GB2117871A

GB2117871A - Dump valve

Info

Publication number: GB2117871A
Application number: GB08225144A
Authority: GB
Inventors: Ronald Norris Whyte
Original assignee: SCHOOLHILL HYDRAULIC ENG
Current assignee: SCHOOLHILL HYDRAULIC ENG
Priority date: 1981-09-01
Filing date: 1982-08-31
Publication date: 1983-10-19
Also published as: GB2117871B

Abstract

A dump valve having a housing 1, an inlet port 3A for flow of pressurised fluid into the housing, an exhaust port 20 for passage of fluid from the housing, a supply port 3B for fluid communication between the housing and means to be acted on by the pressurised fluid, a main valve member 10 movable in the housing to open or close communication between the supply port and the exhaust port, the main valve member being biassed towards its open position and movable into its closed position under the effect of pressurised fluid at the inlet port, a passageway 12 providing fluid communication between the inlet port and the supply port, and a check valve member 13 movable to open or close said passageway, the check valve member being biassed towards its closed position and movable into its open position under the effect of pressurised fluid at the inlet port, the arrangement being such that the pressure of fluid required to move the check valve member from its closed to its open position is greater than that required to move the main valve member from its open to its closed position. <IMAGE>

Description

SPECIFICATION Dump valve This invention relates to a dump valve, especially but not exclusively for use in combination with a hydraulically-actuated gate valve for subsea use.

Hydraulically-actuated gate valves are used extensively concerning the flow of oil and gas.

These valves are generally designed to be fail safe in either the open or closed position. This is usually achieved by the use of a large spring, fitted inside the hydraulic actuator for the valve, on one side of the piston. The spring must have sufficient force to displace the hydraulic fluid in the actuator in the event of, for example, a hydraulic power failure or the control line becoming severed or damaged. Under most circumstances the operation of these valves is satisfactory.

In offshore situations such as the North Sea, however, this spring is not always able to operate the gate valve successfully. Where these valves are situated on the sea bed, or at a great distance from the control station, (usually the rig or platform), two normally negligible factors become important: 1. Small frictional forces requiring to be overcome, to pass hydraulic fluid along control lines to these valves, are much more significant; and 2. Because of differences in the heights of these installations, i.e. platforms above sea level and well heads on the sea bed, hydrostatic forces become increasingly important.

Several attempts have hitherto been made to deal with these factors, and the problem has been partially overcome by: (a) fitting heavier springs. There are limiting mechanical factors involved in this, and these have already been reached; (b) fitting a pressure-compensating accumulator device which compensates for water depth; and (c) using a quick dump/bleed valve directly to the actuator.

This enables water/glycol mixes to be displaced directly into the sea rather than forced back through the supply line to the control station on the platform.

Improved results have been achieved by incorporating these units, but the problem still exists of overcoming the hydrostatic head of fluid between sea water level and the platform.

According to the present invention there is provided a dump valve having a housing, an inlet port for flow of pressurised fluid into the housing, an exhaust port for passage of fluid from the housing, a supply port for fluid communication between the housing and means to be acted on by the pressurised fluid, a main valve member movable in the housing to open or close communication between the supply port and the exhaust port, the main valve member being biassed towards its open position and movable into its closed position under the effect of pressurised fluid at the inlet port, a passageway providing fluid communication between the inlet port and the supply port, and a check valve member movable to open or close said passageway, the check valve member being biassed towards its closed position and movable into its open position under the effect of pressurised fluid at the inlet port, the arrangement being such that the pressure of fluid required to move the check valve member from its closed to its open position is greater than that required to move the main valve member from its open to its closed position.

The main valve member preferably acts as a piston which in its closed position abuts a sealing face in the housing to prevent fluid passing from the supply port to the exhaust port. The sealing face may be for example of PTFE. The sealing face may be formed around the entrance to a bore forming part of the passageway and the main valve member may have a corresponding through bore which forms another part of the passageway.

When the valve member and sealing face separate, fluid may pass from the supply port to the exhaust port between them.

The piston may have a large-diameter portion which is in sliding but sealing engagement with a bore in the housing, and a small-diameter portion adjacent the supply port and spaced from the bore wall, the exhaust port being formed in the bore wall adjacent the small-diameter portion.

The exhaust port preferably has a one-way valve to allow outflow of fluid but prevent ingress of water, sand, silt or other contaminents.

The check valve member may be disposed within the main valve member.

An embodiment of this invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 is a side sectional view of a valve of this invention with the main valve member in a closed position; Fig. 2 is a side sectional view of an alternative form of the valve of the invention with the main valve member in an open position; and Fig. 3 is an end view corresponding to Fig. 2.

In the embodiment of Fig. 1 the valve has a generally cylindrical housing 1 open at both ends.

End caps 2 are provided at each end, the caps 2 each having a through bore 3A, 3B having a screw-threaded portion for receiving a hydraulic line (not shown). The cap 2A is at the inlet end of the valve and is connected in use to a supply of hydraulic fluid from, for example, an oil platform, and the cap 2B is connected in use to means such as a hydraulic actuator of a gate valve in a line at the sea bed.

A PTFE valve seat 4 is held in the housing adjacent the end cap 2B by a stainless steel retaining ring 5, the seat 4 having a through bore 6 communicating with the bore 3B of the cap 2B.

O-rings 7 are provided between the housing 1 and the end caps 2 and seat 4.

A main spring 8 abuts the retaining ring 5 at one end, the other end engaging a shoulder on a stainless steel piston 10 which is sealed against the housings internal wall by an O-ring 7 and slidable within it on synthetic bearing rings 11 which prevent metal-to-metal contact. The piston has a large-diameter portion 1 OA and a smalldiameter portion 1 OB, the latter being sealingly engageable with the end face of the valve seat 4.

The piston 10 has a through bore 12 which houses at the inlet end a check valve formed by a ball 13 biassed by a spring 14 through a locator 1 5 into engagement with a PTFE valve seat 1 6 which is held in place by a screw-threaded end plug 17 in the end of the bore 12.

The housing 1 has a number of exhaust ports 18, usually four, through its wall adjacent the small diameter portion 1 OB of the piston. A oneway valve in the form of an O-ring 19 extends around the housing in a recess 20 between the parts 18.

In use, pressurised fluid is pumped through the bore 3A, causing the piston 10 to move, against the bias of the main spring 8, into sealing engagement with the valve seat 4. This closes off fluid communication between the bore 6 through the seat 4 and the exhaust ports 1 8. The force exerted on the piston 10 by the incoming fluid is relative to the pressure required to pass the check valve 13, 14 plus the action of the main spring 8, in the opposite direction.

The ball 13 is lifted from its seat 16 by the fluid pressure and the fluid flows along the bore 12, into the bore 6 and thence through the bore 3B into the gate valve actuator connected to the end cap 2B. When the gate valve has been actuated fluid flow ceases and the ball 13 returns to its seat 1 6 under the effect of the spring 14, closing the passageway formed by the bores 3, 6 and 12. The valve remains in this mode during normal operation.

In the event of pressure drop in the supply line to the bore through the end cap 2A, the ball 13 prevents any fluid returning from the gate valve actuator along the bores 3, 6 and 12, and the pressure in the actuator acts with the main spring 8 to move the piston 10 out of engagement with the valve seat 4. Fluid then flows from the actuator through the bores 3B and 6, into the housing 1 and out to the sea through the exhaust ports 18 past the O-ring valve 19.

When the gate valve is nearly closed the spring assistance on the actuator is greatly reduced and the main spring 8 ensures that the piston does not close off access to the exhaust ports 1 8 again until pressure is greatly increased at the inlet 3A.

This therefore allows all the fluid to be displaced from the actuator, without hydrostatic head pressure, which has remained in the supply line (even though the pressure at the platform would show zero) having any effect.

The valve illustrated in Fig. 2 and 3 operates in the same manner as that of Fig. 1, the main differences being constructional, in that the check valve member 13 is in the form of a cone instead of a ball, and the relative dimensions are slightly different. Further, a sleeve 21 is located in an end portion of the housing 1 to reduce the area of the piston 10 end face on which the pressurised hydraulic fluid acts, thereby increasing the fluid pressure at which the piston 10 moves within the housing 1. The sleeve 21 thickness is selected according to the requirements of the valve.

The valve of Figs. 2 and 3 is 160.3 mm long and 50.8 mm in diameter.

Modifications and improvements may be made without departing from the scope of the invention.

Claims

1. A dump valve having a housing, an inlet port for flow of pressurised fluid into the housing, an exhaust port for passage of fluid from the housing, a supply port for fluid communication between the housing and means to be acted on by the pressurised fluid, a main valve member movable in the housing to open or close communication between the supply port and the exhaust port, the main valve member being biassed towards its open position and movable into its closed position under the effect of pressurised fluid at the inlet port, a passageway providing fluid communication between the inlet port and the supply port, and a check valve member movable to open or close said passageway, the check valve member being biassed towards its closed position and movable into its open position under the effect of pressurised fluid at the inlet port, the arrangement being such that the pressure of fluid required to move the check valve member from its closed to its open position is greater than that required to move the main valve member from its open to its closed position.

2. A dump valve according to Claim 1, wherein the check valve member is disposed within the main valve member.

3. A dump valve according to Claim 2, wherein the check valve member is disposed in a chamber within the main valve member, the chamber forming part of the passageway between the inlet port and the supply port.

4. A dump valve according to Claim 1, 2 or 3, wherein the housing is cylindrical and the main valve member is slidable longitudinally within it.

5. A dump valve according to Claim 4, wherein the main valve member has a through bore forming part of said passageway and has an annular end sealing face around the end of the bore which engages in its closed position with a corresponding annular face around an entrance to a further part of the passageway, the annular faces becoming separated in the open position of the main valve member to allow fluid to pass between them to the exhaust port.

6. A dump valve according to Claim 4 or 5, wherein the main valve member has a largediameter portion in sliding engagement with the housing wall and a small-diameter portion adjacent the supply port and spaced from the housing wall, the exhaust port being formed in the housing wall adjacent the small-diameter portion.

7. A dump valve according to any one of the preceding Claims, wherein the exhaust port has a one-way valve to allow flow of fluid from the housing and prevent flow into the housing through the exhaust port.

8. A dump valve according to any one of the preceding Claims, wherein the main valve member and the check valve member are biassed by means of respective springs.

9. A dump valve substantially as hereinbefore described with reference to and as shown in Fig. 1 of the accompanying drawings.

10. A dump valve substantially as hereinbefore described with reference to and as shown in Fig. 2 of the accompanying drawings.