Patent Description:
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 control valves, pressure/temperature sensors, and the like.

XMTs typically have various fluid barriers for controlling fluid, pressure, flow 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 a closed position, where the bore (below the XMT) is closed.

<CIT> discloses a valve actuator comprising a screw member coupled to a valve stem and a sleeve such that rotation of the sleeve causes translation of the valve stem. The sleeve has a first end that is rotatably coupled to a housing that is fixably coupled to a valve body and a second end that projects out of the housing. The valve stem is partially disposed within the sleeve and extends into the valve body. A transmission is coupled to the housing and engaged with the sleeve. A motor is coupled to the transmission so that operation of the motor causes rotation of the sleeve.

<CIT> relates to a subsea electric actuator operating a linear valve, the actuator comprising a roller-screw for translating a rotational movement of a motor to a linear movement of a gate rod operating the valve.

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.

According to a first aspect there is provided an actuator as defined in the appended claims. The actuator comprises an electrically-operable actuator. The actuator may be for operating a valve. The actuator comprises a subsea actuator, such as a subsea electrical actuator for providing a subsea electrical actuation of the valve. The actuator comprises a screw assembly. The screw assembly comprises a roller screw. The screw assembly comprises a threaded part, such as a female threaded part (e.g. a nut), for receiving the screw. The screw assembly comprises a roller screw assembly. The roller screw assembly comprises a roller screw and a roller nut. The actuator comprises a housing for the screw assembly. The actuator comprises an axial stop for preventing axial movement relative to the housing of one of the screw and the threaded part. The actuator comprises a primary drive for providing a rotational movement to the screw assembly in a normal mode of operation. The screw assembly is for converting the rotational movement to an axial movement of a valve member relative to the housing. The actuator comprises an override for operating the actuator in an override mode of operation. The override is configured to release at least one of the screw and the threaded part for axial movement relative to the housing. The actuator may be configured to be overridden by release of at least a portion of the screw assembly. The portion for release in override may be otherwise fixed or restrained in normal operation of the actuator. The actuator may be configured for override by release of the entire screw assembly, such as release of the screw assembly relative to a housing of the actuator.

The screw assembly may comprise a longitudinal member for axial movement along a central axis of the longitudinal member. The longitudinal member may comprise the screw of the screw assembly. The screw of the screw assembly may be a spindle. The longitudinal member may comprise a solid member. The longitudinal member may comprise a rigid, solid rod. The screw assembly may comprise a transmission for transferring drive to or from the longitudinal member. A threaded part assembly, such as a roller nut assembly, may comprise the transmission. The roller nut assembly may comprise a plurality of rollers for transmitting drive between the screw and the roller nut of the roller screw assembly. The transmission may convert a rotational motion of the screw to a longitudinal motion of the threaded part. Alternatively the transmission may convert a rotational motion of the threaded part to a longitudinal motion of the screw.

The screw assembly may be operable by converting rotational movement or torque, such as from a motor (e.g. electric), to axial movement or force. The axial movement or force may be relative between the longitudinal member of the screw and the transmission. For example operation of the screw may provide an axial movement of the threaded part relative to the screw. The axial movement may comprise linear movement. The screw assembly may define a linear actuator. The actuator may comprise the motor. The motor may comprise the primary drive for operating the actuator in the normal mode of operation.

The screw assembly may be operable to axially drive the valve between positions. The screw assembly may be operable to selectively drive the valve cyclically between open and closed positions. For example, the screw assembly may be operable to push a valve member to an open position and to pull the valve member to a closed position. The screw assembly may comprise a push member. The push member may comprise a push rod. The push rod may comprise a hollow push rod. Accordingly, the push member may comprise a push tube.

The valve may comprise a valve member, such as a valve rod or stem. The valve stem may extend through a stem seal. In at least some examples, the valve assembly may comprise a bonnet, the bonnet housing the stem seal through which the valve stem may extend. 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 a XMT, such as when a XMT is removed, damaged, being inspected or repaired, etc. The valve may comprise a seat for the bore-sealing member. The bore-sealing member may comprise a gate. The valve stem may be perpendicular to the bore, with the valve stem being axially movable along its axis perpendicular to the bore. Accordingly, 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 threaded part of the screw assembly may be operatively associated with the valve member. For example, the threaded part may be connected to the valve member such that axial movement of the threaded part axially moves the valve member. In other examples, the screw may be connected to the valve member, such that axial movement of the screw axially moves the valve member. The screw or the threaded part may be connected to the push member. The portion of the screw assembly connected to the valve member (e.g. via the push member) may be an axially movable member of the screw assembly. The other portion of the screw assembly may be an axially stationary member of the screw assembly, at least during normal or primary operation of the actuator. For example, the threaded part may be the axially movable member and the screw may be the axially stationary member (or vice versa). The push member may be configured to push the valve stem. The push member may be configured to pull the valve stem. The push member may be attached to the valve stem.

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 threaded part, thereby axially displacing the valve member associated with the threaded part.

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. For example, the bearings may support the screw. The bearings may comprise contact angle bearings. The bearings may provide a high degree of axial stiffness. The bearings may provide a high axial load carrying capacity. The bearings may provide accommodate high speeds and rapid accelerations; and offer high running accuracy. The bearings may provide a safe radial and axial support. The bearings may provide an extremely precise axial guidance of the longitudinal member (e.g. the screw).

The bearings assembly may comprise a bearing sleeve. The bearing sleeve may be configured to transfer loads. The bearings sleeve may be configured to keep the bearings pre-loaded.

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 comprise a cylinder, with the axial movement being along an axis parallel to a central longitudinal axis of the cylinder.

The screw may be electrically operable. The screw may be electrically operable by selectively supplying electrical power to a motor for driving the transmission. For example, an electric motor may be associated with the screw of the screw assembly. Rotation of the screw (e.g. at or towards a first end of the screw) may force the threaded part to move axially, parallel to a central longitudinal axis of the screw. The screw may comprise a spline, such as a screwthread. The threaded part may comprise an interface/s for engaging the screw, such as an interengaging complementary profile. The threaded part may comprise a screwthread/s for engaging the screw. The threaded part may comprise a threaded part assembly.

The actuator may be configured to provide an alternative drive to the valve member. The actuator may be configured to move the valve member in an event of a failure of the screw assembly or a component thereof, or of the primary drive thereto. The actuator may be configured to move the valve member in an event of the screw assembly becoming stuck.

The actuator may comprise an override. The override may be configured to allow operation of the valve without requiring transmission of drive from the primary drive. The primary drive may comprise the drive normally used to operate the screw. The override may be configured to release at least one of the screw and the threaded part of the screw assembly. In at least some examples, the override may be configured to enable movement of the screw assembly in unison. The override may be configured to enable movement of the screw assembly as a single unit. For example, the override may be configured to enable axial movement of the screw and the threaded part together. The override may be configured to move, such as translate, the entire screw assembly. The override may be configured to move the screw assembly without causing or requiring relative movement between the screw and the threaded part. The override may be configured to allow axial movement of the portion of the screw assembly that is normally axially stationary during normal operation of the actuator. For example, where the screw is normally stationary, the override may be configured to allow axial movement of the screw during the override mode of operation.

In at least some examples, the override comprises a release mechanism. The release mechanism may be configured to allow a movement of at least one of the screw and/or the threaded part. The movement may comprise an axial movement. The movement may comprise a movement not otherwise possible without or prior to the operation of the override. The release mechanism may be configured to allow axial movement of the axially stationary member, upon activation of the override. For example, activation of the override, operating the release mechanism, may allow axial movement of the screw not normally possible during normal operation of the actuator.

The override may comprise a releasable stop. The releasable stop may comprise an axial stop defining or limiting axial movement in at least one direction for at least one of the screw and/or threaded part. The releasable stop may define or limit an axial position of the axially stationary member. The axial stop may comprise a shoulder. The axial stop may comprise a bearing shoulder. Operation of the override to release the releasable stop may allow movement of the stationary member of the screw assembly not otherwise possible without or prior to the operation of the override. For example, in normal operation of the actuator the screw may be axially stationary, with driven rotation of the screw consequently driving axial movement of the threaded part. When the actuator override is activated, operation of the actuator in override mode may allow axial movement of the screw. Accordingly, in at least some examples, the override may allow axial movement of both the screw and the threaded part, such as in tandem or unison.

In at least some examples, the releasable stop may comprise a backplate, or at least a portion thereof. The method of override may comprise a release of at least a portion of the backplate. The portion of the backplate may be connected to or associated with the portion of the screw assembly. The release mechanism may comprise a weakness, such as a predefined weakness. The actuator may be reconfigurable from a normal mode of operation to an override mode of operation upon activation or rupturing of the predefined weakness.

The release mechanism may be configured to release the bearing assembly for axial movement. The bearing assembly may normally be axially fixed or limited, such as by the axial stop. Accordingly, operation of the override may allow axial movement of the bearing assembly, such as jointly with the longitudinal member. In at least some examples, the override is configured to release the bearings casing for axial movement. Accordingly, the bearings casing may be axially movable, such as with the screw, upon activation of the override. The bearings casing may be axially stationery during normal operation, such as being stopped by the axial stop.

The release mechanism may be configured to release the longitudinal member from the bearing assembly. For example, the release mechanism may be configured to allow the longitudinal member to move longitudinally relative to the bearing assembly in the override mode. The longitudinal member may be axially immovable relative to the bearings assembly during normal operation of the actuator.

The release mechanism may comprise an external release interface. The external release interface may be external of the actuator housing, such as a cylinder containing the actuator. The release mechanism may comprise a release member. The release mechanism may comprise an external release member. The external release member may comprise an external sleeve, such as located on an exterior of the actuator housing. Accordingly, the release mechanism may be operated externally of the actuator. The release mechanism may normally be locked in position, such as by a mechanical lock. In at least some examples, the mechanical lock comprises a shear pin. The mechanical lock may be for limiting or preventing movement of the release member, such as in normal use of the actuator. The shear pin may be disassociated with the screw assembly. The shear pin may be isolated from forces associated with the screw assembly. For example, forces associated with the screw assembly or bearings therefore may be isolated from the shear pin. Accordingly, the shear pin may be prevented from shearing due to movement or force associated with the normal operation of the screw assembly. The shear pin may be sheared by a movement or force applied to an external portion of the actuator. For example, the shear pin may be, optionally may only be, sheared by a force applied externally to the release member.

Different examples may comprise different release mechanisms. In at least some examples, reconfiguration of the actuator from the normal mode of operation to the override mode of operation may comprise an irreversible process, or at least only reversible by a resetting and/or retrieval of at least a portion of the actuator. For example, the actuator may be reconfigurable to the override mode of operation by activation or rupturing of the predefined weakness. The predefined weakness may comprise a shear pin, rupture disc and/or a portion of another member, such as a predefined thinning or narrowing (e.g. of a portion of the backplate). In other examples, the reconfiguration of the actuator from the normal mode of operation to the override mode of operation may be reversible.

The actuator may be configured for bidirectional operation by the override tool. The actuator may be configured to activate and/or deactivate by the override tool. For example, the actutator may be configured to both open and close the valve with the override tool.

The actuator may comprise a retainer. The retainer may comprise or be associated with the axial stop. In at least some examples, the retainer retains the axial stop axially during normal operation of the actuator. Activation of the release mechanism may comprise a transverse movement of the axial stop or a member associated therewith. The transverse movement may be of the retainer. The retainer may comprise a ring, such as a lock ring. The lock ring may comprise a split lock ring. The retainer may comprise a pretension when assembled in the actuator. For example, the retainer may comprise a transverse, such as radial, pretension when assembled in the actuator. The pretension may assist in maintaining the retainer in its normal retaining position during normal operation of the actuator. Alternatively, the pretension may assist in releasing the retainer from its normal position when the release mechanism is activated. The retainer may normally be locked in position during normal operation of the actuator. The override may release the retainer.

The override may not comprise a bypass, such as a bypass for bypassing one or more of the screw and/or the threaded part. In at least some examples, the override utilises at least some functionality of the screw assembly to operate the valve member. The override may utilise a same connection of the screw assembly to the valve member for operating the valve assembly in override mode as the connection of the screw assembly to the valve member for operating the valve assembly in normal or primary operation, such without or prior to operation of the override. The override may allow operation of the same push member for pushing and/or pulling the valve member as in normal or primary operation of the actuator. The override may be configured to utilise the interface between the screw and the threaded part of the screw assembly. The override may be configured to utilise the interface between the screw and the threaded part of the screw assembly to directly transmit force and/or movement in a same direction or mode. For example, the override may allow a transfer of an axial force and/or axial movement between the screw and the threaded part (e.g. axially pushing/pulling the screw may axially push/pull the threaded part via the spline interface/s therebetween). Additionally, or alternatively, the override may be configured to rotate the screw and/or the threaded part. Accordingly, the actuator may not comprise or require an additional or alternative connection.

The actuator may comprise an interface for an override tool. The override tool 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 override tool interface may be provided at or through an axial end of the cylinder. The override tool interface may be positioned with the screw assembly located between the override tool interface and the valve member. The override tool 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 override tool 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 override tool interface may be configured to drive the at least a portion of the screw assembly axially in a first direction to push the valve member. Additionally, or alternatively, the override tool interface may be configured to drive the at least a portion of the screw assembly axially in a second direction to pull the valve member. The override tool interface may be configured to drive the at least a portion of the screw assembly axially to open the valve member. Additionally, or alternatively, the override tool interface may be configured to drive the at least a portion of the screw assembly rotationally to open the valve member.

The override tool may comprise an alternative drive. The alternative drive may comprise an electric drive, such as an alternative electric motor. Additionally or alternatively, the alternative drive may comprise a hydraulic drive.

The override tool may be operated remotely. The override tool may comprise or may be operated by a ROV. Additionally, or alternatively, the override tool may be operated manually. In at least some examples the actuator may be configured for override operation by a plurality of override tools. For example, the actuator may be configured to be operated by a ROV override tool in a first override operation; and operated manually in a second override operation (e.g. if the first override operation was unsuccessful; or if subsequently the first override operation was desired to be reversed).

The actuator may comprise a rotational stop for at least one of the screw and the threaded part. The rotational stop may prevent or at least limit rotation of the axially-movable member, at least during normal operation of the actuator. Accordingly, the rotational stop may provide for conversion of relative rotation between the screw and the threaded part to axial movement. The axial movement may therefore may be pure, non-rotational linear movement in the axial direction. The rotational stop may comprise at least one anti-rotation pin. The actuator may comprise a guide member for guiding axial movement of the threaded part and/or the screw. For example, the guide member may comprise a pin in an axial channel. The axial channel may be provided in or associated with the housing; and the guide pin provided in or associated with the threaded part. Alternatively, the axial channel may be provided in or associated with the threaded part.

The actuator may comprise an underwater or subsea actuator. The actuator may comprise a subsea electrical actuator for providing a subsea electrical actuation.

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 a 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 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. The lack of axial movement of the screw may not move axially relative to the threaded part. The screw assembly may comprise an inverted screw assembly, such as an inverted roller screw assembly. The 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 as 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 a 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.

According to a further aspect, there is provided an apparatus comprising the actuator 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 method of actuation. The method may comprise providing the actuator 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 providing a subsea electrical actuator for actuating a valve, the actuator comprising a screw assembly comprising a screw and a threaded part. The screw may comprises a roller screw and the threaded part may comprise a nut. The method may comprise using an axial stop of the actuator to prevent axial movement of one of the screw and the threaded part, the axial movement being relative to a housing for the screw assembly. The method may comprise providing a rotational movement to the screw assembly in a normal mode of operation with a primary drive. The method may comprise using the screw assembly to convert the rotational movement to an axial movement of a valve member relative to the housing. The method may comprise using an override to operate the actuator in an override mode of operation. The method may comprise releasing at least one of the screw and the threaded part for axial movement relative to the housing. The method may comprise axially moving at least one of the screw and the threaded part to move the valve member. The method may comprise axially moving the screw assembly as in unison, as a single unit, to move the valve member.

The method may comprise releasing the axial stop to release at least one of the screw and the threaded part for axial movement relative to the housing, with the axial stop comprising a shoulder preventing the axial movement of at least one of the screw and the threaded part in normal operation of the actuator. The method may comprise overriding an electric motor that is used to operate the actuator in the normal mode of operation. The method may comprise using an alternative drive to operate the actuator in the override mode of operation.

The method may comprise operating a valve of a wellhead apparatus for controlling access to a hydrocarbon wellbore.

According to a further aspect there is provided an apparatus designed and/or manufactured according to the method of any other aspect, example, embodiment or claim.

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 actuator and/or the override thereof.

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 actuator and/or the override thereof.

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 screw and the threaded part may also be associated with the other of the screw and the threaded part. For example, where examples or features are disclosed in combination with the screw it will be appreciated that those features may apply equally to the threaded part, and vice versa. In at least some examples, the roles of the screw and the threaded part may be inverted (e.g. the threaded part may be axially stationery and the screw axially movable, in normal operation, to axially move the valve member with the screw).

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.

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

Referring first to <FIG>, there is shown an actuator <NUM> according to the present disclosure. Here, the actuator <NUM> comprises an electrically-operable subsea actuator <NUM> for providing a subsea electrical actuation of a valve <NUM>. The actuator <NUM> comprises a screw assembly <NUM>, here in the form of a roller screw assembly. The screw assembly <NUM> comprises a screw <NUM> and a threaded part <NUM>. Here, the roller screw assembly <NUM> comprises a roller screw <NUM> and a roller nut <NUM>. The actuator <NUM> comprises a housing <NUM> for the roller screw assembly <NUM>; and an axial stop <NUM> for preventing axial movement relative to the housing <NUM> of one of the roller screw <NUM> and the roller nut <NUM>. The actuator <NUM> comprises a primary drive for providing a rotational movement to the roller screw assembly <NUM> in a normal mode of operation. The roller screw assembly <NUM> converts the rotational movement to an axial movement of a valve member <NUM> relative to the housing <NUM>. The actuator <NUM> comprises an override <NUM> for operating the actuator <NUM> in an override <NUM> mode of operation (as shown in <FIG> and <FIG>). The override <NUM> is configured to release at least one of the roller screw <NUM> and the roller nut <NUM> for axial movement relative to the housing <NUM>. In the example shown, the override <NUM> releases the roller screw <NUM> for axial movement in the override <NUM> mode.

The roller screw <NUM> of the roller screw assembly <NUM> here comprises a longitudinal member in the form of a rigid, solid threaded rod. The roller nut <NUM> assembly comprises a plurality of rollers for transmitting drive between the screw <NUM> and the roller nut <NUM> of the roller screw assembly <NUM>. The transmission converts a rotational motion of the roller screw <NUM> to a longitudinal motion of the roller nut <NUM>. In other examples (not shown) the roles of the roller nut <NUM> and the roller screw <NUM> may be reversed, with the transmission converting a rotational motion of the roller nut <NUM> to a longitudinal motion of the roller screw <NUM>.

The roller screw assembly <NUM> is operable by converting rotational movement or torque, such as from a motor (e.g. electric), to axial movement or force. The axial movement or force is relative between the roller screw <NUM> of the roller screw <NUM> and the transmission. Accordingly, operation of the roller screw <NUM> provides an axial movement of the roller nut <NUM> relative to the roller screw <NUM>. The axial movement here comprises linear movement (e.g. of the roller nut <NUM> from right to left, or left to right, as shown in <FIG> and <FIG>). Here, the roller screw assembly <NUM> defines a linear actuator. The actuator <NUM> comprises a motor, which is the primary drive for operating the actuator <NUM> in the normal mode of operation, as shown in <FIG> and <FIG>.

The roller screw assembly <NUM> is operable to selectively axially drive the valve <NUM> cyclically between open and closed positions. For example, the roller screw assembly <NUM> is operable to push the valve member <NUM> to an open position (as shown in <FIG>) and to pull the valve member <NUM> to a closed position (similar to the position of the valve member <NUM> shown in a closed configuration of <FIG>). The roller screw assembly <NUM> comprises a push tube <NUM>.

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

At least one of the screw and the roller nut <NUM> of the roller screw assembly <NUM> is operatively associated with the valve member <NUM>. Here, the roller nut <NUM> is connected to the valve member <NUM> such that axial movement of the roller nut <NUM> axially moves the valve member <NUM>. In other examples (not shown), the screw is connected to the valve member <NUM>, such that axial movement of the screw axially moves the valve member <NUM>. The roller nut <NUM> is connected to the push tube <NUM>, the roller nut <NUM> being the axially movable member of the roller screw assembly <NUM> in the normal mode of operation (as sown in <FIG> and <FIG>). The roller screw <NUM> is the axially stationary member of the roller screw assembly <NUM> as shown here, at least during normal or primary operation of the actuator <NUM>. The push tube <NUM> is configured to push the valve stem <NUM> and also to pull the valve stem <NUM>, with the push tube <NUM> here being attached to the valve stem <NUM>.

The actuator <NUM> comprises a housing <NUM> configured to maintain an axial position of the axially stationary member of the roller screw assembly <NUM>. Here, the housing <NUM> comprises the axial stop <NUM> for maintaining the axial position of the roller screw <NUM>, the axial stop <NUM> preventing axial movement of the axially stationary roller screw in a first axial direction - to the right, towards the valve <NUM>, as shown in <FIG>. Here, a backplate <NUM> at the rear of the housing <NUM> prevents axial movement of the roller screw <NUM> in a second axial direction - to the left, away from the valve <NUM>, as shown in <FIG>. The axial directions are parallel with the longitudinal axis of the roller screw <NUM>. The housing <NUM> limits or prevents axial movement of the roller screw <NUM> during normal operation of the actuator <NUM>. Accordingly, here, the actuator <NUM> is normally operable to actively rotate, driven by the motor, the roller screw <NUM> to axially displace the roller nut <NUM>, thereby axially displacing the valve member <NUM> associated with the roller nut <NUM>.

The actuator <NUM> comprises a bearings assembly <NUM> comprising a bearings casing <NUM> containing contact angle bearings <NUM> for supporting the roller screw <NUM>. The bearings <NUM> 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 <NUM> provide a safe radial and axial support and an extremely precise axial guidance of the roller screw <NUM>.

Here, the housing <NUM> seals the actuator <NUM>, with an interior of the actuator <NUM> sealed from an exterior of the actuator <NUM>. The housing <NUM> here comprises a cylinder, with the axial movement of the roller nut <NUM> being along an axis parallel to a central longitudinal axis of the cylinder.

The roller screw <NUM> is electrically operable. The roller screw <NUM> is electrically operable by selectively supplying electrical power to the motor for driving the transmission. Here, the electric motor is associated with the screw <NUM> of the roller screw assembly <NUM>. Rotation of the screw <NUM> (e.g. at or towards a first end of the screw) forces the roller nut <NUM> to move axially, parallel to the central longitudinal axis of the screw assembly <NUM>. The screw <NUM> has a screwthread, with the roller nut <NUM> comprising an interengaging complementary screwthread profile for engaging the roller screw <NUM>.

The actuator <NUM> here is configured to provide an alternative drive to the valve member <NUM>. The actuator <NUM> is configured to move the valve member <NUM> in an event of a failure of the roller screw assembly <NUM> or a component thereof, or of the primary drive thereto. For example, the actuator <NUM> is configured to move the valve member <NUM> in an event of the roller screw assembly <NUM> becoming stuck.

The actuator <NUM> comprises an override <NUM> configured to allow operation of the valve <NUM> without requiring transmission of drive from the primary drive (motor) normally used to operate the roller screw <NUM>. The override <NUM> is configured to release the roller screw <NUM>. In at least some examples, the override <NUM> is configured to enable movement of the roller screw assembly <NUM> in unison. For example, the override <NUM> is configured to enable axial movement of the roller screw <NUM> and the roller nut <NUM> together. The override <NUM> is configured to allow axial movement of the portion of the roller screw assembly <NUM> that is normally axially stationary during normal operation of the actuator <NUM>. For example, where the roller screw <NUM> is normally axially stationary in the normal mode of operation as shown in <FIG>, the override allows the roller screw <NUM> to move axially in the override mode of operation, as shown in <FIG> and <FIG>.

Here, the override <NUM> comprises a release mechanism <NUM> configured to allow axial movement of the roller screw <NUM> that is not otherwise possible without or prior to the operation of the override <NUM>. The release mechanism <NUM> is configured to allow axial movement of the roller screw <NUM> not normally possible during normal operation of the actuator <NUM>, upon activation of the override <NUM>, as shown in <FIG>.

The override <NUM> here comprises a releasable axial stop <NUM> defining or limiting axial movement in at least one direction for the roller screw <NUM>. Here, the axial stop <NUM> comprises a bearing shoulder. Operation of the override <NUM> to release the releasable stop allows movement of the stationary member of the roller screw assembly <NUM> not otherwise possible without or prior to the operation of the override <NUM>. In normal operation of the actuator <NUM> the roller screw <NUM> is axially stationary, with driven rotation of the roller screw <NUM> consequently driving axial movement of the roller nut <NUM>. As shown in <FIG> and <FIG>, when the actuator override <NUM> is activated, operation of the actuator <NUM> in override <NUM> mode allows axial movement of the roller screw <NUM>. Accordingly, here, the override <NUM> may allow axial movement of both the roller screw <NUM> and the roller nut <NUM>, such as in tandem or unison.

The release mechanism <NUM> is configured to release the bearing assembly <NUM> for axial movement, the bearing assembly <NUM> normally being axially fixed or limited by the axial stop <NUM> in the form of the bearing shoulder. Accordingly, operation of the override <NUM> allows axial movement of the bearing assembly <NUM> jointly with the roller screw <NUM>. Here, the override <NUM> is configured to release the bearings casing <NUM> for axial movement with the roller screw <NUM>, upon activation of the override <NUM>. As shown in <FIG> and <FIG>, the bearings casing is axially stationery during normal operation, being stopped by the axial stop <NUM>.

In other examples, the release mechanism <NUM> releases the roller screw <NUM> from the bearing assembly <NUM>. For example, the release mechanism <NUM> in such examples is configured to allow the roller screw <NUM> to move longitudinally relative to the bearing assembly <NUM> in the override <NUM> mode. The roller screw <NUM> is axially immovable relative to the bearings assembly during normal operation of the actuator <NUM>.

The release mechanism <NUM> here comprises an external release interface, external of the actuator housing <NUM>. The release mechanism <NUM> comprises an external release sleeve <NUM> located on an exterior of the actuator <NUM> housing <NUM>. Accordingly, the release mechanism <NUM> is operated externally of the actuator <NUM>. The release mechanism <NUM> is normally be locked in position, by a mechanical lock, comprising a shear pin <NUM> here for limiting or preventing movement of the external release sleeve <NUM> in normal use of the actuator <NUM>. The shear pin is disassociated with the roller screw assembly <NUM>, being isolated from forces associated with the roller screw assembly <NUM>. Here, forces associated with the roller screw assembly <NUM> and bearings <NUM> therefor are isolated from the shear pin <NUM> by one or more bearings/balls <NUM> providing an interface between the external release sleeve <NUM> and the roller screw assembly <NUM> and bearings <NUM> therefor. Accordingly, the shear pin <NUM> here is prevented from shearing due to movement or force associated with the normal operation of the roller screw assembly <NUM>. The shear pin <NUM> is only sheared by a movement or force applied externally to the external release sleeve <NUM>. The bearings/balls <NUM> provide for a low axial friction (rolling) for sliding movement during release of the external release sleeve <NUM>, whilst providing a rigid or stiff radial connection between the external release sleeve <NUM> and the roller screw assembly <NUM>.

Here the actuator <NUM> comprises a retainer <NUM> associated with the axial stop <NUM>, the retainer <NUM> retaining the axial stop <NUM> axially during normal operation of the actuator <NUM>. Activation of the release mechanism <NUM> entails a transverse movement of the retainer <NUM>. here, the retainer <NUM> comprises a split lock ring. The retainer <NUM> comprises a pretension when assembled in the actuator <NUM>. Here, the retainer <NUM> comprises a transverse, radial, pretension when assembled in the actuator <NUM>. The pretension assists in releasing the retainer <NUM> from its normal position when the release mechanism <NUM> is activated. The retainer <NUM> is normally locked in position during normal operation of the actuator <NUM>, with the override <NUM> releasing the retainer <NUM>. As can be seen in <FIG>, when the external release sleeve <NUM> is released (moved from the left in <FIG> to the right in <FIG>), a cavity <NUM> is progressed to the axial position of the bearings/balls <NUM>, allowing the bearings/balls to be pushed radially outwards with the retainer <NUM>, thereby releasing the axial stop <NUM> for axial movement in the override mode as shown in <FIG>. An offset angle <NUM> assists transverse release of the retainer <NUM>.

Here, the override <NUM> does not comprise a bypass, such as a bypass for bypassing one or more of the roller screw <NUM> and/or the roller nut <NUM>. The override <NUM> utilises at least some functionality of the roller screw assembly <NUM> to operate the valve member <NUM> in the override mode of operation. The override <NUM> here utilises a same connection of the roller screw assembly <NUM> to the valve member <NUM> for operating the valve <NUM> assembly in the override mode as the connection of the roller screw assembly <NUM> to the valve member <NUM> for operating the valve <NUM> assembly in normal or primary operation prior to operation of the override <NUM>. The override <NUM> allows operation of the same push tube <NUM> for pushing and pulling the valve member <NUM> as in normal or primary operation of the actuator <NUM>. The override <NUM> is configured to utilise the interface between the roller screw <NUM> and the roller nut <NUM> of the roller screw assembly <NUM> to directly transmit force and/or movement in a same direction or mode. For example, the override <NUM> allows a transfer of an axial force and/or axial movement between the roller screw <NUM> and the roller nut <NUM> (e.g. axially pushing/pulling the roller screw <NUM> axially pushes/pulls the roller nut <NUM> via the threaded interface/s therebetween). Additionally, the override <NUM> is configured to rotate the roller screw <NUM>. Accordingly, the actuator <NUM> does not comprise or require an additional or alternative connection between the roller screw assembly and the valve member.

The actuator <NUM> comprises an external interface <NUM> for an override tool (not shown) axially external to the actuator <NUM>. Here, where the actuator housing <NUM> comprises a cylinder, the override tool interface <NUM> is provided at or through an axial end of the cylinder. The override tool interface <NUM> is positioned with the roller screw assembly <NUM> located between the override tool interface <NUM> and the valve member <NUM>. The override tool interface <NUM> is configured to transmit torque and/or axial force to the roller screw <NUM> to move the valve member <NUM>. The override tool interface <NUM> comprises a torque interface to allow clockwise and/or counter-clockwise torque to be applied to the roller screw <NUM> to move the valve member <NUM>. The override tool interface <NUM> is configured to drive the roller screw <NUM> axially in the first direction to push the valve member <NUM>. Additionally, the override tool interface <NUM> is configured to drive the roller screw <NUM> axially in the second direction to pull the valve member <NUM>. The override tool interface <NUM> is configured to drive the roller screw <NUM> axially to open and close the valve member <NUM>. Additionally, the override tool interface <NUM> is configured to drive the at least a portion of the roller screw assembly <NUM> rotationally to open and close the valve member <NUM>. Here, it will be appreciated that the roller screw <NUM> has been axially and rotationally drive from the position of <FIG> to the position of <FIG>, thereby axially moving the roller screw <NUM> relative to the roller nut <NUM>. It will be appreciated that the roller screw <NUM> may be driven further (e.g. to the right in <FIG>). Thereafter it may be possible to close the valve <NUM> by driving the roller screw assembly <NUM> in an opposite direction (e.g. to the left from the position as shown in <FIG>) to pull the valve member <NUM> closed (to the left from the position as shown in <FIG>). The override tool (not shown, but may be generally similar to that <NUM> shown in <FIG>) comprises an alternative drive, such as a hydraulic drive.

The override tool is operated remotely, by a ROV. In at least some examples the actuator <NUM> is configured for override operation by a plurality of override tools, such as by a ROV override tool in a first override operation; and operated manually in a second override operation (e.g. if the first override operation was unsuccessful; or if subsequently the first override operation was desired to be reversed).

Here, the actuator <NUM> comprises a rotational stop <NUM> for the roller nut <NUM> to prevent or at least limit rotation of the roller nut <NUM>, during normal and override operation of the actuator <NUM>. Accordingly, the rotational stop <NUM> helps provide for the conversion of relative rotation between the roller screw <NUM> and the roller nut <NUM> to axial movement. The axial movement here is therefore pure, non-rotational linear movement in the axial direction. The rotational stop <NUM> here comprises a plurality of anti-rotation pins associated with the roller nut <NUM>, received in axial guide channels <NUM> associated with the housing <NUM>.

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

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

<FIG> depicts a method of operation of the actuator <NUM> of <FIG>. The method comprises providing the actuator <NUM> of <FIG> for subsea actuation of the valve <NUM>. The method comprises using the axial stop <NUM> of the actuator <NUM> to prevent axial movement of the roller screw <NUM>, the axial movement being relative to the housing <NUM> for the roller screw assembly <NUM>. The method comprises providing the rotational movement to the roller screw assembly <NUM> in the normal mode of operation with the primary drive (electric motor). The method comprises using the roller screw assembly <NUM> to convert the rotational movement to the axial movement of the valve member <NUM> relative to the housing <NUM>. The method comprises using the override <NUM> to operate the actuator <NUM> in the override <NUM> mode of operation. The method comprises releasing the roller screw <NUM> for axial movement relative to the housing <NUM>. The method comprises axially moving the roller screw <NUM> to move the valve member <NUM> in the override mode of operation.

The method comprises releasing the axial stop <NUM> to release the roller screw <NUM> for axial movement relative to the housing <NUM>, with the axial stop <NUM> comprising the shoulder preventing the axial movement of the roller screw <NUM> in normal operation of the actuator <NUM>. The method comprises overriding the electric motor that is used to operate the actuator <NUM> in the normal mode of operation. The method comprises using an alternative drive to operate the actuator <NUM> in the override <NUM> mode of operation. The method comprises operating the valve <NUM> of the wellhead apparatus for controlling access to a hydrocarbon wellbore.

It will be appreciated that in an unlikely circumstance that a portion of the actuator <NUM> fails, the override <NUM> may enable operation of the valve <NUM>.

<FIG> shows a further embodiment of an actuator <NUM> generally similar to that shown in <FIG>. The actuator <NUM> of <FIG> shares features common to the embodiment of <FIG>, with those features represented by reference numerals incremented by <NUM>. For example, the actuator <NUM> comprises a roller screw assembly <NUM> with a roller screw <NUM> and a roller nut <NUM>. Not all features common to both embodiments are repeated here to maintain brevity and clarity. Operation of the actuators <NUM>, <NUM> is generally similar, with override possible by an override tool.

As well as the actuator <NUM>, an example override tool <NUM> is also depicted in <FIG>. The override tool <NUM> is configured to engage with the override tool interface <NUM> at the axial end of the cylinder, as shown in the transition from <FIG>. In <FIG>, the override tool <NUM> is shown here with a pair of arms 192a, 192b positioned around an exterior of the cylindrical actuator housing <NUM>. Each of the override tool arms 192a, 192b comprises an inner protrusion 193a, 193b for engaging the external release sleeve <NUM> of the actuator <NUM>. As shown in <FIG> the override tool has been slid over the housing <NUM> (towards the right) from the positions of <FIG>. It will be appreciated that the protrusions 192a, 192b can be positioned beyond the external release sleeve <NUM> due to flexion of the override tool arms 192a, 192b as the protrusions 193a, 193b ride over the external release sleeve <NUM>. In other examples, the protrusions 193a, 193b may be positioned beyond the external sleeve <NUM> (to the right as shown in <FIG>) by rotating the override tool arms 192a, 192b to align with castellations or gaps in the external release sleeve <NUM> before rotating to align the protrusions 193a, 193b with corresponding protrusions on the external release sleeve <NUM>. It will also be appreciated that in other embodiments the override tool may comprise more or less arms for engaging the external release sleeve <NUM>. For example, in other embodiments, there may be a single arm; or the override tool <NUM> may comprise a sleeve extending fully around the external release sleeve <NUM>. It will also be appreciated that in addition to, or instead of, arms for pulling, an override tool may have a sleeve or arms for pushing the external release sleeve, such as the external release sleeve <NUM> shown in <FIG>.

With the override tool <NUM> positioned as shown in <FIG>, the external release sleeve <NUM> can be operated - here by pulling on the arms 192a, 192b. It will be appreciated that the arms 192a, 192b can be controlled to operate the sleeve <NUM> by applying a force such as from a cylinder or piston. For example, here pressurisation of a chamber <NUM> (shown here as an annular chamber) can force movement of a piston <NUM> to force the arms 192a, 192b to operate the sleeve <NUM>. The piston <NUM> here divides a volume defined by an override tool cylinder <NUM> into two chambers <NUM>, <NUM>. As shown in the transition between <FIG> and <FIG>, the shear pin <NUM> is configured to shear at a force exerted by the arms 192a, 192b of the override tool <NUM> - pulling the release sleeve <NUM> to the left as shown in <FIG> to shear the pin <NUM> (whereas the sleeve <NUM> can be pushed to the right in the transition between <FIG> and <FIG>, and <FIG>, to shear the shear pin <NUM>). It will be appreciated that the override tool <NUM> can be hydraulically operated, such as by supplying or pressurising hydraulic fluid in/into the chamber <NUM> to move the external release sleeve <NUM> to shear the shear pin <NUM>. It will also be appreciated that other activation methods can be used to shear the shear pin <NUM>, such as pressurisation of other chambers (e.g. in some embodiments an inner override tool chamber <NUM> may be pressurisable) or other actuation means, such as electrically-operated or even manual. A detailed view of the shearing of the shear pin can be seen in <FIG>. In the embodiment shown here, the external release sleeve <NUM> comprises a cavity <NUM> that becomes aligned to release the axial stop <NUM> as illustrated in <FIG>.

With the external release sleeve <NUM> released by the override tool <NUM>, as shown in <FIG> (and <FIG>), the axial stop <NUM> can be released, similarly as for the actuator <NUM> of <FIG>. The cavity <NUM> is progressed to the axial position of the bearings/balls <NUM>, allowing the bearings/balls to be pushed radially outwards with the retainer <NUM>, thereby releasing the axial stop <NUM> for axial movement of the roller screw assembly <NUM> in the override mode as shown in <FIG>. Here, an angle <NUM> on the axial stop <NUM> supports transverse release of the retainer <NUM>. The angle <NUM> is configured to assist in transverse movement of the retainer <NUM> away from the axial stop <NUM> when the retainer is urged in an axial direction - the axial direction being that of the actuator <NUM>, with the transverse direction here being perpendicular thereto. The angle is not a right-angle; here the angle <NUM> is defined by a face of the axial stop <NUM> that is inclined rearwards (to the left in <FIG>) by a few degrees. Accordingly, the angle <NUM> is a small acute angle of a few degrees to a radial transverse access of the actuator <NUM>; and defines an obtuse opening of a few degrees more than <NUM> degrees between a side face (e.g. cylindrical outer side wall) of the axial stop <NUM>. It will be appreciated that in other embodiments other configurations of interface between the axial stop <NUM> and the retainer <NUM> may be provided. For example, the retainer <NUM> may comprise an offset angle to assist transverse movement of the retainer <NUM> resultant from an axial force applied (such as by the axial stop <NUM>). With the cavity <NUM> aligned with the bearings/balls <NUM>, the bearings/balls <NUM> are freed to move radially outwards into the cavity <NUM>, such as when urged by the retainer <NUM> - and depicted in the transition from <FIG>. Accordingly, when the retainer <NUM> is urged radially outwards via the angle <NUM> by an axial force urging the axial stop <NUM>, the retainer <NUM> is no longer prevented from radial movement by the external release sleeve <NUM> (via the bearings/balls <NUM>) in the override configuration of <FIG> and <FIG> (and <FIG>), contrary to the normal operation configuration of the actuator <NUM> of <FIG> (and <FIG>). Accordingly, the retainer <NUM> can be released by the override tool <NUM>, freeing the axial stop <NUM>, thus allowing axial movement of the roller screw assembly <NUM> as shown in <FIG>, <FIG> and <FIG>. It will be appreciated that the axial stop <NUM> and/or the retainer <NUM> can be circumferential (e.g. rings here). Although only a single set of bearings/balls <NUM> is shown in the cross-section in the figures, it will be appreciated that multiple sets (e.g. three) may be spaced circumferentially around the actuator <NUM>.

As shown here in <FIG>, once the external release sleeve <NUM> has been actuated to shear the shear pin <NUM>, further movement of the external release sleeve <NUM> is limited. For example, further movement here is prevented from the position shown in <FIG> (e.g. by a stop or shoulder <NUM>, such as associated with the backplate <NUM> or housing <NUM>). Accordingly, further pressurisation of the chamber <NUM> here does not move the arms 192a, 192b or external release <NUM> further from the position of <FIG>. As shown from the transition from <FIG>, further pressurisation of the chamber <NUM> causes the piston <NUM> to move (further) relative to the override tool cylinder housing <NUM>. The piston <NUM> is connected to a tool stem <NUM> that is connected to and engages the actuator override tool interface <NUM>. Accordingly, as shown in <FIG>, axial movement of the piston <NUM> causes axial movement of the tool stem <NUM>, here a stem rod, and actuation of the actuator <NUM> via the actuator override tool interface <NUM>, as described in detail below.

With the axial stop <NUM> released as described above and shown in <FIG>, the roller screw assembly <NUM> is no longer prevented from axial movement as a unit. In the example shown here, the bearing assembly <NUM>, including the bearing casing <NUM>, is freed for axial movement by the actuation of the external release sleeve <NUM>. The application of force from the actuator tool <NUM>, here via the override tool interface <NUM> and the tool stem <NUM> driven by the piston <NUM>, drives the entire roller screw assembly <NUM>, including the bearing assembly <NUM>, axially. Accordingly, even in an event of failure of the roller screw assembly <NUM> or component thereof, the override tool <NUM> can be utilised to operate the valve member <NUM>. The valve member <NUM> can be operated between the closed position (e.g. <FIG>) and the open configuration (e.g. <FIG>). It will be appreciated that the embodiment shown in <FIG> has the roller screw assembly <NUM> being pushed in unison as a single unit to move the valve member <NUM> to the open position. Accordingly it is only necessary for the override tool <NUM> to contact the override tool interface <NUM> to push the roller screw assembly <NUM>; and not necessarily grip the override tool interface <NUM>. However, it will also be appreciated that where the override tool <NUM> engages the override tool interface <NUM> to grip the override tool interface <NUM>, the roller screw assembly <NUM> may additionally be pulled (e.g. to close the valve by pulling the valve member <NUM> from the position of <FIG> to the position of <FIG>). Likewise, in at least some examples, it will also be appreciated that the override tool <NUM> may engage the override tool interface <NUM> to apply torque to the override tool interface <NUM>. Accordingly, in at least some examples, the override tool <NUM> may be used to rotate the roller screw assembly <NUM>, or a component thereof (such as the roller screw). Such rotation may be used to axially move at least a component of the roller screw assembly <NUM>, or assist therein.

<FIG> shows a further embodiment of an actuator <NUM> generally similar to that <NUM> shown in <FIG>. The actuator <NUM> of <FIG> shares features common to the embodiment <NUM> of <FIG>, with those features represented by reference numerals incremented by <NUM>. For example, the actuator <NUM> comprises a roller screw assembly <NUM> with a roller screw <NUM> and a roller nut <NUM>. Not all features common to both embodiments are repeated here to maintain brevity and clarity. Operation of the actuators <NUM>, <NUM> is generally similar, with override possible by an override tool.

The example <NUM> shown here does not comprise an external release sleeve, in contrast to that <NUM> of <FIG>. As shown in <FIG>, and in detail in <FIG>, the actuator <NUM> here is configured for release of the bearings assembly <NUM> by releasing an axial stop, here the backplate <NUM>. Accordingly, similar to the previous examples of overriding the actuator <NUM> (as shown here, also comprised in an actuator linear drive module (ALDM)), the method of override involves the release of the roller screw assembly <NUM> by releasing the bearing assembly <NUM>. The backplate <NUM> has a predefined weakness in the form of an undercut <NUM>, as shown in detail in <FIG>. It will be appreciated that the undercut <NUM> extends around the entire circumference of the backplate <NUM> in the example shown; although in other examples partial undercuts, or multiple discrete undercuts may be used. As shown in <FIG>, the undercut is supported - here with a pair of half-rings <NUM> extending around in the annular space provided by the undercut <NUM>. The backplate <NUM> here has a guide groove <NUM>. The guide groove <NUM> assists in positioning a release tool <NUM>, shown here as a core bit. As shown in <FIG>, and in detail in <FIG>, an inner wall <NUM> of the ROV bucket also assists in guiding and supporting the release tool <NUM>. The release tool <NUM> can be used to free the bearings assembly <NUM> by releasing the backplate <NUM> - shown in <FIG> by rotating the core bit of the release tool <NUM> to cut into the backplate <NUM>, guided by the guide groove <NUM>. As shown here, the bearing assembly <NUM> has a bearings sleeve <NUM> configured to transfer loads and keep the bearings <NUM> pre-loaded.

As shown in <FIG>, the core bit of the release tool <NUM> only needs to penetrate the backplate <NUM> to the undercut <NUM>. Although shown here as having an inner diameter corresponding to the core bit of the release tool <NUM> (and the groove guide <NUM>), it will be appreciated that in other examples, the undercut <NUM> may extend into a smaller diameter - such as to allow for additional tolerance in the positioning and/or cutting of the core bit of the release tool <NUM>. Once the backplate <NUM> has been cut by the core bit of the release tool <NUM> as far as the undercut <NUM>, the bearings assembly <NUM> is released relative to the housing <NUM> - together with an inner portion of the backplate <NUM> that is still attached to the bearing assembly <NUM>.

Once the release tool <NUM> has released the bearing assembly <NUM>, as shown in the configuration of <FIG>, the actuator <NUM> is in a generally similar configuration to that shown in <FIG> and <FIG> - with the roller screw assembly <NUM> able to move axially as a unit together with the bearing assembly <NUM>. With the backplate <NUM> released as described above and shown in <FIG>, the roller screw assembly <NUM> is no longer prevented from axial movement as a unit. In the example shown here, the bearing assembly <NUM>, including the bearing sleeve <NUM>, is freed for axial movement by the cutting of the backplate <NUM>. It will be noted here that where the axial stop <NUM> normally prevents axial movement of the bearings assembly <NUM> (and roller screw assembly <NUM>), the valve-side axial stop <NUM> is connected to the backplate <NUM> such that release of the central portion of the backplate <NUM> also releases the axial stop <NUM> at the other end of the bearings assembly <NUM>. Accordingly, as shown sequentially in <FIG>, an override tool <NUM> can be used to engage the external interface <NUM> of the actuator <NUM> to control the valve <NUM> with the actuator <NUM>. As shown in <FIG>, the override tool <NUM> has a tool stem <NUM> that can be extended to engage the external interface <NUM>, as shown in <FIG> - with the actuator <NUM> and override tool <NUM> in generally similar positions to that shown in <FIG>.

Accordingly, pressurisation of the chamber <NUM> causes the piston <NUM> connected to the tool stem <NUM> to move relative to the override tool cylinder housing <NUM>. As shown in the transition from <FIG>, axial movement of the piston <NUM> (to the right as shown) causes axial movement of the tool stem <NUM>, here a stem rod, and actuation of the actuator <NUM> via the actuator override tool interface <NUM>.

The application of force from the actuator tool <NUM>, here via the override tool interface <NUM> and the tool stem <NUM> driven by the piston <NUM>, drives the entire roller screw assembly <NUM>, including the bearing assembly <NUM>, along with the central portion of the backplate <NUM>, axially. Accordingly, even in an event of failure of the roller screw assembly <NUM> or component or control thereof, the override tool <NUM> can be utilised to operate the valve <NUM>. The valve member <NUM> can be operated between the closed position (e.g. <FIG>) and the open configuration (e.g. <FIG>). It will be appreciated that the embodiment shown in <FIG> has the roller screw assembly <NUM> being pushed in unison as a single unit to move the valve member <NUM> to the open position. Accordingly it is only necessary for the override tool <NUM> to contact the override tool interface <NUM> to push the roller screw assembly <NUM>. However, here, it will also be appreciated that the override tool <NUM> can engage the override tool interface <NUM> to grip the override tool interface <NUM>, such that the roller screw assembly <NUM> can also be pulled (e.g. to close the valve <NUM> by pulling the valve member <NUM> from the position of <FIG> to the position of <FIG>).

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.

Claim 1:
A subsea electrical actuator for providing a subsea electrical actuation of a valve, the actuator comprising:
a screw assembly comprising a screw and a threaded part for receiving the screw;
a housing for the screw assembly;
an axial stop for preventing axial movement relative to the housing of at least one of the screw and the threaded part;
a primary drive for providing a rotational movement to the screw assembly in a normal mode of operation, the screw assembly converting the rotational movement to an axial movement of a valve member relative to the housing;
an override for operating the actuator in an override mode of operation, the override being configured to release at least one of the screw and the threaded part for axial movement relative to the housing and wherein the screw comprises a roller screw and the threaded part comprises a roller nut; and the override is configured to release the axial stop to release at least one of the roller screw and the roller nut for axial movement relative to the housing.