensuring a seal between the gaskets and the inner wall of the body cavity.

Advantageously, a security gland 26 employing a sealing ring 27 is employed in valves of the invention and these are shown in Figure 1. The ring 27 may be PTFE or graphite.

In use of the valve, the operating principle is that the plug 8, in its open position, sits symmetrically within the sleeve 6 and with the fluid passing through the plug passageway 11 and not exerting any great force on the plug itself; in its closed position, however, ie when the plug closes inlet 3 in particular, the upstream pressure A shifts the plug and pushes it to ensure sealing between the plug itself and the sleeve 6, sealing being effected by contact with the internal sleeve cladding 7 and aided by insert 10 in the plug 8. The thrust of the pressure moves the assembly of plug 8, sleeve 6 and external sleeve cladding 7' against the body 1 to provide sealing between the sleeve 6 and the body 1.

The valve of the invention is particularly useful for medium, high and very high pressures but can be employed for lower pressure also. The valve will also operate well with primary and medium vacuum; in the latter case, the suction of the vacuum provides the same effect as those described above for pressure. In both cases, therefore, sealing is ensured all round the outlet aperture and the valve has no need of a packing gland. It is only for double security that the packing gland or security gland 26 is provided in the embodiment described above.

In general, the valves of the invention can be used for all gases and liquids and even slurries, depending on the metallurgical structure and composition of the valve components. They are suitable for high temperatures dependent on the properties of the liner member. The use of the spring 20, or other metallic resilient device, acts, inter alia, as an anti-static device and therefore eliminates, from a fire-prevention point of view, undesirable electric "sparkling" between the plug and the valve body which might otherwise occur if the gasket material was destroyed by fire or otherwise. Even if the gasket material were destroyed, the valve would continue to operate, albeit less efficiently.

The modified valve embodiments shown in Figures 4 and 5 are mainly concerned with high temperature use. They show modifications to the nature of the gaskets which may be useful at such high temperature and which allow the valves to be used safely at such temperatures. Figure 4 shows a gasket of different shape coupled with a special high temperature sealing ring 25 between the body 1 and the cap 17. Figure 5 shows the manner in which lubricating substances may be injected between the plug cavity and plug inserts and in place of the gasket 23, 24 shown in the valve of Figure 1.

The valves may also be used for cryogenic purposes. When used for bi-phase cryogenic operations in particular, the plug may be pierced by a cavity or cavities linking the plug passageway with the relevant plug outer surfaces to provide pressure relief for the plug passageway "dead space" and permit upstream decompression of the passageway.

Pressure relief can also be provided in a similar way to link the plug passageway and the upper and lower parts of the valve body.

Special embodiments of the valves of the invention may have the lower part of the body equipped with means for use in the ready replacement of the plug in cases where the plug is conical. The effect is to control insertion of the plug.

Further special embodiments may also be equipped with an adjustable piston, controlled for example by a screw and handwheel for controlling the flow of fluid through the plug passageway even when the valve is in the open position. In such an arrangement, means are provided to enable the flow crosssection of the plug passageway to be selectively adjusted by means of insertion of the piston into the passageway with the valve in the open position. Sealing of the piston at its exit from the valve body can be ensured by conventional means. When equipped with this device, the valve becomes a 1 /4-turn flow stopping and controlling valve actuated by a plunger piston.

Yet another special embodiment of the valves of the invention may possess supplementary sealing means positioned either on the inner edge of at least one of the liner member apertures or on the valve plug which has been found particularly useful when the valve is to be used at relatively low pressures.

Claims (8)

1. A plug valve comprising a body having an inlet and an outlet linked by a body cavity, a conical or cylindrical plug rotatably mounted in the cavity and having a passageway therethrough and adapted to be selectively turned by means of a spindle from an open position in which the passageway communicates the inlet with the outlet and a closed position in which such communication is prevented, the plug being able, in the closed position, to float within the cavity relative to the spindle along a line linking the inlet and the outlet, and a self-supporting liner member located between the body cavity and the plug, the liner member having an inlet and an outlet aligned with the inlet and outlet respectively of the body and having a gasket material across substantially the whole of both its interior and exterior surfaces to enable a seal to be formed in the area of at least the body outlet firstly between the body and the liner member and secondly between the liner member and the plug.

2. A valve according to Claim 1 in which the liner member is formed from a metal substrate clad with the gasket material.

3. A valve according to Claim 1 or Claim 2 in which the liner member gasket material is a fluorocarbon resin.

4. A valve according to any preceding claim in which the plug is provided with means which can receive and co-operate with an extension of the spindle to enable rotation to be effected and, in the valve closed position, to allow the plug to float.

5. A valve according to any preceding claim in which the plug has an insert contained within a cavity on the surface of the plug and biassed, in the valve closed position, away from the centre of the plug and towards the valve outlet, thereby aiding valve sealing.

6. A valve according to Claim 5 in which the insert completely covers the valve outlet in the closed position.

7. A valve according to Claim 5 or Claim 6 in which the surface of the plug insert adjacent the liner member is also coated with gasket material.

8. A valve according to Claim 1 substantially as described herein with reference to any one of Figures 1 to 5 inclusive.