Valve actuators

Abstract

 An electro-hydraulic actuator having a pump unit (11) for hydraulic fluid to supply a chamber (18) having a movable boundary part (19) and a controlled (21) fluid return (20) from that chamber (18).
Particular features include housing of the pump unit (11) inside an hydraulic fluid reservoir (10), a simple sloppy piston preferred direction provision, very substantial precompression of a bias spring (24) for the boundary part (19), a readily accessible actuator unit driven by the pump unit (11), a compatible position transducer unit, and a two- way driven hydraulic actuator unit.

Description

[0001] The invention relates to valve actuators and is particularly directed to providing an electro-hydraulic acutator that will have wide applicability as has been the case for the hitherto ubiquitous pneumatic diaphragm valves, and be relatively advantageous.

[0002] The well-known pneumatic diaphragm valves usually comprise a diaphragm which carries a valve operating component, such as a rod, and is biassed by a spring from one side of the diaphragm that is opposite to a chamber for receiving compressed air for moving the diaphragm against the biassing spring. For direct action, the valve operating component is on the same side as the biassing spring. For the reverse action, the valve operating component is on the same side of the diaphragm as the air chamber and requires a seal, normally with tolerance of substantial air leakage.

[0003] Such compressed-air-controlled valves are in widespread use throughout industrial manufacturing plants. They are simple in construction and reliable in operation, but are expensive and require a compressed air supply and a distribution system therefor. Considerable maintenance costs are involved and a further capital cost is incurred where operation is desired within modern electronic, usually computer-based, control systems by way of the provision of electro-pneumatic converters to interface between electrical control signals and the pneumatically controlled valves. Also, pneumatically controlled valves usually represent a relative lack of sensitivity in electronic control loops leading to a much lower accuracy and speed of response than the inherent capabilities of the electronic control system.

[0004] Particular factors contributory to what is noted above include normally low operating pressures for the compressed air, heavy-duty biassing springs, large size diaphragms to develop the required diaphragm movement, and uncertainties arising from inherent compressibility of compressed air and leakage thereof leading to loss of pressure.

[0005] Substantial development work leads us to believe that an electrically operated valve actuator using hydraulic fluid is capable of solving these problems with substantial advantages by way of reduced costs, improved operating sensitivity, and ready interfacing with electronic control systems.

[0006] To this end, we now propose an elector-hydraulic valve actuator comprising a chamber for operating hydraulic fluid, which chamber has a movable boundary part to operate a valve operating component coupled thereto; an hydraulic fluid reservoir; a first hydraulic fluid communication between said reservoir and said chamber, arid a pump responsive to an electrical frequency signal for pressurising hydraulic fluid in that first communication when supplying that fluid to said chamber to move said boundary part in one direction; a second hydraulic fluid communication between said reservoir and said chamber, and a controllable bleed return valve for said hydraulic fluid in that second communication to permit movement of said boundary part in the opposite direction.

[0007] In essence, any desired control of'the bleed return valve, relative to operation of the pump, is a matter of choice, though particular relationships may be built-in and thus predetermined if so desired. Thus, whilst the two said communications may have partially common passageways, for example into the said chamber, the bleed return valve will be operative to connect said chamber to hydraulic fluid in said reservoir from the output side of the pump and effectively about the active part, such as a reciprocable piston, of the latter.

[0008] It is a particular advantage hereof that the moving or movable parts serving on the one hand to produce pressurisation of the hydraulic fluid and on the other hand to control return of that fluid are physically separate and distinct. That allows individual control, setting or adjustment of pressurisation and return bleeding each within limits and design criteria for the other and the system as a whole, as well as also permitting interlocking and mutually dependent operation by appropriate electrical signals as may be desired. Also, the pressurisation and bleed means can tnen be designed and configured in the simplest possible manner to achieve their own functions only, if desired both operating at the same time in a dynamic control mode. Specifically, there is no necessity for a reciprocable plunger piston for pressurising also to serve in sealing or unsealing a bleed passage and for electrical actuator means of the plunger piston to react to different types of signal in permitting both normal pressurising reciprocation and additional retraction therefrom to uncover a bleed passageway.

[0009] Our preferred such electro-hydraulic actuator has its said pump housed within its own said reservoir to form an hydraulic pressuriser unit for connection directly to a said chamber, and thus may constitute a diaphragm controller in direct replacement for the pneumatics of compressed-air operated valves as discussed above. Such hydraulic pressurisers may, however, equally well be parts of units also including diaphragm chambers or piston-and-cylinder devices carrying or for coupling to an actual valve operating part or component. Alternatively, a further unit incorporating a diaphargm or a piston-and-cylinder devices could be made available separately from but to interconnect or couple to a pressuriser unit. At least in the latter two cases, we have found that the size of the diaphragms and the rating of a bias spring therefor can be much reduced if the spring is prestressed and thus operative from a very substantial minimum actual compression.

[0010] Our preferred hydraulic units combine features of piston-and-cylinder types and diaphragm types by utilising a naturally cup shaped diaphragm having a rim gripped between cylinder and cover parts and its bottom engaged by a piston part of sufficient clearance in the cylinder part to accommodate a fold of the diaphragm side wall that rolls in the clearance as the piston part moves. Such a unit is well-adapted to utilising a pre-stressed bias spring about a piston connecting rod and located relative to that rod to be operated relative to a desired minimum compression, say by a pin or bar through a slot permitting at least the desired piston stroke. A preferred construction tnat is readily assembled or disassembled, and modified as to stroke or bias spring, has a plate through which the connecting rod extends beyond its spring, which plate is secured spaced from the cylinder and cover parts by tie rods or spacer studs, Said plate is readily similarly coupled to a further plate on the controlled valve. Alternatively, said plate and the cylinder/cover parts may slidably locate a yoke arrangement operated by the connecting rod and secured beyond the cylinder/cover parts to a valve operating component to give reverse action of the controlled valve, said cylinder/cover parts then conveniently being secured relative to the further plate on the controlled valve.

[0011] A mechanically operated position sensor is readily associated with such units conveniently using an adjustable lenght link operated by the piston connecting rod to move a transducer component so that the transducer is operative over a desired.range of movement of its said component. Bodily movement, preferably rotation, say about a tie rod or spacer stud, of a transducer box to move a spindle coupling along a lever as said link is preferred, rotation of such spindle by the lever causing said component, say a wiper, to traverse another component, say a wire of a potentiometer.

[0012] An advantageous hydraulic valve moving unit using hydraulic fluid for both directions of movement comprises cup-shaped diaphragms at each face of a piston, a connecting rod sealed relative to one of the diaphragms, and another smaller piston element on the connecting rod also associated with a further cup-shaped diaphragm to secure sealing against escape of hydraulic fluid.

[0013] Also, our proposed individual hydraulic units, one per valve to be operated, permit us to provide for accurate position control of the controlled valves in another particularly advantageous way. Thus, the actual level of hydraulic fluid in the reservoir will be a direct function of the position of the diaphragm or piston-and-cylinder device, and is readily sensed using a level sensor, say of capacitive or even potentiometer type, to give an electrical signal to be compared with a demand or setting signal for control purposes by an overall electronic system. Again, that is all conveniently achieved within a unit including the reservoir and pump rather than using hitherto customary and troublesome mechanical linkages from the valve operating component or part to be a potentiometer.

[0014] Accuracy of valve actuators hereof can be further enhanced by operation in a dynamic mode where the bleed return valve is operative throughout pump operation with control of the frequency of the latter, or of the effective orifice of the bleed return valve, or of the mark-spaced ratio of an on-off type of bleed return valve, or a combination thereof. Such a control system, or the facility normally to have either pumping or bleed at all times, is, especially in conjunction with accurate positional sensing, particularly effective in maintaining accurate valve settings. However, the basic advantage of the use of an hydraulic fluid, arising from the latter being incompressible, is still available using electrically controlled pumping and bleed return valve means if they both have an available rest position that produces hydraulic lock for the fluid in the chamber.

[0015] Practical implementation of the invention will now be described with reference to the accompanying diagrammatic drawings, in which:

Figure 1 is an exemplary system sketch;

Figure 2 shows a section through one embodiment of a hydraulic pumping unit;

Figure 3 shows an overall system;

Figure 4 shows a section through one embodiment of a valve moving unit;

Figure 5 shows part of Figure 4;

Figure 6 shows a variation concerning Figure 4;

Figure 7 shows another valve moving unit; and

Figures 8 and 9 show variants concerning Figure 2.

[0016] In Figure 1, a hydraulic fluid reservoir 10 supplies a pumping system 11 having a solenoid actuated piston 12 in a hydraulic fluid flow exit cylinder 13. The pumping system is contained in the reservoir 10. The piston 12 is connected by a rod to armature 14 of the solenoid 15 and may incorporate a fluid valve 16 to favour hydraulic fluid from the reservoir into the cylinder rather than reverse flow. The solenoid 15 of the pumping system can be operated at a substantially constant speed, by an electrical signal of suitable frequency.

[0017] Beyond its piston flow accommodation space, the cylinder 13, or an extension thereof, is shown with a non-return valve 17 permitting hydraulic fluid flow into but not out of a diaphragm chamber 18 at one side of a flexible or otherwise deformable sealing diaphragm 19. A hydraulic fluid return conduit or passage 20 is shown between diaphragm chamber 18 and the reservoir, and this conduit or passage 20 includes a solenoid operated bleed valve 21.

[0018] The diaphragm 19 is shown coupled to an actuator rod 22 of a valve 23 to be controlled,

[0019] An electronic control is indicated in block form at 110 and is, in one specific application, to produce three states of the illustrated apparatus. These include firstly a pump drive over lines 112 at substantially constant rate with the solenoid return or bleed valve 21 held closed over lines 113 or at a minimum flow value so that pressure will increase on the control valve diaphragm 19. Closure of the bleed valve 21 may be by a specific hold signal on line 113 from the controller 110 but could also be by a spring bias to be overcome in the second state. This second state is where the pump drive over line 112 is stopped and the return bleed valve 21 is open. Then, the diaphragm pressure will decrease at maximum permitted rate. In the third state, both the pump is stopped and the return bleed valve is closed, tnereby locking hydraulic fluid in the diaphragm chamber and maintaining a particular state of the controlled valve 23.

[0020] It will be clear that other states of such a system, for example variable pump drive rate and/or variable return valve cycling rate or mark-space ratio, may be of value in particular applications. However, the simple version just described or at least the inclusion of those three states as options gives a fast response time for distending diaphragm 18 as full pumping capacity may be used without any bleed whatsoever or at most a minimum thereof. Also, a solenoid type bleed valve 21 can give a high maximum return flow to give a fast diaphragm response in the opposite sense. Pump and bleed valve wear is reduced if they operate only when the diaphragm is to be operated, and manual override or alternative control is readily achieved by open and closed push button switches, especially if of latching type. The tendency of conventional pressure regulators for pneumatic equipment to drift is met as the hydraulic fluid can be locked in and is incompressible. Power failure is further readily dealt with by locking action using a normally closed bleed valve, or by rapid discharge to a desired position via a normally open bleed valve, or by a slow minimum bleed to a desired position if preferred. Clearly, under normal control conditions, normally open bleed valves can be energised to close in rest states maintained by hydraulic lock.

[0021] Turning now to the specific pumping system and bleed valve arrangement of Figure 2, the same reference numerals have been used for similar parts as in Figure 1 and, primed where worthy of further discussion. The piston 12' is in the form of a one way valve using a deformable sleeve 115 which is a clearance or sliding interiorly fluted fit on an extension, see screw 116, of the end 117 of a connecting rod to the armature 14. On the pumping stroke, the sleeve 115 seats on the end of the connecting rod, spreads and stops fluid flow back into the reservoir 10 via passages 118. On the upstroke, the sleeve 115 seats on the screw 116 and allows fluid flow into the cylinder 13 via cut outs 119 and passages 118 of the piston sleeve 115.

[0022] The piston is preferably made of a hardwearing but resiliently flexible plastics material such as Teflon (Registered Trade Mark), thus eliminating the need for an 0-ring which would be necessary if the piston were made of metal, i.e. a part only being deformable.

[0023] The sliding fitment of the piston in the cylinder may be such as will allow less critical alignment of the solenoid armature and piston than would normally be required. A tolerance of 0.005 inches is usual. A simple armature biassing and alignment system is shown using an apertured plate 120 on studs 121 from coil casing 122 with a bias spring 123 about a top extension rod 124 from the armature 141.

[0024] Any suitable solenoid drive circuit may be used to provide a desired pumping frequency range in response to a range of electrical input signals, either analogue or digital. Many electronic controllers in use with pneumatic valved systems give an output in the range 4 to 20 milli-amps and air pressure converters are available for converting such inputs typically to 3 to 15 p.s.i. Embodiments of this invention are eminently suitable as direct replacements of such converters to work directly off the 4 to 20 milliamp electrical signal to drive the diaphragm of the existing valve, i.e. corresponding to that referenced 19 in Figure 1. However, actuators including purpose built diaphragm systems may equally well be used as original equipment and may operate at much higher fluid pressures. Also, a piston-and-cylinder device may be used in place of the diaphragm 19.

[0025] One convenient form of pumping signal circuit comprises a thyristor controlled circuit providing a variable frequency output and working off a mains a.c. supply. For a given type of analogue electrical signal- to frequency converter, operation in response to digital signals can be achieved by the use of an input analogue- to digital converter. Alternatively a digital-to-frequency converter could be used ab initio.

[0026] Figure 3 shows a general outline of solenoid drive signal deriving circuit comprising a power switch 70 driven by a voltage-to-frequency converter 71 supplied witn a control voltage from a process controller 72 that compares a desired parameter value preset at 73 with an actual parameter value over line 74. It will be appreciated that the line 74 may be fed by output from signal deriving circuitry 76 of the probe 24, which may also or alternatively be connected to control the bleed valve. Also the preset at 73 may in fact be a value set by a computer control system.

[0027] Reverting to Figure 2, the solenoid return or bleed valve 21' is shown within the reservoir 10 teed at 130 off a reservoir exit 131 below the non-return valve 17. The valve 21' has an armature 132 controlled by a coil 133 to seat and seal, or not, at 134 on an exit 135 to reservoir from a chamber 136 communicating via 137 with tee fitting 130. The armature 132 is biassed by spring 138 to its seating and sealing position.

[0028] The reservoir can be provided with a level sensing probe 125 to give an electrical signal indicative via associated electronic circuitry to the fluid level in the reservoir to the control block via line 126. That circuitry may be within mount 127, or otherwise within reservoir 10, especially if the probe is axially adjustable rather than relying upon a variable electrical component for calibration according to a basic fluid level. The level of fluid is an indication of the position of the diaphragm operated valve. The level signal can be compared with a desired value position input signal or a process error signal so that appropriate adjustment of pump speed and/or bleed value restriction can be made.

[0029] The hydraulic fluid pumping system of Figure 2 is advantageously used in association with the valve moving system of Figure 4 where the diaphragm 19' is shown as being of a type resembling a cup on a piston 140 in a guide sleeve or cylinder 141 set in the lower of two plates 142, 143 that sandwich and seal the periphery of the diaphragm 19' with the latter free to "roll" at 144 between the piston 140 and the guide sleeve or cylinder 141. Coupling between the upper plate 142 at 145 and the reservoir exit 131 of Figure 2 may be direct or via suitable piping.

[0030] The piston 140 constitutes a loose crown on a connecting rod 146 end-flanged at 147 to nest in a well 148 of the piston 140 and be biassed to an unextended position as shown by a prestressed spring 149 acting between end flange 147 and a plate 150 secured to the plates 142, 143 in spaced relation by studs 151. The connecting rod 146 passes freely through the plate 150 and is slotted at 152 along its length to cooperate with a pin 153 in prestressing of the spring at assembly, and also controlling the permitted stroke of the connected rod 146 to suit a particular valve 23 to be controlled. The assembly thus far described is susceptible of ready assembly, disassembly, changes of bias spring 149, and generally tailoring to the requirements of a particular valve 23 to be controlled.

[0031] Furthermore, to the same ends, the plate 150 is shown spaced from a valve seating plate 154 by further studs 155. A simple coupling 156 below plate 150 between the connecting rod 146 and the valve spindle 157 uses a block screwed at 158 on the spindle 157 and a grubscrew 159 to latch in a groove 160 on the end of the connecting rod.

[0032] Clearly, the arrangement of Figure 4 will serve to operate a valve 23 from a rest position with its spindle 157 extended. The opposite action is available using an arrangement as shown in Figure 6 where similar references are used as appropriate. There, however, the connecting rod 146 is coupled to a plate or cross head bar 161 carried by additional studs 162 that pass freely through the plates 142, 143, 150 to a further plate or cross head bar 163 that is coupled at 164 to valve spindle 157'. Also studs 165 are shown locating the plate 142 relative to valve seating plate 154".

[0033] Reverting to Figure 4, and also referring to Figure 5, one of the studs 155 is used to mount a particularly advantageous positional sensor 170 alternative to the level sensor 125 of Figures 1 and 2. Sensor 170 comprises a box 171 containing a suitable lubricant 172 such as oil. Within the lubricant 172 is a potentiometer wire 173 and a wiper 174 attached to a spindle 175. On rotation of the spindle 175, the wiper 173 traverses the potentiometer wire 172, and both are shown to be straight, with the former of suitable length, and the latter at a suitable height, to rely only on sliding contact at their crossing.

[0034] The box 171 has an indent 176 low along its major face visiable in Figure 4 and a similar indent, but at right angles near one end, in its other major face. In Figure 4 that latter indent is used to straddle a stud 155 and be secured thereto but still rotatable thereon by a plate 177 (Figure 5). The orthogonal indents allow positioning of the box 171 on a stud 155 with the latter in either of a vertical position as shown or a horizontal position, and at least some positions between, to ensure coverage of the potentiometer wire 173 by the lubricant, which ensures long trouble- free life.

[0035] The spindle 175 passes through the box 171 and carries a coupling 178 for an arm 179 bent at 180 to present an end 181 to engage between the connecting rod coupling 156 and a step 182 in the connecting rod itself. The coupling 178 allows, or is adjustable to allow, sliding along the arm 179 so a desired range of turn applied to the spindle 175 can be maintained for varying strokes of the connecting rod 146 merely by angular adjustment of the box 171 on the stud 155. In that way, maximum sensitivity of the potentiometer and flexibility of fitment of the sensor is achieved. Locking of the box 171 in a desired position is readily achieved either via plate 177 or coupling 178.

[0036] Another advantageous valve moving unit is shown in Figure 7 and is of a fluid displacement type in both directions, i.e. does not use any bias spring. Basically, it uses a piston 240 in a cylinder 241 with a cup-like rolling-fold diaphragm 242 peripherally sandwiched and sealed at243 between the cylinder 241 and a cover 244 ported at 245 for supply of drive fluid from a pumping unit. The piston 240 carries a connecting rod 246 screwed therein at one reduced and threaded end to bear on a dished clamp washer 247 for sealing a further cup-like, rolling-fold diaphragm 248 peripherally sandwiched and sealed between the other end of the cylinder 241 and a closure plate 249 itself apertured to form part of a cylinder 250, 251 for a further piston 252. The connecting rod 246 has a central part of relatively large section and flatted for engagement by a spanner. Cylinder extension 251 is secured in place by ring plate 254 peripherally sandwiching a third cup-like, rolling-fold diaphragm 255 for the piston 252. The piston 252 is screwed to the other, also reduced and threaded, end of the connecting rod 246 to bear on a dished clamp washer 256 for sealing the diaphragm 255. The other end of piston 252 carries a coupler 258 for operation of the valve to be controlled. Closure plate 249 is ported at 259 for supply of drive fluid past clearance of washer 255 in the cylinder port 250 to the space 260 between diaphragms 255 and 248 on pistons 242 and 240. As the latter is the larger, drive fluid supplied at port 259 will force the piston assembly 240, 246, 252 in the opposite direction to drive fluid applied to port 245, though the latter would prevail if both were applied together which could have fail-safe application additional to hydraulic lock also available at total deenergisation.

[0037] We prefer that hydraulic drive for the ports 245 and 259 be by way of separate pumping units 261, 262, each such as shown in Figure 2, usually and advantageously both in the same reservoir 263 and interlocked 264 so that only one will be energised at any tine.

[0038] Figure 8 shows two further features concerning modifications of the solenoid pump of Figure 2, either of which can be implemented alone. One feature is the use of two solenoids 80, 82, one for retraction of the piston or plunger and the other for its drive stroke. Clearly, associated electronic control will still then allow for solenoid coil pulsing at varying frequencies in order to obtain desired or required pumping rates. However, basically, retraction solenoid actuation should follow full drive stroke automatically with de-energisation of the drive solenoid, but retraction solenoid actuation will persist until the next requirements of a drive stroke. The other further feature is the mounting of solenoid coil means outside a non-magnetic tube 84 within which respective armatures 86, 88 run in an oil and are secured to spindle 90 for the piston or plunger. The non-magnetic tube 84 will, of course, be such as not to interfere with solenoid operation, and the solenoid coils are advantageously spaced by ring or sleeve 92 about the tube 84 by the same amount as the armature spacing and are shorter in length than the associated solenoid coils thereby ensuring a highly positive action due not only to two-solenoid action but also to braking effects of the solenoids. Securement of the solenoid coils to the tube is completed by clamping ring 94, clamping washer 96 against blind end 98 of the tube and clamping screw 100.

[0039] Figure 9 shows an alternative restriction arrangement in which a body block 40 is bored to provide a cylinder bore 41 within which the solenoid actuated piston operates, and communication therefrom to a chamber 42 open to a tapped non-return valve mount and communicating by a transverse bore with a needle valve housing bore 44 and also with another bore 46. Both of the bores 44 and 46 communicate with the hydraulic fluid reservoir and the bore 46 has a flow blocking and unblocking valve 47 in a larger transverse bore 48.

[0040] A piston of the valve 47 communicates with the cylinder bore 41 below the maximum travel of the solenoid actuated pumping piston which has bores 49 therein as part of a ball-type one-way valve to allow hydraulic fluid flow through the piston from the reservoir space towards the chamber 12. The valve 47 has a spring bias to open the passageway 46 but will respond to working strokes of the pumping piston to close before the one-way ball-type valve 17 operates to allow hydraulic fluid into the diaphragm chamber.

[0041] The restrictor valve 45 is of fixed orifice type but is adjustable as to its orifice so that the restriction system comprises a fixed predetermined orifice and a periodic flow via and valve 47 which will be open except on the work stroke of the pumping piston 12. This system is particularly advantageous where, as will usually be the case, the work stroke of the pumping piston occupies lower proportionate amounts of the total cycle time at low frequencies than at high frequencies of its operation. The pumping system will, of course, normally be designed so that maximum required diaphragm displacement corresponds to the highest operating frequency whereat the pumping piston work stroke occupies its maximum proportion of the cycle time, conveniently equal to or less than one half-cycle. At lower pumping frequencies the diaphragm chamber fluid pressure will be lower, or at least declining, so that the work stroke time may well be less and will certainly take a less proportion of the available half-cycle, so that the percentage of time during which the valve 48 opens passage 46 to reservoir will be greater at lower pumping frequencies as desired.

[0042] To maximise efficiency, the movement of the piston of valve 47 may be kept to the minimum required to cover and uncover the passage 46, say by a stop at a central stepped part of a closure and spring seating plug, and by the end of the bore 48.

[0043] Substantial advantages arise from our proposed use of prestressed bias spring effectively between the diaphragm and the valve operating component. Thus, all controlled valves require a substantial minimum force to be applied to secure the valve state from which the diaphragm will move the valve operating component. If that is done conventionally, as hitherto for pneumatic valve actuators, using a spring stressed only by applied pressure, the spring must produce its minimum force at the lowest applied pressure, usually 3 p.s.i., and will be rated to produce a multiple of that force over a short operating movement, say of about one inch. That will produce the desired linearity of response between the valve operating component and the applied pressure and the multiple will be the ratio of maximum to minimum of the applied pressure. The high forces required at the diaphragm can be delivered only by using a large area diaphragm. Whilst the latter requirement will be reduced by increased applied pressures to be expected from our hydraulic system, yet further reductions are available from prestressing a much lower rated bias spring very substantially to give the desired minimum force and thereafter to require increase of such force to operate the valve through its desired operating stroke by only a fraction, say as little as 20% of that minimum force. The result is particularly compact and less expensive units requiring much lower rated bias springs and small size diaphragms/pistons.

Claims

1. An electro-hydraulic valve actuator comprising a chamber for hydraulic fluid, which chamber has a movable boundary part to operate a valve operating component coupled thereto, an hydraulic fluid reservoir; a first hydraulic fluid communication between said reservoir and said chamber, and a pump responsive to an electrical frequency signal for pressurising hydraulic fluid in said first communication when supplying that fluid to that chamber to move said boundary part in one direction; a second hydraulic fluid communication between said reservoir and said chamber, and controllable oleed return valve means for said hydraulic fluid in that second communication to permit movement of said boundary part in the opposite direction.

2. An electro-hydraulic valve actuator according to claim 1, wherein said pump is within said reservoir.

3. An electro-hydraulic valve according to claim 2, wherein said bleed return valve is electrically controlled and is also within said reservoir.

4. An electro-hydraulic valve according to any preceding claim, wherein the pump is solenoid operated using spaced solenoids one for retraction and another for drive strokes of armature means thereof.

; An electro-hydraulic valve actuator according to claim 4, wherein said solenoids are outside a non-magnetic tube within which respective armatures run immersed in oil.

6. An electro-hydraulic valve actuator according to any preceding claim, wherein the pump drives a piston operative in a cylinder on the hydraulic fluid, such piston comprising a deformable sleeve slidable and deformable to seal against hydraulic fluid flow therepast on drive strokes but permitting such flow on retraction strokes.

7. An electro-hydraulic valve actuator according to any preceding claim, wherein said bleed return valve means affords a presettable permanent bleed flow of hydraulic fluido

8. An electro-hydraulic valve actuator according to any preceding claim, wherein the chamber has a level sensor to provide a signal indicating position of said valve operating component.

90 An electro-hydraulic valve actuator according to any preceding claim, wherein the movable boundary part is biassed by a spring prestressed to require an increase in its applied force over the operating movement of the boundary part that is a fraction only of that resulting from the prestressing.

10. An electro-hydraulic valve actuator according to claim 9, wherein the spring is about a rod from a part bearing on said movable boundary part to move therewith and the spring is constrained to a minimum compression by a coupling to said rod.

11. An electro-hydraulic valve actuator according to claim 10, wherein the rod extends through a plate spaced from parts of said chamber by securing means therefor.

12. An electro-hydraulic valve actuator according to claim 11, wherein a further plate securable to a valve to be controlled is spaced from said plate by further securing means therefor.

13. An electro-hydraulic valve actuator according to claim 11, wherein a further plate securable to a valve to be controlled is spaced from said parts of said chamber by further securing means and said rod is connected to means straddling and guided by said plate and chamber parts for connection to said valve operating component.

14. An electro-hydraulic valve actuator according to claim 13 or claim 14, wherein said further securing means has associated therewith a level sensor in the form of a transducer box rotatable thereon to vary the effective length of a lever extending from a transducer spindle to be operated by movement of said rod, and the transducer box holds a lubricant for a potentiometer wire traversed by a wiper on said spindle, the box having alternative formations for association with said further securing means at different altitudes of the boxo

15. An electro-hydraulic valve actuator according to any preceding claim, wherein the movable boundary part comprises a cup-like diaphragm secured peripherally at a rim by parts of said chamber and having its side. wall present a rolling fold between a valve operating piston and a cylinder therefor during their relative movement.

Drawing