GB2091346A

GB2091346A - Valve Actuator

Info

Publication number: GB2091346A
Application number: GB8200707A
Authority: GB
Original assignee: CAMTORC Ltd
Current assignee: CAMTORC Ltd
Priority date: 1981-01-12
Filing date: 1982-01-11
Publication date: 1982-07-28

Abstract

A rotary or linear valve actuator comprises a cylinder (1), a piston (6, 7) movable in the cylinder (1), a valve actuating member (9) actuable by the piston (6, 7) and means for supplying pressurised fluid, for example a hydraulic fluid, to the cylinder (1) for moving the piston (6, 7) in the cylinder. The pressurised fluid-supplying means includes a pressure intensifier (13) driven by a pressurised medium, for example compressed air, at a first pressure and arranged to deliver said pressurised fluid to the cylinder (1) of the actuator at a pressure higher than that of said pressurised medium. The pressure intensifier (13) conveniently comprises a first double-acting piston and cylinder assembly having a first piston (17) which is mechanically connected to a second piston (16) of a second double-acting piston and cylinder assembly, the second piston (16) having an area which is smaller than the area of the first piston (17) and the cylinders (15, 14) of the two piston and cylinder assemblies having their axes aligned with one another, and means (34-38) for supplying pressurised medium at said first pressure to the first piston and cylinder assembly for the purpose of reciprocating the first piston (17) in its cylinder (15). The second piston and cylinder assembly then constitutes the means for supplying pressurised fluid at said higher pressure to the actuator cylinder (1). <IMAGE>

Description

SPECIFICATION Valve Actuator Technical Field This invention relates to a valve actuator of the kind comprising a pressurised fluid-operated piston and cylinder assembly in which the piston is arranged to actuate the valve member of a valve. Although primarily intended for the actuation of rotary fluid-control valves, the actuator in accordance with the invention may be employed to actuate linearly actuable valves, for example gate valves.

Background Art It is known (see Published European Appiication No. 0 034 882) to actuate a rotary fluid-control valve by means of pressure fluidoperated actuator of the kind comprising a housing with a cylindrical bore, a piston assembly comprising a pair of spaced-apart pistons coupled together for simultaneous sliding movement within said cylindrical bore, a cam situated between the two pistons and secured to a valve actuating shaft rotatable about an axis fixed relative to the housing and disposed substantially at right angles to the longitudinal axis of said cylindrical bore with the peripheral surface of the cam engaging the confronting surfaces of the two pistons of said piston assembly, and means for supplying pressurised fluid to a space in said cylindrical bore for moving said piston assembly within the cylindrical bore.

By supplying a pressurised fluid, usually compressed air, to said space, the resulting movement of the piston assembly is converted by said cam into a rotary movement of said valve actuating shaft. The actuator may be of the single-acting type, in which rotation of the valve actuating shaft in only one direction, for example in the opening direction of the valve, can be effected by supplying pressurised fluid to said space, spring means then being provided for effecting rotation of the valve actuating shaft in the opposite direction. Alternatively, the actuator may be of the double-acting type, so that rotation of the valve actuating shaft in either direction can be effected by supplying pressurised fluid to different spaced in said cylindrical bore.Also in this case, spring means may be provided to assist rotation of the shaft in the closing direction of the valve, so that the valve can be closed in the event of failure of the pressurised fluid supply.

It is also known to actuate a linearly operable fluid-control valve by an actuator in the form of a single-or double-acting piston and cylinder assembly, in which the linear movement of the piston rod of the actuator actuates the linearly movable valve member of the valve. This type of actuator may also comprise spring means for effecting or assisting movement of the piston, usually in the valve closing direction.

These rotary and linear valve actuators are usually operated by a pressurised fluid supply (generally compressed air) at a pressure of up to about 10 kg/cm2 (gauge). When moderately low valve actuating torques or thrusts are involved, for example torques of up to 1000 Nm or thrusts of up to 500 kg, the actuator does not have an unacceptably large size. However, there is an ever-increasing demand valve actuators capable of producing considerably higher torques or thrusts than those quoted above, especially for operating valves on oil rigs.These higher torques or thrusts can, of course, be obtained by increasing the working pressure of the pressurised fluid without substantially increasing the overall dimensions of the actuator, but this leads to the disadvantage of having to provide very much more expensive auxiliary equipment for producing and storing the pressurised fluid at the considerably higher working pressure.

The present invention aims to provide a valve actuator of the kind referred to which does not have the disadvantage just referred to.

Disclosure of the Invention According to the invention, a valve actuator comprising an actuator cylinder, an actuator piston movable in the cylinder, a valve actuating member actuable by said piston, and means for supplying pressurised fluid to said cylinder for moving said piston in said cylinder, is characterised in that said pressurised fluidsupplying means comprises a pressure intensifier driven by a pressurised medium at a first pressure and arranged to deliver said pressurised fluid to said actuator cylinder at a pressure higher than that of said pressurised medium.

Said pressure intensifier may comprise first and second piston and cylinder assemblies having their cylinders axially aligned with one another and their pistons mechanically connected, the piston of said first piston and cylinder assembly having a larger area than the piston of said second piston and cylinder assembly, and means for supplying said pressurised medium at said first pressure to said first piston and cylinder assembly, said second piston and cylinder assembly constituting the means for supplying pressurised fluid at said higher pressure to said actuator cylinder. Said first piston and cylinder assembly may be double-acting, so that the piston of said first piston and cylinder assembly may be reciprocated in its cylinder by said pressurised medium.Then, by connecting the cylinder of said second piston and cylinder assembly to said actuator cylinder via a system of non-return valves, reciprocation of th piston of said second piston cylinder assembly can be made to cause movement of said actuator piston in one direction in said actuator cylinder.

In one embodiment of a valve actuator in accordance with the invention, said pressure intensifier comprises a first double-acting piston and cylinder assembly having a piston of a first diameter D which is mechanically connected to the piston of a second double-acting piston and cylinder assembly having a piston of a second diameter dwhich is smaller than D, the cylinders of the two assemblies having their axes aligned with one another. The piston of the first assembly is reciprocated in its cylinder by supplying a pressurised fluid medium, for example compressed air, to its cylinder at a pressure p, which is the aforesaid first pressure. The pressure p may, for example, be in the range of from 4 to 10 kg/cm2 (gauge).This reciprocation of the piston of the first assembly results in reciprocation of the piston of the second assembly and the creation of a pressure P in the fluid in the aforesaid pressurised fluid-supplying means, the pressure P, which is the aforesaid second pressure, being higher than the pressure p in accordance with the equation: D2 P=p.

d2 Thus, for example, by giving the piston of the first assembly a diameter D which is equal to 5d, the pressure P created in said pressurised fluidsupplying means will be 25p. Therefore, for example if the first piston and cylinder assembly is actuated with compressed air at a pressure of 8 kg/cm2 (gauge), it is possible to create a pressure of 200 kg/cm2 (gauge) in said pressurised fluidsupplying means.

In the embodiment just described, the pressurised fluid at the pressure P is contained in a closed, or substantially closed, circuit which includes the second piston and cylinder assembly of the pressure intensifier and the actuator cylinder of the valve actuator. In this case the pressurised fluid at the pressure P may be a fluid of the same or a different nature from the pressurised medium at the pressure p. At present, we prefer to employ a hydraulic fluid for the fluid atthe pressure P and compressed air for the medium at the pressure p. If, however, in the above described embodiment, the second piston and cylinder assembly is single-acting instead of double-acting, it is possible to use one and the same pressurised fluid in both of the piston and cylinder assemblies of the pressure intensifier.

A single pressure intensifier may be common to a plurality of valve actuators, the actuator cylinders of the various actuators then being connected in parallel with the pressure intensifier.

Brief Description of the Drawings The invention will now be described, by way of example, with reference to the accompanying drawings, in which Figure 1 is a schematic sectional view of a first embodiment of a valve actuator in accordance with the invention, and Figures 2 and 3 are schematic sectional views of parts of two modified forms of the embodiment of Figure 1.

Best Mode of Carrying out the Invention The valve actuator shown in Figure 1 comprises a housing 1 having a circular cylindrical bore 2 therein and end closure members 3 and 4.

Slidable within the bore 2 is a piston assembly, generally designated by the reference numeral 5 which comprises two pistons 6, 7 held together in spaced-apart relationship by rods 8.

A valve actuating shaft 9 is rotatably mounted in the wall of the housing 1, the axis of the shaft being disposed at right angles to the longitudinal axis of the bore 2. The shaft 9 is part of, or may be connected to, the valve member of a rotary fluidcontrol valve (not shown). A disc cam 10 is secured to the shaft 9 and has its peripheral surface bearing against the confronting surfaces of the pistons 6,7.

The space 11 in the bore 2 between the end closure member 3 and the piston 6 and the space 12 between the end closure member 4 and the piston 7 form part of a pressurised fluid-supplying means for moving the piston assembly 5 in the bore 2. In addition to the spaces 11 and 12, the pressurised fluid-supplying means comprises a pressure intensifier, generally designated by the numeral 13, connected to the spaces 11,12 by piping described hereinafter in greater detail.

The pressure intensifier 13 comprises axially aligned cylinders 14 and 1 5 having bores of diameters dand D, respectively, dbeing smaller than D. Pistons 1 6 and 1 7 are slidable in the cylinders 14 and 15, respectively, and the two pistons are joined to one another by a rod 18 which is slidable, in a fluid-tight manner in a wall 19 between the two cylinders 14, 15. Opposite ends of the cylinder 14 are connected by pipes 20 and 21, respectively, to a pipe 22 which is connected to a valve 23. A pipe 24 leads from the valve 23 to the space 11 in the bore 2. Non-return valves 25 and 26 are provided in the pipes 20 and 21, respectively, these valves allowing the flow of fluid from the cylinder 14 in the direction towards the valve 23, but not in the opposite direction.

Opposite ends of the cylinder 14 are also connected by pipes 27 and 28, respectively, to a pipe 29 which is connected to the valve 23. A further pipe 30 connects the valve 23 to the space 12 in the bore 2. Non-return valves 31 and 32 are provided in the pipes 27 and 28, respectively, these valves allowing the flow of fluid into the cylinder 14 in the direction from the valve 23, but not in the opposite directjon.

The valve 23 is a change-over valve which can be adjusted into either one of first and second limit positions. In its first limit position, shown in Figure 1, the valve 23 connects the pipe 22 to the pipe 24 and connects the pipe 29 to the pipe 30.

In its second limit position, the valve 23 connects the pipe 22 to the pipe 30 and connects the pipe 29 to the pipe 24.

The cylinder 14, the cylinder spaces 11 and 12 and the pipes 20-22, 24 and 27-30 are all filled with hydraulic fluid. The space 31 between the pistons 6 and 7 serves as a reservoir of hydraulic fluid and is connected by a pipe 32 to the pipe 29. The space 31 is vented to atmosphere at 33.

The cylinder 1 5 has its opposite ends connected to pipes 34 and 35, respectively, which are connected, via a changeover valve 36, similar to the valve 23, to a reservoir 37 of compressed air and to exhaust 38.

Let it be assumed that the various items described above are in their respective positions shown in Figure 1. Under these conditions, compressed air at a pressure p in the reservoir 37 flows to the cylinder space 39 in the cylinder 1 5 and the cylinder space 40 is connected to exhaust 38. The piston 1 7 therefore rises in the cylinder 1 5 and forces the piston 1 6 to rise in the cylinder 14. Hydraulic fluid in the cylinder space 41 above the piston 1 6 is forced out via pipes 20, 22 and 24 into the cylinder space 11 and moves the piston assembly 5 to the right in the bore 2, as viewed in Figure 1.Hydraulic fluid in the cylinder space 12 is forced out of this space via the pipes 30, 29 and 28 into the cylinder space 42 below the piston 1 6. The pressure P in the hydraulic fluid delivered to the cylinder space 11 is considerably higher than the pressure p of the compressed air in the reservoir 37, as determined by the equation D2 P=p.

d2 Movement of the piston assembly 5 to the right, as described above, causes rotation of the cam 10, and hence rotation of the valve actuating shaft 9 in a clockwise direction, as viewed in Figure 1.

When the piston 1 7 reaches the upper end of its stroke in the cylinder 15, the change-over valve 36 is moved to its other limit position, so that the cylinder space 40 is connected to the reservoir 37 and the cylinder space 39 is connected to exhaust 38. The piston 1 7 then moves downwardly in the cylinder 1 5 and forces the piston 16 to move downwardly in the cylinder 14. Hydraulic fluid in the cylinder space 42 below the piston 1 6 is then forced out via pipes 21, 22 and 24 into the cylinder space 11 and again moves the piston assembly 5 to the right in the bore 2. Hydraulic fluid in the cylinder space 12 is forced out of this space via the pipes 30, 29 and 27 into the cylinder space 41 above the piston 16.

From the above description it will be appreciated that, by reciprocating the piston 1 7 in the cylinder 15, which is effected by moving the change-over valve 36 between its two limit positions, the piston assembly 5 can be moved to the right to turn the valve actuating shaft in a clockwise direction.

By moving the change-over valve 23 to its other limit position, in which the pipes 22 and 30 are connected to one another and the pipes 24 and 29 are connected to one another, reciprocation of the piston 1 7 in the cylinder 1 5 results in movement of the piston assembly 5 to the left, as viewed in Figure 1, and consequent anticlockwise rotation of the valve actuating shaft 9.

In the event of failure of the compressed air supply to the cylinder 15, manual reciprocation of the pistons 16 and 1 7 may be effected using a lever arm 43 pivotally connected to a rod 44 connected to the piston 1 6 and passing out of the upper end of the cylinder 14.

The valve actuator shown in Figure 1 employs different pressurised media in the cylinders 14 and 1 5. If the wall 19 between the cylinders 14 and 1 5 is omitted, it is possible to use the same pressurised medium in both the cylinders 14 and 1 5. In this case, however, pressurised fluid at the pressure P will only be delivered to the cylinder space 11 (or 12) during upward movements (as viewed in Figure 1) of the piston 16 in the cylinder 14. During downward movements of the piston 16 only the pressure p will arise in the cylinder space 42. This means that it would take twice as long to turn the valve actuating shaft 9 through a given angle compared with the embodiment shown in Figure 1.

Figures 2 and 3 show modified embodiments of the actuator of Figure 1 which employ the same pressure intensifier as the actuator of Figure 1. To simplify the drawings, the pressure intensifiers have been omitted from Figures 2 and 3, but it can be assumed that the parts shown in Figure 1 below the chain line A-A are also present in each of the embodiments of Figures 2 and 3 below the chain lines A-A in each of those Figures.

Parts in Figures 2 and 3 which are the same as, or similar to, parts in Figure 1 have been designated with the same reference numerals as in Figure 1.

The valve actuator shown in Figure 2 again comprises a housing 1 with a cylindrical bore 2 and end closure members 3 and 4, a piston assembly 5 with spaced-apart pistons 6, 7 connected together by rods 8, a valve actuating shaft 9 and a disc cam 10, all as described with reference to Figure 1.

The numeral 50 designates a hollow cylindrical casing secured to the end closure member 4, the longitudinal axis of the casing 50 being aligned with the longitudinal axis of the bore 2. A piston 51 is slidable in the casing 50 and a helical spring 52 is housed in the casing 50 between the end 53 of the casing and the piston 51. A rod 54, which is slidable in fluid-tight manner in the end closure member 4, has one end connected to the piston 51 and its other end abutting the piston 7.

A space 55 in the casing 50, between the end closure member 4 and the piston 51, is connected by a pipe 56 to the pipe 24 which connects the valve 23 to the space 11 in the bore 2. The space 57 in the casing 50, between the piston 51 and the end 53 of the casing, is vented to atmosphere via a hole 58 in the end 53.

The change-over valve 23 again has two limit positions. In the first limit position, shown in Figure 2, the valve connects the pipe 22 to the pipe 24. In its second limit position, the valve 23 connects the pipe 29 to the pipe 24.

In use of the actuator shown in Figure 2, hydraulic fluid at pressure P from the pressure intensifier 1 3 (see Figure 1) is delivered via pipes 22 and 24 to the space 11 in the bore 2 and to the space 55 in the casing 50. At this time, the pressure intensifier 13 draws hydraulic fluid from the space 31 in the bore 2 via pipe 32. The action of the pressure intensifier 13 results in movement of the piston assembly 5 to the right, as viewed in Figure 2, and clockwise rotation of the valve actuating shaft 9. At the same time, the hydraulic fluid supplied to the space 55 in the casing 50 moves the piston 51 to the right, as viewed in Figure 2, compressing the spring 52 and relieving the piston assembly 5 from the action of the spring 52.Consequently, a substantially constant torque is applied to the valve actuating shaft 9 as the piston assembly 5 moves to the right along the bore 2.

If the change-over valve 23 is now moved to its previously mentioned second limit position, the pipe 24 is connected to the pipe 29, so that the spaces 11 and 55 become connected to the space 31 in the bore 2 via the pipes 24,29 and 32. The spring 52 then re-asserts itself and moves the piston assembly 5 to the left (as viewed in Figure 2) via the piston 51 and the rod 54. This results in rotation of the valve actuating shaft 9 in the anticlockwise direction.

The valve actuators of Figures 1 and 2 are rotary actuators. Figure 3 shows a linear actuator comprising a housing 1, with a cylindrical bore 2 and end closure members 3 and 4, in which a piston 60 is slidable. The piston 60 has a piston rod 61 which passes through the end closure member 3 and forms part of, or is connected to, the linearly movable valve member of a fluid control valve (not shown), for example a gate valve.

A helical spring 62 is located in the housing 1 between the piston 60 and the end closure member 4. The space 11 in the bore 2 is connected to the valve 23 by the pipe 24 and the space 63 in the bore 2, between the piston 60 and the end closure member 4, is connected to the pipe 32. The change-over valve 23 is constructed in the same way as the change-over valve 23 of Figure 2.

In use of the actuator shown in Figure 3, hydraulic fluid at pressure P from the pressure intensifier 13 (see Figure 1) is delivered via pipes 22 and 24 to the space 11 in the bore 2. At this time the pressure intensifier 13 draws the hydraulic fluid from the space 63 in the bore 2 via pipe 32. The action of the pressure intensifier 13 results in movement of the piston 60 to the right, as viewed in Figure 3, and consequent movement to the right of the valve actuating rod 61. At the same time the spring 62 is compressed.

If the change-over valve 23 is now moved to its previously mentioned second limit position, the pipe 24 is connected to the pipe 29, so that the space 11 becomes connected to the space 63 in the bore 2 via the pipes 24, 29 and 32. The spring 62 then re-asserts itself and moves the piston 60 to the left (as viewed in Figure 3). This results in movement to the left of the valve actuating rod 61.

The invention is not, of course, limited to the particular construction of the pressure intensifier 13 shown in Figure 1. For example, reciprocation of the piston 17 in the cylinder 15 may be effected with a pressurised medium in other ways than that described.

Again, it must also be appreciated that the drawings are of a purely schematic nature and that in practice the parts 1, 1 3 and 23 would not necessarily be separate from one another, but could be assembled together in a single unit.

Claims

1. A valve actuator comprising an actuator cylinder, an actuator piston movable in the cylinder, a valve actuating member actuable by said piston, and means for supplying pressurised fluid to said cylinder for moving said piston in said cylinder, in which said pressurised fluid-supplying means comprises a pressure intensifier driven by a pressurised medium at a first pressure and arranged to deliver said pressurised fluid to said actuator cylinder at a pressure higher than that of said pressurised medium.

2. A valve actuator according to claim 1, in which said pressure intensifier comprises first and second piston and cylinder assemblies having their cylinders axially aligned with one another and their pistons mechanically connected, the piston of said first piston and cylinder assembly having a larger area than the piston of said second piston and cylinder assembly, and means for supplying said pressurised medium at said first pressure to said first piston and cylinder assembly, said second piston and cylinder assembly constituting the means for supplying pressurised fluid at said higher pressure to said actuator cylinder.

3. A valve actuator according to claim 2, in which said first piston and cylinder assembly is double-acting, whereby the piston of said first piston and cylinder assembly may be reciprocated in its cylinder by said pressurised medium.

4. A valve actuator according to claim 3, in which the cylinder of said second piston and cylinder assembly is connected to said actuator cylinder via a system of non-return valves, whereby reciprocation of the piston of said second piston and cylinder assembly causes movement of said actuator piston in one direction in said actuator cylinder.

5. A valve actuator according to any of the preceding claims, in which said actuator piston and actuator cylinder provide a double-acting assembly.

6. A valve actuator according to any of claims 1 to 4, in which said actuator piston and actuator cylinder provide a single-acting assembly in which said pressurised fluid is employed to drive said actuator piston in one direction and spring means is arranged to drive said actuator piston in the opposite direction.

7. A valve actuator according to any of the preceding claims, in which said valve actuating member is rotatable by said actuator piston.

8. A valve actuator according to any of claims 1 to 6, in which said valve actuating member is linearly movable by said actuator piston.

9. A valve actuator constructed and arranged substantially as herein described with reference to, and as illustrated in, Figure 1, Figure 2 or Figure 3 of the accompanying drawings.