The present invention relates to a self-contained hydraulic pulsation valve that generates a pulsating hydraulic flow without external pilot control .

For off-shore operations such as oil and gas production, equipment is usually placed on the sea bed. Valves are usually part of this subsea equipment. Most of these valves are opened and closed by actuators, some of which are step-actuators which open or close the valves in small incremental steps so as to be able to control the valve position accurately.

The most common way to operate subsea actuators is by direct hydraulic control using a topside (i.e. on the surface) hydraulic power unit on a fixed or floating installation, such as a rig or vessel, and hydraulic control umbilicals to deliver hydraulic power to these subsea actuators. Step-actuators have to be stroked numerous times to achieve the required valve operation, which in turn requires the umbilical to be pressurised and depressurised an equal number of times. The distance between the subsea step actuators and the topside hydraulic power unit often results in slow valve operation and this can lead to operational and/or safety problems.

One way to solve these problems is by applying subsea hydraulic power units. However, such units can be difficult to replace and have many moving components that can cause failure. Subsea maintenance of these units is impossible. Another way to reduce the time required to operate a remote step-actuator is by applying a quick dump valve. A quick dump valve depressurises the actuator before the umbilical is fully depressurised. This reduces the time required to operate the actuator, increasing the distance at which a topside remote hydraulic power unit can be used to operate subsea actuators. However, the time required to open or close a subsea valve can still be much longer than is required for operational or safety purposes.

Thus, there is a need to control remote hydraulic step-actuators from a hydraulic power unit without the use of quick dump valves or separate power units for individual actuator locations, when the distance between the power unit and the actuator would normally require such means.

Accordingly, the present invention provides a hydraulic valve for producing a pulsating hydraulic flow without external pilot control , comprising: a valve body defining an internal cavity and a plurality of ports, a spool movable in the cavity between first and second positions and shaped so as to divide the cavity into at least three chambers, an inlet port connectable to a hydraulic power source, an outlet port connectable to a hydraulic user, a venting port, spring means to bias the spool towards a first position, and a control port arranged such that pressure applied thereto acts in opposition to the spring means, wherein the arrangement is such that in the first position pressure applied to the inlet port is communicated to the outlet port and to the control port and causes the spool to move against the action of the spring into the second position in which the inlet port is isolated from the outlet and control ports and the outlet port communicates with the venting port .

Preferably, the spring means is located in a first chamber of the cavity, which is also provided with a leakage port allowing flow into and out of the first chamber as the spool moves, the inlet port communicates with a second chamber of the cavity, the venting port communicates with a third chamber of the cavity, and the outlet port communicates with the second chamber when the spool is in the first position and communicates with the third chamber when the spool is in the second position.

Preferably, the cavity comprises a primary cavity and a secondary cavity, and the spool comprises a primary spool located in the primary cavity and a secondary spool extending into the second cavity to define a fourth chamber therein, communicating with the control port.

Preferably, the primary spool comprises a core with at least two radially projecting flanges that contact the walls of the primary cavity with a sliding seal to define the first, second and third chambers.

Preferably, the secondary spool comprises a core forming a sliding seal with the wall of the secondary cavity.

Preferably, the inlet port is connected to a hydraulic power source by a first hydraulic line, the outlet port is connected to a hydraulic user by a second hydraulic line, the first and second lines are connected by a first control line including a flow restrictor, and the first and second - A -

lines are connected to the control port by a second control line.

Preferably, the venting port is connected to the environment by a third hydraulic line including a flow restrictor.

Preferably, the leakage port is connected to the third hydraulic line by a leakage line.

Preferably, the first, second and third hydraulic lines, the first and second control lines and the leakage line are flow paths within the valve body.

Alternatively, the first, second and third hydraulic lines, the first and second control lines and the leakage line consists of tubing members being external to the valve body.

The present invention also provides a method of providing a pulsating hydraulic flow comprising the steps of providing a hydraulic valve of the type set out above and pressurising the inlet port of the hydraulic valve continuously, thereby causing the spool to reciprocate between the first and second positions.

The present invention further provides a hydraulic actuation system comprising a hydraulic step actuator, a hydraulic power source and a hydraulic pulsation valve of the type set out above, the power source and the valve both being located remote from the actuator, and a hydraulic connection between the valve and the actuator. The present invention will now be described in detail, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a schematic cross-sectional view of a hydraulic pulsation valve in accordance with one embodiment of the present invention, at one end of its stroke; and

Figure 2 is a schematic cross-sectional view of the valve of Figure 1, at the other end of its stroke.

In the following description, the terms left and right are used for ease of understanding with reference to the arrangements shown in Figures 1 and 2. However, it will be appreciated that these terms are not restrictive and the arrangement of the valve could be reversed.

Figure 1 shows a hydraulic pulsation valve 10 in accordance with an embodiment of the present invention which comprises a valve body 12 defining an internal cavity within which a main spool 14 and a control spool 18 are movable from left to right. The cavity is vented by various ports, Pl, P2, Xl, Tl and L. These ports in the valve body 12 are connected as described further below to main ports P, A and T which represent the main entry and exit points into the valve system. Although ports Pl, P2, Xl, Tl and L are all contained within the valve body, it will be appreciated that the same functionality can be arranged via connections of tubing and components external to the valve body, as shown in the schematic. The main spool 14 comprises a central core 16, and two radially projecting flanges 22, 24. The outer perimeters of the two flanges 22, 24 form lands which sealingly contact the walls of the cavity and divide it into a number of chambers 28, 30 and 32. The control spool 18 is sealingly received in a longitudinal extension of the cavity in the valve body 12, creating another chamber 26.

A spring 34 is located in the chamber 32 between the flange 24 and valve body closing plate 56 to bias the spools 14, 18 towards the left hand side.

Port P represents a main entry point into the system and is connected to a hydraulic power source. Port A represents a main exit point from the system and is connected to a hydraulic user, e.g. to a subsea actuator. Port T is effectively a venting port for the system, venting to the environment. Typically, port T may be connected to a device that reduces the likelihood of seawater ingress.

Main port P is connected to port Pl in the valve body 12 by line 36. Main port A is connected to port P2 in the valve body 12 by line 46. Lines 36 and 46 are connected by a control line 40, which includes a flow restrictor 42. The port A is also connected to port Xl in the valve body 12 by control line 44.

Port T is connected to port Tl in the valve body 12 by line 48, which includes a flow restrictor 50. Port L in a valve casing 12 connects to line 48 by leakage path 54. In use, operation of the valve 10 is as follows, starting from the position of Figure 1 in which ports Pl, P2, L, Xl and Tl are open, although port Tl and port L are isolated from ports Pl, P2 and Xl by flanges 22 and 24 respectively.

Port P is pressurised by the hydraulic power source. Pressure is transmitted by line 36 and port Pl through chamber 30 and via port P2 and line 46 to port A. This will also pressurise port Xl via line 44.

When port P is pressurised in this way and flow to port A stops, the pressure increases sufficiently to begin to move the spool 14 towards the right hand side against the action of spring 34 by means of the force generated by spool 18. As this happens, port P2 is closed and fluid escapes from chamber 32 via port L and control line 54, flows through line 48 and flow restrictor 50 and enter chamber 28 via port Tl .

With port P2 closed, hydraulic fluid flows via control line 40, flow restrictor 42 and control line 44 to port Xl and chamber 26. The resulting further movement of the control spool 18 and main spool 14 to the right causes port P2 to open so that pressure can be transmitted into chamber 28 to act on the left hand end face of core 16 and flange 22. Pressure is also acting on the end face of the control spool 18 via the port Xl. The main spool 14 can then be fully stroked against the force of the spring 34 and moved to the extreme right hand position shown in Figure 2. In this position of the main spool 14, all the ports are open, although port Pl is isolated from ports P2, Xl, Tl and L by flanges 22 and 24.

In this fully stroked position, the port A is no longer subject to pressure from the port P and therefore there is return flow from port A to port T via port P2, chamber 28 and port Tl .

Once this return flow stops, the pressure decreases such that the force of the spring 34 becomes sufficient to push the main spool 14 and the control spool 18 back from the right hand side position of Figure 2 to the left hand side position of Figure 1.

Provided that pressure to port P from the power source is maintained, the cycle will begin again and the main spool 14 will stroke back and forth from left to right, thereby generating a pulsating flow to port A.

In this way, the valve 10 generates a pulsating hydraulic flow without any external pilot control, whether hydraulic, electric or pneumatic. It allows the use of a hydraulic power unit instead of a subsea power unit without increasing valve operation times to unsafe or unsuitably long periods. This means that almost all of the hydraulic components can be easily maintained and replaced if necessary, because they are not in a subsea location.