This invention relates to the remote operation of control elements, such as valves, of subsea equipment as used in the offshore oil and gas industry. The invention is particularly concerned with the challenges of operating multiple control elements at locations deep underwater.

Subsea structures used in hydrocarbon production, such as manifolds or Christmas trees (X-trees), comprise several valves that require actuation to be opened, closed or otherwise adjusted from time to time. Subsea valves may be operated manually by divers in shallow water applications or by remotely operated vehicles (ROVs) in deep water applications. However, deploying a diver or an ROV requires costly support, involves operational risk, and is only possible over a protracted timescale as it requires extensive planning and relocation of resources. Thus, conventionally, routine operation of the valves of subsea equipment is entrusted to remote control systems, leaving a diver or an ROV to be deployed only as a back-up provision.

Each valve comprises a body or housing containing a valve element, such as a gate or a ball, and a stem or a shaft to move the valve element, usually by rotation although rotation may also cause translational movement of a valve element. Valves additionally comprise a drive arrangement for moving the stem or shaft and hence the valve element. For example, a subsea valve may comprise a drive formation (known in the art as a ‘bucket’) that can be engaged directly by a torque tool of an ROV to transmit torque that turns the stem or shaft. Additionally, or instead, a subsea valve may comprise a built-in actuator that acts on the stem or shaft to drive the motion of the valve element required to open or close the valve. The actuator can be powered and energised by an ROV, or remotely. Often, a bucket in provided in addition to an actuator so that the bucket can be used as an override if the actuator fails.

Commonly, remote control of the valves of subsea equipment is effected by hydraulic circuits that operate hydraulic actuators remotely, one for each valve. For example, an electro-hydraulic control system comprises a hydraulic power unit at the surface, a subsea control unit, and an umbilical that conveys power and control signals from the hydraulic power unit to the subsea control unit. However, this solution is complex, heavy and requires long and expensive umbilical connections extending from the surface to the seabed. In view of the complications of hydraulic control, electric control systems and electrically actuated valves are finding increasing acceptance in the field of subsea engineering. In such systems, each subsea valve has an electric actuator connected to a subsea power grid that conveys electrical power and remote-control signals to the actuators. The grid is powered via a subsea cable or a simple umbilical that connects the subsea system to a source of electrical power located underwater or at the surface. Whilst simpler and less bulky than a hydraulic system, electric control systems with electrically actuated valves remain complex and expensive.

Another approach to controlling multiple control elements such as valves is to employ a shared actuation (SAC) system. In known SAC systems, an actuation tool is moved from valve to valve and into engagement with a selected individual valve to be actuated, whenever actuation of that valve is required. For this purpose, an electro- hydraulic control system uses Cartesian coordinates to move the actuation tool into alignment and engagement with a selected valve.

As an example of an SAC system, GB 2284839 discloses a common actuator that is shared between all of the valves of an item of equipment and can circulate on a guide to actuate any of those valves. Similarly, US 10570701 discloses a unique actuator that moves from valve to valve on a frame whereas in EP 3317489 and EP 3165709, a robotic arm can move to actuate individual valves of a set. Individual actuators associated with each valve can therefore be omitted. Thus, an SAC system could, in principle, employ only manual valves without individual actuators. However, at the cost of further complication, an SAC system could instead be used as a back-up to a system in which valves are equipped with actuators.

Prior art SAC solutions such as these are also bulky, complex and inflexible, requiring bespoke design and fabrication to suit a particular layout of valves and to enable a single actuator to be moved from valve to valve. They also suffer from the drawback of only allowing sequential valve actuation, meaning that they cannot allow simultaneous actuation of two or more valves. This wastes time in routine operation and introduces a time lag that could be crucial in an emergency shut-down situation, for example.

GB 2596530 discloses a system that is capable of controlling at least one subsea actuator associated with a wellhead. The system can output mechanical drive from a single source to control multiple subsea actuators simultaneously. However, the direction of movement of the actuators is aiways dependent upon the direction of the drive from the source. This undermines operationai flexibility.

Against this background, the invention resides in a subsea control mechanism comprising a transmission system for transmitting drive from a common input to two or more outputs. Each output may comprise an interface formation arranged to be advanced into engagement with a control element of a subsea structure. The transmission system comprises two or more branches, each for conveying drive to a respective one of the outputs. Each branch comprises a respective coupling upstream of the respective output, the couplings being selectively operable, preferably electrically, to engage each output with, or to disengage each output from, drive transmitted from the input. Each branch further comprises a respective drive reverser. The drive reversers of the branches are selectively operable to reverse drive transmitted from the input.

The mechanism may further comprise at least one drive splitter downstream of the input for dividing drive from the input between the branches. The branches may extend from a common drive distribution rail downstream of the input. Each branch may further comprise a respective position sensor arranged to output a feedback signal representing angular position of the respective output. A controller may be provided for controlling operation of the couplings and/or the drive reversers, and for receiving feedback signals from the sensors.

A drive source such as an electric motor may be provided for providing drive to the input. The drive source may be a module that is arranged to be advanced into engagement with the input, that engagement then being effected by complementary interface formations.

The transmission system could be modular, for example comprising a series of shafts connected by nodes that can be configured in various ways. For example, at least one of the shafts may be of variable length.

At least one of the nodes may divide the drive from an upstream shaft between two or more downstream shafts. The upstream shaft and at least one of the downstream shafts may be in mutually orthogonal relation. More generally, at least one of the nodes may redirect the drive from an upstream shaft to at least one downstream shaft that lies on a different axis to the upstream shaft. For example, the upstream and downstream shafts could be in mutually orthogonal relation.

The mechanism may comprise an assembly of at least two shafts in mutual alignment, which shafts may differ from each other in length. Such an assembly can distribute drive to the branches. The branches may be mutually parallel but horizontal and vertical spacing between the branches may vary.

The mechanism may further comprise a frame that is capable of supporting any of the aforesaid components of the mechanism. This allows the mechanism to be attached to the subsea structure as a unit, and potentially to be attached to the subsea structure underwater.

The inventive concept extends to subsea structures fitted with the mechanism of the invention, and also embraces a method of controlling a subsea system. That method comprises: transmitting drive mechanically from a common drive input toward two or more control outputs engaged with control elements of the subsea system; selectively engaging each control output with, or disengaging each control output from, drive transmitted from the drive input to control movement of the control elements; and selectively reversing the drive transmitted from the common drive input to reverse motion of at least one of the control outputs without reversing the direction of drive at the common drive input. Preliminarily, a drive source may be coupled to the drive input underwater.

The drive may be divided downstream of the drive input and upstream of the control outputs.

The drive may be transmitted through a subsea control mechanism that comprises the drive input and the control outputs linked by a transmission system comprising shafts connected by nodes. Preliminarily, such a mechanism may be attached, as a unit, to the subsea system underwater. The method of the invention may comprise a further preliminary step of configuring the mechanism to position the control outputs in alignment with the control elements of the subsea system. This may be achieved by changing or selecting lengths of the shafts, and/or by changing or selecting a quantity of shafts and/or nodes. In summary, preferred embodiments of the invention provide a subsea low-profile shared actuation system that employs a single or common electrical actuator shared between a plurality of electrically activated couplings. The actuator and the couplings are assembled into a drive system to operate a plurality of subsea control elements such as valves installed on a subsea structure or tree. In exemplary embodiments, the system compromises the following main components, namely: a drive system; at least one electrical actuator; electrically activated couplings; rotary position sensors; and standardised interfaces to subsea valves.

The system can operate one or more subsea valves by activating one or more of the couplings. The couplings could work on the principle of any clutch used in rotating machinery. The rotary position sensors provide subsea valve position feedback to a control system. The system could be installed with more than one electrical actuator to provide redundancy and to increase system availability.

Thus, the invention addresses the challenges of electrical operation of two or more subsea valves installed on a subsea structure or tree using a single or common electrical actuator such as an electric motor.

The approach of the present invention is akin to prior art SAC solutions in that the invention shares one actuation system between two or more valves to drive movement of their valve elements, thus providing an alternative to individual electrical or hydraulic actuation of each valve. However, the invention provides a notably simpler and more flexible and effective solution than in the SAC prior art. The invention provides a resident valve actuation system that requires no hydraulic power or hydraulic fluid and that can easily be designed to retrofit an existing structure.

The invention also has the time-saving benefit of enabling any of the valves to be actuated without the delay of relocating an actuator from one valve to another, and the major time-saving benefit of enabling two or more valves of a set to be actuated simultaneously. Indeed, in principle, the invention could actuate an entire set of several valves simultaneously.

Embodiments of the invention provide a mechatronic valve actuation system for actuating multiple valves of a subsea structure. The valve actuation system comprises: a frame mounted on the subsea structure; couplings, which may be electrically activated, mounted on distinct valve actuators or valve stems; a rotary power source comprising at least one motor on the frame; and a transmission system, which may comprise shafts and gears, to transmit torque from the rotary power source to the couplings. The rotary power source can simultaneously rotate multiple valves via the transmission system and the couplings, and may also be electrically powered.

Elegantly, the couplings can clutch the valve actuators or stems individually to the transmission system or de-clutch the valve actuators or stems individually from the transmission system, thus allowing individual control of each valve.

The rotary power source can change its direction of rotation to change the direction of rotation of the actuators or stems. The transmission system, or the couplings, can also be arranged to reverse the direction of incoming drive to change the direction of rotation of any of the actuators or stems.

Electrical power for the motor and control signals for the motor, the couplings and/or other parts of the transmission system may be provided via an umbilical or a subsea cable.

The valve actuation system may also comprise at least one torque sensor, mounted on the motor, the couplings and/or other parts of the transmission system. A control system for controlling the couplings and/or other parts of the transmission system may be located on the actuation system or remotely.

Conveniently, the valve actuation system can be decoupled from the subsea structure to be removed or replaced if required.

Thus, the invention provides a subsea control mechanism comprising a transmission system for transmitting drive mechanically from a common drive input to multiple control outputs engaged with respective control elements of a subsea system, such as a manifold. The transmission system comprises multiple branches, each conveying drive to a respective one of the outputs. Each branch includes a coupling that is operable individually to engage the associated output with, or to disengage that output from, drive transmitted from the input. Each branch further includes a respective drive reverser. The couplings selectively engage the outputs with, or disengage the outputs from, drive transmitted from the input to control movement of the control elements individually. The drive reversers of the branches are selectively operable to reverse drive transmitted from the input to allow simultaneous control movement of the control elements in opposite directions.

In order that the present invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings in which:

Figure 1 is a diagrammatic view of a subsea control system of the invention comprising first and second valves, each shown here in a closed state;

Figure 2 corresponds to Figure 1 but shows both of the valves driven into an open state by application of torque to a common actuation point;

Figure 3 corresponds to Figure 2 but shows only the second valve driven into an open state by application of torque to the common actuation point, the first valve being left closed by disengaging a coupling disposed between the first valve and the actuation point;

Figure 4 corresponds to Figure 3 but shows the second valve driven back into a closed state by continued unidirectional application of torque to the actuation point, by virtue of activating a drive reverser disposed between the second valve and the actuation point;

Figure 5 is a perspective view of a practical embodiment of the invention;

Figure 6 is a perspective view showing how the embodiment of Figure 5 is tailored to suit the layout of control elements on a subsea X-tree structure;

Figure 7 is a perspective view of a further practical embodiment of the invention, also showing the system engaged with an array of subsea valves; and

Figure 8 is a perspective view showing how an embodiment like that in Figure 7 can be extended to suit the layout of control elements on a subsea manifold structure.

Referring firstly to the diagrammatic views of Figures 1 to 4, these drawings illustrate the principles of the invention in a simplified form. In each case, a subsea control system 10 of the invention comprises a drive input 12 defined by a common actuation point and a plurality of drive outputs 14 exemplified here by interface formations 16 that are shaped to cooperate and engage with complementary formations such as buckets 18 of respective subsea valves 20A, 20B, As is conventional, the valves 20A, 20B are shown here shaded black when closed and white when open.

The valves 20A, 20B are supported by a subsea structure 22 such as a manifold or X- tree. Optionally, the valves 20A, 20B also have individual actuators 24 for redundancy, as shown in dashed lines, but the invention has no need for such actuators 24, and indeed has the benefit that such actuators 24 can be omitted if desired.

In these examples, the subsea control system 10 is shown schematically by a box in broken lines. Those dashed lines could also represent a structural frame that supports the components of the subsea control system 10 and that could be attached to the subsea structure 22, for example by releasable connectors 26 also shown schematically here in broken lines. In this way, the subsea control system 10 can be readily removed, recovered and replaced as a unit or module without disturbing the subsea structure 22.

An electrically-driven actuator module 28 is coupled to the common actuation point that defines the drive input 12. In this example, the actuator module 28 is removable so that it can be recovered and replaced without disturbing the subsea control system 10 or the subsea structure 22. To this end, the actuator module 28 has an interface formation 30 that is shaped to cooperate and engage with a complementary formation of the common actuation point, such as a bucket 32. In other examples, the actuator module 28 could be integrated with the subsea control system 10 and so may conveniently be supported by a structural frame of the subsea control system 10.

A transmission system 34 transmits rotary drive applied to the input 12 by the actuator module 28 in a downstream direction from the input 12 to the outputs 14. The transmission system 34 therefore comprises at least one drive splitter 36 that divides the drive between branches 38 that lead to, and terminate in, the respective outputs 14. The drive splitter 36 therefore divides the drive energy entering the system 10 at the input 12 into portions that are conveyed along the respective branches 36 to the outputs 14. The branches 38 are parallel in function but are not necessarily parallel or co-planar in disposition as shown in these drawings. As later examples will show, there could be many more than two valves 20A, 20B and hence a corresponding number of branches 38 leading to respective outputs 14.

In addition to the splitter 32, each branch 38 comprises a series of components interspersed or alternating with shafts 40 that transmit drive downstream from one component to the next. Two such shafts 40 radiate from the splitter 36 in mutually- opposed directions and in mutual alignment. Together, the splitter 36 and the shafts 40 that extend from it may be regarded as a distribution rail that distributes drive between the branches 38. Each of those shafts 40 terminates in a joint 42 that transmits drive between mutually misaligned shafts 40, in this case between shafts 40 that are in mutually orthogonal relation and hence through an angle of 90°.

Each branch 38 further comprises a coupling 44 upstream of the respective output 14. The coupling 44 comprises an individually-operable clutch mechanism 46 that can be engaged to transmit drive from the input 12 to the associated output 14 or disengaged to interrupt drive from the input 12 to that output 14. The clutch mechanism 46 comprises mutually-opposed friction plates in this simplified example but could comprise any suitable mechanical, electromechanical or electrohydraulic clutch arrangement, for example a magnetic coupling.

Each branch 38 further comprises a drive reverser 48 as shown in broken lines. The drive reverser 48 may, for example, be a simple gearbox with a selectable reverse gear. Each drive reverser 48 is placed upstream of the output 14 of each branch and may be disposed upstream or downstream of the coupling 44 of each branch 38. The drive reversers 48 are operable individually to reverse the angular direction of rotary drive between an upstream shaft 40 and a downstream shaft 40 in each branch 38, thus reversing the direction of drive between the input 12 and the associated output 14. In this way, unidirectional rotary movement at the input 12 can both open and close a valve 20A. 20B, without requiring reversal of rotary movement at the input 12 or affecting the direction of rotation of the other outputs 14.

The splitter 36, the joints 42 and the drive reversers 48 may perform their functions by virtue of various mechanisms such as meshed gear arrangements comprising bevel gears or other suitable gear elements. Gearing ratios between the input and output of any of those components can be in any desired relation, for example 1 :1 or a reduction ratio in which a shaft downstream of a component turns more slowly than a shaft upstream of that component, it may also be possible to vary the gearing ratio of any such component continuously or in steps, under individual control, so as to adjust the speed of rotation of one output 14 relative to another output 14. Usefully, reduction gearing may reduce fast rotation from the actuator module 28 at the input 12 to slower rotation at the outputs 14, hence also multiplying torque exerted by the actuator module 28 at the input 12.

Operation of the couplings 44 and the drive reversers 48 is controlled individually by a controller 50 that may also control the actuator module 28 as shown. Control inputs and feedback signals may be conveyed to the controller 50 via an umbilical or subsea cable that also conveys power to the actuator module 28.

The controller 50 can be integrated into the subsea control system 10 and hence may be at a subsea location in use or may be located above the surface in use, for example on a platform or FPSO that receives hydrocarbon production fluids from the subsea structure 22. Different elements of the controller 50 could instead be distributed between subsea and surface locations. For example, control inputs will usually originate from a control room aboard a platform or FPSO but in principle such inputs could originate from anywhere, such as a control room on land.

Figure 1 shows a starting state in which, by way of example, both of the valves 20A and 20B are closed. If it is decided to open both of the valves 20A and 20B as shown in Figure 2, this is achieved simply by activating the actuator module 28 to apply torque to the input 12 in the appropriate direction of rotation. The splitter 36 divides the torque into the branches 38, where it is transmitted to the outputs 14 by the successive shafts 40 all turning in the same direction of rotation. Thus, with a single torque input, the outputs 14 and hence the buckets 18 are driven simultaneously in the angular direction that is appropriate to open the respective valves 20A, 20B.

It will be appreciated that this arrangement is simple but highly effective and saves a great deal of time compared with the sequential valve operation inherent in SAC systems of the prior art, especially in arrangements that have many more than two valves 20A, 20B.

Similarly, the valves 20A and 20B can be closed simultaneously simply by operating the actuator module 28 in reverse. Alternatively, as the branches 38 comprise respective drive reversers 48, the drive imparted by the actuator moduie 28 need not be reversed, instead, the drive reversers 48 can be operated simultaneously to reverse the direction of rotation of the outputs 14 and hence the buckets 18 relative to the direction of rotation at the input 12. This eliminates the need for the drive imparted by the actuator module 28 to be reversed altogether, hence potentially simplifying the actuator module 28 as it would be required to rotate in one direction only.

Figures 3 and 4 illustrate benefits of flexibility arising from independent operation of the couplings 44 and the drive reversers 48. This allows individual outputs 14 to respond differently to other outputs 14 when torque is applied at the input 12, thus allowing individual control of each valve 20A, 20B, and simultaneous control of both valves 20A, 20B without necessarily adjusting the output of the actuator module 28.

Figure 3 presupposes that the starting point was as shown in Figure 1, hence with both valves 20A, 20B closed, and shows how it is possible to keep the first valve 20A closed while opening the second valve 20B. This is achieved by interrupting the transmission of drive along the branch 38 that leads to the first valve 20A while maintaining drive along the branch 38 that leads to the second valve 20B. In this example, drive is interrupted by separating the plates of the clutch mechanism 46 to open the coupling 44 associated with the first valve 20A. The plates of the clutch mechanism 46 of the coupling 44 associated with the second valve 20B remain engaged to convey drive to the second valve 20B through that closed coupling 44.

Figure 4 presupposes that the starting point was as shown in Figure 3, hence with the first valve 20A closed and the second valve 20B open. This drawing shows how it is possible now to close the second valve 20B without reversing the actuator module 28 or disturbing the first valve 20A. Again, the coupling 44 associated with the first valve 20A is held open to interrupt transmission of drive along the branch 38 that leads to the first valve 20A; and again, the coupling 44 associated with the second valve 20B remains closed, with the plates of its clutch mechanism 46 engaged to transmit drive through that coupling 44. In this instance, however, the drive reverser 48 in the branch 38 leading to the second valve 20B is activated to reverse drive along that branch 38. Thus, the second valve 20B is closed without reversing the drive imparted to the input 12 by the actuator module 28.

It will be apparent that with both couplings 44 closed and one of the drive reversers 48 activated, it would be possible to open one valve 20A at the same time as closing the other valve 20B, while operating the actuator module 28 in a single direction of rotation. Thus, the valves 20A, 20B can not only be operated simultaneously but potentially can be operated to pursue different or opposed outcomes at the same time. More generally, operation of one valve 20A is not dependent on operation of the other valve 20B. More generally still, operation of any one or more of a set of valves is independent of the operation of any other valve or valves of that set, even though all of the valves can be driven by a single driving input.

Moving on now to Figures 5 to 8, these drawings show practical applications of the concepts explained above and illustrated in Figures 1 to 4. Like numerals are used for like features.

The embodiments shown in Figures 5 to 8 omit the controller 50 for clarity but add torque sensors or position sensors 52 for providing control feedback signals to the controller 50. The sensors 52 are shown here mounted conveniently on the couplings 44 of each branch 38 but in principle they could be located elsewhere in each branch 38 of the transmission system.

Whilst Figures 5 to 8 do not show drive reversers 48, such drive reversers 48 can be included in the embodiments shown in those drawings. .

In Figures 5 to 8, the subsea control system 10 is shown without a supporting frame. Such a frame may be added if required or could be omitted if the components of the system 10 are self-supporting. For example, the shafts 40 could turn within fixed structural tubes that rigidly link the components and so together define a frame.

The subsea control system 10 shown in Figures 5 and 6 is arranged to suit the positions of control elements on a subsea X-tree structure 54 shown in Figure 6. The control elements are exemplified here by sockets or buckets 18 that are connected to valves 20 hidden within the structure 54.

It will be noted that the buckets 18 all lie on a planar face of the structure 54, although this will not necessarily always be the case. However, the buckets 18 are in an irregular array in which some buckets 18 do not lie on the same vertical or horizontal axes as other buckets 18. Also, the arrangement of buckets 18 in the array, and indeed the number of buckets 18 in the array, may vary from one structure 54 to another. It follows that the positions of the outputs 14, defined by formations on the couplings 44 complementary to the buckets 18, must also match the positions of the buckets 18 in at least two dimensions and possibly three dimensions. It also follows that the number of outputs 14, and hence branches 38, in the system 10 may vary between applications to suit the number of buckets 18 on a particular structure 54.

In view of these challenges, it is advantageous that the assembled components of the system 10 together form a modular frame in which the shafts 40, analogous to struts, are joined by other components such as splitters 36 or joints 42, analogous to nodes. The shape and dimensions of the frame can be adjusted simply by changing the lengths of individual shafts 40 to change the spacing between one component and the next in the drivetrain. Indeed, it is possible for the length at least some of the shafts 40 to be variable, for example by telescopic action. This allows a standard shaft 40 to be adjusted readily to different lengths. However, a variety or selection of different fixed- length shafts 40 is also possible.

It is also advantageous that additional splitters 36 can be provided to divide drive into additional branches 38, thus dividing rotary drive from the input 12 between an appropriate number of outputs 14. For this purpose, some splitters 36 output drive to shafts 40 that are not in mutual alignment as shown in Figures 1 to 4. Specifically, in this example, shafts 40 receiving outputs from a first splitter 36A immediately downstream of the input 12 are in mutual alignment like the arrangement shown in Figures 1 to 4 but convey drive to further splitters 36B in mutual alignment along a horizontal first distribution rail 56. Each splitter 36B has a first output to an output shaft 40 that is in horizontal alignment with the input shaft 40 and with the first distribution rail 56 and a second output to a vertical output shaft 40 between, and orthogonal to, both the input shaft 40 and the other output shaft 40. The shaft 40 extending from the second output lies in a vertical plane that also contains the first distribution rail 56.

By turning drive through 90° between the input shaft 40 and one of the output shafts 40, the splitters 36B are analogous to joints 42 but with an additional output. Thus, the splitters 36B can not only initiate drive to a respective branch 38 but can also convey drive to one or more further splitters 36 or joints 42 and hence to further branches 38 and outputs 14.

Similarly, the first distribution rail 56 terminates in upper joints 42 that turn drive through 90° in the aforementioned vertical plane. Additional lower joints 42 turn drive through 90° out of that plane so that the branches 38 and their associated outputs 14 all extend horizontally and in parallel toward the structure 54.

Differences in horizontal spacing between outputs 14 are effected by varying the lengths of the horizontal shafts 40 in the first distribution rail 56. Conversely, differences in vertical levels of the outputs 14 are effected by varying the lengths of the vertical shafts 40 downstream of the first distribution rail 56.

It will be noted that one of the splitters 36B in the first distribution rail 56 transmits drive to a second, vertical, distribution rail 58 that contains an additional splitter 36B, hence transmitting drive to vertically-stacked outputs 14 along respective branches 38.

Further to illustrate the adaptability of the inventive concept, Figures 7 and 8 show a subsea control system 10 that is arranged to suit the positions of control elements on a subsea manifold 60 shown in Figure 8. The control elements are exemplified here by sockets or buckets 18 that surmount respective valves 20 of the manifold 60. The valves 20 are shown in Figure 7 engaged with the couplings 44 defining outputs of the system 10. The system 10 shown in Figure 7 is shorter than the system 10 shown in Figure 8 and has fewer branches 38, and hence outputs, but it will be apparent that their layouts are otherwise essentially identical.

In the example shown in Figures 7 and 8, a splitter 36A divides rotary drive from an input 12 and feeds that drive along a first distribution rail 62 disposed between, and orthogonal to, parallel further distribution rails 64. The distribution rails 62, 64 all lie in a common horizontal plane in this example. The first distribution rail 62 has splitters 36A at each end that divide the drive between sections of the further distribution rails 64.

Each of the further distribution rails 64 comprises at least one splitter 36B between joints 42 that distribute and turn the drive onto respective branches 38, each branch 38 terminating in a respective coupling 44 that selectively outputs drive to the valves 20. As Figure 8 makes clear, extending the length of the further distribution rails 64 and the number of branches 38 is simply a matter of adding the necessary number of further splitters 36B and shafts 40 in longitudinal series.

Several variations have been described above but many other variations are possible within the inventive concept. For example, the couplings 44 and the drive reversers 48 could be positioned adjacent to a splitter 36 or could be integrated with a splitter 36, for example as parts of a gearbox unit with multiple outputs corresponding to each branch

38.