GB2147051A - Fluid pressure actuator - Google Patents

Abstract

A fluid pressure actuator having a pair of diaphragms 61, 63 on a single actuator rod assembly. The actuator housing defines a pair of spaced diaphragm chambers 94, 96 and includes a spacer spool 53 which is bolted to the adjacent chamber defining members 51, 56. The rod assembly comprises aligned stem members 71, 72, 28 which are normally maintained in engagement by gravity. A single inlet 91 is provided for simultaneous delivery of pressurized fluid to the diaphragm chambers by passages 93, 95, 97 in the upper stem 71 of the rod assembly. A stem sealing means 85, 86 between the stem member 72 of the rod assembly and the member 56 for the lower diaphragm 63 is of weld-free construction and allows limited relative lateral movement of the actuator stem members 71, 72, 28 which together with their disjointed association avoids binding and galling of the actuator rod assembly and permits independent operation of the diaphragms. An adapter member 43 for connection with a device to be actuated is secured within the axial opening of a lower housing member 52. A spring 76 between the adapter 43 and a spring support plate 74 affixed to the actuator rod assembly biases the diaphragms and rod assembly in an axial direction opposed to the fluid pressure. Travel of the actuator rod assembly is controlled by a downstop member 75 mounted on the spring support plate 74. <IMAGE>

Description

SPECIFICATION Fluid pressure actuator This invention relates to fluid pressure actuators of the diaphragm type and more particularly to actuators employing multiple diaphragms on a single actuator rod.

Fluid diaphragam actuators are widely used in wellhead safety systems. Typically, the systems detect pressures in excess of predetermined high and low pressure limits and respond automatically to control the operation of a fluid actuator for opening or closing a safety valve. In limited space applications, dual piston or dual diaphragm actuators are particularly useful. Since the total diaphragm area is doubled, there is a virtual doubling of the actuator output force for a given fluid pressure supply. Although the length of such actuators is greater than that of a single piston actuator of corresponding piston area, the cross-sectional area of the actuator is considerably less.When these actuators are mounted in other than vertical orientations, however, there is a tendency of the actuator rod to "bind" and in some instances prevent its full operation as well as that of the actuated device, as for instance, an actuated valve from fully opening or closing. Such "binding" effects also lead to galling of the actuator rod or valve stem and therefore more frequent repairs are necessary. It is also common to use a welded construction throughout much of the dual diaphragm actuators which therefore makes it expensive and time consuming to undertake repairs and maintenance. In addition, adjusting the thrust of the actuator, and, for example, the drift of a valve gate connected therewith has heretofore been a difficult and complex operation.

The object of the invention is to provide a fluid pressure actuator in a simple and convenient form.

According to the invention a fluid pressure actuator comprises an actuator housing including a first upper casing member, a second casing member, and a spacer member releasably interconnecting and separating said casing members in coaxial aligned relationship, a first diaphragm secured to said first casing member and defining therewith a first sealed fluid chamber, a second diaphragm secured to said second casing member and defining therewith a second sealed fluid chamber, an actuator rod means extending through said chambers and comprising an upper stem, an intermediate stub stem and a lower stem disposed in abutting coaxial relation, said upper stem extending through central openings provided in said first casing member, said first diaphragm, said spacer member, and said casing member respectively, and said lower stem being adapted for connection to a device to be actuated, first seal means mounted in the central opening through said first casing member for establishing a fluid-tight seal between the first casing member and said upper stem, said upper stem being adapted for axial reciprocating motion therethrough, first clamp means for clamping said diaphragm to said upper stem in fluid-tight sealing relation therewith, an annular plug disposed in sleeved relation to said upper stem and mounted within the central opening in said second casing member, said plug being of slightly smaller diameter than the casing opening in which it is disposed to accommodate limited lateral movement of the plug, second seal means mounted on said plug for establishing a fluid-tight seal between said second casing member and said upper stem and between said plug and second casing member, said upper stem being adapted for axial reciprocating motion through said plug, second clamp means for clamping said second diaphragm to the intermediate stub stem in fluid-tight sealing relation, a cup-shaped lower housing member having an axial opening therein and being releasably secured to said second casing member and said spacer member in coaxial alignment with said actuator rod means, said lower housing member adapted to be secured on a device to be actuated, an annular adapter member secured within said axial opening in coaxial alignment with said actuator rod means and said lower stem extending through said adapter member, a coiled compression spring disposed in sleeved relation to said lower actuator stem with its lower end supported on the annular adapter member, a spring support plate seated atop the other end of the coiled spring and secured atop the lower actuator stem in coaxial alignment therewith whereby said spring exerts a constant biasing force on said actuator rod means and said diaphragms in one direction of axial movement, and fluid inlet means provided in said actuator housing and adapted for connection to a source of pressurized fluid whereby pressurized fluid may be selectively and simultaneously admitted to said first and second fluid chambers to drive the diaphragms and actuator rod means in the axial direction opposed to the spring biasing force.

One example of an actuator in accordance with the invention will now be described with reference to the accompanying drawing which is a sectional side elevation of fluid control valve including the actuator.

The plural diaphragm actuator 10 is shown in an installation for controlling the operation of a gate valve 11, which is shown in the closed position. The valve 11 comprises a valve body 1 2 having a valve chamber 1 3 therein and a flow passage 14 which extends through the valve body and intersects the valve chamber 1 3. End flanges 1 5 are provided on the valve body to allow its installation in a flowline.The valve is provided with a bonnet 1 9 which is bolted to the valve body 12 by means of studs 1 6 and closes off the valve chamber 1 3. The valve element is a gate 20 which is located within the chamber 1 3 between a pair of valve guides 21 and which is movable in a direction transverse to the flow passage 14 to open and close the valve.

A pair of seat rings 25, 26 disposed in surrounding relation to the flow passage on each side of the gate provide a fluid-tight seal against the flat side faces of the gate for sealing off the flow passage.

The gate 20 is also provided with a port 23 which is of a configuration conforming to that of the cross section of the flow passage 14 and in the open position of the valve is disposed in registry with the flow passage 14.

The gate 20 is connected to a valve stem 28 by means of a connection wherein the lower threaded end of the stem 28 is received in a drive nut 29 positioned within a transverse slot 31 formed adjacent the top end of the gate 20 and secured to the stem by means of a pin 29A. However, a stem-togate connection as shown in U.S. Patent No.

3,463,446 or U.S. Patent No. 4,376,524 might also be employed.

The stem 28 extends through an axial bore 33 formed through the bonnet 1 9 and also through a packing gland assembly which is mounted in an enlarged diameter portion of the bore 33. Annular packing members 36 of the packing assembly provide fluid-tight sealing between the valve bonnet and the valve stem when compressed by the packing adapter 37 which is threaded into the enlargement of the stem bore which receives the packing gland assembly. O-rings 38, 39 located in the inner and outer walls, respectively, of the packing adapter 37 provide additional seals between the bonnet and stem. The upper end portion of the bonnet 1 9 is provided with a cylindrical portion of reduced external diameter which provides an upward facing annular shoulder 41.

An annular bonnet adapter 43 is seated on the shoulder 41 and disposed in sleeved relation about the cylindrical upper portion of the bonnet 19 and seals 35 provide for sealing between the bonnet and adapter 43. The bonnet adapter 43 is secured by a split ring 44 which is received in an accommodating circumfferential groove in the cylindrical surface 40 of the bonnet 1 9. A shear pin 45 which is located between the bonnet 1 9 and the bonnet adapter 43 in adjacent vertical grooves in the inner wall of the bonnet adapter and the external surface of the bonnet 19, respectively, serves to prevent rotation of the bonnet adapter on the bonnet 1 9.

The actuator 10 comprises upper and lower bowl shaped housing members 51, 52, and a spacer spool 53 disposed therebetween which together define a housing of the actuator. The lower housing member 52 is of a generally bowl shape configuration with a central bottom opening defined by a cylindrical end portion 52A having an inner diameter corresponding to the external diameter of the bonnet adapter 43. The cylindrical end 52A of the lower housing is dispoed in sleeved relation to the bonnet adapter 43 and bolted thereto by a plurality of circumferentially spaced bolts 55. The upper and lower housing members are provided with circumferential radial flanges 51B, 52B, respectively, at their wide open ends and the spacer spool 53 is similarly provided with radial flanges 53A, 53B at its upper and lower ends, respectively.

A bowl-shaped divider member 56, also provided with a peripheral flange 56A, is positioned with its periphery clamped between the spacer spool 53 and the lower housing 52.

A flexible diaphragm 61 is mounted within the chamber defined by the upper housing member 51, the spacer spool 53 and the divider member 56. Diaphragm 61 is disposed with its periphery clamped between the flanges 51 B, 53A of the upper housing member 51 and spacer spool 53 by means of a plurality of bolts 62 through the flanges 51 B, 53A. In like manner, the periphery of a second flexible diaphragm 63 and the bowlshaped divider member 56 are clamped between the radial flanges 53B and 52B of the spacer spool and lower housing member 52.

The divider member 56 is formed with a bowl shape configuration substantially identical to that of the upper housing member 51 and is disposed with its convex surface facing the concave surface of the upper housing member 51. The flange 56A of the divider 56 is of a diameter and configuration conforming substantially with the flange 52B of the lower housing member 52 and is disposed atop the peripheral portion of the diaphragm 63. A plurality of circumferentially spaced bolts 64 extend through the flanges 53B and 52B and clamp the diaphragm 63 in fluid-tight sealing relationship therebetween, with the diaphragm 63 being disposed within the chamber defined by the divider 56 and lower housing member 52.

The diaphragms 61, 63, the upper housing member 51 and the divider member 56 are each provided with a central opening for accommodating the actuator rod assembly which extends therethrough. The actuator rod assembly is comprised of an upper stem 71 which rests atop an intermediate stub stem 72 in axial alignment therewith. The stub stem 72, in turn, rests atop the head of a bolt 73 which passes through the central opening of an annular spring support plate 74 and is threaded into a threaded axial bore provided in the top end of the stem 28.

The spring support plate 74 is provided with an annular radial flange at its upper end and is externally threaded from the flange to its lower end for accommodating a cylindrical downstop member 75 which is adjustably threaded thereon. A coiled spring 76 is disposed with its upper end abutting the underside of the support plate flange in coaxial relationship with the cylindrical downstop 75.

The bottom end of the spring 76 is supported on an upwardly facing annular shoulder of the bonnet adapter 43.

The diaphragm 63 is supported on a circular retainer plate 77 having a central opening which receives the intermediate stub stem 72 therethrough. The retainer plate 77 is supported on a split ring 78 which is mounted in a circumferential groove formed in the stub stem 72 adjacent its lower end. A nut 79 is threaded onto the upper end of the stub stem 72 for clamping the diaphragm 63 against the flat upper surface of the retainer plate 77 and the retainer plate against the split ring 78.

In like manner the upper diaphragm 61 is supported on a circular retainer plate 81 having a central opening which receives the upper stem 71 therethrough. The retainer plate 81 is supported on a split ring 82 which is mounted in a circumferential groove formed in the external surface of the stem 71. A nut 83 is threaded onto a threaded portion of the stem 71 and clamps the diaphragm 61 against the upper surface of the retainer plate 81 and also the retainer plate 81 against the split ring 82.

It is also to be noted that the upper end portion of the stem 71 is provided with a smooth surface of reduced diameter which is slidably received in the smooth bore of an externally threaded boss 89 which is located at the centre of the upper housing member 51. The boss 89 is externally threaded to allow connection to the actuator of a manual override mechanism which may be provided, if desired, for locking the actuator in a valve open position wherein the gate port 23 is in registry with the flow passage through the valve. For sealing purposes, O-rings 84 are provided in the wall of the bore through the boss 89 for sealing against the stem 71.

The lower end portion of the stem 71 is slidably received in the smooth bore of an annular plug 85 which is mounted in the opening at the centre of the chamber divider 56. The plug 85 is provided with an annular radial flange at its lower end which abuts against the underside of the chamber divider 56 in sealing relationship therewith by virtue of an O-ring 86 located in the upper face of the plug flange. The plug 85 is secured to the divider 56 by a retainer ring 87 which clamps the plug in sealing relationship with the divider 56. An O-ring 88 in the bore wall of the plug 85 seals against the stem 71. The external diameter of the plug 85 is designed so as to be slightly smaller than that of the opening through the divider 56 in which it is received, to provide for limited lateral movement of the plug for purposes later described herein.

The actuator is adapted to receive pressurized actuating fluid through a threaded port 91 in the upper housing member 51 for accommodating connection of a fluid supply conduit, which for most uses, would supply a pressurized pneumatic fluid. An outlet port 92 is also provided in the upper housing member 51 and includes threads for receiving a pressure relief valve, or the like, therein.

It will also be seen that the upper stem 41 is provided with an axial longitudinal passage 93 which communicates with the chamber space 94 directly above the upper diaphragm 61 by means of a cross port 95 and communicates with the chamber 96 defined by the lower diaphragm 63 and the divider member 56 by means of one or more laterally extending passages 97 which open to the chamber 96.

It will therefore be seen that pressurized fluid delivered to the chamber 94 through the port 91 will be. instantly communicated to the chamber 96 by means of the stem passages 95, 93 and 97 to drive both of the diaphragms and the valve stem downwardly against the upward biasing force of the spring 76. This diaphragm action is facilitated by the provision of ports 98 through the wall of the spacer spool 53 and similar ports 99 through the wall of the cylindrical extension 52A of the lower housing member 52 so that the undersides of the diaphragms are exposed to ambient atmospheric pressure. The downward movement of the actuator rod assembly and valve stem 37 moves the gate 20 to the open position of the valve wherein the gate port 23 is aligned with the flow passage 14.

In order to assure a proper setting of the gate travel or drift, adjustment thereof may be accomplished by adjusting the position of the cylindrical downstop member 75 on the spring support plate 74. The downward movement of the actuator rod and the gate element 20 is arrested by the engagement of the bottom surface 100 of the cylindrical downstop member 75 with the top surface of the bonnet adapter 43. By use of a drift mandrel through the flow passage 14 and the gate port 23, the position of the downstop member on the spring support plate can be axially adjusted so that its engagement with the bonnet adapter 43 occurs when the gate port 23 is in registry with the flow passage 14. A set screw 102 may then be inserted through an opening in the wall of the downstop member 75 to lock the downstop member on the spring support plate.

It is also to be noted that while the stem members 71 and 72 of the actuator rod assembly are disposed in axial alignment with one another and the valve stem 28, these three members are not connected to one another but are merely disposed in stacked arrangement where contact is maintained by the force of gravity. Should the actuator be employed in an installation wherein the actuator rod assembly is disposed horizontal or in any orientation other than vertical, a limited relative lateral movement between the stem members 28, 71 and 72 is permitted in view of their relative disjointed association and the limited lateral movement of the plug 85 in the divider 56. Accordingly, "binding" of the actuator stem members as might cause malfunction of the actuator or galling of the stem members is alleviated.

Another important feature of the invention is the incorporation of a through-the-stem pneumatic fluid supply to provide actuating fluid to each of the actuator diaphragms which avoids the necessity of two feed lines and two or more outlets and the problems which can be presented thereby, such as derive from a differential in supply pressures and the requirement for many more components. So long as fluid pressure is applied to the diaphragms 61, 63 to create a downwards force which exceeds the upwards biasing force of the spring 76, the diaphragms will be driven downward to the position controlled by the downstop 75. Upon removal of fluid pressure, of course, the diaphragms are returned to the position shown in the drawing by the coiled spring 76.

By virtue of the simple construction of the actuator, which is essentially weld-free, it is easy to disassemble the actuator for maintenance or repair. It also makes it very easy to convert a single diaphragm actuator to a multiple diaphragm actuator if such becomes desirable by replacing the actuator rod with an actuator rod assembly as shown in the preferred embodiment of this invention and by adding the structure which is shown mounted atop the divider 56.

It will be understood that the actuator need not be limited to two diaphragms but may employ three or more diaphragms if desired.

Moreover, the actuator fluid supply might be hydraulic as well as pneumatic. Furthermore, the actuator may be employed in a variety of applications other than the operation of a gate valve.

Claims (5)

1. A fluid pressure actuator comprising an actuator housing including a first upper casing member, a second casing member, and a spacer member releasably interconnecting and separating said casing members in coaxial aligned relationship, a first diaphragm secured to said first casing member and defining therewith a first sealed fluid chamber, a second diaphragm secured to said second casing member and defining therewith a second sealed fluid chamber, an actuator rod means extending through said chambers and comprising an upper stem, an intermediate stub stem and a lower stem disposed in abutting coaxial relation, said upper stem extending through central openings provided in said first casing member, said first diaphragm, said spacer member, and said casing member respectively, and said lower stem being adapted for connection to a device to be actuated, first seal means mounted in the central opening through said first casing member for establishing a fluid-tight seal between the first casing member and said upper stem, said upper stem being adapted for axial reciprocating motion therethrough, first clamp means for clamping said diaphragm to said upper stem in fluid-tight sealing relation therewith, an annular plug disposed in sleeved relation to said upper stem and mounted within the central opening in said second casing member, said plug being of slightly smaller diameter than the casing opening in which it is disposed to accommodate limited lateral movement of the plug, second seal means mounted on said plug for establishing a fluidtight seal between said second casing member and said upper stem and between said plug and second casing member, said upper stem being adapted for axial reciprocating motion through said plug, second clamp means for clamping said second diaphragm to the intermediate stub stem in fluid-tight sealing relation, a cup-shaped lower housing member having an axial opening therein and being releasably secured to said second casing member and said spacer member in coaxial alignment with said actuator rod means, said lower housing member adapted to be secured on a device to be actuated, an annular adapter member secured within said axial opening in coaxial alignment with said actuator rod means and said lower stem extending through said adapter member, a coiled compression spring disposed in sleeved relation to said lower actuator stem with its lower end supported on the annular adapter member, a spring support plate seated atop the other end of the coiled spring and secured atop the lower actuator stem in coaxial alignment therewith whereby said spring exerts a constant biasing force on said actuator rod means and said diaphragms in one direction of axial movement, and fluid inlet means provided in said actuator housing and adapted for connection to a source of pressurized fluid whereby pressurized fluid may be selectively and simultaneously admitted to said first and second fluid chambers to drive the diaphragms and actuator rod means in the axial direction opposed to the spring biasing force.

2. A fluid pressure actuator comprising an actuator housing including a first upper casing member, a second casing member, and a spacer spool releasably interconnecting and separating said casing members in coaxial aligned relationship, a first diaphragm secured to said first casing member and defining therewith a first sealed fluid chamber, a second diaphragm secured to said second casing member and defining therewith a second sealed fluid chamber, an actuator rod means extending through said chambers and comprising an upper stem, an intermediate stub stem and a lower stem disposed in abutting coaxial relation, said upper stem extending through central openings provided in said first casing member, said first diaphragm, and said second casing member respectively, and said lower stem being adapted for connection to a device to be actuated, first seal means mounted in the central opening through said first casing member for establishing a fluidtight seal between the first casing member and said upper stem, said upper stem being adapted for axial reciprocating motion therethrough, first clamp means for clamping said first diaphragm to said upper stem in fluidtight sealing relation therewith, an annular plug disposed in sleeved relation to said upper stem and mounted within the central opening in said second casing member, said plug being of slightly smaller diameter than the casing opening in which it is disposed to accommodate limited lateral movement of the plug, second seal means mounted on said plug for establishing a fluid-tight seal between said second casing member and said upper stem and between said plug and second casing member, said upper stem being adapted for axial reciprocating motion through said plug, second clamp means for clamping said second diaphragm to the intermediate stem in fluid-tight sealing relation, a cup-shaped lower housing member having an axial opening therein and being releasably secured to said spacer spool in coaxial alignment therewith, an annular adapter member secured within said axial opening in coaxial alignment with said actuator rod means and said lower stem extending through said adapter member, a coiled compression spring disposed in sleeved relation to said lower actuator stem with its lower end supported on the annular adapter member, a spring support plate seated atop the other end of the coiled spring and bolted atop the lower actuator stem in coaxial alignment therewith whereby said spring exerts a constant biasing force on said actuator rod means and said diaphragms in one direction of axial movement, passage means provided in said upper stem for establishing fluid communication between said first and second fluid chambers, inlet means provided through the wall of said first casing member and adapted for connection in use to a source of pressurized fluid whereby pressurized fluid may be selectively admitted to said first fluid chamber and simultaneously therewith the said second fluid chamber by means of said passage means to drive said diaphragms and actuator rod means in an axial direction opposed to the spring biasing force, and an adjustable stop member threadedly mounted on the spring support plate for relative axial adjustment thereon, said stop member being disposed to engage said adapter member and to limit the axial movement of the actuator rod against the action of said spring.

3. A fluid pressure actuator comprising an actuator housing including a first cup-shaped casing member having a first flange means, a second cup-shaped casing member having a second flange means, and a spacer spool having annular flanges at each of the ends thereof, respectively, a first diaphragm spanning said first casing member and having its outer peripheral portion held between said first flange means and a flange of said spacer spool and defining therewith a first sealed fluid chamber, first releasable fastening means for fastening said first casing member to said spacer member in coaxial alignment therewith, a second diaphragm spanning said second casing member and having its outer peripheral portion held between said second flange means of said second casing member and the third flange means of said lower housing member and defining therewith a second sealed fluid chamber with said second casing member, a cup-shaped lower housing member having an axial opening therein and a third flange means at the lip thereof, second releasable fastening means extending through the other flange of said spacer tool and said second and third flange means to secure said second casing member and spacer spool in coaxial aligned relation, actuator rod means extending through central openings in said casing members, said diaphragms, and the axial opening in said lower housing member, and having an end thereof adapted for connection to a device to be actuated, first seal means mounted in the central opening through said first casing member for establishing a fluid-tight seal between the first casing member and said actuator rod means, said rod means being adapted for axial reciprocating motion therethrough, first clamp means for clamping said first diaphragm to said actuator rod in fluid-tight sealing relation therewith, second seal means mounted in the central opening through said second casing member for establishing a fluid-tight seal between said second casing member and said actuator rod means, said actuator rod means being adapted for axial reciprocating motion therethrough, second clamp means for clamping said second diaphragm to said actuator rod means in fluid-tight sealing relation therewith, an annular adapter member secured within the axial opening of said lower housing member in coaxial alignment with said actuator rod means extending through said adapter member, a coiled compression spring disposed in sleeved relation to said actuator rod means with its lower end supported on the annular adapter member, a spring support plate seated atop the other end of the coiled spring and secured to the actuator rod means in coaxial alignment therewith whereby said spring exerts a constant biasing force on said actuator rod means and diaphragms in one direction of axial movement, and fluid inlet means in said actuator housing adapted for connection to a source of pressurized fluid whereby pressurized fluid may be simultaneously admitted to said first and second fluid chambers to drive the diaphragms and actuator rod means in the axial direction opposed to the spring biasing force.

4. A fluid pressure actuator as claimed in Claim 3 wherein said first and second releasable fastening means are a plurality of bolts extending through superposed flanges on the fastened members.

5. A fluid pressure actuator comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawing.