GB2276209A

GB2276209A - Electrohydraulic valve actuator

Info

Publication number: GB2276209A
Application number: GB9403879A
Authority: GB
Inventors: Sigbjorn Sangesland
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-03-01
Filing date: 1994-03-01
Publication date: 1994-09-21
Also published as: NO177241C; NO930753L; NO177241B; NO930753D0; GB9403879D0

Abstract

An electro-hydraulic valve actuator (30) comprises a stem (6) which presses the valve to closed position by at least one spiral spring (4, 5), as the upper part of the stem (6) forms a piston in a cylindrical chamber which is activated by pressurize hydraulic fluid from pressure control means (16, 27, 12, 15). The latter comprises a pump assembly (16, 27), a pressure limiter (12) and a remotly controllable magnetic valve (15). The valve actuator (30) is pressure compensated and hermetically closed from the environment, and comprises at least two bellows (11, 25). The first bellows (11) is situated around the upper part of the stem (6), to ensure a hermetic seal against the valve medium and the second bellows (25) is arranged to compensate the pressure in the low pressure part of the actuator (30) against the environment, so that the actuator force stays constant and independent from the pressure of the environment. <IMAGE>

Description

E=lYDRPllLIC VALVE AFlUATOR The present invention concerns a hermetically closed and pressure compensated electrohydraulic valve actuator, having fail safe shutdown means. The invention is specifically designed for use in connection with controlling valves in downhole production systems, and blowout preventers in production or injection wells.

Conventional methods for controlling downhole valves are based upon hydraulic means. It is previously known to direct hydraulic oil from a platform and to a downhole well through large cables containing electrical conductors and a number of hydraulic pipes. This implies a substantial cost.

It is common that the fail-safe shut-down is being performed with a spiral spring.

At great depth and in deep wells the difference in hydrostatical pressure between the well fluid and the medium in the controll line will be substantial. This implies among other things that the spiral spring in the actuator must be upscaled, which means that the actuator is very space consuming.

Previously it is suggested to use electrical energy to solve the above mentioned problem.

From UK 2 198 766 and 4 920 811 are known means for electrical activation of valves. However, these devices have substantial disadvantages, which mainly are connected to the fail-safe shut-down mecanism.

UK 2 198 766 disclose a valve actuator where the rotational movement from an electrical engine is converted to linear movement. A leaf spring is put under tension by rotation of the valve stem which opens the valve. The valve is kept open as long as electrical energy is being supplied to the engine. When the energy suppy disappear, the screw is forced back by the spring, and the valve is closed. The device demands a substanitial amount of power to keep the valve open. Besides, the leaf springs requires a large construction space and the friction between the individual layers in the leaf spring barrel will probably involve reduced reliability for fail-safe shut-down of the valve.

UK 4 920 811 disclose a valve actuator where a mechanical shut-down device is used to keep the valve in open position. This shut-down device, which must receive a substantial rotational momentum, will be complex and will probably have a limited reliability. Besides, it will require a substantial amount of power to keep the valve open.

US 4 452 422 disclose a hydroelectric actuator for controlling globe valves used in turbines. The compact actuator comprises an electrical engine, a hydraulic pump, a valve, a hydraulic cylinder and accumulator. The accumulator is used to acheive large activation power and speed.

US 2 746 251 disclose a compact electohydraulic actuator which uses an electrical magnet valve to direct hydraulic fluid to the actuator. A spiral spring surrounding the valve stem ensures rapid shut-down of the valve.

US 3 675 420 disclose an electrohydraulic rotational actuator having an electrically activated fail-safe shut-down device. A hydraulic accumulator ensures that the valve takes closed or open position when electrical energy to the magnet valve ceases.

FR 7 443 373, 7 317 438 and 7 131 998 also disclose different electrohydraulic valve actuators. None of the above cited known electrohydraulic actuators have a function or a mode of operation which is required for operating a downhole gate valve having a fail-safe shut-down device. Generally, the necessary stem power for opening a 4-5 inches gate valve having a differential pressure of 700-1000 bar, will be approximately 700 000 Newton.

Preferably, the present invention provides an electrical actuator which can be controlled by electrical signals, and which does not have the disadvantages which are present in prior art.

Accordingly, the present invention provides an electrohydraulic valve actuator for a valve, comprising a stem which presses the valve to closed valve position by at least one spring means, wherein the upper part of the stem forms a piston in a chamber which is activated by pressurized hydraulic fluid fran pressure control means, wherein:: the valve actuator is pressure compensated and hermetically closed from the environment, wherein at least two bellows are used, where a first bellows is situated around the upper part of the stem, to provide a hermetic seal against the valve medium, and a second bellows is arranged to compensate the pressure in the low pressure part of the actuator against the environment, so that the actuator force stays substantially constant and independent fran the pressure of the environment.

Further features are clear from the dependent claims. Preferably, an actuator according to the invention is provided with a built-in hydraulic unit. An electrical engine operates a hydraulic pump which leads the oil flow to a piston in a cylinder which is connected to the valve stem over an electrically operated magnetic valve.

When the piston on the valve stem is in its end position, the engine stops and an electrical magnetic valve stops the return flow of oil from the cylinder chamber as long as electrical energy is supplied. The gate valve is then in its open position.

When the electrical energy supply ceases, the magnetic valve opens and the gate valve is moved to its closed position by a spiral spring.

Preferably, further, the invention comprises a metal bellows for pressure compensation against the hydrostatic water pressure, by which also is achieved a hermetically closed system.

The invention will now be described more in details using an example of an embodiment, and reference to the enclosed drawing, where: Fig. 1 shows a section view of a prefered embodiment of a valve acutator according to present invention, in its closed position, Fig. 2 shows a section view of a valve actuator according to present invention, particularly intended for use in connection with a blowout preventer, Fig. 3 shows a section view of a blowout preventer and the valve actuator from fig. 2, in its closed position, and Fig. 4 shows a detail of an alternative of the embodiment shown in fig. 1.

By first referring to fig. 1, is disclosed a valve comprising a housing 1 and a gate 3. The gate 3 leads the flow through the valve, and for opening the valve an actuator have to move the gate 3 downwards so that a hole in the gate 3 is in aligned with a bore in the housing 1.

The gate 3 is controlled by a stem 6 of an actuator, generally denoted 30. The actuator 30 and the gate 3 is kept in position by an internally threaded collar 2. To the stem 6 is connected a piston having dynamic seals 13. The upper part of the stem 6 is surrounded by a metal bellows 11. The effective cross section area of the bellows 11 is similar to the cross section area of lower part of the stem 6. This implies that the volum between the metall bellows 11 and the stem 6 is constant when the stem 6 moves up and down. Together with an elastomeric seal between the valve stems lower part and the actuator housing, this implies that the bellows 11 is minimally exposed to the environment (sea water and valve fluid), simultaneously as a hermetic seal between the environment and the content of the actuator is achieved.

Two springs 4, 5 bias the piston to ensure fail-safe shut-down. A sleeve 14 forms a stop for the piston when the piston reaches its lower position. The piston is moved by pressurized hydraulic oil. Hydraulic oil is supplied through a supply line from a pump 27 which is operated by an electrical engine 16, and a reduction gear.

The pump 27 pressurize the supply line connected to a magnetic line 15 which also contains a check valve. The magnetic valve 15 shut down the supply line when it is energized. The supply line is also connected to a pressure limiter 12.

An electrical cabel supply power to the magnetic valve 15 and the engine 16 by an electrical connection unit 17.

A linear variabel differencial transformer 24 is used for indicating the position of the valve. A further metal bellows 25 is used to equalize the pressure between the hydraulic oil on the inside of the actuator and the environment.

The pressure control devices (pump 27, pump engine 16, magnetic valve 15 and pressure limiter 12) are situated in a cylindrical housing 20. This cylindrical housing 20 can be moved axially by a mechanical external override, so that the valve can be opend in an emergency situation. This override axle has an outer part 22 having a quadratic section, and which can be rotated by a tool. The threaded part of the override axle comprises a ball screw arrangement and a ball nut.

By turning the override axle, the ball nut is axially moved when the override axle is prevented from axial movement by a bearing 21. The ball nut is fixed in the sylindric house 20 and thus the sylindrical housing 20 will force the piston downwards for opening the valve. By reversing the rotational direction produced by the tool, the valve can be closed when the compressed spring 4, 5 force the piston to follow the sylindrical housing 20.

The electrical engine 16 is started by an externally controlled device and runs the pump 27. The magnetical valve 15 is energized and the return flow to the oil reservoir is closed, so that oil from the pump 27 is directed down to the piston. The piston is moved downwards, opens the gate 3 and compresses the springs 4, 5. When the piston reaches its lowermost position, the electrical engine 16 is turned off. The hydraulic oil is prevented from flowing from return flow by a check valve.

If the electrical effect is lost, the magnetic valve 15 will open and the hydraulic oil keeping the piston down will be free, and the compressed springs 4, 5 will return the piston the to its original position and the gate valve will close.

By further referring to fig. 2 and 3, is disclosed a valve actuator 30 particularly inteded for a blowout preventer.

The actuator 30 shown in fig. 2 is situated in a side pocket of the production pipe conventional locking mechanism 31.

Transferring electrical energy and optionally two-way communication with control logic 32 can be achieved by an inductive connector 33. There is no mechanical connection between the two coils, and all possibilities for leakage through the wall of the production pipe is therefore eliminated.

An electrical engine 16 operates a hydraulic pump 27 which pressurize an actuator bellows 11 through a supply line 34, which actuator bellows 11 is connected to the valve stem.

The supply line 34 is flexible, and provides an opportunity to vary the length of the pressure-compensation bellows 25, dependending upon the position of the actuator bellows 11. The exterior of the bellows 25 is in contact with the surrounding valve fluid through a hole 35.

The supply line 34 has a check valve 36 and branches off into a magnetic controlled globe valve 15. The globe valve 15 is used for safe shut-down of the actuator.

The electric engine 16 is started by an external control device and operates the pump 27. The magnetic controlled globe valve 15 is energized and the supply line 34 is closed so that all oil from the pump 27 is directed down towards the bellows 11.

The actuator bellows 25 will expand axially and force the stem to open the flap (not shown) of the blowout preventor. When the stem is in its lowermost position the electrical engine 16 is turned off. Hydrualic oil is prevented from return flow by the check valve 36.

If electrical effect is lost, the magnetical controlled globe valve 15 will not open for the pressure of the supply line 34, and hydraulic oil-which keeps the actuator bellows 11 in expanded position will be set free and the stem will return to its original position by a spring, so that blowout preventer is closed.

In fig. 3 is shown a valve actuator 30 according to present invention, which is installed in connection with a blowout preventer.

In fig. 4 is shown an example of how the metal bellows can be arranged for achieving a hermetically closed actuator, simultaneously as a movement of the valve stem back and forth do not imply "breathing" against the environment. The upper part of the stem 6 is, as in the embodiment shown in fig. 1, surrounded by a metal bellows 11 having an inner sectional area similar to the lower sectional area of the stem. This implies that the volum between the metal bellows 11 and the stem 6 is constant when the stem is moved up and down. An upper elastomeric seal 36 ensures that the bellows 11 is not exposed unnecessarily to valve fluid and similar which could leak through a lower elastomeric seal 37. A check valve 45 prevents pressure build-up, and prevents external pollution from going into the sealing surfaces.

Claims

We claim:

1. An electrohydraulic valve actuator for a valve, comprising a stem which presses the valve to closed valve position by at least one spring means, wherein the upper part of the stem forms a piston in a chamber which is activated by pressurized hydraulic fluid from pressure control means, wherein: the valve actuator is pressure compensated and hermetically closed from the environment, wherein at least two bellows is used, where a first bellows is situated around the upper part of the stem, to provide a hermetic seal against the valve medium, and a second bellows is arranged to compensate the pressure in the low pressure part of the actuator against the environment, so that the actuator force stays substantially constant and independent from the pressure of the environment.

2. Valve actuator according to claim 1, wherein the first bellows (11) further is arranged to form a piston to generate an axial force.

3. Valve actuator according to claim 1, wherein the pressure controll means (16, 27, 12, 15) are situated in an axially movable housing (20) which by a ball connection (23) is connected to a threaded override axel, which is situated for at rotation in one direction to open the valve by pressing the housing (20) and thereby the stem (6) downwards.

4. Valve actuator according to claim 1, wherein the pressure controll means (16, 27, 12, 15) is situated in a movable housing (20) which by an externally controlled hydraulic unit facilitates opening of the valve by pressing the housing (20) and thereby the stem (6) downwards.

5. Valve actuator according to any one of claims 1 - 4, wherein a remotly controllable magnetic valve (15) drains hydraulic fluid from the cylinder chamber when the electric effect ceases.

6. Valve actuator according to any of claims 1 - 5, wherein: the first bellows has an effective area similar to the area of the lower part of the valve stem, so that the volume between the bellows and the valve stem is constant when the valve stem is moved up and down.

7. Valve actuator according to any one of claims 1 - 6, including a position indicator which automatically disconnects the pump assembly when the gate valve is entirely open.

8. Valve actuator according to any one of claims 1 - 7, wherein: the pump assembly is arranged to stop automatically after a certain time.

9. A valve actuator according to claim 1, wherein the pressure control means comprises a pump assembly, a pressure limiter and a remotely controllable magnetic valve.

10. A valve actuator substantially as any one embodiment herein described with reference to the accompany drawings.