GB2277792A - Flow control valve - Google Patents

Abstract

A valve comprises a plug 3 which is movable within an apertured sleeve so as to open or close (depending on the direction of plug movement) apertures therein. The plug has a seating surface 18s which is provided behind a flange 19 which acts as a shroud to protect the seating surface from the main flow stream. The seating surface 18s locates on a seat 23 which is again positioned outside the main flow stream. The seating surface 18s and the seat 23 are protected against erosion by particulate matter contained in fluid entering the valve. Additionally, the plug has a nose (13) which provides two effects. Firstly, the nose causes fluid to be deflected along the central axis of the sleeve thus reducing the possibility of internal erosion. Secondly, an axial passage through the plug to the nose causes a reduced pressure to be generated in a space (11) behind the plug. As a result, the surfaces within this space are continuously scavenged thus preventing particulate debris building up behind the plug. <IMAGE>

Description

VALVE The present invention relates to valves, particularly but not exclusively valves for regulating the flow of a fluid which may contain particulate debris material, e.g. sand.

Valves for use with fluids containing particulate debris suffer from the problem that the particulate matter can cause valve stiction, blockage, and erosion of critical working surfaces. This problem manifests itself particularly in control and choke valves used in offshore applications.

According to a first aspect of the present invention there is provided a valve comprising a valve plug having a seating surface for location, in a closed position of the valve, against a seat within the valve wherein the seating surface of the plug is protected by a shroud so as not to be directly exposed to the main flow stream through the valve when the latter is in an open condition.

The shroud protects the seating surface of the plug from the abrasive action of particulate debris in the flow stream therefore reducing or eliminating erosion of this seating surface.

The valve may be such that fluid flows laterally inwardly towards the axis of the plug and the shroud may comprise an annular flange projecting from the plug transversely to the direction of fluid flow into the valve, the seating surface being an annular surface located on the face of the plug behind the flange in the direction of said fluid flow.

According to a second aspect of the present invention there is provided a valve comprising a valve plug having a seating surface for location, in a closed position of the valve, against a seat within the valve wherein the seat is located outside the main flow stream on opening of the valve.

By positioning the seat outside the main flow stream, erosion of the seat by particulate debris in the flow stream is reduced or eliminated.

It is of course possible to apply the first and second aspects of the invention to a valve so that both the seating surface of the plug and the valve seat are outside the main flow stream.

A valve in accordance with the first or second aspect of the invention may comprise the plug, and a flow control sleeve on the inner surface of which the plug is slidable. The sleeve has a plurality of axially spaced apertures (e.g. arranged in axially spaced rows) which are progressively exposed as the plug moves to open the valve. Fluid flow through the sleeve is laterally in towards the axis of the plug. In accordance with the first aspect of the invention the shroud may comprise a flange projecting from, and extending around, an end face of the plug. The seating face of the plug is an annular (or other ring shaped) area of the plug face immediately inwards of the shroud. In accordance with the second aspect of the invention, the valve seat may be provided on a ring and be located beyond the first aperture to be exposed upon initial opening of the plug.When the first and second aspects are applied in combination, it is preferred that the shroud on the valve plug locates within a recess defined between the inner surface of the trim and a facing surface of the seating ring.

According to a third aspect of the present invention there is provided a valve comprising a valve plug which is slidable within a tubular valve guide having a plurality of apertures through which fluid enters the guide wherein the valve plug has a nose on which fluid entering the guide impinges so as to be directed axially along the tubular guide away from the inner walls thereof.

Preferably the nose is symmetrical about the longitudinal axis of the plug.

The plug nose angle presented to the flow stream is preferably generated by a frustoconical shape located centrally on the plug. It is preferred that the root of the plug nose has a diameter of 3/8 to 5/8 (e.g. about 1/2) that of the plug and a depth equal to 1/4 to 112 (preferably about 1/3) that of the plug travel in the guide. These criteria are particularly suitable since they give the best overall performance by minimising flow impingement effects thus reducing wear rates. Blending of the shapes generated by these criteria is effected according to individual construction materials and sizes.

The combined effect of impinging flow streams from the apertures in the valve guide and the nose profile concentrates the flow down the central axis of the valve. For a nose formation in accordance with the above criteria, a velocity profile taken across the outlet stream typically shows a concentration to the centre of at least four times the valve taken 1/3 in from the wall.

According to a fourth aspect of the present invention there is provided a valve comprising a valve plug which is slidable within a tubular valve guide having a plurality of apertures through which fluid enters the guide, said plug having a nose on which fluid entering the guide impinges, said nose having a bore which is in communication with the space behind the plug whereby fluid flow over the nose causes a reduced pressure to be generated in said space.

The reduced pressure in the space provides a continuous scavenging action on surfaces of said space (in which the valve plug moves) so as to remove particulate debris which has entered the space.

This particulate debris passes through the bore in the nose and into the main flow stream leaving the valve.

The nose may be such as to generate the reduced pressure by a coanda effect.

The invention will be further described, by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a part sectional view of one embodiment of valve in accordance with the invention, the valve being shown in the closed position; Fig. 2 is an enlarged view of part of the valve shown in Fig. 1; Fig. 3 is a detail illustrating the valve in an open condition.

Fig. 4 is a sectional view of a second embodiment of valve.

Referring to Fig. 1 there is illustrated a pressure reducing valve 1 comprising a cylindrical cage guide or valve trim assembly 2 within which works a valve plug assembly 3 for controlling fluid flow through the trim between a valve inlet conduit 4 and a valve outlet conduit 5 which is perpendicular thereto.

Valve trim assembly 2 comprises an inner sleeve 6 located concentrically within an outer sleeve 7 each sleeve having respective apertures 6a and 7a arranged in axially spaced rows around the sleeves. Apertures 6a are of larger diameter than apertures 7a. An annular chamber 8 is defined between the two sleeves as shown.

Valve plug assembly 3 is mounted on an actuator rod 9 which traverses an end cap 10 of the valve. Between the valve plug 2 and end cap 10 is a space 11 within which the plug assembly 3 is able to travel during movement between its upper and lower positions (Figs 1 and 2 show the plug assembly in its lower positions).

In its lowermost position, the plug assembly 3 covers all of the apertures 6a so that there is no fluid flow through the valve. As plug assembly 3 is raised, the apertures 6a are progressively exposed so that fluid flows from inlet 4 to outlet 5. Pressure reduction of the fluid occurs due to its passage through apertures 7a and 6a with intermediate expansion into chamber 8. This mechanism is well known in the art.

As thus far described the valve is conventional. The illustrated valve does however incorporate a number of features to render the valve particularly suitable in duties in which the line fluids may contain debris in the form of sand or other particulate matter. These features will now be described.

Valve plug assembly 3 includes a central head 12 the lower portion of which is formed with a generally frustoconical nose 13 which projects from a lower peripheral annular face 14 of the head 12.

The angled surfaces of the nose are connected to the free end surface thereof by radiussed edges.

The head 12 is penetrated by an axial bore 15 of the actuator rod 9 which remote from the head is provided with two axially spaced, radially extending apertures 16a and 16b which provide communication (via the bore 15) between the space 12 and the outlet conduit 5.

Surrounding the plug head 12 is a sleeve 17 (the outer face of which is in sliding contact with the inner surface of apertured sleeve 6) extending downwardly to the level of face 14 of the head 12. The lower face 18 of sleeve 17 is however provided around its outer marginal edge with a depending flange 19. This flange 19 surrounds an annular region 18s of face 18 (see Fig. 3). This annular region 18s provides a seating surface for the plug assembly 3. The sleeve 17 may for example be fabricated from titanium carbide.

Incorporated in the valve 1 is a ring 20 on which the plug assembly seats (in the closed position of the valve) in the manner to be described. The ring 20 is of stepped cross-section so as to be formed (on its outer side) with lower and upper lips 21 and 22 respectively and (on its upper face) with a seating surface 23 - see Fig. 3.

The lower surface of the inner apertured sleeve 6 locates on the lower lip 21 as shown and it will be seen that an annular recess 24 is defined above the upper lip 22 by the radially inner surface of sleeve 6 and that portion of the radially outer surface of ring 20 between lip 22 and seating surface 23.

It should be noted that the seating surface 23 (of ring 20) is below the lowermost aperture 6a in sleeve 6.

In the closed position of the valve, the plug assembly 3 is in its lowermost position such that its seating surface 18s (on the underside of sleeve 17) locates against the seat 23 on the ring 20, and the annular flange 19 locates within the recess 24. In this closed position, the distance between the lower face of flange 19 and the lowermost point of the apertures 6a provides a flow deadband (indicated in the drawing as F.D).

On opening of the valve, the plug assembly must rise by a distance F.D. before the apertures 6a in sleeve 6 are exposed by the plug assembly 3. The flow deadband F.D. serves to reduce erosion potential to the seating surfaces at low valve lifts. Once this movement past the flow deadband has been achieved, fluid may pass through the trim 2 via those portions of the apertures 6a (in sleeve 6) exposed by the plug assembly 3.

Referring now to Fig. 3 it will be seen that the seating surface 18s of the plug assembly is outside the main flow stream since it is behind the annular flange 19. This flange 19 therefore acts as a shroud protecting the seating surface 18s. Similarly the seating surface 23 on the ring 20 is also outside the main flow stream due to the fact that it is beneath the level of apertures 6a. Thus the two critical seating surfaces 18s and 22 are both outside the main flow stream and therefore not directly exposed to debris in the form of sand or other particulate matter in the line fluid. Therefore the surfaces 18s and 22 are protected from the abrasive action of such debris.

Further features of the valve are the effects produced by provision of the nose 13. Fluid passing through the trim 2 impinges on the nose 13 and is deflected along the central axis of the trim 2 whereby the flow is 'concentrated' along the central axis. When the plug is in a high lift position, the flow from the apertures 6a which does not impinge directly on the plug is induced into the main flow stream. The possibility of internal erosion is therefore reduced.

Furthermore, the provision of the central bore 15 in the plug provides a coanda effect as a result of the main flow stream passing over the nose. This results in a reduced pressure being generated in the space 11 giving a continuous scavenging action of the surfaces above the valve plug. This avoids any tendency for debris to build up behind the plug which would be the case with a conventional valve design.

In a modification of the illustrated embodiment, the plug nose may be used simply to deflect the flow along the valve axis without generating a scavenging effect. In this case, the nose profile would be such that the angled faces of the nose are connected to the free end face thereof by relatively sharp edges (as compared to the radiussed edges in the illustrated embodiment). Additionally, balance holes in the plug would be positioned outboard of the nose root instead of a bore being provided centrally within the nose.

If desired, the trim seat can be fitted with a seat exit diffuser so as further to reduce high velocity erosion effects. Such a seat exit diffuser would be constructed to deflect the flow stream away from vulnerable surfaces and is of particular value for in-line choke valves in preventing erosion of the primary pressure wall.

Reference is now made to Fig. 4 which illustrates a further embodiment of valve 101. The valve of Fig. 4 is an in-line valve in contrast to that of Fig. 1 in which the exit flow is at right angles to the inlet flow.

As in the case of the valve shown in Figs. 1-3 the valve of Fig.

4 includes an apertured trim 102 within which works a plug assembly 103. This plug assembly incorporates a generally frustoconical flow deflecting nose 104. and an annular flange 105 which surrounds a seating surface of the plug.

The plug assembly 103 incorporates a bore 106 which extends between the annular surface (of the face of the plug) surrounding the nose 104, and the rear surface of the head of the plug assembly 103.

The bore 106 serves as a balancing hole but does not lead to the generation of a reduced pressure behind the head of the plug assembly. As such, there is no 'scavenging' of particles from behind the head of the plug (such as occurs in the valve of Fig. 1).

The valve of Fig. 4 is further provided with a seat exit diffuser 107 incorporating apertures 108 as shown.

Claims (13)

1. A valve comprising a valve plug having a seating surface for location, in a closed position of the valve, against a seat within the valve wherein the seating surface of the plug is protected by a shroud so as not to be directly exposed to the main flow stream through the valve when the latter is in an open condition.

2. A valve as claimed in claim 1 wherein fluid flows laterally inwardly towards the axis of the plug and the shroud comprises a flange projecting from the plug transversely to the direction of fluid flow into the valve, the seating surface being located behind the flange in the direction of said fluid flow.

3. A valve as claimed in claim 1 or 2 comprising said plug and a flow control sleeve on the inner surface of which the plug is slidable, the sleeve having a plurality of axially spaced apertures which are progressively exposed as the plug moves to open the valve, wherein the shroud is a flange projecting from, and extending around, an end face of the plug, said flange surrounding the seating face of the plug.

4. A valve as claimed in any one of claims 1 to 3 wherein, in a closed position of the valve, the valve plug locates against a seat which is located outside the main flow stream on opening of the valve.

5. A valve as claimed in claim 3 wherein the valve plug has a nose on which fluid entering the sleeve impinges so as to be directed axially along the sleeve away from the inner walls thereof.

6. A valve as claimed in claim 5 wherein the nose has a bore which is in communication with the space behind the plug whereby fluid flow over the nose causes a reduced pressure to be generated in said space.

7. A valve comprising a valve plug having a seating surface for location, in a closed position of the valve, against a seat within the valve wherein the seat is located outside the main flow stream on opening of the valve.

8. A valve as claimed in claim 7 comprising said plug and a flow control sleeve on the inner surface of which the plug is slidable, the sleeve having a plurality of axially spaced apertures which are progressively exposed as the plug moves to open the valve, wherein the valve seat is located beyond the first aperture to be exposed upon initial opening of the plug.

9. A valve comprising a valve plug which is slidable within a tubular valve guide having a plurality of apertures through which fluid enters the guide wherein the valve plug has a nose on which fluid entering the guide impinges so as to be directed axially along the tubular guide away from the inner walls thereof.

10. A valve comprising a valve plug which is slidable within a tubular valve guide having a plurality of apertures through which fluid enters the guide, said plug having a nose on which fluid entering the guide impinges, said nose having a bore which is in communication with the space behind the plug whereby fluid flow over the nose causes a reduced pressure to be generated in said space.

11. A valve as claimed in claim 10 wherein the nose generates the reduced pressure by a coanda effect.

12. A valve as claimed in any one of claims 6 to 11 wherein the nose is symmetrical about the longitudinal axis of the plug.

13. A valve as claimed in any one of claims 9 to 12 wherein the nose is frustoconical.