Gas spring actuator

Abstract: The gas spring actuator (10), when attached to a valve (29), will return the valve (29) to its initial position after the valve (29) has been moved to a second position by application of a pressurized fluid that opposes the gas spring. The gas spring is charged to a predetermined gas pressure. A hydraulic fluid is applied in an opposing manner to drive the piston (26, 28) in one direction to operate the valve (29) and simultaneously pressurize the gas in the gas spring. Upon removal of the hydraulic pressure, the pressurized gas returns the piston (26, 28), and the valve (29), to its initial position.

Description: FIELD OF THE INVENTION The present invention relates in general to actuators and in particular to a valve actuator having a gas spring in which gas is compressed when the piston moves from its initial position to a second position under a hydraulic force and which returns the piston to its initial position when the hydraulic force is removed. BACKGROUND OF THE INVENTION It is well known in the petroleum industry that gate valves are required for use in the piping at various locations and in particular in piping known in the industry as a christmas tree located at a drilling location. The gate valve opens and closes to contain pressure within the well bore. It is also well known in the industry that wireline is used to lower tools of various types into the well bore in an oil or gas well through the bore of the safety valve in the upper master valve of the christmas tree. It is necessary therefore to attach an actuator to the safety valve, which may be of the gate valve type, that will provide the forces necessary to move the valve between the open and closed positions by application or removal of a pressurized fluid. In a typical application the valve would incorporate a reverse-acting gate in a conventional manner which would be moved to the open position by application of a pressurized fluid through the inlet port to the top of the actuator piston. Upon removal of the pressure applied to the inlet port, the safety valve would move to the closed position due to the force developed by valve body pressure acting on the area of the valve stem. The actuator design in the prior art incorporates a linear force storage device which assists in closing and is capable of closing the valve when valve body pressure is not present. This type of operation is conventional in safety valves. On occasion, however, wireline may be extending through the safety valve because of tools of various types that have been lowered into the well bore. It may be necessary to close the valve with sufficient force to cut the wireline. The additional factor in wireline cutting actuators is that the closing force must be sufficient not only to close the valve when valve body pressure is absent, but also to provide the additional force to cause the valve gate to shear through any wireline that is in the valve bore at the time of closing. Wireline cutting actuators to perform this function are common in the industry. In most cases, the design force at the wire cutting position is over eight thousand pounds. Traditionally, this force has been developed by large coil springs, cams, helical springs, spring washers or other type devices. The prior art devices have a number of disadvantages. First, they must be very large to accommodate the size of springs that are necessary to develop the force that must be present to cut wirelines. Thus, they are very heavy and very large. In addition, the force generated by the metal springs is in proportion to the size and weight. Thus, there is a limit to the force that can be generated inasmuch as the size of the actuator is a factor to be considered in the use of the devices at the wellhead. Further, in order to have a predetermined force necessary to close the valves without any well pressure, there must be a predetermined compression built into the springs which creates a hazard condition when disassembling and handling the valves. Also, it is difficult to provide a variable and adjustable closing force with the use of metal springs. Further, there is no way to indicate the force units available in such a device. One simply has to know from the construction and the age of the device how much force it can provide. A gas spring valve actuator as defined in the precharacterizing portion of independent claim 1 is disclosed in US-A-4,563,941 which discloses a hydraulically actuated cylinder and piston assembly having a gas spring comprising an end cap secured to the actuator cylinder and an abutment fixed to the actuator piston. The gas charge is contained in a chamber between the end cap and the abutment. The use of an air spring in an auto-return actuator cylinder piston assembly is also referred to in US-A-4,759,260 and 4,216,703. SUMMARY OF THE INVENTION In accordance with the invention there is provided a gas spring valve actuator for moving a valve between open and closed states comprising: an actuator housing; a hydraulic piston slidable in said housing between first and second positions and having a rod for transferring power and a head for receiving hydraulic pressure; means for coupling the piston rod to the valve to change the valve position between open and closed states by moving the piston rod; a gas spring in the actuator housing operatively associated with one side of the hydraulic piston and having a compressible fluid therein; and means for pressurising the actuator housing on the other side of the piston with a predetermined fluid pressure to actuate the valve from a first state to a second state by moving the piston from a first to a second position and compressing the fluid in the gas spring such that when the fluid pressure is removed, the compressed fluid returns the piston to its first position and the valve to its first state, characterized in that said gas spring comprises: a first movable gas spring body member positioned on said one side of the piston, i. e. under the piston head, and surrounding the hydraulic piston rod; a hollow chamber at least partly formed by the first body member surrounding the hydraulic piston rod for receiving the compressible fluid; a second stationary gas spring body member positioned in the actuator housing and surrounding the piston rod, said second gas spring body member having one end thereof sealably and slidably inserted in the hollow chamber formed by the first movable gas spring body member; and an annular chamber in the second gas spring body member in gas transfer relationship with the hollow chamber formed by the first gas spring body member. The gas spring body members fitting around the valve stem create a uniform force in a minimum size envelope. The gas spring can develop the high forces required in a smaller package than that which must be used with standard metal springs. Pressure in the gas spring forces the first body member and piston in a direction to exert force on top of the valve bonnet and the gas spring housing to exert force on the actuator piston and gate valve stem urging the stem to move the sealing element of the gate valve to the closed position. An integral gas charging device can be connected to the interior of the second body member of the gas spring by a sealed connection. The side force generated by the gas charge pressure acting on this connection can be balanced by a connection of equal size on the opposite side of the second body member. This design counteracts all side forces developed at the pressure ports. The force of the gas spring depends upon pressure trapped in the spring cylinder created by the first and second spring body members. By having an integral charging device, the pressure can be changed, thus changing the closing force without changing any parts or disassembling the actuator. Thus, a variable and adjustable closing spring force can be provided. Further, the integral charging device for the gas spring may include a pressure gauge that will constantly indicate the pressure trapped inside the gas spring cylinder. Since the areas exposed to pressure are constant, the pressure is in a direct relationship with force and the gauge may be calibrated in force units available. In this way, the actuator can be checked regularly for available closing force without disassembly. In addition, the gas spring can produce forces in excess of that available with other types of conventional metal springs in the same overall size outer housing. The smaller size and weight are important in applications on wellheads on offshore oil and gas production platforms. This becomes an advantage in installation and maintenance, especially on high density production platforms. In an advantageous embodiment the gas spring charging device extends through a window in the actuator housing and is connected to the second gas spring body member, the piston rod comprises a piston rod head portion fixed by means of a threaded connection to a piston rod extension portion, a compressed fluid inlet connection carried on said actuator housing has projections engageable with said piston head to unthread the piston rod head portion from said piston rod extension portion by turning the inlet connection, the actuator housing is removably connectable to a valve bonnet surrounding the piston rod extension portion by a retainer ring, and that a removable positioning ring is disposed about the valve bonnet and engages the actuator housing to retain it against axial movement in a direction towards the valve bonnet, removal of the positioning ring allowing the actuator housing to be pushed towards the valve bonnet to engage the projections of the inlet fitting with the piston head and rotation of the inlet connection causing unthreading of the threaded connection between the piston rod head portion and the piston rod extension portion for removal of the actuator housing and the charged gas spring from the valve bonnet and the piston rod extension portion after removal of the retainer ring. The actuator of this embodiment prevents disassembly of the actuator without first removing all fluid pressure from the actuator. Further, the gas spring in this embodiment contributes to safety over conventional spring designs. The gas spring must be depressurized prior to removal from the actuator housing. The integral charging device must be removed before the gas spring body members can be removed from the housing. To do this requires that the gas spring be partially compressed for removal of the integral charging device. Compression of the gas spring cannot be readily accomplished without removal of the gas charge, thus removing the spring force. Once the gas charge is removed, there are no retained forces. Also, since the gas spring is charged after installation, there is no requirement for the compression of springs and the use of special tools during assembly as with conventional mechanical springs. Further, the gas spring lends itself inherently to a variety of operating procedures. The actuator may be used as a spring return actuator to the outward or closed position. By simply connecting the gas spring integral pressurizing device to a second fluid pressure source, the actuator becomes a "double acting" actuator that may be powered in either direction by application of fluid pressure to the appropriate chamber while venting fluid pressure from the opposite chamber. A third way in which the actuator may be used is as a spring return to the inward or open position by simply charging the actuator chamber above the piston with the gas charge and admitting the pressurized actuating fluid to the gas spring integral charging device. This simply reverses the operation of the actuator. Due to the attachment of the outer actuator housing to the valve bonnet by the use of a retaining ring, the outer housing may be rotated to any convenient position to align a window therein for the gas spring position indication. The fluid connection to the actuator is made through the top center of the outer actuator housing which allows the actuator supply pressure inlet to remain fixed. The unit of the advantageous embodiment referred to is safe and easy to disassemble. On removal of pressure from the actuator by disconnection of the actuator pressure inlet piping from a fluid connection port on the top of the actuator housing, a square positioning ring at the bottom of the actuator housing may be snapped out of its position. The fluid connection port is designed so that it is necessary that it be pushed inwardly and rotated to engage a slot in the piston head to commence disassembly of the valve. The fluid connection port cannot be pushed inwardly while pressure is maintained in the actuator, thus making disassembly under pressure virtually impossible. The actuator housing can then be pushed downwardly. A retainer ring may then be removed from a groove in the actuator housing. Rotation of the piston by turning the inlet connection on top of the housing (which is now locked to the piston) will unthread the piston from its stem, thus allowing the actuator to move outwardly from the bonnet. Bearings are located between the piston and the top of the gas spring to provide easier rotation of the stem without rotating the gas spring. The gas spring may retain the gas charge and remain pressurized because it can only extend to the limit of a retainer ring between the first gas spring body member and the second gas spring body member. Once this point of spring extension is reached, all force from the gas spring is internally retained and the piston may be fully unthreaded from the valve stem allowing removal of the actuator assembly from the bonnet of the valve. The actuator assembly may be reinstalled on the bonnet in the reverse procedure without changing the gas spring setting or the charge. In addition, a slot is provided in the side of the actuator housing to reveal the position of the first gas spring body member which is relative to the position of the valve. Position indicating switches, such as microswitches, may be adapted to this area for remote position indication. The downstop position of the actuator is dependent upon the relative location of a downstop nut on the valve stem. This may easily be adjusted for the proper valve stroke prior to or after the assembly of the actuator to the bonnet. In one embodiment the first gas spring body member has an inner wall engaging said piston rod and an outer wall engaging said actuator housing. The second gas spring body member is received between the inner and outer walls and sealing rings are provided between the inner and outer walls and the second gas spring body member. In another embodiment the first gas spring body member has an outer wall engaging the actuator housing and an end wall sealingly engaging the piston rod. The second gas spring body member is received between said outer wall and said piston rod and sealingly and slidably engages said outer wall and said piston rod. BRIEF DESCRIPTION OF THE DRAWINGS These and other features of the present invention will be more fully understood in conjunction with the accompanying drawings in which like numbers indicate like components and in which: FIG. 1 is a cross-sectional view of the novel gas spring valve actuator; FIG. 2 is a cross-sectional view of the valve actuator in FIG. 1 taken along lines 2-2; FIG. 3 is a cross-sectional view taken along lines 3-3 illustrating the slot in the top of the piston which can be engaged by the hydraulic fluid connection fitting to remove the piston during disassembly of the actuator; FIG. 3A is a side view of the hydraulic fluid connection fitting that can be used to uncouple the piston from the piston stem; FIG. 3B is a partial side view indicating the hydraulic fluid connection being coupled to the piston for removal thereof; FIG. 3C is a top view of the piston indicating the slot for receiving the hydraulic fluid connection for removal of the piston during disassembly of the actuator; and FIG. 4 is a partial view of an alternate embodiment of the novel gas spring actuator. DETAILED DESCRIPTION The novel gas spring actuator 10 is illustrated in cross-sectional detail in FIG. 1. While the actuator in FIG. 1 will be described herein with relation to a gate valve for use in a well bore, it is to be understood that the gas spring actuator may be used in other applications and is not limited to the actuation of a gate valve for a well bore. The gas spring actuator 10 includes an actuator housing 12 and a first moveable gas spring body member 14. The first gas spring body member 14 has an annular hollow chamber 16. A second gas spring body member 18 has a second annular hollow chamber 20 and is slidably mounted in the hollow chamber 16 of first gas spring body member 14. Seals 22 prevent any pressurized fluid in annular hollow chambers 16 and 20 from escaping. A retaining ring 24 enables sliding movement of the first gas spring body member 14 with respect to the second gas spring body member 18, but limits the amount of travel of the first body member 14 with respect to the second body member 18. A piston head 26 is mounted in said housing 12 and has a piston rod or arm 28 integrally formed therewith and extending through the center of the first and second gas spring body members 14 and 18. Seals 27 prevent any fluid pressure above the piston head 26 from bypassing the piston head 26 into the area of housing 12 below the piston head 26. An elongated piston extension 30 is threadedly connected to piston shaft or arm 28 by means of threads 32. Bonnet 34 surrounds the elongated piston extension 30 and the stem or end 42 of the piston extension 30. The stem 42 may be coupled in any well-known manner 31 to a gate valve 29 for actuation thereof. In actual operation, the gate valve 29 is bolted to the bonnet 34 with bolts 43 and the full well pressure in the gate valve 29 is present around stem 42. An actuator housing retaining ring 36 couples the housing 12 to the bonnet 34. packing retainer 38 has seals 39 and 41 therein to prevent any well pressure from entering into the area around elongated piston extension 30. In addition, a metal-to-metal seal at 37 between a portion of the stem 42 and the bonnet 34 is designed to prevent well pressure in the gate valve 29 from entering the area around the elongated piston extension 30. A back seat check valve fitting 35 may be utilized if desired to check the metal-to-metal seals 37. Appropriate grease fittings 40 may be utilized to lubricate the engagement of the packing retainer with the piston extension 30. An actuator position ring 44 is located at the bottom of the actuator housing 12 and may be snapped out of its position to allow the housing 12 to be moved to the left in FIG. 1, thus disengaging the retaining ring 36 and allowing the unit to be disassembled as will be explained hereafter. An integral charging device 46 is coupled through a window 54 in the actuator housing 12 and engages the second gas spring body portion 18. The charging device 46 has an annular bore 48 which couples with the chamber 20 of second gas spring body member 18 to allow the charging of the gas spring by forcing gas into hollow annular chambers 16 and 20. It will be noted in FIGURE 2 that charging device 46 has a wing-like body portion 60 for mounting the second gas spring body portion 18 in the center of the housing 12. A second wing-like mounting member 62 is utilized on the opposite side of the second gas spring body portion 18 to center the second body portion 18 in the housing 12. It will also be noted that annular hollow chamber 20 has a fluid connection to the bottom of mounting member 62 to provide an equal and opposite pressure to that applied to the other side of second gas spring body portion 18 by the integral charging device 46. Thus, the forces are balanced and there are no side forces applied to second gas spring body portion 18. Seals 47 and 63 prevent the pressure applied through the integral charging device 46 from escaping around the mounting members 60 and 62. A pressure gauge 49 may be attached to the integral charging device 46 as illustrated in FIG. 2 to provide a visual indication of the pressure in the hollow annular chambers 16 and 20. Since the areas exposed to pressure inside the hollow annular chambers 16 and 20 are constant, the pressure has a direct relationship with force and the gauge 49 may be calibrated in force units available. In this way, the actuator can be checked regularly for available closing force without disassembly. Finally, a downstop position of the actuator 10 is dependent upon the relative location of a downstop nut 64 on the valve stem 30. Since it is mounted on the stem 30 with threads 66, it can easily be rotated to be adjusted for the proper valve stroke prior to the assembly of the actuator to the bonnet. The novel gas spring actuator 10 lends itself inherently to a variety of operating procedures. The actuator 10 may be used as a spring return actuator to the closed valve position as described earlier. Simply by connecting the gas spring integral pressurizing device 46 to a second fluid pressure source, and a first fluid pressure source coupled to connector 50, the actuator 10 becomes a "double acting" actuator that may be powered in either direction by application of fluid pressure to the appropriate chamber either above the piston 26 or below the piston in annular chambers 16 and 20 while venting fluid pressure from the other chamber. A third way in which the actuator 10 may be used is as a spring return to the open position by simply charging the upper actuator chamber on the top of piston 26 with the gas charge and admitting the pressurized actuating fluid to the gas spring integral charging device 46. This simply reverses the operation of the actuator 10. Because the actuator housing 12 is attached to the valve bonnet 34 by the use of retaining ring 36, the housing 12 may be rotated to any desired position to align the window 54 in the direction of the viewer for noting the indication of the position of the first gas spring body member 14. The fluid connection fitting 50 to the actuator 10 is made through the top center of the actuator housing 12 which allows actuator supply pressure inlet 50 to remain fixed even though the housing 12 is rotated. The actuator 10 is designed so that it cannot be disassembled without first removing all the fluid pressure from the actuator. The gas pressure in chambers 16 and 20 must be released and the chambers depressurized prior to removal from the actuator housing 12. The integral charging device 46 must be removed before the gas spring second body portion 18 can be removed from the housing 12. To do this requires that the gas spring be partially compressed for removal of the integral charging device 46. Compression of the gas spring cannot be readily accomplished without removal of the gas charge, thus removing the spring force. Once the gas charge is removed, there are no retained forces. Also, since the gas spring is charged after installation, there is no requirement for the compression of springs and the use of special tools during assembly as with the prior art mechanical springs. To disassemble the actuator 10, pressure is removed from the actuator 10 by disconnecting the actuator pressure from the inlet fitting 50 on the top of the actuator 10. The square positioning ring 44 at the bottom of the actuator housing 12 is snapped out of its position. The fluid connection port housing or fitting 50 on the top of the actuator housing 12 is so designed that it is necessary that it be pushed inwardly to engage a slot in the piston before disassembly of the valve can begin. The fluid connection port housing or fitting 50 cannot be pushed inwardly while pressure is maintained in the actuator 10, thus making disassembly under pressure virtually impossible. With the pressure removed, however, the actuator housing 12 can be pushed downwardly. The retainer ring 36 can then be removed from the groove in which it is positioned in the actuator housing 12 and the bonnet 34. Rotation of the piston 26 can take place by turning the inlet connection 50 on top of the housing 12 (which is now locked to the piston 26 by projections 69 and 70 as shown in FIG. 3B engaging the slot 76 in the top of piston 26) will unthread the piston rod 28 from the stem 30 allowing the actuator housing 12 to move outward from the bonnet 34. Bearings 72 and 74 are located between the bottom of the piston 26 and the top of the first gas spring body member 14 to provide easier rotation of the piston 26 without rotating the first gas spring body-member 14. The hollow annular chambers 16 and 20 may retain the gas charge and remain pressurized because the first gas spring body member 14 can extend only to the limit of the retaining ring 24 between the first and second gas spring body members 14 and 18. Once this point of spring extension is reached, all force from the gas spring is internally retained and the piston may be fully unthreaded from the valve stem 30 allowing removal of the actuator assembly from the bonnet 34 of the valve. The actuator 10 may be reinstalled on the bonnet 34 in the reverse procedure without changing the gas spring setting or charge. The window or slot 54 in the side of the actuator housing 12 reveals the position of the first gas spring body member 14 with respect to the housing 12 which indicates the relative position of the valve being operated. Position indicating microswitches 56 may be positioned with their actuating arms extending in the window or slot 54 such that as the first gas spring body member 14 moves in the housing 12, it successively contacts the microswitch arms and gives a remote position indication of the valve. In an alternate embodiment shown on FIG. 4, the inner wall of the first gas spring body member 14 has been removed. Seal 22A extends from the inner end of second gas spring body member 18 to the surface of piston rod 28. Seal 22B seals the first gas spring body member 14 to the second gas spring body member 18. Also, seals 78 and 80 seal the other end of first gas spring body member to the piston rod 28. This design simplifies the construction of the gas spring. In addition, the adjustment of downstop nut 64 in FIG. 1 must be done before assembly of the novel gas spring. The modification shown in FIG. 4 allows the adjustment to be made after assembly of the device. As can be seen in FIG. 4, the stop nuts 75 and 76 are rotatably mounted on threads 77 on the outer surface of second gas spring body member 18. Stop nuts 75 and 76 are accessible through window 54 in housing 12 and thus can be positioned as desired after assembly to provide the proper piston stroke. The more the stop nuts 75 and 76 are moved to the right in FIG. 4, the less travel distance is available for first gas spring body member 14 and, thus, piston 26. The length of the piston stroke is therefore adjustable after assembly of the gas spring. Two stop nuts 75 and 76 are used to provide a locking mechanism so that they stay in the position in which they are placed. Thus, there has been disclosed a novel gas spring actuator which has variable and adjustable closing force by varying the pressure in the enclosed chambers forming the gas spring. A pressure gauge may be provided to indicate the force units available since the areas exposed to pressure are constant and the pressure is in a direct relationship with force. The novel gas spring is approximately 15 cm (6 inches) in diameter and 60 cm (24 inches) in length and, for its size, can produce forces in excess of that available with other types of conventional metal springs with the same overall size and weight. Further, the first and second gas spring body members cannot be disassembled without first removing all gas pressure from the annular hollow chambers therein. The integral charging device must be removed before the first gas spring body member can be removed from the housing. To do this requires that the gas spring be partially compressed for removal of the integral charging device. The second gas spring body member can then be moved towards the first gas spring body member moving the integral charging device in the window in the wall of the housing. The integral charging device can then be rotated and dropped out of the housing through the window. Once the gas charge is removed, there are no retained forces and since the gas spring is charged after installation, there is no requirement for the compression of mechanical springs or the use of special tools during assembly.

Claims: A gas spring valve actuator for moving a valve (29) between open and closed states comprising: an actuator housing (12); a hydraulic piston slidable in said housing (12) between first and second positions and having a rod (28, 30) for transferring power and a head (26) for receiving hydraulic pressure; means (42) for coupling the piston rod (28, 30) to the valve (29) to change the valve position between open and closed states by moving the piston rod (28, 30); a gas spring in the actuator housing (12) operatively associated with one side of the hydraulic piston and having a compressible fluid therein; and means for pressurizing the actuator housing (12) on the other side of the piston with a predetermined fluid pressure to actuate the valve (29) from a first state to a second state by moving the piston from a first to a second position and compressing the fluid in the gas spring such that when the fluid pressure is removed, the compressed fluid returns the piston to its first position and the valve (29) to its first state, characterized in that said gas spring comprises: a first movable gas spring body member (14) positioned on said one side of the piston, i. e. under the piston head (29), and surrounding the hydraulic piston rod (28, 30); a hollow chamber (16) at least partly formed by the first body member (14) surrounding the hydraulic piston rod (28, 30) for receiving the compressible fluid; a second stationary gas spring body member (18) positioned in the actuator housing (12) and surrounding the piston rod (28, 30), said second gas spring body member (18) having one end thereof sealably and slidably inserted in the hollow chamber (16) formed by the first movable gas spring body member (14); and an annular chamber (20) in the second gas spring body member (18) in gas transfer relationship with the hollow chamber (16) formed by the first gas spring body member (14). A gas spring valve actuator according to claim 1, characterized in that a gas spring charging device (46) is connected to the annular chamber (20) of the second gas spring body member (18). A gas spring valve actuator according to any one of claims 1 or 2, characterized in that the gas spring charging device (46) extends through a window (54) in the actuator housing (12), that the piston rod comprises a piston rod head portion (28) fixed by means of a threaded connection (32) to a piston rod extension portion (30), that a compressed fluid inlet connection (50) carried on said actuator housing has projections (69, 70) engageable with said piston head (26) to unthread the piston rod head portion (28) from said piston rod extension portion (30) by turning the inlet connection (50), that the actuator housing (12) is removably connectable to a valve bonnet (34) surrounding the piston rod extension portion (30) by a retainer ring (36), and that a removable positioning ring (44) is disposed about the valve bonnet (34) and engages the actuator housing (12) to retain it against axial movement in a direction towards the valve bonnet (34), removal of the positioning ring (44) allowing the actuator housing (12) to be pushed towards the valve bonnet (34) to engage the projections (69, 70) of the inlet fitting (50) with the piston head (26) and rotation of the inlet connection (50) causing unthreading of the threaded connection (32) between the piston rod head portion (28) and the piston rod extension portion (30) for removal of the actuator housing (12) and the charged gas spring from the valve bonnet (34) and the piston rod extension portion (30) after removal of the retainer ring (36). A gas spring valve actuator according to claim 2 or 3, characterized in that a pressure gauge (49) is attached to the charging device (46). A gas spring valve actuator according to any one of claims 1 to 4, characterized by a retaining ring (24) limiting maximum extension of the gas spring body members (14, 18). A gas spring valve actuator according to claim 2 or 3, characterized in that the charging device (46) has a wing-like body portion (60) received in an annular space between the actuator housing (12) and the second gas spring body member (18) and a second wing-like mounting member (62) is provided on the opposite side of said second gas spring body member (18) in said annular space to center said second gas spring body member (18) in said actuator housing (12). A gas spring valve actuator according to claim 6, characterized in that the annular gas chamber (20) in the second gas spring body member (18) has a fluid connection to the bottom of the second mounting member (62). A gas spring valve actuator according to any one of claims 1 to 7, characterized in that a stroke limiting nut (64) is adjustably mounted on a threaded portion (66) of the piston rod (28, 30). A gas spring valve actuator according to any one of claims 1 to 7, characterized in that stroke limiting stop nuts (75, 76) are mounted on a threaded portion (77) of said second gas spring body member (18). A gas spring valve actuator according to any one of claims 1 to 9, characterized in that the first gas spring body member (14) has an inner wall engaging said piston rod (28, 30) and an outer wall engaging said actuator housing (12) and that said second gas spring body member (18) is received between said inner and outer walls, with sealing rings (22) being provided between the inner and outer walls and the second gas spring body member (18). A gas spring valve actuator according to any one of claims 1 to 9, characterized in that the first gas spring body member (14) has an outer wall engaging the actuator housing (12) and an end wall sealingly engaging the piston rod (28, 30), and that the second gas spring body member (18) is received between said outer wall and said piston rod (28, 30) and sealingly and slidably engages said outer wall and said piston rod (28, 30). A gas spring valve actuator according to any one of claims 1 to 11, characterized in that a position indicator (56) is mounted on said actuator housing (12). A gas spring valve actuator according to one of claims 1 to 12, characterized in that the actuator housing (12) is attached to a bonnet (34) of said valve (29) for rotation of the actuator housing (12) on the valve bonnet (34). A gas spring valve actuator according to claim 3, characterized in that bearings (72, 74) are provided between the piston head (26) and said first gas spring body member (14).

Inventors: MAXWELL JOE D, PERKINS M WAYNE, SNYDER DAVID E, MAXWELL, JOE D., PERKINS, M. WAYNE, SNYDER, DAVID E.
Applicants: AXELSON INC, AXELSON, INC.
Application year: 1992
Main classification: F16K31
IPC codes: F16K31