TECHNICAL FIELD

This disclosure concerns a subsea control and/or an actuator, such as a subsea actuator for actuating subsea apparatus; systems incorporating the subsea control and/or actuator/s; and associated methods, such as methods of actuating subsea valves.

BACKGROUND

In the oil/gas industry, wellheads are typically at least partly controlled using Subsea Control Modules (“SCMs”), such as where an SCM controls a Xmas Tree (“XMT”) associated with a production wellhead. The SCM provides well control functions, particularly during the production phase of subsea oil/gas production. The SCM contains electronics for performing a variety of functions, often including: processing communications signals, conditioning electrical power supplies, providing status information; and distributing signals and power to/from actuators and/or control valves, pressure/temperature sensors, and the like.

XMTs typically have various fluid barriers for controlling fluid, pressure, flow, etc. in the well. Periodically XMTs may require maintenance, inspection, etc. Often temporary barriers are placed using bores below the XMT. These bores are typically dedicated for such temporary use and access via these bores is only enabled when particular valves are open to allow such access. The valves are typically gate valves operable between an open and a closed position, where the bore (below the XMT) is closed.

Wellhead valves are often hydraulically controlled. Operation of some subsea valves is controlled by actuators, the actuators in turn being controlled from or by subsea modules.

The subject matter of at least some examples of the present disclosure may be directed to overcoming, or at least reducing the effects of, one or more of the problems of the prior art, such as may be described above.

SUMMARY

According to a first aspect there is provided a method of controlling a subsea actuator. The method may comprise controlling at least two subsea actuators, such as associated with a wellhead. The method may comprise controlling the at least two subsea actuators with a single subsea control unit. The subsea control unit may comprise a module. The method may comprise driving the at least two actuators from a single subsea drive source. The method may comprise transferring mechanical drive from the subsea control unit to the actuator/s. The method may comprise providing a mechanical output from the subsea control unit. The method may comprise transferring mechanical drive from the subsea control unit to the actuator/s. The method may comprise transferring drive via a mechanical connector.

The subsea control unit may comprise a subsea Actuator Control Module (“ACM”), such as an Actuator Electronics Control Module (AECM). The subsea control unit may comprise an electronics device for electronics control of the one or more actuator/s to which the subsea control unit is, or is/are to be, connected. The electronics device may comprise electronics communications, such as for remote communication (e.g. to surface). The subsea control unit may comprise a deployable module. The subsea control unit may comprise a retrievable module. The subsea control unit may be deployable and/or retrievable independently of the actuator/s. The subsea control unit may be fluidly isolated from the actuator. For example, the subsea control unit may comprise a sealed module; and the actuator may be separated from the subsea control unit by a fluid, such as a pressurised fluid (e.g. seawater) therebetween.

The method may comprise an electrical method. The method may comprise electrically powering the actuation of the actuators. The method may comprise controlling actuators in or on an all-electric system.

The actuator may comprise a linear actuator. The actuator may comprise or be comprised in an actuator linear drive module (ALDM). The actuator may comprise a linear drive or actuator, such as selected from a solenoid and/or a screw.

The subsea control unit may comprise a drive source. The drive source may comprise an electrically-powered drive source. The drive source may comprise an electric motor. The motor may comprise a rotary motor, providing a rotational output. The drive source may comprise a subsea electric motor, such as powered by a DC subsea power supply. The power supply may comprise a battery; such as housed in the subsea control unit. The power supplied from the subsea power supply may be controlled, such as by or from a controller or control unit associated therewith. The controller or control unit may be housed in the subsea control unit. The method may comprise transferring mechanical drive from the subsea control unit. The method may comprise transferring mechanical drive from the subsea control unit to the actuator/s. The method may comprise transferring mechanical drive from the subsea control unit to the actuator/s via a mechanical transmission. The method may comprise outputting mechanical drive from the subsea control unit, such as outputting rotational mechanical drive. The mechanical transmission may comprise a drive shaft. The mechanical transmission may comprise a mechanical seal, such as a shaft seal/s. The transmission may comprise a plurality of drive shafts.

The transmission may comprise an adjustable transmission, such as to allow or enable adjustment in the positioning of one or more ends of a transmission line or chain.

The drive shaft may comprise a flexible drive shaft. The flexible drive shaft may be expressly flexible, such as in contrast to a standard drive shaft. The flexible drive shaft may not be a rigid drive shaft. The flexible drive shaft may comprise a rotary drive shaft for transmitting rotary drive. The flexible shaft may be plastically deformable laterally, such as perpendicularly to a longitudinal central axis of the shaft. The flexibility of the shaft may enable the shaft to be malleable. The shaft may be flexible so as to allow flexibility in a positioning of at least a portion of the drive shaft, such as at least one terminal end (e.g. output end portion) of the drive shaft. The drive shaft may be flexible so as to enable the shaft to flex or be flexed at a non-predetermined point. The flexible shaft may be bendable. The flexible shaft may be bendable so as to provide a discrete change in angular orientation of the shaft. The flexible drive shaft may be flexible so as to allow at least one bend or angular transition at an intermediate position along the length of the drive shaft, located between each terminal end portion of the shaft (e.g. between the respective input and output ends pf the drive shaft). The at least one bend or angular transition may be positionable at any position along the length of the shaft. The position of the bend or angular transition may be variable along the length of the drive shaft. The at least one bend or angular transition may comprise a relatively sharp bend or angular transition. The bend or angular transition may be localised, such as restricted to only a portion of the shaft along its length.

The flexible drive shaft may be flexible for transmitting rotary motion between two objects which are not fixed relative to one another. For example, at least one of the drive source and/or the actuator/s may be movable relative to the other of the drive source and the actuator/s whilst maintaining transmissibility of rotation drive therebetween. The flexible drive shaft may be flexible for transmitting rotary drive between the drive source and the actuator/s, where the position of at least one of the drive source and/or the actuator/s is not predefined or predetermined. The flexible shaft may comprise a rotatable wire rope or coil which is flexible laterally, such as bendable with a radius about an axis perpendicular to the longitudinal axis of the shaft. The flexible shaft may comprise a torsional stiffness. The torsional stiffness may be greater than a bending stiffness of the shaft.

The method may comprise connecting the subsea control unit (e.g. an AECM) to the actuator. The method may comprise deploying the subsea control unit subsea, such as to or at depth, such as with the aid of a ROV, diver/s or the like. The method may comprise docking the subsea control unit. The method may comprise positioning the subsea control unit, such as relative to the actuator. The actuator may already have been deployed and positioned, such as in a previous operation. Additionally, or alternatively, the actuator may be positioned or deployed simultaneously or after the subsea control unit. For example, in at least some methods, the subsea control unit may be positioned subsea (e.g. at a wellhead, or apparatus associated therewith); and connected to a first actuator; with a second actuator only being subsequently deployed and/or connected to the subsea control unit thereafter. In at least some examples, the method may comprise varying the actuator/s connected to the subsea control unit. For example, the method may comprise having a different actuator and/or combination of actuator/s connected to the subsea control unit at different times. The method may comprise maintaining the position of the subsea control unit (e.g. deployed at or proximate a wellhead) and connecting a different actuator or combination of actuators over a period of time.

The method may comprise locking the subsea control unit to the subsea actuator/s. The method may comprise mechanically locking a main stem, such as locking the main stem in a retracted position only. The method may comprise connecting the drive source to a Remotely Operated Vehicle (ROV) or XMT to operate the actuator during installation.

The method may comprise connecting a mechanical drive connector of the subsea control unit to a mechanical drive connector of the actuator. The method may comprise connecting a portion of the drivetrain in the subsea control unit to a portion of the drivetrain in or associated with the actuator. The method may comprise the subsea completion of the drivetrain by the subsea connection of the subsea control unit to the subsea actuator. The method may comprise a wet mechanical interface between the subsea control unit and the actuator. The method may comprise the wet mechanical coupling of the subsea control unit to the actuator. The method may comprise connecting the subsea control unit with the subsea actuator via one or more penetrators. The penetrator/s may be configured to provide a sealed connection at operational depth/s.

In at least some examples, the method may comprise electrically coupling the subsea control unit to the actuator/s. The method may comprise a wet mate coupling of the subsea control unit to the subsea actuator. The method may comprise an electrical connection for data communication, such as to transfer status and/or sensor data between the actuator and the subsea control unit. Alternatively, the connection between the subsea control unit and the subsea actuator may be purely mechanical. In at least some examples, the method avoids or at least mitigates a use of hydraulics.

The method may comprise connecting the actuator to the drive source via a gearbox/es. The gearbox may be comprised in the subsea control unit. Additionally, or alternatively, the gearbox may be external to the subsea control unit, such as associated with the actuator. In at least some examples, a gearbox may be provided with or associated with the actuator, such that drive provided to the actuator from the subsea control unit is adapted by the gearbox. The method may comprise adapting the torque and/or velocity for the actuator with the gearbox.

In at least some examples, the method may comprise providing or associating a gearbox with each respective actuator. The method may comprise providing a plurality of gearboxes, each respective actuator being associated with a discrete gearbox. The method may comprise providing a gearbox for each actuator, each gearbox being provided in the subsea control unit. Additionally, or alternatively, a gearbox may be comprised within the/each actuator, for connection thereto by the subsea control unit.

The method may comprise providing a plurality of mechanical outputs from the subsea control unit. The method may comprise providing a mechanical output from the subsea control unit for each of ta plurality of actuators. Accordingly, the subsea control unit may provide a plurality of mechanical outputs. The method may comprise providing a gearbox for each actuator.

The method may comprise utilising the gearbox/es to provide a predetermined torque and/or drive speed. For example, the method may comprise adapting a rotational drive speed. The method may comprise adapting a rotational drive speed to reduce a specification, rating or requirement, such as of the drive source and/or a seal or the like. For example, the method may comprise the incorporation of a gearbox to enable the provision of a cheaper, lighter and/or more efficient motor.

In at least some examples, the method may comprise controlling the actuator, such as a state of the actuator with or via the gearbox. The method may comprise controlling drive to the actuator/s via the gearbox/es.

In at least some examples, the method may comprise splitting drive from the drive source via the gearbox. For example, the method may comprise splitting drive from the single drive source to a plurality of actuators. The method may comprise selectively splitting drive from the single drive source. The method may comprise noncontemporaneously splitting drive from the single drive source. The method may comprise sequentially splitting drive from the single drive source. Additionally, or alternatively, the method may comprise simultaneously splitting drive from the single drive source, such as to direct a first portion of drive from the drive source to a first actuator and simultaneously directing a second portion of drive to a second actuator.

The method may comprise transferring drive from the subsea control unit to the actuator/s via a bevel gear, such as a worm gear. The bevel gear may comprise a selflocking gear. The bevel gear may comprise a self-locking gear with a relatively high efficiency, such as 50% or more. The bevel gear may enable use of a smaller brake, such as compared to a similar or equivalent system whereby the bevel gear was omitted. In at least some example, the provision of a bevel gear/s may enable elimination of a brake. The bevel gear may assist in changing an angle of drive transmission, such as translating rotational drive perpendicularly, providing the rotational output about a longitudinal axis of output that is at 90° to a longitudinal axis of input.

The method may comprise controlling the actuation of the at least two actuators by controlling a supply of power to the drive source in the subsea control unit. The method may comprise a provision of electrical power from a single power source. The method may comprise the provision of electrical power from the single electrical power source to the single drive source. The electrical power source may comprise a subsea power supply, such as a subsea battery or power cell. The single electrical power source may comprise a plurality of cells or batteries (e.g. connected in series). The power source may be comprised with or within the subsea control unit. The method may comprise transmitting the drive from the single drive source to the at least two actuators. The method may comprise transmitting the drive from the single drive source to the at least two actuators simultaneously. Additionally, or alternatively, the method may comprise selectively transmitting drive to (only) one of the actuators, such as to only one of the actuators. The method may comprise selection of transmission of drive from: to a first actuator only; a second actuator only; both the first and second actuators; or to no actuator.

The method may comprise selecting an actuator/s for receipt of drive from the single drive source. The method may comprise apportioning drive from the single drive source to each actuator in dependence on a selection of actuator/s for actuation.

The method may comprise providing multiple drive outputs from the single subsea control unit, the subsea control unit comprising a plurality of mechanical output interfaces, such as drive shafts or torque interfaces or the like.

The method may comprise transmitting the drive from the single drive source to each actuator via a respective drive chain. The drive chain may comprise a drive shaft. Each actuator may be associated with a respective drive shaft thereto. The method may comprise the provision of drive to each actuator via a respective drive shaft. The drive shafts may be arranged in parallel, such as to allow simultaneous provision of drive to each actuator. The method may comprise providing a branch drive shaft to each actuator.

The method may comprise controlling drive transmission with at least one brake and/or clutch. It will be appreciated that the brake may effectively operate as a clutch, allowing selection of output or transfer of drive. The method may comprise braking the drive transmission within the subsea control unit. Accordingly, the brake/s and/or clutch/es may be comprised within the subsea control unit. Additionally, or alternatively, the brake/s and/or clutch/es may be comprised with or within the actuator/s.

The method may comprise limiting torque. In at least some examples, the method may comprise providing a torque limiter in the drive chain. The torque limiter/s may be comprised in the subsea control unit. Additionally, or alternatively, the torque limiter/s may be housed in the actuator/s. The method may comprise providing or associating a respective torque limiter and/or brake with each actuator. The torque limiter/s may enable a provision of drive to each actuator simultaneously. The method may comprise not activating the brake/s to allow simultaneous or at least coordinated operation of a plurality of actuators. The method may comprise the torque limiter/s breaking free when an/each actuator reaches an end stop.

The method may comprise driving a pair of actuators with or from a single subsea control unit. The method may comprise driving three or more actuators from the single control unit. The method may comprise the simultaneous connection of the subsea control unit to the plurality of actuators. In at least some examples, the method may comprise the simultaneous provision of drive to the plurality of actuators.

According to a further aspect, there is provided a subsea control unit. The subsea control unit may be configured to perform any of the method steps described herein, as appropriate. The subsea control unit may be configured to provide a mechanical output for driving a subsea actuator. The subsea control unit may comprise a subsea Actuator Control Module (“ACM”), such as an Actuator Electronics Control Module (AECM). The subsea control unit may comprise an electronics device for electronics control of the one or more actuator/s to which the subsea control unit is, or is/are to be, connected. The electronics device may comprise electronics communications, such as for remote communication (e.g. to surface). The subsea control unit may comprise a deployable module. The subsea control unit may comprise a retrievable module. The subsea control unit may be deployable and/or retrievable independently of the actuator/s. The subsea control unit may be fluidly isolated from the actuator. For example, the subsea control unit may comprise a sealed module; and the actuator may be separated from the subsea control unit by a fluid, such as a pressurised fluid (e.g. seawater) therebetween.

According to a further aspect, there is provided a subsea actuator. The actuator may comprise an ALDM. The actuator may be configured to perform any of the method steps described herein, as appropriate. The actuator may be configured to be externally driven, such as by or from the subsea control unit of any other aspect, embodiment, example or claim. The actuator may comprise an external interface, the external interface being configured for receiving drive transmitted from an external source, such as the subsea control unit. The actuator may comprise an electrically-operable actuator. The actuator may be for operating a valve. The actuator may comprise a subsea actuator, such as a subsea actuator for providing a subsea actuation of a subsea valve. The actuator and/or the valve may be associated with a wellhead. The actuator and/or the valve may be associated with a subsea manifold. The actuator and/or the valve may be associated with an XMT. The actuator may comprise an electrically-operable actuator. The actuator may comprise a portion of a drive chain for moving the valve between positions or configurations. For example, the actuator may comprise a portion of a drive chain for selectively opening and/or closing the valve. The actuator may comprise or be for one or more of: a linear actuator; a rotary actuator; a rotary disc valve; a choke; a pump; a valve; a hydraulic function; an electric function; a control function; a monitoring function.

The rotational drive provided to the actuator’s external interface may be for rotating a portion of a screw assembly of the actuator. The actuator may be configured to convert the received rotational drive input, such as to a different rotational drive output and/or a linear drive or output. In at least some examples, the rotational drive may be for direct actuation, such as directly rotating a valve or other subsea device. The screw assembly may comprise one or more of: a roller screw; an ACME screw; a lead screw; a ball screw.

According to a further aspect there is provided a subsea system. The subsea system may comprise the subsea control unit and/or the subsea actuator of any other aspect, claim, example or embodiment. The subsea system may optionally comprise a valve, such as a bore access valve.

The valve may comprise a subsea valve. The valve may comprise a linear valve, such as a gate valve. The valve may be for selectively providing access via a bore below an XMT. The valve may be normally closed, such as during normal operation of the XMT. The valve may be selectively openable by operation of the actuator.

The valve may comprise a bore-sealing member, the bore-sealing member being configured to sealingly occlude access via a bore. The bore may be for providing access below an XMT, such as when an XMT is removed, damaged, being inspected or repaired, etc. The bore-sealing member may comprise a gate. The bore-sealing member may be movable transversely into and out of the bore to respectively close and open the bore (e.g. for access via the bore). At least one of the screw and the nut of the screw assembly may be operatively associated with the valve member. For example, the screw may be connected to the valve member such that axial movement of the screw axially moves the valve member. In other examples, the nut may be connected to the valve member, such that axial movement of the nut axially moves the valve member.

The actuator may comprise a housing. The housing may be configured to maintain an axial position of the axially stationary member of the screw assembly. For example, the housing may comprise an axial stop for maintaining the axial position of the screw. The axial stop may prevent axial movement of the axially stationary member in a first and/or a second axial direction. In at least some examples, the housing may prevent axial movement in both axial directions. The axial directions may be parallel with the longitudinal axis of the screw. The housing may limit or prevent movement of the axially stationary member during normal operation of the actuator. Accordingly, in at least some examples, the actuator may be normally operable to actively rotate, such as driven by the motor, the screw to axially displace the nut, thereby axially displacing the valve member associated with the nut. The actuator may comprise a bearings assembly comprising a bearings casing containing bearings. The bearings may support at least a portion of the screw assembly. In at least some examples, the housing may at least partially seal the actuator. For example, the housing may seal an interior of the actuator from an exterior of the actuator. The housing may seal the interior of the actuator from an external environment, such as seawater, particularly seawater at depth (e.g. 50m+, 100m+, etc). The housing may comprise a cylinder, with the axial movement being along an axis parallel to a central longitudinal axis of the cylinder.

The actuator may comprise an interface for an external connection. The external connection interface may comprise an external interface. The external interface may be axially external to the actuator. For example, where the actuator housing comprises a cylinder, the actuator external interface may be provided at or through an axial end of the cylinder. The actuator external interface may be positioned with the screw assembly located between the actuator external interface and the valve member. The actuator external interface may be configured to transmit torque and/or axial force to at least a portion of the screw assembly to move the valve member. The actuator external interface may comprise a torque interface to allow clockwise and/or counter-clockwise torque to be applied to at least a portion of the screw assembly to move the valve member. The actuator external interface may be configured to drive the at least a portion of the screw assembly rotationally in a first direction to cause the actuator to push the valve member. Additionally, or alternatively, the actuator external interface may be configured to drive the at least a portion of the screw assembly rotationally in a second direction to cause the actuator to pull the valve member. The actuator external interface may be configured to drive the at least a portion of the screw assembly rotationally to open the valve member. Additionally, or alternatively, the actuator external interface may be configured to drive the at least a portion of the screw assembly axially to open the valve member.

The screw assembly may comprise a planetary screw assembly, such as a planetary roller screw assembly. The screw assembly may comprise a non -recirculating screw assembly, such as a non-recirculating roller screw assembly. The lack of axial movement of the roller may not move axially relative to the nut. The screw assembly may comprise an inverted screw assembly, such as an inverted roller screw assembly. The roller screw assembly may comprise a reverse screw assembly, such as a reverse roller screw assembly.

The screw may comprise a recirculating screw, such as a recirculating roller screw. The rollers may move axially within the nut. The rollers may be reset, such after one orbit about the screw.

The actuator may be configured for high-precision. The actuator may be configured for high-speed. The actuator may be configured for heavy-load applications. The actuator may be configured for long-life applications. The actuator may be configured for heavy- use applications.

In at least some examples, the actuator is used as a subsea actuator to provide an axial force to an element. The actuator may be used to operate one or more valves, such as a gate valve/s. The valve may form part of an XMT, such as a vertical XMT. The XMT may comprise an Enhanced Vertical Deepwater Tree. The actuator may be used in an all-electric application, such as an all-electric XMT, Wellhead, SCM or the like.

The subsea system may comprise a gearbox/es, such as of any other aspect, embodiment, example or claim.

In at least some examples, the gearbox may be provided 'downstream’ of the brake, that is between the gearing and the actuator. Accordingly, the torque for the brake may be reduced. Thereby the brake power required may be reduced; or a brake requirement even eliminated. In other examples, the gearbox may be provided ‘upstream’ of the brake, that is between the drive source and the brake. In at least some examples, a single gearbox may be provided for a plurality of actuators, the plurality of actuators each having a brake associated therewith. Positioning the gearbox upstream of the brake may enable a single gearbox to be utilised with multiple brakes.

The drive chain may comprise a differential. In at least some examples, the differential may be provided by a ball lock mechanism. The ball lock mechanism may enable a selection of output from the drive source. For example the ball lock mechanism may be operable by a mechanism, such as a controllable solenoid, to vary a position of the ball lock mechanism to selectively transfer drive to a first and/or a second portion or branch of a drive chain/s. The solenoid may operate a shaft extending through the motor, such as centrally through the motor.

The system may comprise a drive head as a portion of the drive chain for transmitting drive between the drive source in the subsea control unit and the actuator. The drive head may be comprised in or with the subsea control unit. Alternatively, the drive head may be comprised with or in the actuator. In yet further examples, the drive head may be discrete from the subsea control unit and the actuator; the drive head being positioned intermediate the subsea control unit and the actuator, such as in a discrete drive head module. The gearbox/es may be provided discrete from both the subsea control unit and the actuator/s, such as in a discrete drive head, the drive head being separate and/or separable from the subsea control unit and the actuator/s. The drive head/s may be separately deployable and/or retrievable.

The drive head may comprise the gearbox. The drive head may comprise the brake and/or clutch. The drive head may provide the drive output to the actuator.

The drive head may comprise the motor. Where the drive head comprises the motor, the drive head may comprise an electrical input for receiving electrical power for the motor. The drive head/s may be connected with an electrical cable/s to the subsea control unit.

The drive head may receive drive input from the drive source in the subsea control unit and output a drive output from the drive head to the actuator, such as via the actuator’s external interface. In at least some examples, a single subsea control unit may comprise, or be connected to, multiple drive heads. The drive head may be connected to the subsea control unit by the flexible shaft for transferring mechanical drive. Additionally, or alternatively, the drive head may be connected to the actuator by the flexible shaft for transferring mechanical drive.

The drive head may be permanently incorporated, mounted or installed in or with the actuator. Alternatively, the drive head may be retrievably mounted or installed in or with the actuator. In such examples, the drive head may be deployed and/or retrieved separately from the actuator.

The system may comprise redundancy or back-up. In at least some examples, a redundant or backup portion of the drive chain is provided. For example, the subsea control unit may comprise a plurality of drive sources, such as a pair of motors. Additionally, or alternatively the system may comprise a plurality of subsea control units. A plurality of subsea control units may be connected or connectable to the drive chain. In at least some examples, a second or further subsea control unit, or portion thereof, can be connected to the drive chain to control the actuator/s. Accordingly, in an event of failure of a first subsea control unit, or portion thereof, a second subsea control unit can be utilised to control the actuator/s. The system may be configured to accommodate the plurality of subsea control units, such as without requiring removal and/or disconnection of the first subsea control unit to enable operation and/or connection of the second control unit to control the actuator/s.

According to a further aspect, there is provided an apparatus comprising the actuator and/or subsea control unit of any other aspect, example, embodiment or claim. The apparatus may comprise a subsea apparatus for the oil/gas industry. The apparatus may comprise a wellhead apparatus for controlling access to a hydrocarbon wellbore. The apparatus may comprise a subsea valve. The apparatus may comprise a subsea control module (“SCM”). The apparatus may comprise a subsea electronics module (“SEM”).

According to a further aspect, there is provided a transmission differential, such as comprising the ball lock mechanism of any other aspect, example, claim or embodiment.

According to a further aspect, there is provided a method of transmitting drive. The method may comprise selectively transmitting drive. The method may comprise differentially transmitting drive, such as with the ball lock mechanism of any other aspect, example, claim or embodiment. According to a further aspect, there is provided a method of actuation. The method may comprise providing the actuator and/or subsea control unit of any other example, embodiment, claim or aspect. The method may comprise a method of subsea or underwater actuation. The method may comprise providing the actuation in the apparatus of any other aspect, example, embodiment or claim. The method may comprise operating a valve of a wellhead apparatus for controlling access to a hydrocarbon wellbore.

According to a further aspect there are provided at least some examples of an oil/gas apparatus comprising the apparatus of any other aspect, example, embodiment or claim. The oil/gas apparatus may comprise wellhead apparatus, such as a manifold.

Another aspect of the present disclosure provides a computer program comprising instructions arranged, when executed, to implement a method in accordance with any other aspect, example, claim or embodiment. A further aspect provides machine- readable storage storing such a program. The storage may be non-transitory. In at least some examples, the computer program may be for controlling the subsea control unit and/or the actuator/s.

According to an aspect of the invention, there is provided computer software which, when executed by a processing means, is arranged to perform a method according to any other aspect, example, claim or embodiment. The computer software may be stored on a computer readable medium. The computer software may be tangibly stored on a computer readable medium. The computer readable medium may be non-transitory. For example, the computer software may be configured to control the subsea control unit and/or the actuator.

The invention includes one or more corresponding aspects, embodiments or features in isolation or in various combinations whether or not specifically stated (including claimed) in that combination or in isolation. For example, it will readily be appreciated that features recited as optional with respect to the first aspect may be additionally applicable with respect to the other aspects without the need to explicitly and unnecessarily list those various combinations and permutations here (e.g. the apparatus of one aspect may comprise features of any other aspect). Optional features as recited in respect of a method may be additionally applicable to an apparatus or device; and vice versa. The apparatus or device of one aspect, example, embodiment or claim may be configured to perform a feature of a method of any aspect, example, embodiment or claim. In addition, corresponding means for performing one or more of the discussed functions are also within the present disclosure. It will also be appreciated that features associated with one of the subsea control unit and the actuator may also be associated with the other of the subsea control unit and the actuator. For example, where examples or features are disclosed in combination with the subsea control unit it will be appreciated that those features may apply equally to the actuator, and vice versa, as appropriate. In at least some examples, the position of the gearbox may be inverted (e.g. the gearbox may be provided ‘upstream’ of the external interface, within the subsea control unit - instead of ‘downstream’ of the external interface, such as in the actuator, or associated therewith).

It will be appreciated that one or more embodiments/aspects may be useful in at least providing a subsea actuation.

The above summary is intended to be merely exemplary and non-limiting.

Various respective aspects and features of the present disclosure are defined in the appended claims.

It may be an aim of certain embodiments of the present disclosure to solve, mitigate or obviate, at least partly, at least one of the problems and/or disadvantages associated with the prior art. Certain embodiments or examples may aim to provide at least one of the advantages described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a schematic representation of a method according to the present disclosure;

Figure 2 is a schematic diagram of a subsea control unit connected to a subsea actuator and associated valve;

Figure 3 is a schematic diagram of a subsea control unit connected to a pair of subsea actuators and associated valves;

Figure 4 is a schematic diagram of a further subsea control unit connected to a pair of subsea actuators and associated valves;

Figure 5 is a schematic diagram of a further subsea control unit connected to a pair of subsea actuators and associated valves; Figure 6 is a schematic diagram of a further subsea control unit connected to a pair of subsea actuators and associated valves, and a further drive head;

Figure 7 is a schematic diagram of a further subsea control unit connected to a pair of subsea actuators and associated valves;

Figure 8 is a schematic diagram of a further subsea control unit connected to a pair of subsea actuators and associated valves;

Figure 9 is a schematic diagram of a further subsea control unit connected to a pair of subsea actuators and associated valves;

Figure 10 is a cross-sectional view of a motor and drive transmission;

Figure 11 is a schematic view of a further subsea control unit connected to a plurality of subsea actuators; and

Figure 11 is a schematic view of a pair of subsea control units connected to a plurality of subsea actuators.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring first to Figure 1 , there is shown a method of controlling a subsea actuator. The method comprises a step 4 of transferring mechanical drive from a subsea control unit to a subsea actuator. In at least some examples, the method previously comprises a deployment step 2 whereby the subsea control unit is deployed to a subsea location. The method further comprises a step 6 of mechanically actuating the subsea actuator using the drive from the subsea control unit. Where the actuator is for actuating a valve, the method comprises a step 8 of actuating the subsea valve.

Referring now to Figure 2, there is shown a subsea control unit 50 connected to a subsea actuator 10 according to the present disclosure. Here, the actuator 10 comprises a subsea actuator 10 for providing a subsea actuation of a valve 16. The subsea control unit 50, subsea actuator 10 and subsea valve are comprised in a subsea system 1 , as shown in Figure 2. As shown here, the subsea control unit 50 is mounted in-line with the actuator 10, with the subsea unit’s drive shaft 54 and motor 60 being mounted on a longitudinal axis colinear with the longitudinal axis of the actuator 10.

The actuator 10 here comprises an ALDM. The actuator 10 comprises a bearings assembly 42 with bearings 46 for supporting the roller screw 20. The bearings 46 provide a high degree of axial stiffness, high axial load carrying capacity; accommodate high speeds and rapid accelerations; and offer high running accuracy. The bearings 46 provide a safe radial and axial support and an extremely precise axial guidance of the roller screw 20. In at least some examples, the actuator 10 is used as a subsea actuator 10 to provide an axial force to an element. The actuator 10 is used to operate one or more valves 16, such as gate valves 16. The valve 16 may form part of an XMT, such as a vertical XMT. The XMT comprises an Enhanced Vertical Deepwater Tree. The actuator 10 is used in an all-electric application, such as an all-electric XMT, Wellhead, SCM or the like.

The valve 16 comprises a subsea gate valve 16 for selectively providing access via the bore 36 below an XMT. The valve 16 is normally closed, such as during normal operation of the XMT. The valve 16 is selectively openable by operation of the actuator 10. Here, the roller screw assembly 18 comprises a planetary roller screw assembly 18. The actuator 10 is configured for high-precision. The actuator 10 is configured for high-speed. The actuator 10 is configured for heavy-load applications. The actuator 10 is configured for long-life applications. The actuator 10 is configured for heavy-use applications. It will be appreciated that the actuator 10 for the valve 16 shown here forms part of a subsea wellhead apparatus for controlling access to a hydrocarbon wellbore.

The valve 16 here has a valve rod or stem 12. The valve stem 12 extends through a stem seal 32 housed in a bonnet 34. The valve member 14 comprises a bore-sealing member, the bore-sealing member being configured to sealingly occlude access via a bore 36. The bore 36 here is for providing access below an XMT (not shown), such as when an XMT is removed, damaged, being inspected or repaired, etc. The valve 16 comprises a seat 38 for the bore-sealing member. As shown here, the valve 16 is a gate valve. The valve stem 12 is perpendicular to the bore 36, with the valve stem 12 being axially movable along its axis perpendicular to the bore 36. Accordingly, the bore-sealing member 14 is movable transversely into and out of the bore 36 to respectively close and open the bore 36 (e.g. for access via the bore 36).

The actuator 10 comprises an external interface 70 for receiving mechanical drive to the actuator 10. Here, where the actuator housing 24 comprises a cylinder, the external interface 70 is provided at or through an axial end of the cylinder. The external interface 70 is positioned with the roller screw assembly 18 located between the external interface 70 and the valve member 14. The external interface 70 is configured to transmit torque and/or axial force to the roller screw 20 to move the valve member 14. Here, the external interface 70 comprises a torque interface to allow clockwise and/or counter-clockwise torque to be applied to the roller screw 20, via the roller nut 22, to move the valve member 14. The external interface 70 is configured to drive the roller screw 20 axially in the first direction to push the valve member 14. Additionally, the external interface 70 is configured to drive the roller screw 20 axially in the second direction to pull the valve member 14. The external interface 70 is configured to drive the roller screw 20 axially to open and close the valve member 14.

Here, it will be appreciated that the roller screw 20 can be axially and rotationally driven to the position of Figure 2, thereby axially moving the roller screw 20 relative to the roller nut 22. Here, the valve 16 is shown in the open configuration in Figure 2. In at least some examples, it is possible to close the valve 16 by driving the roller screw assembly 18 in an opposite direction (e.g. to the left from the position as shown in Figure 2) to pull the valve member 14 closed (to the left from the position as shown in Figure 2).

The subsea control unit 50 shown in Figure 2 comprises an AECM, shown here connected with a connection 52 to the actuator 10. The subsea control unit 50 comprises an electronics device 56 for electronics control of the one or more actuator/s 10 to which the subsea control unit 50 is connected. The electronics device 56 comprises electronics communications, such as for remote communication (e.g. to surface). Here, the subsea control unit 50 comprises a deployable and retrievable module, the subsea control unit 50 being deployable and retrievable independently of the actuator 10. The subsea control unit 50 is fluidly isolated from the actuator 10, the subsea control unit 50 comprising a sealed module; and the actuator 10 can be separate from the subsea control unit 50 by seawater therebetween - each of the subsea control unit 50 and the actuator 10 comprising seals at their respective interfaces 54, 70 that form the connection 52 therebetween.

Within the subsea control unit 50 here, a series of batteries 58 provides electrical power to the electronics device 56 and a rotary electric motor 60. The electric motor 60 outputs rotary drive via the output shaft 54 as controlled by the electronics device 56. It will be appreciated that the subsea control unit 50 is sealed and preferably pressurised for protection against and prevention of water ingress, such as when deployed at depths.

Actuation comprises transferring mechanical drive from the subsea control unit 50 to the actuator 10 via a mechanical transmission. Here, actuation comprises outputting mechanical drive from the subsea control unit 50, shown here as outputting rotational mechanical drive via the output drive shaft 54 of the subsea control unit 50. It will be appreciated that a shaft seal can be provided about the output drive shaft 54. As appropriate, the subsea control unit can comprise a penetrator for mating with the actuator 10.

Here a single electric motor 60 is housed in the subsea control unit 50; and along with a gearbox (not shown) defines a drive head 64, here within the subsea control unit 50. The gearbox adapts the torque and rotational velocity output by the drive shaft 54 for the actuator 10. The gearbox steps up the torque output from the motor 60 to allow provision of a suitably high torque to power the actuator 10, whilst enabling use of a lower torque motor 60, typically smaller, lighter, requiring less power and cheaper (e.g. compared to a motor directly providing sufficient torque for the actuator 10).

Referring now to Figure 3, there is shown a subsea system 101 generally similar to that 1 shown in Figure 2, with like features referenced by like numerals incremented by 100. Accordingly, the subsea system 101 comprises a control unit 150 connected to a pair of subsea actuators 110a, 110b for providing a subsea actuation of a pair of subsea valves 116a, 116b. For brevity, not all descriptions of similar features are repeated.

As shown in Figure 3, a single AECM with a single motor 160 and a single gearbox 166 can control two (or more, not shown) actuators 110a, 110b to drive two (or more, not shown) valves 116. As shown here, the transmission comprises a branched drive chain with two parallel (schematically, not necessarily geometrically) drive chain branches 168a, 168b being provided ‘downstream’ of the single gearbox 166. Each branch 168a, 168b here has a respctive brake/clutch 172a, 172b. The brake 172a, 172b can be used to select which/whether drive is trsnamitted further along each branch 168a, 168b, effectively operating as a clutch (and can be a clutch, such as for disengagement, in other examples). The brake/clutch 172a, 172b can be inependently activated to limit drive being passed to only a single one of the actuators 110a, 110b at a particular time when the motor 160 is active. As shown here, each branch 168a, 168b also has a torque limiter 174a, 174b. The torque limiters 174a, 174b enable drive to be passed to both actuators 110a, 110b at the same time (with neither brake/clutch 172a, 172b activated) and when one actuator 110a, 110b (or effectively one valve 116a, 116b) reaches an end stop at the end of a stroke, then the associated torque limiter 174a or 174b will break free. Accordingly, each actuator 110a, 110b (and associated respective valve 116a, 116b) can either be operated together or separately - as selected by controlling the respective brakes/clutches 172a, 172b. As shown in Figure 3, the motor 160, gearbox 166, brakes/clutches 172a, 172b and the torque limiters 174a, 174b are all comprised within the subsea control unit 150, which is deployable and retrievable independently of the actuator 110 as shown here. Accordingly, the connections 154a, 154b between the subsea control unit 150 and the actuators 110a, 110b here comprise a pair of output drive shafts 154a, 154b, each selectively providing rotational drive to the respective external interfaces 170a, 170b of the actuators 110a, 110b.

Referring now to Figure 4, there is shown a subsea system 201 generally similar to that 101 shown in Figure 3, with like features referenced by like numerals incremented by 100. Accordingly, the subsea system 201 comprises a control unit 250 connected to a pair of subsea actuators 210a 210b for providing a subsea actuation of a pair of subsea valves 216a, 216b. For brevity, not all descriptions of similar features are repeated.

As shown in Figure 4, each respective branch 268a, 268b comprises a respective gearbox 266a, 266b. Here, the gearbox 266a, 266b is located after or ‘downstream’ of the brake/clutch 272a, 272b, between the brake/clutch 272a, 272 and the respective actuator 210a, 210b. Accordingly the torque supplied to each brake/clutch 272a, 272b can be minimised or reduced, with a relatively low torque (e.g. compared to the example of Figure 3) being supplied to the brake/clutch 272a, 274b - thereby effectively reducing a power required to operate the brake/clutch 272a, 272b.

As with the example 150 shown in Figure 3, the motor 260, gearboxes 266a, 266b, brakes/clutches 272a, 272b and the torque limiters 274a, 274b are all comprised within the subsea control unit 250, which is deployable and retrievable independently of the actuators 210a, 210b as shown here. Accordingly, the connections 254a, 254b between the subsea control unit 250 and the actuators 210a, 210b here comprise a pair of output drive shafts 254a, 254b, each selectively providing rotational drive to the respective external interfaces 270a, 270b of the actuators 210a, 210b.

Referring now to Figure 5, there is shown a subsea system 301 generally similar to that 201 shown in Figure 4, with like features referenced by like numerals incremented by 100. Accordingly, the subsea system 301 comprises a control unit 350 connected to a pair of subsea actuators 310a, 310b for providing a subsea actuation of a pair of subsea valves 316a, 316b. For brevity, not all descriptions of similar features are repeated. Here the drive transmission comprises a bevel gear 376a, 376b in each branch 368a, 368b. Accordingly, actuation here comprises transferring drive from the subsea control unit 350 to the actuators 310a, 310b via a self-locking gear 376a, 376b, shown here as worm gear with a relatively high efficiency, such as 50% or more. The bevel gear 376a, 376b enables use of a smaller brake 372a, 372b, such as compared to a similar or equivalent system 201 whereby the bevel gear 376a, 376b was omitted (e.g. as shown in Figure 4). In at least some examples (not shown), the provision of the bevel gear 376a, 376b enables elimination of a brake 372a, 372b. It will also be appreciated that the bevel gears 376a, 376b assist in changing an angle of drive transmission, here translating rotational drive perpendicularly, providing the rotational output about a longitudinal axis of output that is at 90° to a longitudinal axis of input.

As with the example 250 shown in Figure 4, the motor 360, gearboxes 366a, 366b, brakes/clutches 372a, 372b and the torque limiters 374a, 274b are all comprised within the subsea control unit 350, which is deployable and retrievable independently of the actuators 310a, 310b as shown here. Accordingly, the connections 354a, 354b between the subsea control unit 350 and the actuators 310a, 310b here comprise a pair of output drive shafts 354a, 354b, each selectively providing rotational drive to the respective external interfaces 370a, 370b of the actuators 310a, 310b.

Referring now to Figure 6, there is shown a subsea system 401 generally similar to that 301 shown in Figure 5, with like features referenced by like numerals incremented by 100. Accordingly, the subsea system 401 comprises a control unit 450 connected to a pair of subsea actuators 410a, 410b for providing a subsea actuation of a pair of subsea valves 416a, 416b. For brevity, not all descriptions of similar features are repeated.

As shown here, a respective motor 460a, 460b and gearbox 466a, 466b is provided for each actuator 410a, 410b. Here a respective motor and gearbox combination 460a, 466b and 460b, 466b is each provided in a discrete drive head 464a and 464b. As shown here, a further drive head 464c can be provided, such as for an additional actuator (not shown); or a possible future actuator to be deployed at later time - or to provide a backup drive for interchanging with one of the other drive heads 464a, 464b in an event of failure thereof.

The subsea control unit is connected to teach drive head via a respective jumper cable 478a, 478b, 478c. Accordingly, here the subsea control unit 450 comprises the power source, in the form of batteries 458, and the electronics control device (AECM) 456, but no mechanical drive (e.g. motor 460a, 460b, 460c). Unlike the example 350 shown in Figure 5, the motors 460a, 460b, 460c gearboxes 466a, 466b, 466b are all comprised outside the subsea control unit 450, which is deployable and retrievable independently of the actuators 410a, 410b as shown here; and in some examples (not shown) may be deployable and/or retrievable independently of at least one of the drive heads 464a, 464b, 464c. In other examples (not shown) the drive heads 464a, 464b, 46c can be deployed and retrieved independently of the subsea control unit 450, with (electric) connections thereto being completed subsea. It will also be appreciated that the drive heads 464a, 464b can be deployed together with or separately from the actuators 410a, 410b. Likewise, some methods may involve separate deployments of the drive heads 464a, 464b, 464c. For example, the further drive head 464c may be deployed during a later operation than the first two drive heads 464a, 464b, such as in conjunction with or anticipation of an installation of a later or subsequent (third) actuator.

Referring now to Figure 7, there is shown a subsea system 501 generally similar to that 401 shown in Figure 6, with like features referenced by like numerals incremented by 100. Accordingly, the subsea system comprises a control unit 550 connected to a pair of subsea actuators 510a, 510b for providing a subsea actuation of a pair of valves 516a, 516b. For brevity, not all descriptions of similar features are repeated.

The transmission here comprises an adjustable transmission, such as to allow or enable adjustment in the positioning of one or more ends of a transmission line or chain. The drive shaft 554a, 554b comprises a flexible drive shaft. The flexible drive shaft 554a, 554b is expressly flexible, such as in contrast to a standard rigid drive shaft. The flexible drive shaft 554a, 554b comprises a rotary drive shaft for transmitting rotary drive. The flexible shaft 554a, 554b is malleable and plastically deformable laterally, such as perpendicularly to a longitudinal central axis of the shaft 554a, 554b. The shaft 554a, 554b is flexible so as to allow flexibility in a positioning of at least a portion of the drive shaft 554a, 554b, such as at least one terminal end (e.g. output end portion) of the drive shaft 554a, 554b. The drive shaft 554a, 554b is flexible so as to enable the shaft 554a, 554b to flex or be flexed at a non-predetermined point. The flexible shaft 54 is bendable so as to provide a discrete change in angular orientation of the shaft 554a, 554b, allowing at least one bend or angular transition at an intermediate position along the length of the drive shaft 554a, 554b, located between each terminal end portion of the shaft 554a, 554b (e.g. between the respective input and output ends pf the drive shaft 554a, 554b). The at least one bend or angular transition is positionable at any position along the length of the shaft 554a, 554b. As can be seen from Figure 7, the bend or angular transition is localised, such as restricted to only a portion of the shaft 554a, 554b along its length; and there can multiple bends in different directions (x, y and z) along the length of the shaft 554a, 554b.

The flexible drive shaft 554a, 554b is flexible for transmitting rotary motion between two objects which are not fixed relative to one another. For example, at least one of the drive source (here in the subsea control unit 550) and/or the actuator/s 510a and 510b can be movable relative to the other of the drive source 550 and the actuator/s 510a, 510b whilst maintaining transmissibility of rotation drive therebetween; and optionally where the position of at least one of the drive source 550 and the actuator/s 510a, 510b is not predefined or predetermined. The flexible shaft 554a, 554b here comprises a rotatable wire rope or coil which is flexible laterally, such as bendable with a radius about an axis perpendicular to the longitudinal axis of the shaft 554a, 554b. The flexible shaft 554a, 554b has a torsional stiffness that is greater than an axial bending stiffness of the shaft 554a, 554b.

As shown in Figure 7, the flexible shafts 554a, 554b transmit drive from a central unit to respective drive heads 564a, 564b. As shown in Figure 7, the respective drive heads 564a, 564b are retrievable, independently of the actuators 510a, 510b. Accordingly, here a single motor 560 drives a pair of actuators 510a, 510b, which in turn control a pair of subsea valves 516a, 516b.

Referring now to Figure 8, there is shown a subsea system 601 generally similar to that 501 shown in Figure 7, with like features referenced by like numerals incremented by 100. Accordingly, the subsea system comprises a control unit 650 connected to a pair of subsea actuators 610a, 610b for providing a subsea actuation of a pair of valves 616a, 616b. For brevity, not all descriptions of similar features are repeated.

Here the drive heads 664a, 664b are mounted with the respective actuator 610a, 610b. The drive heads 664a, 664b may be mounted and deployed and retrieved together with the actuators 610a, 610b. The respective drive heads 664a, 664b are connected to an external interface 670 via flexible drive shafts 654a, 654b. The flexible drive shafts 654a, 654b allow variation or adaptability in the relative positions of the actuators 610a, 610b and can centralise an interface, facilitating common drive provision to each actuator from a single subsea control unit 650. Here, the subsea control unit comprises a general architecture similar to that 150 of Figure 3, with a pair of rotational drive outputs, albeit a primary difference between Figures 3 and 8 is the flexible drive shafts 654a, 654b between the subsea control unit 650 and the actuators 610a, 610b. As with the example 501 shown in Figure 7, gearboxes 666a, 666b are provided downstream of the flexible drive shafts 654a, 654b.

Referring now to Figure 9, there is shown a subsea system 701 generally similar to that 601 shown in Figure 8, with like features referenced by like numerals incremented by 100. Accordingly, the subsea system comprises a control unit 750 connected to a pair of subsea actuators 710a, 710b for providing a subsea actuation of a pair of valves 716a, 716b. For brevity, not all descriptions of similar features are repeated.

Rather than flexible drive shafts 654a, 654b, drive is transmitted between the respective actuators 710a, 710b and the subsea control unit 750 via transmission branches 768a, 768b comprising rigid drive shafts and gears. Such an arrangement can allow some variation or adaptability in the relative positions of the actuators 710a, 710b; at least when designing a subsea system; and can centralise an interface 770, facilitating common drive provision to each actuatorfrom a single subsea control unit 750. As shown in Figure 9, the subsea control unit comprises a pair of gearboxes 766a, 766b. The provision of gearing within the subsea control unit enable a lower rotational velocity to be output from the subsea control unit (e.g. compared to that of Figure 8), thereby simplifying sealing requirements or at least reducing loading thereon.

Referring now to Figure 10, there is shown a portion of a subsea system 801 wherein a ball lock mechanism 890 provides an operable differential in the transmission, allowing selective engagement of drive to either of rotational drive output shafts 854a, 854b of the control unit 850. The ball lock mechanism 890 is controlled by operation of a solenoid 892. The solenoid 892 here has a solenoid shaft 894 which runs through a hollow motor shaft 861 from an opposite side of the motor 860 to the outputs 854a, 854b. Operation of the solenoid 892 controls a longitudinal position of the ball mechanism 890 via the solenoid shaft 894. Depending on a longitudinal position of the solenoid shaft 894, balls 897a, 897b associated with each respective drive output 854a, 854b cause the motor shaft to be selectively engaged or disengaged with a respective gear wheel. Accordingly drive from the motor 860 can be selectively engaged and disengaged to each of the drive outputs 854a, 854b.

Referring now to Figure 11 , there is shown a subsea system 901 generally similar to that 501 shown in Figure 7, with like features referenced by like numerals incremented by 400. Accordingly, the subsea system 901 comprises a control unit 950 with a single motor 960. For brevity, not all descriptions of similar features are repeated.

Here the single subsea control unit 950 is connected to a plurality of actuators, 910a, 910b, 910c, 91 Od, 91 Oe, 91 Of, 91 Og. It will be appreciated that although shown here with flexible drive shafts 954a, 954b, 954c, 954d, 954e, 954f, 954g, other transmissions such as shown in other preceding examples may be applied on other example systems (not shown). It will also be appreciated that alternative selection mechanisms, such as based on that of Figure 10, may be incorporated in or replace the selection mechanism 966 shown in Figure 11 . It will also be appreciated that the total number of actuators driven by the single subsea control unit 950 may be varied -at a planning stage, or thereafter, such as after deployment of apparatus (including some actuators) and/or the subsea control unit. The subsea control unit may be deployed with redundant output/s, such as for backup in event of failure or for subsequent expansion to operate additional actuators.

Referring now to Figure 12, there is shown a subsea system 1001 generally similar to that 901 shown in Figure 11 , with like features referenced by like numerals incremented by 100. Accordingly, the subsea system 1001 comprises a control unit 1050 with a single motor 1060. For brevity, not all descriptions of similar features are repeated.

Here a redundant or backup subsea control unit 1050b is provided. The second subsea control unit 1050b provides a secondary or backup motor 1060, such as in an event of failure or insufficient power provision by the first motor 1060 of the first subsea control unit 1060. It will be appreciated in other examples (not shown), that redundancy may be provided in a single subsea control unit, such as where a backup motor may be provided.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims.

The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. It should be understood that the embodiments described herein are merely exemplary and that various modifications may be made thereto without departing from the scope or spirit of the invention. For example, it will be appreciated that although shown here as actuators for valves, in other examples the actuator/s may be for other actuations.