Linear actuator for actuating a process valve

Abstract

The invention relates to a linear actuator (20) for linear actuation of a process valve (30), said linear actuator having a housing (200), wherein an electronic control unit (40), at least one electric drive unit (41), and at least one hydraulic drive (27, 21) are located in the housing (200). The hydraulic drive (27, 21) comprises at least one hydraulic cylinder (21) having a piston (24) and a piston rod (23), wherein the piston rod (23) extends outwardly through an opening in the housing (200). The hydraulic drive (27, 21) is designed to convert an electric drive power of the electric drive unit (41) into a hydraulic driving force which generates a linear movement of the at least one hydraulic cylinder (21) in a first direction. A linear movement of the piston (23) of the hydraulic cylinder (21) in a second direction opposite to the first direction is generated by a restoring force on the piston rod (23), which restoring force acts on the piston rod (23) outside the housing (200).

Description

[0001] Linear actuator for operating a process valve

[0002] Description

[0003] The present invention relates to a linear actuator for actuating a process valve and a system comprising the linear actuator.

[0004] Background of the invention

[0005] In oil and gas production facilities operating at great depths offshore, process valves are used to regulate or shut off the flow of the medium being pumped. These process valves are operated by electrohydraulic actuators, such as a hydrostatic linear actuator. This can contain a hydraulic cylinder with one or more springs that move the piston of the hydraulic cylinder to a predetermined position in the event of a hydraulic drive failure. This places the process valve in a safe position in the event of a fault.

[0006] DE 10 2020 200 263 A1 shows a hydrostatic linear actuator that exerts a tensile force on a safety-relevant component in an emergency. The tensile force is initially generated by a relaxing emergency spring. In the final part of the movement, a hydraulic accumulator is activated via a travel-dependent control system, whose pressure fluid is pumped into a cylinder chamber, which acts on a piston to which the component is coupled.

[0007] A disadvantage of a linear actuator according to DE 10 2020 200 263 A1 is its increased weight due to the safety elements integrated into the actuator (spring systems, additional hydraulic components). This complicates the replacement of a defective linear actuator at great depths using an underwater vehicle (remotely operated vehicle - ROV). Disclosure of the invention

[0008] According to the invention, a linear actuator for actuating a process valve and a system comprising the linear actuator are proposed, having the features of the independent patent claims. Advantageous embodiments are the subject of the dependent claims and the following description.

[0009] The invention provides a compact and simple linear actuator that requires only a few elements to operate a process valve and is therefore lightweight. The linear actuator can be coupled to a safety device using a standard interface.

[0010] The linear actuator according to the invention for the linear actuation of a process valve comprises a housing in which an electronic control unit, at least one electric drive unit, and at least one hydraulic drive unit are arranged. The hydraulic drive unit comprises at least one hydraulic cylinder with a piston and a piston rod. The piston rod extends outward through an opening in the housing. The hydraulic drive unit is configured to convert an electrical drive power of the electric drive unit into a hydraulic drive force, which generates a linear movement of the piston of the at least one hydraulic cylinder in a first direction.A linear movement of the piston of the hydraulic cylinder in a second direction, opposite to the first direction, is generated by a restoring force acting on the piston rod outside the housing, and in particular not by a spring force of a mechanical spring of the linear actuator. In particular, no hydraulic drive force is exerted on the opposite side of the piston to move it in the second direction.

[0011] The housing preferably serves as a tank for the hydraulic drive and is filled with a hydraulic fluid. The hydraulic fluid preferably also serves to resist external pressure acting on the linear actuator and to protect against corrosion and lubricate the elements of the safety device. The hydraulic fluid can be hydraulic oil, for example. The hydraulic drive preferably comprises at least one pump and at least one hydraulic cylinder. The electric drive unit can be an electric motor that drives the pump via a common shaft. The hydraulic cylinder is preferably designed as a double-action cylinder. The pump preferably conveys hydraulic fluid from an interior space of the linear actuator via a line into a working space of the hydraulic cylinder. A check valve is particularly preferably arranged downstream of the pump.The hydraulic fluid pumped into the working chamber exerts a hydraulic drive force on the piston, causing the piston rod of the hydraulic cylinder to move in a first direction. The piston rod of the hydraulic cylinder is moved in a second direction, opposite to the first, by a restoring force acting on the piston rod outside the housing, which is greater than the instantaneous drive force. Ideally, the drive force should then be as small as possible, or even zero. To achieve this, the electric drive unit can first be switched off, and then the hydraulic fluid can be drained from the working chamber of the hydraulic cylinder or forced out by the return movement of the piston.

[0012] The linear actuator preferably has at least one relief valve designed to reduce the hydraulic drive force. The relief valve is arranged in a line between the working chamber of the hydraulic cylinder and the interior of the linear actuator. It is preferably an electric relief valve that can be opened and closed by means of a control current / voltage. Particularly preferably, the relief valve is closed when energized or open when deenergized (NO, normally open). As long as the pump delivers hydraulic fluid into the working chamber of the hydraulic cylinder to build up the hydraulic drive force, the relief valve can be controlled so that it is in a closed position.To reduce the hydraulic drive force, the relief valve can be opened by switching off the control current, so that the hydraulic fluid can flow from the working chamber of the hydraulic cylinder into the interior of the linear actuator. The relief valve is expediently a normally open (NO) valve that opens when the control voltage drops. Since the relief valve is normally open, the hydraulic drive force is automatically reduced if the control system fails, thereby increasing the safety of the system. The linear actuator preferably contains at least one variable throttle valve designed to control the reduction of the hydraulic drive force. The variable throttle valve is preferably arranged upstream of the relief valve in the line between the working chamber of the hydraulic cylinder and the interior of the linear actuator.Preferably, an opening cross-section of the throttle valve and thus a flow through the throttle valve can be controlled. Particularly preferably, the variable throttle valve is an electric valve whose cross-section can be varied by means of a control current or a control voltage. The electronic control unit can contain predetermined values / characteristic curves for the control signal with which various force reduction characteristics can be set. It is also possible for the reduction of the hydraulic drive force to take place in a controlled manner. For this purpose, for example, the piston position of the hydraulic cylinder can be measured and the opening cross-section of the throttle valve can be adjusted such that the piston assumes the desired position at all times during the force reduction. The throttle valve is expediently a normally open valve (NO), which opens when the control voltage drops.Since the throttle valve is open when de-energized, the reduction of the hydraulic drive force is not hindered in the event of a control failure, thus increasing the safety of the system.

[0013] The linear actuator preferably also has a pressure compensation device designed to equalize pressure between the surroundings and the interior of the linear actuator. The pressure compensation device is preferably a diaphragm accumulator or a bladder accumulator that has a fluid connection to a housing opening. The pressure compensation device is particularly advantageous when the linear actuator is used in underwater applications. The pressure compensation device is particularly preferably a bladder accumulator. The bladder accumulator can be designed with a flexible wall that encloses a predeterminable bladder storage volume and can move axially and radially in response to the pressure prevailing inside the accumulator. The flexible wall of the bladder accumulator can be made, for example, from an elastomer and can be fluid-tight and resistant to contact with seawater under high pressure.

[0014] Particularly preferably, the pressure compensation device is configured to adjust the pressure in the interior of the linear actuator within a range between ambient pressure and 10 bar above ambient pressure. This can be achieved, for example, by means of a spring that preloads a diaphragm attached to the pressure compensation device. The preload force of the spring allows the pressure in the interior of the pressure compensation device to be adjusted to a desired value above ambient pressure.

[0015] The linear actuator preferably also has at least one mechanical interface by means of which a safety device can be connected to the linear actuator. The mechanical interface can preferably comprise a quick-release fastener, in particular a rotary fastener (i.e., a connection that can be closed by rotating one of the components involved, preferably by a maximum of 360°, a maximum of 180°, a maximum of 90°, or a maximum of 45°), e.g., a bayonet fastener or a quick-release fastener according to EN ISO 13628-8, "Linear (push) interface", Type A or Type C. This quick-release fastener comprises, on one side, a flange with recesses arranged around a first shaft. Claw-shaped projections of a second shaft of an opposite side can be axially inserted into the recesses of the flange, and the two sides of the quick-release fastener can be connected to one another by rotating the second shaft 45° clockwise.By rotating the second shaft 45° clockwise, its claw-shaped projections rest axially and radially on the flange of the first shaft, creating a positive connection between the two sides of the quick-release fastener.

[0016] The safety device may comprise one side of the quick release described above, and the linear actuator may comprise the second side of the quick release.

[0017] The safety device can comprise a housing and a piston rod, wherein the piston rod is mounted in the housing for linear displacement and can be connected to a process valve. The safety device can also have a piston connected to the piston rod and at least one spring clamped between the piston and an end face of the housing. This means that the piston rod and the piston are held in a predetermined position (end position) by the spring force as long as no hydraulic drive force of the linear actuator acts on the piston rod that is counter to or greater than the spring force. A process valve connected to the safety device is preferably in a safe position when the piston rod is in this end position. The safe position is particularly preferably a closed position of the process valve.The safety device therefore serves to accelerate the reduction of the hydraulic drive force of the linear actuator in the event of a fault, for example in the event of a power failure, and to bring the process valve into a safe position in a short time.

[0018] Decoupling the safety device from the linear actuator makes it possible to reduce its weight so that it can be swapped with an ROV via the mechanical interface. This can be done without having to remove or open the safety device. This significantly simplifies maintenance and installation of the linear actuator, especially at great depths.

[0019] Particularly preferably, the linear actuator has a hydraulic circuit for tensioning at least one spring of the safety device. This allows the process valve to be opened by means of the linear actuator without having to overcome the spring force of the safety device. Thus, a lower hydraulic drive force of the linear actuator is required. The safety device can have a separate mechanical interface for pretensioning the spring, for example, an additional shaft through which a force can be exerted on the spring. A piston rod of a hydraulic cylinder can engage this shaft.

[0020] The hydraulic circuit for tensioning the at least one spring of the safety device preferably contains a hydraulic cylinder with a first cylinder chamber, which is connected to the pump via a first line and to a relief valve via a second line. Pressurized fluid can be enclosed in the second cylinder chamber of the hydraulic cylinder via a shut-off valve. To tension the at least one spring of the safety device, pressurized fluid is first pumped into the first cylinder chamber, causing the piston rod of the hydraulic cylinder to move towards the safety device and exert a force on the separate mechanical interface of the safety device. Once the desired preload of the spring is achieved, the shut-off valve on the second cylinder chamber can be closed, thus fixing the position of the piston rod.Deviations from the set piston rod position due to leakage of hydraulic fluid from the second cylinder chamber can be compensated for by permanently connecting the first cylinder chamber to the pump. If a power failure occurs, both the relief valve in the first cylinder chamber and the shut-off valve in the second cylinder chamber open, preventing any further force from being transferred from the hydraulic cylinder to the spring. This ensures the safety device's functionality even when the spring is preloaded separately.

[0021] According to a preferred embodiment, the at least one hydraulic cylinder comprises three cylinder chambers, one of which is hermetically sealed, so that a vacuum is created therein upon movement of the piston rod. The hydraulic cylinder is preferably a double-acting cylinder, on which a third, hermetically sealed cylinder chamber is additionally arranged or can be created at an outer end of the piston rod of the double-acting cylinder. This can mean that this cylinder chamber is at least partially formed or delimited by the piston rod. In particular, a volume of the hermetically sealed cylinder chamber can be changed by means of the piston rod and can also be zero when the piston rod stops. A change in volume of the third cylinder chamber upon movement of the piston expediently corresponds to a change in volume of the portion of the piston rod outside the housing.This allows the piston rod to move without changing the volume of the pressure compensation device, i.e. the pendulum volume of the hydraulic cylinder can be reduced.

[0022] Preferably, the vacuum-loaded cylinder chamber is a vacuum bushing or vacuum sleeve. It is possible for the hermetically sealed cylinder chamber to be designed as a separate component.

[0023] Preferably, the linear actuator further comprises at least one sensor configured to detect the position of the linear actuator and a display device configured to display the position of the linear actuator on an exterior side of its housing. Furthermore, the linear actuator may include pressure sensors for monitoring the pressure in the individual chambers of the linear actuator. The display device may include a physical display (e.g., a movable arrow) that displays the position of the linear actuator (e.g., the position of the piston or piston rod of the hydraulic cylinder) on the exterior of the housing. The physical display may be mechanically connected to the piston and / or piston rod of the hydraulic cylinder of the linear actuator. The display device may be used by an ROV and / or monitored via a camera.The system according to the invention comprises a linear actuator for linearly actuating a process valve and at least one safety device as described above. The safety device is connected to the linear actuator via a mechanical interface as described above.

[0024] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0025] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0026] The invention is illustrated schematically in the drawings using exemplary embodiments and is described in detail below with reference to the drawings.

[0027] Character description

[0028] Figures 1a and 1b show a preferred embodiment of a linear actuator according to the invention, respectively in a spatial external view and in a longitudinal section;

[0029] Figure 2 shows a hydraulic circuit diagram of a linear actuator according to a preferred embodiment of the invention;

[0030] Figure 3 shows a hydraulic circuit diagram of a linear actuator according to another preferred embodiment of the invention;

[0031] Figure 4 shows an example of a mechanical interface between a linear actuator and a safety device according to a preferred embodiment of the invention in longitudinal section; and

[0032] Figure 5 shows a linear actuator and a safety device according to a preferred embodiment of the invention in a spatial external view. Detailed description of the drawing

[0033] Figures 1a and 1b show a preferred embodiment of the linear actuator 20 according to the invention. Figure 1a shows a three-dimensional external view of the linear actuator 20. Standardized handles 204, 205 for assembling / disassembling the linear actuator 20 using an ROV are mounted on the cylindrical surface of the linear actuator housing 200 and on its left end face in the figure.

[0034] In addition, a connector 203 is located on the left end of the linear actuator 20, to which the power and signal supply of the linear actuator 20 is connected. Furthermore, a display device 206 can be seen on the end of the linear actuator 20, which indicates the position of the linear actuator 20.

[0035] Figure 1b shows the linear actuator in a longitudinal section. An electronic control unit (not shown), an electric drive unit (not shown), and a hydraulic drive are arranged in the housing 200. The hydraulic drive comprises a pump (not shown) and a hydraulic cylinder 21. A piston rod 23, which is fixedly connected to a piston 24, is arranged in the hydraulic cylinder 21. The piston rod can be moved to the right in the figure and then extends outside the housing 200. In addition, the linear actuator 20 shown has a mechanical interface 22 to which a safety device can be coupled. The mechanical interface 22 is described in more detail below in connection with Figure 4.

[0036] Figure 2 shows a hydraulic circuit diagram of a linear actuator 20 according to a preferred embodiment of the invention. Shown are a linear actuator 20 and a safety device 10, which is connected to the linear actuator 20 by means of a mechanical interface 2a. For this purpose, the mechanical interface 2a of the safety device 10 is coupled to a corresponding interface 22 of the linear actuator 20. On a side of the safety device 10 opposite the first interface 2a, a further interface 2b is arranged on the safety device 10, by means of which the safety device can be connected to a process valve 30. For coupling, the linear actuator 20 is attached, for example, to the safety device with intermeshing interfaces 22, 2a and rotated by 45°.The safety device 10 according to Figure 2 contains, in addition to the interfaces 2a, 2b, a housing 1 in which an axially movable piston rod 3 is arranged with a piston 4 rigidly connected to the piston rod 3. A spring 6 is clamped between the piston 4 and an end face of the housing 1. The housing 1 of the safety device 10 can be filled with a hydraulic fluid.

[0037] The process valve 30 shown comprises a disc 31 which opens and closes a valve channel 34 as a result of a movement of the piston rod 3 of the safety device 10.

[0038] The linear actuator 20 shown in Figure 2 contains an electronic control unit 40 with, for example, analog and digital inputs and outputs, which can receive signals from pressure and position sensors (not shown) and can control / regulate the electric and hydraulic drive. Furthermore, the linear actuator 20 contains a pump 27, which is driven by an electric motor 41 and conveys hydraulic fluid from an interior space T of the linear actuator 20 via a line 25 into a working chamber 21 aa of a hydraulic cylinder 21.

[0039] The illustrated hydraulic cylinder 21 is designed as a double-action cylinder and comprises a piston rod 23 to which a piston 24 is attached. The piston 24 separates the working chamber 21aa from a second cylinder chamber 21ab, which is hydraulically connected to the interior of the linear actuator 20. Furthermore, the linear actuator 20 contains a relief valve 28, which is also connected to the working chamber 21aa of the hydraulic cylinder 21 via line 25. Figure 2 shows the position of the hydraulic cylinder 21 with the relief valve 28 open, in which the working chamber 21aa has a minimum size, while the opposite cylinder chamber 21ab has a maximum size.

[0040] At an outer end of the piston rod 23, a hermetically sealed cylinder chamber 21ac is arranged or can be created, in which a vacuum is formed upon movement of the piston rod 23. A change in the volume of the cylinder chamber 21ac upon movement of the piston expediently corresponds to a change in the volume of the portion of the piston rod outside the housing, i.e., the pendulum volume of the hydraulic cylinder 21 can be reduced.

[0041] Between the pump 27 and the connection 29 of the pressure relief valve 28, a check valve 26 is arranged in the line 25. This check valve prevents the hydraulic fluid from flowing back into the pump 27 when the working chamber 21aa is relieved. Furthermore, a variable throttle valve 28aa is located upstream of the pressure relief valve 28, with which the amount of hydraulic fluid flowing out of the working chamber 21aa can be controlled. Preferably, an opening cross-section of the throttle valve 28aa and thus a flow through the throttle valve 28aa can be controlled. Particularly preferably, the variable throttle valve 28aa is an electric valve whose cross-section can be varied by means of a control current or a control voltage. The electronic control unit 40 can contain predetermined values / characteristic curves for the control signal, with which various force reduction characteristics can be set.It is also possible for the reduction of the hydraulic drive force to be controlled. For this purpose, for example, the piston position or the pressure in the hydraulic cylinder 21 can be measured and the opening cross-section of the throttle valve 28aa can be adjusted such that the piston 24 always assumes the desired position during the force reduction.

[0042] If the relief valve 28 is opened, the spring force of the spring 6 of the safety device 10 acts on its piston 4 and displaces – via the piston rod 3 of the safety device 10 and the interface 2a, 22 between the safety device 10 and the linear actuator 20 – the piston rod 23 with the piston 24 until the working chamber 21aa has reached its minimum volume. In this state, shown in Figure 2, the piston rod 3 with the piston 4 of the safety device 10 is in a predetermined position (end position), and the valve channel 34 of the process valve 30 is closed by the disc 31. The disc 31 of the process valve 30 is connected to the piston rod 3 of the safety device 10 via the interface 2b. Due to the movement of the piston rod 3 in the direction of the spring force, the disc 31 closes the valve channel 34.

[0043] If, however, the relief valve 28 is closed and hydraulic fluid is pumped from the pump 27 into the working chamber 21aa, the force of the hydraulic cylinder 21 acts against the spring force of the spring 6 of the safety device 10, so that the spring 6 is pretensioned / compressed. The piston rods 23, 3 of the linear actuator 20 and the safety device 10 move against the direction of the spring force and displace the connected disc 31 of the process valve 30 such that the valve channel 34 is opened (not shown). Figure 3 shows a hydraulic circuit diagram of a linear actuator according to a further preferred embodiment of the system according to the invention. In this case, the linear actuator 20 contains, in addition to the elements described in Figure 2, an additional hydraulic circuit for tensioning the spring 6 of the safety device 10.The piston 4 of the safety device 10 is not fixed, but is connected unidirectionally to the piston rod 3 of the safety device 10 via a driver 3c. This allows the piston 4 to be moved and thus the spring 6 to be preloaded independently of the movement of the piston rod 3 of the safety device 10.

[0044] The additional hydraulic circuit according to Figure 3 contains a hydraulic cylinder 21b with a first cylinder chamber 21ba, which is connected to the pump 27 via a line 25b. A relief valve 28b is connected to the first cylinder chamber 21ba via a connection 29b. The second cylinder chamber 21bb of the hydraulic cylinder 21b is connected to a shut-off valve 42, by means of which hydraulic fluid can be enclosed in the second cylinder chamber 21bb.

[0045] The piston rod 23b of the hydraulic cylinder 21b acts via a mechanical interface 22b, 2a1 on a shaft 4a of the safety device 10, which in turn acts on the spring 6 via the piston 4. In the state shown in Figure 3, the spring 6 is still completely relaxed and the piston 24b of the hydraulic cylinder is in its initial position.

[0046] To tension the spring 6, hydraulic fluid is first pumped into the first cylinder chamber 21ba, causing the piston rod 23b to move in the direction of the safety device 10 by means of the piston 24b and to exert a force on the spring 6 of the safety device 10 via the shaft 4a and the piston 4. Once the desired preload of the spring 6 has been achieved, the shut-off valve 42 on the second cylinder chamber 21bb can be closed, thus fixing the position of the piston rod 23b. Deviations from the set piston rod position due to leakage of hydraulic fluid from the second cylinder chamber 21bb can be compensated for by permanently connecting the first cylinder chamber 21ba to the pump 27.

[0047] If a power failure occurs, both the relief valve 28b, which is connected to the first cylinder chamber 21ba, and the shut-off valve 42, which is connected to the second cylinder chamber 21bb, open. Consequently, no more force is transmitted from the hydraulic cylinder 21b to the spring 6. Therefore, the spring 6 can expand toward the linear actuator 10 and move the piston 4 to its end position (predetermined position). In this way, the piston 4 comes into contact with the driver 3c of the piston rod, so that the piston rod 3 also moves to its end position and brings the process valve 30 into a safe position.

[0048] Figure 4 shows an example of a mechanical interface between a linear actuator 20 and a safety device 10 according to a preferred embodiment of the invention in longitudinal section. On the right side of Figure 5, a section of the safety device 10 is shown, showing parts of the piston rod 3, the piston 4, and the spring 6, as well as an end face 1a of the housing 1 facing the linear actuator 20 with the first mechanical interface 2a. The interface 2a is designed as a quick-release fastener ("Linear (push) interface", Type A or Type C) according to EN ISO 13628-8. It comprises a first shaft 2aa, around which a flange 2ab with recesses (not shown) is arranged. The linear actuator 20 is coupled to this interface 2a by means of the interface 22, which represents the counterpart of the quick-release fastener.The section of the linear actuator 20 shown on the left side of Figure 4 shows, in addition to the interface 22, a part of the hydraulic cylinder 21 with the piston rod 23 facing the safety device 10. The interface 22 of the linear actuator 20 comprises a second shaft 22aa with claw-shaped projections 22ab that engage around the flange 2ab of the safety device 10. To connect the linear actuator 20 to the safety device 10, the claw-shaped projections 22ab are inserted axially into the recesses (not shown) of the flange 2ab and engaged with the flange 2ab by rotating the linear actuator 20 45° clockwise. Thus, in the closed state of the quick-release fastener 2a, 22 shown in Figure 4, the claw-shaped projections 22ab rest axially and radially on the flange 2ab of the first shaft, so that a positive connection between the two sides of the quick-release fastener 2a, 22 is established.Due to this connection by means of the quick-release fastener 2a, 22, the opposite ends of the piston rods 23, 3 of the linear actuator 20 and the safety device 10 are connected to each other in a force-locking manner.

[0049] The quick-release fastener 2a, 22 allows the linear actuator 20 to be exchanged with an ROV without having to remove or open the safety device. This significantly simplifies maintenance and installation of the linear actuator, especially at great depths.

[0050] Figure 5 shows a linear actuator 20 and a securing device 10 according to a preferred embodiment of the system according to the invention in a spatial external view. In this figure, the linear actuator 20 and the securing device 10 are connected by means of the quick-release fastener 2a, 22, as shown in Figure 4. Standardized handles 202, 204, 205 are attached to the outside of the linear actuator 20 for assembly / disassembly of the linear actuator 20 using an ROV.

[0051] In addition, there is a cable guide 201 on the front side of the linear actuator 20, which leads to a plug connection 203 to which the power and signal supply of the linear actuator 20 is connected.

[0052] Furthermore, a display device 206 (shown schematically) is arranged on the front side of the linear actuator 20, which displays the position of the piston 24, 4 and / or the piston rod 23, 3 of the linear actuator 20 and the safety device 10. According to Figure 6, the display device is in the U ("unlocked") position, i.e., the system comprising the linear actuator 20 and the safety device 10 is in a normal operating state in which the working chamber 21 aa of the hydraulic cylinder 21 is pressurized and occupies its maximum volume, so that neither the piston 24 of the hydraulic cylinder nor the piston 4 of the safety device are in contact with their end stops (see Figure 2).

[0053] The handle 202 allows the ROV to disconnect the electrical wiring of the linear actuator 20 at the plug connection 203. This interrupts the power supply to the pump 27 and the relief valve 28, causing the relief valve 28 to open and the pressure in the working chamber 21aa of the hydraulic cylinder 21 to drop. Consequently, the pistons 4, 24 of the safety device 10 and the linear actuator 20 are pushed to their respective end stops by the spring force of the spring 6 (see Figure 2), and the indicator changes to the L ("locked") position. The ROV can then disconnect the linear actuator 20 from the safety device 10 by turning it 45° counterclockwise using the handle 204 and the quick-release fastener 2a, 22 (see Figure 5). The handle 205 can then be used to transport the linear actuator 20.

Claims

Claims 1. Linear actuator (20) for the linear actuation of a process valve (30), comprising a housing (200), wherein an electronic control unit (40), at least one electric drive unit (41), and at least one hydraulic drive (27, 21) are arranged in the housing (200), wherein the hydraulic drive (27, 21) comprises at least one hydraulic cylinder (21) with a piston (24) and a piston rod (23), wherein the piston rod (23) extends outwards through an opening in the housing (200), and the hydraulic drive (27, 21) is configured to convert an electric drive power from the electric drive unit (41) into a hydraulic drive force, which generates a linear movement of the piston (23) of the at least one hydraulic cylinder (21) in a first direction, wherein a linear movement of the piston (23) of the hydraulic cylinder (21) in a second direction opposite to the first direction,is generated by a restoring force acting on the piston rod (23) outside the housing (200).

2. Linear actuator (20) according to claim 1, comprising at least one relief valve (28) configured to reduce the hydraulic drive force.

3. Linear actuator (20) according to one of the preceding claims, comprising at least one variable throttle valve (28aa) configured to control the reduction of the hydraulic drive force.

4. Linear actuator (20) according to one of the preceding claims, wherein the housing (200) is filled with a pressurised fluid.

5. Linear actuator (20) according to one of the preceding claims, comprising a pressure compensation device configured to effect pressure equalization between an environment and an interior of the linear actuator (20).

6. Linear actuator according to claim 5, wherein the pressure compensation device is configured to set a pressure inside the linear actuator (20) in a range between ambient pressure and 10 bar above ambient pressure.

7. Linear actuator (20) according to one of the preceding claims, comprising at least one mechanical interface (22) by means of which a safety device (10) for generating the restoring force can be connected to the linear actuator (20).

8. Linear actuator (20) according to claim 7, comprising a hydraulic circuit for tensioning at least one spring (6) of the safety device (10).

9. Linear actuator (20) according to one of the preceding claims, wherein the at least one hydraulic cylinder (21) has three cylinder chambers (21aa, 21ab, 21ac), one of which cylinder chambers (21ac) is hermetically sealed, so that a vacuum is formed when the piston rod (23) is moved.

10. Linear actuator (20) according to one of the preceding claims further comprising at least one sensor configured to detect the position of the linear actuator (20) to detect, and a display device (206) configured to indicate the position of the linear actuator (20) on an outside surface of its housing (200).

11. System for the linear actuation of a process valve (30), comprising a linear actuator (20) according to one of the preceding claims, and at least one safety device (10) which is connected to the linear actuator (20) by means of the mechanical interface (2, 2a).

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