GB2328492A

GB2328492A - Electrothermal actuator

Info

Publication number: GB2328492A
Application number: GB9717944A
Authority: GB
Inventors: Peter John Davey; James Brian Wilson; David John Luckhurst
Original assignee: ABB Seatec Ltd
Current assignee: Baker Hughes International Treasury Services Ltd
Priority date: 1997-08-22
Filing date: 1997-08-22
Publication date: 1999-02-24
Anticipated expiration: 2017-08-22
Also published as: NO983835L; GB2328492B; GB9717944D0; NO983835D0

Abstract

. An electro-thermal actuator 40, for use in subsea pipeline valve actuation, comprises a piston 43 displaced by controlling heating elements 59 to heat a phase change wax M. The wax expands by 15 - 20% in volume between 60C and 70'C. Displacement of piston 43 is communicated to a drive rod 49, by drive piston 48 and oil D contained in chambers 66, 67 and 72. When position sensor 75 detects the piston 48 has reached an actuating position, heating elements 59 are switched off and a hydraulic lock 74 is operated to block flow of oil D in a channel 73 locking rod 49. Contraction of wax M as it cools allows a compensation piston 44 to move toward piston 43. Actuator 40 is reset, upon release of the lock 74, by the force of a return spring 76. In a second embodiment (Figure 1) a rotary solenoid and a helical spring are used to lock a drive rod in an actuating position. In this case, actuation occurs directly from a piston rod fixed to an actuating piston. In a third embodiment (Figure 3), rapid de-actuation is obtainable by controlled displacement of a drive fluid into an external reservoir.

Description

Electro-thermal Actuators The present invention relates to electro-thermal actuators and more particularly, although not exclusively, to electro-thermal actuators for use in the actuation of sub sea pipeline valves.

Recovery of oil and gas from underwater wells is often achieved by the use of apparatus collectively known as a "Christmas Tree". This apparatus is connected to the well head and comprises devices which function to monitor conditions such as pressure and temperature, and devices which are controllable to allow the piped flow of displacing agents, such as water, into the well or to allow the piped flow of oil or gas from the well. A Christmas Tree will be connected to an operating station by an "untilical cord", carrying electricaVoptical communication links and both hydraulic and electrical power supply lines.. Monitoring and control of a number of Christmas trees, each associated with a particular well-head, is usually carried out by a single operating station, which may be located on an oil rig or on a ship, or may be shore based.

Valves used in Christmas Tree arrangements are generally operated by actuators which are controlled by an operating station. These actuators, along with the rest of the devices forming the Christmas Tree, are expected to operate for at least twenty years without any maintenance. They are often expected to operate in deep sea locations where water pressures are high and where corrosion of metallic components can be quite rapid. It is desired that, for future designs, Christmas Trees should comprise devices which require only electrical power, so that a hydraulic power supply line need not be built into its associated umbilical cord. However, many electrically powered actuation devices are difficult to design so that they "fail safe", that is adopt a predetermined condition if their power supply fails or there is a failure somewhere in their internal mechanism. Electrically powered actuation devices comprising motors and gears have been found to interfere with communications canied on the electrical power supply line connecting a Christmas Tree and an operating station, which makes their use quite complicated. They also tend to be more susceptible to failure, and hence have a statistically shorter life, than hydraulic powered actuators.

In accordance with a first aspect of the present invention, an electro-thermal actuator comprises an actuator piston supported for movement in a chamber containing a thermal expansion medium, and an electrical heating means controllable to heat the thermal expansion medium to provide a displacement of the piston.

The actuator may further comprise a means to transmit the displacement of the actuator piston to provide a required displacement of a drive means. In this case, the actuator may further comprise locking means controllable to lock the drive means at the required displacement.

The drive means may comprise a drive rod including a threaded portion which is arranged to be aligned, at the required displacement, with a helical locking spring forming part of the locking means. Here, the locking means may further comprise a rotary solenoid operable to tighten the helical locking spring onto said threaded portion.

The actuator may also comprising a position sensor to detect that a predetermined displacement has been reached, means responsive to said detection to control said heating means to substantially cease heating the thermal expansion medium and means similarly responsive to control said locking means to lock the drive rod at the required displacement.

Alternatively, displacement of the actuator piston may be transmitted to the drive means by a drive fluid associated with the actuator piston. In this case, the drive means may comprise a drive piston and displacement of the actuator piston may be translated to a required displacement of the drive piston by the drive fluid. The locking means of the actuator may comprise fluid control means controllable to block flow of the drive fluid and thereby lock the drive means. The fluid control means may comprise any form of electrically controllable valve such as a ball valve, a gate valve or a check valve. The actuator may further comprise a compensation piston supported for movement in the chamber to allow the volume of the thermal expansion medium to change without substantial displacement of the actuator piston. The actuator may further comprise a position sensor to provide a signal indicative of a predetermined displacement having been reached, means responsive to said signal to cease heating the thermal expansion medium and means similarly responsive to control said fluid control locking means to lock the drive means at the required displacement. In this case, control of the fluid control means to lock the drive means may allow movement of the compensation piston.

This feature will allow the volume of the cooling thermal expansion medium to change without movement of the actuator piston. Where the drive means comprises a drive piston, the actuator may further comprise a reservoir fluidly connected to a chamber adjacent the drive piston containing the drive fluid by a channel including fluid control means controllable to allow or to block flow of the drive fluid between the reservoir and the drive fluid containing chamber. The fluid control means may comprise any form of electrically controllable valve such as a ball valve, a gate valve or a check valve. This actuator may further comprise a position sensor to provide a signal indicative of a predetermined displacement having been reached, and means responsive to said signal to control the electrical heating means to heat the thermal expansion medium to substantially retain said predetermined displacement. Preferably, control of the fluid control means allows flow between said drive fluid containing chamber and said reservoir to allow said drive piston to move to a non-actuating displacement. Here, deactuation can be rapid even when the thermal expansion medium is in its heated state.

The thermal expansion medium may comprise a phase-change wax. The term "phase change wax" will be understand by the skilled person to mean a wax material which shows a notable increase in volume during transition from a solid state to a liquid state. The thermal expansion medium may alternatively comprise a material having a boiling point around or less than 50 C above a temperature at which the actuator is to be operated.

In accordance with a second aspect of the present invention, the combination of a control device, movable between actuated and unactuated positions and an actuator, in accordance with the first aspect, further comprises fail safe spring means arranged to bias the device into the unactuated position, the actuator being operable to move the device into the actuated position.

In accordance with a third aspect of the present invention, a method of actuating a control device comprises electrically heating a thermal expansion medium, and using the expansion of the medium to actuate the control device.

In accordance with a fourth aspect of the present invention, a method of actuating a remotely located control device comprises conducting an electrical energy supply to an actuate associated with the control device, using the electrical energy supply to heat a thermal expansion medium arranged within the actuator, thereby changing its volume, and using the change in volume of the medium to actuate the control device.

In accordance with a fifth aspect of the present invention, a method of actuating a control valve device of an underwater installation from a remote surface based station comprises conducting an electrical energy supply from the remote station to a position adjacent the control valve, using the electrical supply to heat a thermal expansion medium, and using the expansion of the medium to actuate the control valve device.

Preferably, a fail safe method in accordance with any of the third, fourth and fifth aspects of the present invention has the feature that interruption of the electrical energy supply will allow the control device to return to an unactuated position. Alternatively or additionally, the method may comprise locking the control valve in a predetermined actuated position and then interrupting the electrical energy supply used for heating the medium. In this case, the method may further comprise using an electrical locking signal to lock the control valve in the predetermined actuated position whereby interruption of the electrical locking signal will allow the control device to return to an unactuated condition.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is an axial section through a first embodiment of an e1ectrthermal actuator in accordance with the present invention; Figure 2 is an axial section through a second embodiment of an electro-thermal actuator in accordance with the present invention; Figure 3 is an axial section through a third embodiment of an electro-thermal actuator in accordance with the present inventionl; and Figure 4 is an axial section through a typical subsea valve connected to the actuator of Figure 1.

Referring first to Figure 1, an actuator 1 is shown comprising a piston 2 slidably mounted in a cylindrical bore 3 defined by a body 4. A chamber 5, defined by the left face of piston 2 with the right face of an end plug 6 and the bore 3, contains a thermal expansion medium M and a plurality of electrical heating elements 7. A pressure transducer 8 and a temperature transducer 9 are arranged to observe the pressure and the temperature respectively of the thermal expansion medium M by way of unshown channels through the end plug 6. The heating elements 7 are connected to an electrical power connection 10 through other unshown channels. Ring seals 11 and 12 are located on the plug 6 and on the piston 2 respectively, to prevent leakage of the thermal expansion medium from the chamber 5.

In this embodiment, the thermal expansion medium is a phase change wax taken from a very narrow cut in the distillation of linear synthetic hydrocarbons, i.e. an 'alcane'. Such waxes are used by the automotive industry in thermostatically controlled valves, as well as being used in domestic radiator valves and other small temperature sensitive mechanisms. These waxes are suitable because they have a low compressablilty and good expansion properties. For example, a wax exhibiting a 2S 25% increase in volume when heated from 60 C to 70"C is envisaged as being suitable for subsea applications, although a different cut may equally well be selected. This alternative selection would simply provide a different temperature range over which the wax changes phase, or a different percentage increase in volume.

A piston rod 13, having a perforated flange 14 adjacent its left end, is supported by a bush 15 for sliding relative to the actuator body 4. A second piston 16 is attached to the piston rod 13 to be carried thereby in a further cylindrical bore 17 also defined by the actuator body 4. The piston 16 also carries a ring seal 18. Thus, the piston rod 13 is operable to displace the piston 16 along the bore 17 to the same extent as the piston 2 is displaced along the bore 3, although it should be noted that the piston 2 is not fixed either to the rod 13 or the flange 14. A return spring 19 is located within the bore 3 to apply continuously a leftward force on the flange 14 by reacting against the actuator body 4. A drive rod 20, having a threaded portion 21, is movable axially along the bore 17 to transmit displacement of the piston 2 to actuate a valve (shown in Figure 4, described below).

A chamber 24 is defined by the piston 2, the bore 3, the drive rod 13 and the actuator body 4. The chamber 24 is filled with a lubricating oil which is displaceable through a channel 27, into a chamber 25 within a flexible bellow 26, and through an unshown channel formed in the bush 18 into a chamber 28 adjacent the piston 16. The purpose of this oil is to prevent the ingress of sea water into the actuator body 4, which could cause corrosion of the moving parts thereinside. A heat insulation sleeve 33 surrounds the actuator body 4 to retain thermal energy within the chamber 5, thereby minimising actuation time and contributing to the energy efficiency figure.

The operation of the actuator 1 will now be described with reference to the same Figure, which shows a non-actuating position. To provide actuation, control means (not shown) cause the heating elements 7 to be provided with electrical energy such that they become effective to heat the wax. The expansion thereby caused increases the pressure of the wax in the chamber 5 relative to the pressure of the oil in the chamber 24 such that the piston 2 is displaced to the right. This displacement is transmitted by the piston rod 13 and the piston 16 to the drive rod 20. The heating elements 7 are controlled by the unshown control means to continue heating the wax until a position sensor 29 detects that a known displacement of the piston 2, and hence a required displacement of the drive rod 20, has been reached. This detection, as well as initiating the controlled switching off of the heating elements 7, is used to initiate the energisation of a rotary solenoid 30 which thereby tightens a spring 31 around the threaded section 21 of the drive rod 20. The solenoid 30 is a low power device operable to force the spring 31 into the thread ofthe threaded section 21, for as long as it is energised. As the spring 31 is locked against movement both toward the piston 16 and toward the unshown valve respectively by the solenoid 30 and a spring ring 32, the drive rod 20 and the piston rod 13 are locked against movement relative to the actuator body 4 for as long as the solenoid 30 is energised.

Once the heating elements 7 cease heating the wax in the chamber 5, the wax begins to cool by conduction of its stored heat through the actuator body 4 and the insulation sleeve 33 to the environment surrounding the actuator 1. The decrease in volume resulting from the cooling, and more significantly from the reverse phase change, causes the piston 2 to be returned to the left. Oil then retums from the chamber 28 and from the chamber 25 into the chamber 24, the bellow 26 contracting to the left. This oil is free to flow to the part of the chamber 24 adjacent the piston 2 by virtue of the perforations in the flange 14. However, as long as power is applied to the solenoid 30, the drive rod 20 is held in its actuating position, despite the piston rod 13 having moved from contact with the piston 2. The drive rod 20 can be made to return to its nonactuating position only by de-energising the solenoid 30, when the resilience of the spring 31 causes its grip on the threaded section 21 of the drive rod 20 to be released.

The drive rod 20 is then forced leftwards by the action of the fail safe return spring 19 on the flange 14, to rest against the piston 16.

As will be appreciated, the actuator 1 is fail safe as loss of power to the heating elements 7 will either prevent the drive rod 20 being moved to its actuating position or, if the drive rod 20 is already in its actuating position, loss of power to the solenoid 30, allows the drive rod 20 to return to its non-actuating position under the leftwards force applied by the fail safe return spring 19 on the flange. If desired the return spring 19 could be repositioned either in the unshown valve, or between the valve and the actuator 1.

The actuator 1 also has advantages in that power consumption is very low when the drive rod 20 is locked in its actuated position, because only the rotary solenoid 30 is energised, and is nil when neither actuated or actuating. Power consumption will only be significant for the short time that the heating elements 7 are energised i.e. for the time it takes to complete actuation from switching on.

Referring now to Figure 2, a second embodied actuator 40 in accordance with the present invention is schematically shown in section.

The actuator 40 comprises generally a body 41 having a first cylindrical bore 42 in which a primary piston 43 and a compensation piston 44 are mounted; a second cylindrical bore 45 in which a primary piston rod 46, fixed to the fixed to the primary piston 43, is mounted; and a third cylindrical bore 47 in which a drive piston 48 is mounted, a drive rod 49 being fixed to the drive piston 48 such as to be movable axially along the bore 47.

The compensation piston 44 has a compensation piston rod 50 fixed thereto, the rod SO being supported by a bush 51 in an end cap 52 such that the compensation piston 44is movable axially along the bore 42. The end cap 52 is fixed to the body 41 and thus also provides means by which the compensation piston 44 is prevented from being displaced outside of the actuator body 41.

The compensation piston rod 50 is protected from the environment surrounding the astuator 40, typically a high pressure sea water environment, by the inclusion of a bellow 53 which defines a chamber 54. This chamber 54 is preferably filled with an oil L which provides protection of components inside the actuator 40 from the surrounding environment, which is typically a sea water environment. The chamber 54 is fluidly connected to a chamber 55 between the piston 44 and the end plug 52 by a connecting channel 56. This allows separation of the piston 44 and the end plug 52 with relative ease although it should be noted that the pressure of the sea water on the bellow 53 is communicated to the compensation piston 44.

The compensation piston 44 with the primary piston 43 define a chamber 57 within the bore 42 which is filled with a thermal expansion medium M, in this embodiment a phase change wax. A plurality of electrical heating elements 59 are fixed to a face of the compensation piston 44 such as to be contained within the chamber 57.

The heating elements 59 are connected to an insulated electrical power connector 60 by way of connecting wires 61, which extend through a channel in the compensation piston rod 50 and through the piston 44. The wax is retained within the chamber 57 by ring seals 62 and 63 on respective ones of the pistons 44 and 43. The phase change wax is the same as that described above as being particularly suitable for use in the first embodiment, although many other cuts may also be suitable.

A pressure transducer 64 and a temperature transducer 65 are mounted in the actuator body 41 such as to observe the conditions within the wax containing chamber 57. Heat insulation 58 is provided on the actuator body 41 to retain thermal energy within the chamber 57, thereby minimising actuation time and contributing to the energy efficiency figure.

The primary piston 43 and the primary piston rod 46 define a third chamber 66 within the bore 42. This chamber 66 is filled with a hydraulic drive fluid D, such as an oil, which is fluidly connected to a fourth chamber 67 through a connecting channel 68 formed in the piston rod 46. The fourth chamber 67 is defined by an end face 69 of the piston rod 46, the bore 45 and its end 70 and, to a limited extent, by a bush 71 acting to support the piston rod 46 for axial movement of the piston 43 along the bore 42. The chamber 67 is fluidly connected to a drive chamber 72 by a channel 73 such that displacement of the primary piston 43 is communicated by the fluid D in the reservoirs 66,67 and 72 to cause a related displacement of the drive piston 48. A fail safe return spring 76 is provided within the bore 42 to apply continuously a leftward force on the piston 43 against the actuator body 41.

A hydraulic lock 74 is positioned within the actuator body 41 controllably to allow or to block the flow of the hydraulic drive fluid along the channel 73. This lock 74 may comprise a ball valve comprising an electrical solenoid arranged to control the position of the ball on a seat within the valve, a check valve, a gate valve or any other suitable controllable valve.

The operation of the actuator 40 will now be described with reference to the same Figure, which shows an unactuated position. To provide actuation, control means (not shown) operate to apply an electrical energy supply to the insulated electrical power supply connector 60, which is hence applied to the heating elements 59 by virtue of the connecting wires 61. The heating elements then are operable to heat the wax which is thus caused to expand, significantly so as it changes state. Because the compensation piston 44 is prevented from leftward movement by the endcap 52, the force generated by the expansion of the wax causes displacement of the primary piston 43, which displacement is transmitted by the hydraulic drive fluid D in the chambers 66 and 67 to the drive piston 48. As the decrease in volume of the hydraulic drive fluid D under pressure should be negligible, the drive piston 48 is displaced by an amount related to the ratio of the squares of the diameters of the bores 47 and 42 and the displacement of the primary piston 43. This displacement also compresses the fail safe return spring 76.

When a position sensor 75 detects that a required displacement of the drive piston 48, and hence drive rod 49, has occurred, unshown control means both energises the hydraulic lock such that flow of the hydraulic drive fluid D in the channel 73 is blocked and removes the electrical power from the heating elements 59. The energisation of the hydraulic lock 74 prevents any flow of the hydraulic drive fluid D between the chamber 67 and the chamber 72, and hence prevents also any significant movement of the drive rod 49 and the primary piston 43. As the wax cools, therefore, the compensation piston 44 is moved rightwards, under the pressure of the environment surrounding the bellow 53, to allow for the reduction in volume of the wax in its chamber 57.

Controlled deenergisation of the hydraulic lock 74 allows fluid to flow in the channel 73 and thus allows the pistons 44, 43 and 48 to return leftwards. In this embodiment, this occurs by virtue of the force generated by the fail safe return spring 76.

It is necessary, then, that the return spring 76 applies a force to the drive rod 49 which is greater than the sum of the frictional resistance force of the actuator 40 and the force applied to the compensation piston 44 by the atmosphere surrounding the bellow 53.

Alternatively, the actuator 40 need not be provided with fail safe spring 76 if one is included instead in the unshown valve to which drive rod 49 is connected, or in an arrangement between the valve and the actuator 40.

As will be appreciated, the actuator 40 thus provided is fail safe in so far as loss of power to either or both of the heating elements 59 and the hydraulic lock 74 allows the drive rod 49 to return to its non-actuating position. The actuator 40 also has advantages in that power consumption is very low when the drive rod 49 is locked in the actuating position because only the hydraulic lock 74 is energised, and is nil when neher actuated or actuating. Power consumption will only be significant for the short time that the heating elements 59 are energised i.e. for the time it takes to complete actuation from switching on.

Referring now to Figure 3, a third embodiment actuator 100 in accordance with the present invention is schematically shown in section.

The actuate 100 comprises generally a body 101 baving a cylindrical bore 102 in which an actuator piston 103 and a drive piston 104 are mounted, a drive rod 105 fixed to the drive piston 104 such as to be moveable axially along the bore 102, and an external reservoir 106.

The piston 103 and an end plug 107 define a chamber 108 within the bore 102 which is filled with a thermal expansion medium M which, in this prefened embodiment, is a phase change wax. A plurality of electrical heating elements 109 are fixed to a face of the end plug 107 such as to be contained within the chamber 108. A temperature transducer 110 and a pressure transducer 111 are mounted with an electrical power connector 112 in the end plug 107 in much the same way as those described above with respect to the Figure 1 actuator.

The drive piston 104 and the actuator piston 103 define a further chamber 113 with the bore 102, which is filled with a hydraulic drive fluid D such as an oil. This chamber 113 is fluidly connected to the reservoir 106 by a connecting channel 114 which includes a gate valve 115 operable by a solenoid 116. The reservoir is of the sealed variable volume type whereby, when the valve 115 is open, drive fluid D can flow to or from the reservoir 106, if the chamber 113 respectively contains a surplus or experiences a shortage of fluid D with respect to its volume at a particular time.

A bush 117 supports the drive rod 105 in the actuator body 101 such that displacement of the drive piston 104 is transmitted to an equal displacement of the drive rod 105, thence to displace a component of an unshown valve. The drive piston 104 with the actuator body 101 and, to a limited extent, the bush 117 define a further chamber 118 within the bore 102 which is filled with a lubricating oil L. This oil L is displaceable into an unshown bellow through a channel 119 in the same way as in the Figure 2 actuator arrangement. A fail safe return spring 120 is included within the chamber 118 continuously to apply a leftwards force on the drive piston 104 by reaction against the actuator body 101 although the drive piston 104 is restricted in its movement by stops 121 which are formed as part of the actuator body 101.

Operation of the actuator 100 will now be described with reference to the same Figure, which shows a non-actuating pOsition.

To provide actuation, unshown control means energise the solenoid 116 to close the valve 115, and thus prevent flow of drive fluid between the reservoir 106 and the chamber 118, and provide electrical power to the heating elements 109 which then heat the wax The resultant expansion causes displacement of the piston 103 which, because the valve 115 is closed, is transmitted by the drive fluid D to displace the drive piston 104 and hence the drive rod 105. This displacement also compresses the return spring 120. When a position sensor 122 detects that a known displacement of the actuator piston 103, and hence that a required displacement of the drive rod 105, has be reached, the unshown control means provide the heating elements 109 with electrical power to maintain the piston 103 at the known displacement. This may be by reducing the voltage applied to the heating elements 109, by controlled switching between a high power and no power, or by a combination of the two. If the heat insulation provided by an insulation sheath 123 is sufficient, it should take only a small fraction of the electrical power used to provide action to maintain the piston 103 at the required displacement.

When it is desired to actuate the actuator 100, the unshown control means operate to remove electrical power from the heating elements 109, hereby ceasing the heating of the wax, and to cease energisation of the solenoid 116, thereby opening the valve 115. As the pressure within the reservoir 106 will be less than that within the chamber 113, the force applied on the drive piston 104 by the return spring 120 causes the flow of the drive fluid D from the chamber 113 into the reservoir 106 which reduces the volume of the chamber 113 and thus allows the drive piston 104 to move leftwards, to rest against the stops 121.

Thus, the actuator 100 is fail safe in that loss of power to either the heating elements 109 or to the solenoid 116 allows the drive piston 104 to move to rest in its non-actuating position against the stops, even when the wax is in its heated state.

Referring now to Figure 4, the drive rod 20 of an actuator 1 is connected by a connecting rod 80 to a gate 81 of a valve 82 having a product flow channel 83 formed in a steel body 84. In use, unshown pipes are secured in alignment with the channel 83 on opposite ends of the valve 82 by way of bolts passing both through flanges of the pipes and flanges 85, 86 of the valve body 84.

The gate 81 consists of a flat plate whose upper and lower surfaces are lapped to allow sealed movement between two annular seat members 87, 88, which form part of the product flow channel 83. The gate is displaceable by actuation of the actuator 1 from the position shown, where product flow in the channel 83 is blocked, to a position where a bore 89 through the gate 81 is aligned with the channel 83, thereby allowing flow of a product, typically gas and/or oil, through the valve 82.

The actuator drive rod 20 has an unshown yoke joint connection to the connecting rod 80 to allow an amount of misalignment therebetwee connecting rod 80 is located a seal 90 which acts both to prevent the leaking of oil, gas andlor grease from a cavity 91 around the gate into the actuator 1, and to support for axial movement the connecting rod 20 which thus allows proper movement of the gate 81 between the mernbers 87,88.

Although the embodiments have been described with a phase change wax being used as the thermal expansion medium, it will be appreciated that the present invention is not limited to such Fluid materials such as greases and oils could be used with little, if any, change to the arrangements shown in the drawings and described above It is envisaged also that Freon and other such materials that exhibit a large expansion in volume when changing state could be used in such actuators, although considerations would need to be made in the actuate design with regard to the highly pressurised gases which may be involved. It is not necessary either to provide electrical heating elements in contact with the thermal expansion medium For example, it may be preferable to heat externally a chamber containing the thermal expansion medium, especially if the medium is not as stable as the wax described above.

Actuation of down hole valves and choke devices where ambient tempers of around 170"C and pressures of the order of 1000 Bar can be found, is obtainable using an actuator or a method in accordance with the present invention. In this extreme environment, it may be desirable to use a medium which changes from a liquid to a gaseous state at a temperature of around 20 c higher than that expected at the actuator installation location. Actuation can then be achieved by electrically heating the medium, which may be an alcohol or an alcohol derivative, above its boiling point and using the resulting volume increase to displace a piston. A phase change wax having a suitable transition temperature may alternatively be used.

Claims

1. An electro-thermal actuator comprising an actuator piston supported for movement in a chamber containing a thermal expansion medium, and an electrical heating means controllable to heat the thermal expansion medium to provide a displacement of the piston.

2. An actuator, according to Claim 1, further comprising a means to transmit the displacement of the actuator piston to provide a required displacement of a drive means.

3. An actuate, according to Claim 2, further comprising locking means controllable to lock the drive means at the required displacement.

4. An actuator, according to Claim 3, in which said drive means comprises a drive rod including a threaded portion which is arranged to be aligned, at the required displacement, with a helical locking spring forming part of the locking means.

5. An actuate, according to Claim 4, in which the locking means further comprises a rotary solenoid operable to tighten the helical locking spring onto said threaded portion.

6. An actuator, according to any of Claims 3 to 5, further comprising a position sensor to detect that a predetermined displacement has been reached, means responsive to said detection to control said heating means to substantially cease heating the thermal expansion medium and means similarly responsive to control said locking means to lock the drive means at the required displacement.

7. An actuator, according to any of Claims 2 to 6, in which displacement of the actuator piston is transmitted to the drive means by a drive fluid associated with the actuator piston.

8. An actuator, according to Claim 7, in which the drive means comprises a drive piston and displacement of the actuator piston is transmitted to a required displacement of the drive piston by the drive fluid.

9. An actuator, according to Claim 3 and Claim 7 or Claim 8, in which the locking means comprise fluid control means controllable to block flow of the drive fluid and thereby lock the drive means.

10. An actuator, according to Claim 9, in which the fluid control means comprises a ball valve.

11. An actuator, according to Claim 9, in which the fluid control means comprises a check valve.

12. An actuator, according to Claim 9, in which the fluid control means comprises a gate valve.

13. An actuator, according to any of Claims 9 to 12, further comprising a compensation piston supported for movement in the chamber to allow the volume of the thermal expansion medium to change without substantial displacement of the actuator piston.

14. An actuator, according to Claim 8 and any of Claims 9 to 13, further comprising a position sensor to provide a signal indicative of a predetermined displacement having been reached, means responsive to said signal to cease heating the thermal expansion medium and means similarly responsive to control said fluid control means to lock the drive means at the required displacement.

15. An actuator, according to Claim 13 and Claim 14, in which control of the fluid control means to lock the drive means allows movement of the compensation piston.

16. An actuator, according to Claim 8, further comprising a reservoir fluidly connected to a chamber adjacent the drive piston containing the drive fluid by a channel including fluid control means controllable to allow or to block flow of the drive fluid between the reservoir and the drive fluid containing chamber.

17. An actuator, according to Claim 16, in which the fluid control means comprises a ball valve.

18. An actuator, according to Claim 16, in which the fluid control means comprises a check valve.

19. An actuator, according to Claim 16, in which the fluid control means comprises a gate valve.

20. An actuator, according to any of Claims 16 to 19, further comprising a position sensor to provide a signal indicative of a predetermined displacement having been reached, and means responsive to said signal to control the electrical heating means to heat the thermal expansion medium to substantially retain said predetermined displacement.

21. An actuator, according to any of Claims 16 to 20, in which control of the fluid control means to allow flow between said drive fluid containing chamber and said reservoir allows said drive piston to move to a non-actuating displacement.

22. An actuator, according to any preceding claim, in which the thermal expansion medium comprises a phase-change wax.

23. An actuator, according to any of Claims 1 to 21, in which the thermal expansion medium comprises a material having a boiling point around or less than 50 C above a temperature at which the actuator is to be operated.

24. An actuator substantially as herein described with reference to, or as shown in, Figure 1 of the accompanying drawings.

25. An actuator substantially as herein described with reference to, or as shown in, Figure 2 of the accompanying drawings.

26. An actuator substantially as herein described with reference to, or as claimed in Figure 3 of the accompanying drawings.

27. The combination of a control device, movable between actuated and unactuated positions, and an actuator in accordance with any preceding claim, furrier comprising fail safe spring means arranged to bias the device into the unactuated position, the actuator being operable to move the device into the actuated position.

28. A method of actuating a control device comprising electrically heating a thermal expansion medium, and using the expansion of the medium to actuate the control device.

29. A method of actuating a remotely located control device comprising conducting an electrical energy supply to an actuator associated with the control device, using the electrical energy supply to heat a thermal expansion medium arranged within the actuator, thereby changing its volume, and using the change in volume of the medium to actuate the control device.

30. A method of actuating a control valve device of an underwater installation from a remote surface based station, comprising conducting an electrical energy supply from the remote station to a position adjacent the control valve, using the electrical supply to heat a thermal expansion medium, and using the expansion of the medium to actuate the control valve device.

31. A fail safe method, according to any of Claims 28 to 30, whereby interruption of the electrical energy supply will allow the control device to return to an unactuated position.

32. A method, according to any of Claims 28 to 31, further comprising locking the control valve in a predetermined actuated position and then interrupting the electrical energy supply used for heating the medium.

33. A fail safe method, according to Claim 32, further using an electrical locking signal to lock the control valve in the predetermined actuated position whereby interruption of the electrical locking signal will allow the control device to return to an unactuated condition.

34. A method, according to any of Claims 28 to 33, using a phase change wax as a thermal expansion medium.

35. A method, according to any of Claims 28 to 33, using a material having a boiling point around or less than 50 C above a temperature at which the method is to be used as the thermal expansion medium.