GB2279131A - Choke valve - Google Patents

Abstract

A pressure-balanced stem choke valve comprises a casing (5, 10) providing inlet ports (10A) and a fluid discharge (15), fluid flow between the ports being regulated by a flow control element (7) moveable by means of a stem. The element (7) moves relative to a pressure balance chamber (18) and includes an inner fluid chamber (14) controlled fluid flow being possible between the inlet ports (10A) and the fluid chamber (14) via ports (13). Conduit means (19, 20) between the chambers (14, 18) ensure pressure balance conditions. The choke valve eliminates sand sedimentation therein by eliminating any stagnant flow area at or within the flow control element. This is achieved by recirculation flow between the chambers (14, 18), the conduit means including outward (20) and return (19) passages to this end, whilst fluid entering the element fluid chamber (14) is biassed to flow towards the outward fluid passage (20). Further, strategically positioned in-line twin porting (13L, 13R) is provided in the element (7) to encourage a continuous flow loop around the pressure balance chamber (18) for the avoidance of solid sedimentation. <IMAGE>

Description

"CHOKE VALVE" The present invention relates to a choke valve for controlling a fluid flow.

In particular, the present invention concerns a choke valve comprising a casing including a fluid opening to a fluid chamber, fluid control means in said fluid chamber for controlling fluid flow to an outlet, said fluid control means including port means permitting fluid flow between the fluid opening and said outlet and further comprising a stem and a receiving member for the stem, one of said stem and receiving members defining a moveable member to provide relative movement between the stem and the receiving member for controlling the opening of said port means, said moveable member including a piston moving in a cylinder means. Such a choke valve is referred to as "a choke valve as aforesaid".

In a choke valve as aforesaid, it is desirable to maintain substantial equal pressure on either side of the piston (to avoid a differential piston effect) and to this end a fluid passage is provided in the moveable member leading from the fluid chamber, at fluid outlet pressure, to the outer end of the cylinder means (referred to as the pressure equalisation chamber) to maintain said outer end at substantially fluid outlet pressure, and it is the principle object of the present invention to provide improvements in a choke valve having such a fluid passage. Therefore in accordance with the present invention, a choke valve as aforesaid includes means to promote a recirculation of fluid between said fluid chamber and the pressure equalisation chamber.

By virtue of the present invention, the fluid recirculation means discourages the accumulation of particle material carried by the fluid in the pressure equalisation chamber while still permitting equalisation of pressure on either side of the piston; said particle accumulation resulting previously from fluid stagnation in the equalisation chamber adversely affected the operation of the choke valve. Choke valves are frequently called to handle fluid with suspended particles or sediment, and this is particularly true for choke valves used in oil and gas fields both for drilling and production as fluids in this environment are generally heavily laden with particle material especially in the form of sand or rock cuttings.

In a preferred embodiment the recirculation means comprises fluid passage means in the moveable member for equalisation of pressure on either side of the piston, said fluid passage means including a first fluid passage arranged for outward flow of fluid from the fluid chamber to the pressure equalisation chamber and a second fluid passage for return of fluid from said equalisation chamber to the fluid chamber. In a preferred embodiment, to achieve the fluid recirculation, the fluid flow in the valve is arranged so that a fluid speed imbalance is present with respect to inlet fluid discharges via an annular series of ports on the moveable member.

Preferably said moveable member in cross-section defines a leading portion and a back portion, and at least one port of said annular port series is present in said leading portion and directly faces incoming fluid so that the velocity of fluid discharged from said one port is greater than that from other ports on the annular series, said first fluid passage communicating with said back portion while said second fluid passage communicates with said leading portion.

Preferably the chamber within the moveable member has an inner surface of general hemispherical form, and can additionally include a tapering annular wall leading to said inner surface.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings wherein: Fig. 1 shows a sectional side view of a choke valve in accordance with the present invention; Fig. 2 shows a schematic plan view through secion X - X in Fig. 1; 'and Fig. 3 is a sectional elevation of the valve with a simulation of recirculatory fluid flow in the valve indicated.

Referring to the drawings, a choke valve 1 basically as described in the applicent's U.K. Patent Application No.

9202533.7 comprises a main valve casing 2 including a through-bore 3, an end member 4 sealingly secured to the casing 2 and including a cylinder sleeve 5 projecting into the bore 3, a flow control head or tip 6 in the bore 3 having an upper piston portion 7 sliding in the cylinder sleeve 5, an actuating stem 6A of the tip 6 passing through an upper wall of the end member 4, a receiving member for the tip 6 in the form of an open bottomed cup 8 located in a shoulder 9 in the bore 3 oppositely from the sleeve 5, and a joining sleeve 10 between the cylinder sleeve 5 and the cup 8. A lateral inlet duct 11 directs inlet fluid to an annular chamber 12 surrounding the sleeve 10.An annular series of ports 13 on the tip 6 leads fluid to an internal space 14 of the tip whence the fluid can flow to a discharge 15 at the outlet from the open bottom cup 8, while transfer ports lOA on the sleeve 10 permit transfer of fluid from the annular chamber 12 to the ports 13. Downwards movement of the stem 6A moves the tip 6 into cup 8 and ultimately a frusto-conical surface 16 on the tip 6 engages a seating 17 on the cup 8 for full valve closure. A chamber 18 is present in the cylinder sleeve 5 at the outer end of the piston portion 7 and by virtue of the ducts 19, 20 leading from the space 14 to the chamber 18, this latter chamber 18 constitutes a pressure balance chamber. This minimises any adverse effect the pressure of the fluid may have on the operation of the valve.

Previously fluid stagnation occurred in the chamber 18 with the result that there arose a build-up of sand or other particles (brought in by the fluid) in the chamber 18, and this had the deleterious effect of limiting the full working movement of the valve.

The present valve 1 overcomes this problem by removing the stagnant flow. This is achieved by inducing a continual fluid flow loop around the pressure balance chamber 18. In this embodiment this recirculation is achieved by the way the fluid is induced to flow into the interior space 14 of the tip 6. Thus considering Fig 2, the tip 6 in cross-section divides into a leading half 6L and a rear half 6R relative to the input flow direction in inlet 11, thefluid flowing around the tip 6 in annular chamber 12 whence it passes to the interior 14 of tip 6 via ports 13 after transfer through transfer ports 10A. In each annular series of ports 13 as shown in Fig. 2 a port 13L in the leading half 6L directly faces the inlet flow, while there are additional ports 6R and 6S in the tip at the rear half 6R and the sides respectively.The ducts 19 and 20 communicate respectively with the leading and rear halves 6L, 6R.

Consequently, with regard to inlet flow passing through each annular series of ports 13 into the interior of the tip 6, the flow through the leading port 13L of the series will have a greater velocity than the flow through the other ports 13S, 13R, as the energy and fluid velocity is reduced as the fluid passes round the chamber 12 and turns into the ports 13S/R, the flow speed through the rear port 13R being especially reduced. There is an impact in the interior 14 of the fluid jets passing from the ports 13L, 13R and the jet of port 13R is forced back on itself due to the natural imbalance of the fluid velocities as explained above, the jet from port 13R being weaker. This imbalance creates the recirculation flow via the back duct 20 across the balance chamber 18 then a flow return via duct 19. The small arrows in Fig. 3 represent a simulation of the fluid pattern of this recirculating flow, and the significant characteristic of this pattern namely the greater fluid build-up in the rear half 6R of the tip 6 will be observed in Fig. 3. To assist the recirculatory flow, the inner wall 14B of the interior 14 is essentially of hemispherical form, with the annular wall of the interior converging to this hemispherical portion. Thus during valve operation, there is a continuous non-stagnant flow in the chamber 18 and this mitigates against sand or other particle build-up in the chamber 18.

Claims (7)

1. A choke valve as aforesaid including recirculation means to promote a recirculation of fluid between said fluid chamber and the pressure equalisation chamber to promote elimination of stagnant low pressure voids causing solid accummulation, said recirculation means comprising first conduit means for outward fluid flow from the fluid chamber to the pressure equalisation chamber and second conduit means for return of fluid from the pressure equalisation chamber to the fluid chamber, and biassing means to bias fluid entering the fluid chamber to flow towards said first conduit means.

2. A choke valve as aforesaid including recirculation means to promote a recirculation of fluid between said fluid chamber and the pressure equalisation chamber to promote elimination of stagnant low pressure voids causing solid accummulation, said recirculation means comprising first conduit means for outward fluid flow from the fluid chamber to the pressure equalisation chamber and second conduit means for return of fluid from the pressure equalisation chamber to the fluid chamber, wherein biassing means is provided by arranging the inner end surface of the fluid chamber to have a solid hemispherical profile compatible with the flow pattern through the flow control means, said first and second conduit means being arranged at said hemispherical profile.

3. A choke valve as claimed in claim 1 or 2, wherein the biassing means is such that, in fluid flow in the valve, a fluid speed imbalance is present with respect to inlet fluid discharges via an annular series of ports on the moveable member.

4. A choke valve as claimed in claim 3, wherein said moveable member in cross-section defines a leading portion and a back portion, and at least one port of said annular port series is present in said leading portion and directly faces incoming fluid so that the velocity of fluid discharged from said one port is greater than that from other ports on the annular series, said first fluid conduit means communicating with said back portion while said second fluid conduit means communicates with said leading portion.

5. A choke valve as claimed in claim 4, wherein a pair of ports are present respectively in said leading portion and in said back portion of the moveable member, said port pair being aligned to encourage a continuous fluid flow loop around the pressure equalisation chamber.

6. A choke valve as claimed in claim 2, wherein the fluid chamber in the moveable member includes an annular wall which converges towards the hemisperical inner end of the fluid chamber.

7. A choke valve substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.