The control of hydraulically operated actuators is generally effected by the use of electrically operated pilot valves, typically directional control valves (DCVs) fitted in the hydraulic power feed lines to the actuators. Typically these valves are of the shear seal design with the two most common types being rotary and linear, examples being diagrammatically illustrated in Figs. 1 and 2. Both valves use the simple principle of alignment of an orifice 1 through a rotatable rod or movable piston with an orifice 2 through a cylinder wall 3 to open the valve, and total misalignment as the closed position.

In a rotary valve (Fig. 1), the rod, 4, is rotated to open the valve (to allow flow of hydraulic fluid from a source to pass through the valve to an actuator from an inlet I to an outlet O) and close the valve, whereas in a linear type (Fig. 2), the piston, 5, is displaced laterally for that purpose.

In practice, a DCV is a changeover device in order to vent hydraulic fluid under pressure in an actuator to a local reservoir via a second orifice through the cylinder wall. Thus, when the DCV opens the hydraulic fluid feed to an actuator, the vent (V in Figs. 1 and 2) is closed. When the DCV closes the hydraulic feed to an actuator, the vent is opened, allowing the hydraulic fluid in the actuator to rapidly exhaust to the reservoir. The reason for this is that, in applications such as a subsea well, the supply of hydraulic fluid to a multiplicity of actuators is supplied via a long umbilical, which presents friction to an exhausting actuator, thus slowing its return.

Referring to Fig. 3, a rotary DCV 6 is typically driven by an electric motor 7 through a gearbox 8 as schematically illustrated. Typically, the electric motor 7 is powered to provide rotation in one direction until the valve 6 is fully open to feed the actuator, whereupon electric power is switched off, leaving the valve in this position. Electric power is supplied to the motor 7 to rotate it in the opposite direction, typically by 90 degrees, in order to close the feed to the actuator and open it to the vent.

Referring to Fig. 4, a linear DCV 9 is typically fitted with two solenoids 10 and 11 as schematically illustrated. One solenoid is electrically powered to pull the piston laterally to open the feed to the actuator, whereupon electric power is switched off leaving the valve in this position. Electric power is applied to the other to pull the piston in the opposite direction to close the valve and open it to the vent, whereupon electric power is switched off, leaving the valve in this position.

Both types of DCV are thus bi-stable devices in that they remain in either a closed or an open position when electric power is removed. In some applications, such as fluid extraction from subsea wells, electric power is at a premium, as it has to be supplied from, typically, a long umbilical and thus bi-stable operation is important, as the supply of continuous power to a multiplicity ofDCVs becomes impractical. Such applications, however, require DCVs to change state rapidly in the event of a failure of either or both of electric and hydraulic power.

In the event of a failure of the source hydraulic power, it is essential, for safety reasons, that each actuator returns rapidly to its'dormant'state, i. e. exhausting through a vent.

In order to do this, the hydraulic pressure in each actuator must fall rapidly, which would only be achieved by rapidly exhausting its hydraulic fluid. When the hydraulic fluid source is a long umbilical, the exhausting of the fluid via the umbilical would be slow, and the actuator would return to its'dormant'state slowly, which is unacceptable.

Thus a DCV has to operate under such circumstances as to open the vent to allow the hydraulic fluid to exhaust rapidly to the local reservoir.

Various mechanisms exist to achieve this requirement, usually involving springs to return a valve to the desired state in such emergencies. The problem is that the energy retained by the spring has to be provided by the electrical device that operates the valve.

Thus, in the case of a rotary DCV, this means a larger electric motor, and thus more electric power to'wind the spring'or slower operation through a higher gear ratio gearbox, so that sufficient energy is available to operate the valve when the power has failed. In the case of a linear DCV, the solenoid has to be larger and requires more power to compress a spring to also provide sufficient energy to operate the valve under power failure conditions.

According to the present invention, there is provided a control valve for controlling the flow of fluid to a fluid-operated actuator, the valve, in an open condition in use, allowing the flow of fluid from a fluid source to the actuator and, in a closed condition in use, preventing the flow of fluid from the fluid source to the actuator, there being a vent for fluid supplied to the actuator, which vent is closed in said open condition of the valve and is open in said closed condition of the valve, wherein the valve is provided with energy storage means which, in use of the valve, stores energy from the fluid source and, in the event of a failure of the supply of fluid to the valve if the valve is in said open condition, uses such stored energy to cause said vent to be open.

The control valve may be a rotary or a linear control valve.

Said energy storage means may comprise spring means, such as helical spring means.

Said fluid may be a hydraulic fluid.

The present invention will now be described, by way of example, with reference to Figs.

5-10 of the accompanying drawings, in which:- Fig. 5 shows, diagrammatically, an application of an example of the invention to a rotary DCV, the latter being in a'closed'position; Fig. 6 shows what is shown in Fig. 5 but with the DCV being in an'open'position; Fig. 7 shows what is shown in Fig. 5 but after failure of a hydraulic power source, allowing venting of an actuator ; Fig. 8 shows, diagrammatically, an application of an example of the invention applied to a linear DCV, the latter being in a'closed'position; Fig. 9 shows what is shown in Fig. 8 but with the DCV being in an'open'position; and

Fig. 10 shows what is shown in Fig. 8 but after failure of a hydraulic power source, allowing venting of an actuator.

The examples of the present invention use a hydraulic power source to provide stored energy to enable a DCV to revert rapidly back to its venting position in the event of a later failure of the hydraulic source, thus permitting rapid exhausting of the hydraulic fluid from a hydraulic actuator. The invention is applicable to both rotary and linear DCVs.

Referring to Fig. 5, an electric motor (not shown) drives a conventional gearbox 12, an output shaft 13 of which is attached to an ann 14, fitted with a peg 15. The peg 15 engages a slot 16 cut in a disc 17 having two diametrically opposite arms 18, thus forming a simple Geneva mechanism. The disc 17 is attached to a shaft 19 of a rotary DCV. One of the arms 18 is connected via a pivot 20 to a piston 21 within a cylinder 22. The other of the arms 18 is connected via a pivot 23 to a rod 24 in contact with a helical spring 25 housed in a retaining cylinder 26. The cylinder 26 is connected via a pivot 27 to one end of an arm 28 attached to a disc 29 with a slot 30 in its side and pivots on a bearing 31. The other end of arm 28 is connected to the cylinder 22 via a pivot 32. The cylinder 22 and piston 21 assembly is shown as a sectioned view to aid understanding. Likewise, the spring 25 and cylinder 26 assembly is also shown as a sectioned view. The gearbox 12, the DCV and the pivot 31 are all mounted on a base plate 33. The mechanism is shown with hydraulic pressure from the hydraulic source applied via inlet H to the cylinder 22 such that the piston 21 is forced towards the end (upper as shown) of the cylinder 21, thus resulting in compression of the spring 25. The compressed spring, resulting from the hydraulic pressure in the cylinder 22, provides stored energy required to operate the DCV at hydraulic pressure failure. At this stage the DCV is'closed'with its vent open.

Fig. 6 shows the state of the mechanism after the DCV has'opened'. Electric power has been applied to the motor, which, via the gearbox 12, has rotated the arm 14 anticlockwise, causing the peg 15, engaged in the slot 16 of the disc 17, to rotate the disc clockwise and thus the shaft of the DCV. This'opens'the DCV, so that hydraulic power is fed to an actuator and its vent outlet is closed. At the same time, the arms 18 cause

the arm 28 and its attached disc 29 to rotate clockwise, by virtue of its linkage via the cylinder 22 and piston 21 assembly and cylinder 26 and rod 24. The arm 28 is lightly 'latched'in, position by a ball 34 slipping into the slot 30 in the disc by virtue of a spring 35.

Fig. 7 shows the state of the mechanism after a failure of the hydraulic source pressure.

The compression force of spring 25 is arranged so that when the hydraulic source pressure fails by falling by a small percentage of the normal operating pressure, typically 10%, the disc 17 with its arms 18 is rotated anticlockwise by 90 degrees via the rod 24.

This rotation of the disc is permitted by the exhaust of the small volume of hydraulic fluid in the cylinder and thus the return of the piston 21 to the bottom of the cylinder 22.

Arm 28 remains unmoved due to the light latch of the ball 34 in the slot 30 of the disc 29 attached to the arm 28. Rotation of the arms 18 rotates the DCV shaft 19 back to its position as in Fig. 5 and thus the actuator is connected to the vent and the hydraulic source disconnected from the actuator. This permits rapid exhausting of the hydraulic fluid in the actuator.

Resetting of the mechanism is effected by further application of electric power to the motor to rotate the arm 14 anticlockwise until the peg 15 re-engages with the slot 16 in the disc 17, i. e. as in Fig. 5, and restoration of the hydraulic source pressure to the cylinder 22.

Fig. 8 shows a linear DCV, which incorporates a piston 36, housed in a cylinder 37.

This piston 36 is held in the position shown, compressing a helical spring 38, by virtue of the pressure from the hydraulic source within the cylinder 37. Four seals 39 seal the piston 38 to the cylinder 37. The cylinder 37 slides within a second cylinder 40 and is sealed to it by four seals 41 and retained in position typically by friction or by a mechanism such as a spring-loaded ball locating in an indent in the cylinder, not shown in the figures. Cylinder 37 is shown in its lowest position, and with the piston 36 in the position shown the hydraulic source is isolated from the actuator, the latter being connected to the vent V. Thus the DCV is'closed' Fig. 9 illustrates the DCV in the'open'position. A solenoid 42 is momentarily supplied

with electric power so that the cylinder 37 is moved upwards. With the position of the piston 36 relative to the cylinder 37 being unchanged, the hydraulic source is connected to the actuator and the vent V closed. Thus the DCV is'open'.

Fig. 10 illustrates the DCV when the hydraulic source pressure fails. The position of the cylinder 37 remains unchanged, but the piston 36 reverts to its lower position due to the force provided by the spring 38. This results in closure of the inlet I from the hydraulic source and the opening of the actuator to the vent V, thus allowing the actuator to return rapidly to its quiescent position. The DCV is thus'closed'again.

Following failure of the hydraulic pressure source, and reversion of the DCV to the closed position, the device is reset to the conditions of Fig. 8 by applying electric power momentarily to a second solenoid 43.

Normal operation of the linear DCV, with sustained hydraulic source pressure, is effected by application of momentary electric power to the solenoid 42 to'open'the DCV and likewise to solenoid 42 to'close'it