GB2258498A

GB2258498A - An actuator

Info

Publication number: GB2258498A
Application number: GB9214159A
Authority: GB
Inventors: Michael John Rimmer
Original assignee: NAT OILWELL; National Oilwell LP
Current assignee: NAT OILWELL; National Oilwell Varco LP
Priority date: 1991-08-05
Filing date: 1992-07-02
Publication date: 1993-02-10
Also published as: GB9214159D0; GB9116842D0

Abstract

An actuator comprises a housing 10 having an internal chamber 26 and a piston 12 mounted for reciprocating motion within the chamber 26. A stem 14 is coupled to the piston 12 and passes to the outside of the housing 10 via a stem aperture 32 in the housing 10, whereby reciprocating motion of the piston 12 can be transferred to a device to be operated by the actuator. First bellows 16 is connected between the piston 12 and the housing 10 to divide the chamber 26 to provide for operating fluid to be used to reciprocate the piston 12 within the chamber 26. Second bellows 18 is connected between the stem 14 and the housing 10 to close the said stem aperture 32 against fluid communication between the chamber 26 and the outside of the housing 10. <IMAGE>

Description

AN ACTUATOR The present invention relates to an actuator which finds particular application in the operation of oil field equipment such as, for example, valves, hydraulic connectors etc.

Conventionally, springs of one type or another have in general been used to store energy, such that a piece of equipment will be moved to the desired fail safe mode subsequent to any failure in the operating system.

These springs present many problems, some of which are as follows: (a) They can be very big for large diameter, high pressure equipment.

(b) They are somewhat difficult to design properly.

(c) They are generally difficult to assemble and install.

(d) When operating they create debris which can pollute the hydraulic operating fluid.

In addition to the springs described above, most actuators have an hydraulically operated piston which is used to operate the equipment. This piston requires the use of seals which can deteriorate over a period of time.

With a view to providing an improved arrangement the present invention provides an actuator comprising; a housing having an internal chamber, a piston mounted for reciprocating motion within the chamber, a stem coupled to the piston and passing to the outside of the housing via an aperture in the housing, whereby reciprocating motion of the piston can be transferred to a device to be operated by the actuator, first bellows sealingly connected between the piston and the housing to divide the chamber to provide for operating fluid to be used to reciprocate the piston within the chamber, and second bellows sealingly connected between the stem and the housing to prevent fluid communication between the chamber and the outside of the housing through the said aperture.

Preferably, the first bellows and the second bellows will have respectively different diameters. In a preferred embodiment, the first bellows will have a greater diameter than the second bellows.

An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawing, in which Figure 1 is a diagrammatic cross-section through an actuator which embodies the present invention.

As shown in figure 1 the main components of the actuator are; a housing 10, a piston 12, a stem 14, primary bellows 16 and secondary bellows 18.

Housing 10 comprises a hollow metal cylinder or barrel 20, a stem end cap 22 and a port end cap 24. The components of the housing 10 define an internal chamber 26.

Disc shaped piston 12 is a sliding fit within chamber 26, thus effectively dividing chamber 26 into two sections, 28 and 30, on respective sides of the piston 12. Of course, as piston 12 reciprocates within chamber 26, there is a proportional change in the respective volumes of the two chamber sections 28 and 30. As illustrated in figure 1, stem 14 is a cylindrical rod integral with piston 12. Stem 14 could, of course, equally well be a separate component attached to piston 12. In any event, the stem 14 passes through an aperture 32 located centrally in the stem end cap 22.

It is important to note that whereas in a conventional housing/piston/stem arrangement seals would be provided between piston 12 and barrel 20 and between stem 14 and end cap 22, the arrangement shown in figure 1 does not use such seals. Respective guide rings 34 are used in place of the conventional seals and the guide rings 34 need not provide a fluid tight seal between the respective components. In fact, it may be possible to omit guide rings 34, depending upon manufacturing tolerances and potential wear between components 12/20 and 14/22. Most importantly, the illustrated arrangement, by using bellows, enables conventional seals to be dispensed with and thus all problems associated with deterioration, leakage and the like associated with conventional seals can be avoided.

The bellows 16 and 18 are preferably made of metal such as Inconel (Trade Mark), Stainless Steel, Titanium and the like. Alternatively, plastics material, GRP, Revlar (Trade Mark) or carbon fibre, for example, could be used for forming the bellows 16, 18.

Primary bellows 16 are at one end attached to the piston 12. The other end of bellows 16 is attached to the internal face of end cap 24.

Stem 14 is provided with a shoulder 36, at a position on the stem which always remains outside of the assembled actuator, regardless of the location of piston 12 within chamber 26. This shoulder is used to accurately position a collar 38. However, other means may be provided to locate collar 38.

Secondary bellows 18 has one end attached to the collar 38 which is passed over the free end of stem 14 and welded in abutment against shoulder 36. The other end of bellows 18 is attached to the external face of end cap 22.

One sequence of construction of the actuator would be as follows. The respective guide rings 34 are located in piston 12 and end cap 22. Bellows 16 is attached to piston 12 and end cap 24. Bellows 18 is attached to collar 38 and end cap 22. Barrel 20 is then attached to end cap 22. The stem, piston and primary bellows are then inserted into chamber 26, with stem 14 passing through aperture 32 until shoulder 36 abuts collar 38 and end cap 24 abuts barrel 20. Barrel 20 is welded to end cap 24 and collar 38 is welded to stem 14. There are other means of assembly which all achieve the same end result.

Where appropriate, the preferred means of attaching the bellows to the other actuator components is welding.

In construction of the actuator, it is prudent to ensure that collar 38 is only welded to stem 14 when piston 12 is in a predetermined position within chamber 26, in order to avoid the risk of over or under-extending either of the bellows. Once assembled as described, the actuator can effectively be considered to be sealed for life with no seals that could cause any failure.

It should be noted, that the two bellows 16 and 18 are of different diameter. Bellows 18 has a smaller diameter than bellows 16; this means that the two act together as a fail safe actuator. If the situation were to be reversed, that is to say, bellows 16 had a diameter smaller than bellows 18, then the device could act as a permanent lock, which could find many useful applications.

Various ports are provided to enable the transfer of fluids within chamber 26 in order to operate the actuator. In the illustrated arrangement, chamber section 28 is charged with a gas. Chamber 40 defined by piston 12, primary bellows 16 and end cap 24, is charged with a liquid.

End cap 24 has at least one port 42 which passes therethrough so as to enable liquid to be introduced into or expelled from chamber 40. End cap 24 additionally has one or more ports 44 which pass therethrough so as to enable the introduction or expulsion of gas, into that portion of chamber section 30 which is external to primary bellows 16. That is, gas is introduced into or expelled from the volume defined by piston 12, barrel 10, end cap 24 and bellows 16. Gas in this volume passes into and out of chamber section 28 via one or more ports 46 which extend through piston 12. Gas in chamber section 28 also passes into and out of the volume defined by end cap 22, bellows 18, collar 38 and stem 14. This is achieved by means of one or more ports 48 which extend through end cap 22.

The transfer of gas via ports 46 and 48 may or may not be supplemented by leakage between piston 12 and barrel 20 and between stem 14 and end cap 22. Any such leakage will depend upon manufacturing tolerances, including those of guide rings 34, if present. However, it is important to note that any such leakage does not in any way affect operation of the actuator, since any such leakage would merely supplement the transfer of gas which occurs via ports 46 and 48.

Primary bellows 16 permanently separates the gas and liquid within the actuator and allows for reciprocating movement of piston 12 within chamber 26. Secondary bellows 18 contains the gas within the actuator and allows for sufficient movement of the stem to enable the equipment, to which the actuator is attached, to be operated.

Thus, after the above described construction of the actuator, liquid chamber 40 is filled and flushed (if required) with operating liquid. The lines to the ports 42 can then be sealed with small line valves. The various volumes into which the gas is introduced can then be charged to a predetermined pressure, via gas ports 44. Gas ports 44 would normally be provided with back pressure valves such that the gas pressure is contained while the gas charging line is removed and respective charging port plugs are welded in place.

The gas used to charge the actuator is preferably an inert gas such as nitrogen or helium.

Operation of the actuator is quite straightforward.

Pressure applied to liquid chamber 40 will cause piston 12 to move within chamber 26, thus opening or closing the equipment (via stem 14) to which the actuator is attached. As the piston 12 moves, due to operating fluid being pumped into liquid chamber 40, the inert gas in chamber section 28 is compressed. When the equipment to which the actuator is attached has completed its full travel, there will be no further compression of the gas. Thereafter, any decrease in pressure in the liquid chamber (for whatever reason) will allow the gas to expand against the piston, thus causing expansion of the gas chamber and consequently reversing the movement of piston 12 within chamber 26.

It will be appreciated that the gas pressure also acts over the outside surface of primary bellows 16, thus reducing the pressure differential across the wall of bellows 16. However, it is conceivable that in some circumstances it may be desirable to exclude this feature.

The fact that gas is introduced into and expelled from the volume defined by the secondary bellows 18 prevents the possibility of any pressure decrease due to operation of the equipment to which the actuator is attached.

As has already been mentioned, it may be feasible to omit guide rings 34. This may particularly be the case when the actuator is to be used in a vertical position, rather than the illustrated horizontal position.

The actuator finds particular application in fail-safe valve systems.

It is immediately apparent from the foregoing description of the actuator, and the illustration given in figure 1, that the actuator is simple in construction and easily made very rugged and reliable. In particular, the actuator has no conventional seals and therefore its failure rate will be extremely low, if not negligible. As a result, it may not be necessary to make provision for the normal manual over-ride facilities, because such facilities will not be necessary. Furthermore, the actuator can be made compact, easy to handle and lighter and safer than conventional actuators.

In practice, additional components may be added to the actuator, (for example, so as to indicate the position of the piston and/or stem actuator within the valve, when the actuator is in place attached to the equipment).

It will be readily apparent to persons skilled in the art, from the foregoing description and accompanying illustration, that many variations of the specific embodiment may be made without departing from the scope of the invention.

Claims

1. An actuator comprising; a housing having an internal chamber, a piston mounted for reciprocating motion within the chamber, a stem coupled to the piston and passing to the outside of the housing via a stem aperture in the housing, whereby reciprocating motion of the piston can be transferred to a device to be operated by the actuator, first bellows sealingly connected between the piston and the housing to divide the chamber to provide for operating fluid to be used to reciprocate the piston within the chamber, and second bellows sealingly connected between the stem and the housing to prevent fluid communication between the chamber and the outside of the housing through the said aperture.

2. An actuator according to claim 1, wherein the said piston divides the said chamber into a first volume on one side thereof and a second volume on the other side thereof, the said first bellows being disposed within the said first volume and the said stem extending through the said second volume.

3. An actuator according to claim 2, wherein the said first bellows divides the said first volume into an inner volume and an outer volume, the said inner and outer volumes being mutually concentrically arranged about an axis parallel with the axis of reciprocation of the said piston.

4. An actuator according to claim 2 or 3, wherein the said second volume communicates with the working volume of the second bellows.

5. An actuator according to any preceding claim wherein the first bellows and the second bellows are of respectively different diameters.

6. An actuator according to claim 5, wherein the said first bellows has a diameter greater than that of the second bellows

7. An actuator according to any one of claims 2 to 6, wherein the said inner volume is charged with a liquid.

8. An actuator according to any one of claims 2 to 7, wherein the said second volume is charged with a gas.

9. An actuator according to one of claims 3 to 8, wherein the said outer volume communicates with the said second volume.

10. An actuator according to any one of claims 3 to 9 wherein the said inner volume is fed by means of an aperture provided in an end wall of the chamber distant the said stem aperture.

11. An actuator according to any one of claims 3 to 10, wherein the said outer volume is fed by an aperture provided in an end wall of the chamber distant the said stem aperture.

12. An actuator according to claim 9, 10 or 11, wherein the said outer volume communicates with the said second volume by means of an aperture provided in the said piston.

13. An actuator according to claim 9, 10, 11, or 12, wherein the said outer volume communicates with the said second volume by leakage between the said piston and an inner wall of the said chamber.

14. An actuator according to any one of claims 4 to 13, wherein the said second volume communicates with the working volume of the said second bellows by means of an aperture provided in a wall of the housing to which the second bellows is connected.

15. An actuator according to any one of claims 4 to 14 wherein the said second volume communicates with the working volume of the second bellows by means of leakage through the stem aperture.

16. An actuator according to any preceding claim wherein the said piston is supported in relation to the wall of the chamber by means of an annular support ring extending about the periphery of the said piston.

17. An actuator according to any preceding claim, wherein the said stem is supported in relation to the said stem aperture by means of a support ring provided about the periphery of the said stem aperture.

18. An actuator according to any preceding claim, wherein at least one of the said bellows is made from metal.

19. An actuator according to claim 18, wherein at least one of the said bellows is made from titanium, stainless steel or inconel.

20. An actuator according to any preceding claim, wherein a portion of the stem projecting from the housing comprises a reduced diameter portion which defines a shoulder and an annular collar is fitted about the said reduced diameter portion directly adjacent the said shoulder, one end of the said second bellows being secured to the collar.

21. An actuator according to any one of claims 8 to 20, wherein the said second volume is charged with helium or nitrogen.

22. An actuator according to any preceding claim, further comprising means for indicating the position of the piston relative to the chamber.

23. An actuator substantially as herein described with reference to the accompanying drawing.