Fail safe gate valves and actuators therefor

• US 4,691,893 A
• Filed: 01/28/1987
• Issued: 09/08/1987
• Est. Priority Date: 01/25/1982
• Status: Expired due to Term

• Current Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Original Assignee: AVA International Corp (Halliburton Company)
• Inventors: Akkerman, Neil H., Vazquez, Gonzalo
• Primary Examiner(s): Tapolcai, William E.
• Application Number:
  US07/009,655
• Time in Patent Office: 223 Days
• Field of Search: 251/14, 251/89, 74/625, 60/400, 60/401, 137/79, 137/80, 137/456, 137/457, 137/553
• US Class Current: 251/14
• CPC Class Codes: F16K 17/36 actuated in consequence of extraneous circumstances, e.g. shock, change of position
• CPC Class Codes: F16K 31/143 the fluid acting on a piston
• CPC Class Codes: F16K 37/00 Special means in or on valves or other cut-off apparatus for indicating or recording operation thereof, or for enabling an alarm to be given
• CPC Class Codes: Y10T 137/1963 Temperature
• CPC Class Codes: Y10T 137/7723 Safety cut-off requiring reset
• CPC Class Codes: Y10T 137/8225 Position or extent of motion indicator

Abstract

There are disclosed several embodiments of a fail safe gate valve and actuator having means for yieldably urging the gate from one position to which it is moved under one or more controlled conditions to its other position upon failure of one such condition, means including a handwheel mounted on the actuator for moving the gate to its one position, and means automatically responsive to a control signal for rendering the handwheel inoperative to move the gate to its one position upon reestablishment of said one controlled condition. In certain embodiments, the control signal is automatically responsive to the reestablishment of said one controlled condition; and, in another embodiment, it is automatically responsive to the failure of said one controlled condition. The controlled conditions are disclosed as being one or both of a predetermined fluid pressure condition, and or a predetermined environmental temperature condition.

Claims

1. A fail safe valve, comprising

a body having a flowway therethrough and a closure member movable therein between positions opening and closing the flowway, an actuator having a stem including one portion connected to the closure member and mounted for reciprocation in opposite directions to move the closure member between said positions, piston means responsive to the supply of a control fluid thereto for urging the one stem portion in one direction in order to move the closure member to one position and maintain it in that position as long as the control fluid is maintained at a predetermined pressure level, means for yieldably urging the one stem portion in the other direction in order to move the closure member to its other position in the event the control fluid is not so maintained, operating means mounted on the actuator and manipulatable from the exterior thereof for moving another portion of the stem in the one direction to move the closure member to its one position, and means automatically responsive to the failure of a predetermined environmental temperature condition for rendering said operating means inoperative to move said other portion of the stem in said one direction upon reestablishment of said control fluid to said piston means at said predetermined pressure level.

2. A fail safe valve of the character defined in claim 1, wherein said means is also automatically responsive to the supply of control fluid to said piston means at said predetermined pressure level.

3. A fail safe valve, comprising a body having a flowway therethrough and a closure member movable therein between positions opening and closing the flowway, an actuator having a stem including one portion connected to the closure member and mounted for reciprocation in opposite directions to move the closure member between the said positions, means for yieldably urging the one stem portion in a direction to move the closure member from one position in which it may be maintained under a predetermined temperature condition to its other position upon failure of such condition, operating means mounted on the actuator for manipulation from the exterior thereof into one position in which it is operative to move another portion of the stem in the other direction in order to move the closure member to its one position, and another position in which the operating means is inoperative to move said other stem portion in said other direction, and means automatically responsive to failure of said temperature condition for moving said operating means from said one to its other position so that it is inoperative to move the closure member to its one position upon reestablishment of said temperature condition.

4. A fail safe valve, comprising a body having a flowway therethrough and a closure member movable therein between positions opening and closing the flowway, an actuator having a stem including one portion connected to the closure member, a member threadedly connected to another portion of the stem and mounted in the body for rotation without reciprocation, means for yieldably urging the one stem portion in the other direction to move the closure member from its one position, in which it may be maintained under one or more controlled conditions, to its other position upon failure of one of those conditions, operating means mounted on the actuator for manipulation from the exterior thereof, means shiftable between a first position rotatably connecting the operating means and the member for moving the stem in the one direction only in response to manipulation of the operating means, and a second position rotatably disconnecting the member and operating means so that the operating means is inoperative to move the stem in said one direction or resist movement of the stem in the opposite direction, and means automatically responsive to a control signal for shifting said shiftable means from the first to its second position so that the operating means is inoperative to move the closure member to said one position upon reestablishment of said one controlled condition.

5. A fail safe valve of the character defined in claim 4, wherein one of the member and other stem portion is a ball nut, and a means is movable into engagement with the member to prevent rotation thereof in a direction to move the stem in the other direction upon shifting of the connecting and disconnecting means into rotatable connection with the member, and out of engagement therewith to permit such rotation, upon shifting of the connecting and disconnecting means out of rotatable connection with the member.

6. A fail safe valve of the character defined in claim 4, wherein the operating means has a shaft which is mounted for rotation and reciprocation between inner and outer positions, and said shaft has means thereon for rotative engagement with the member upon movement of the shaft into one of said inner and outer positions.

7. A fail safe valve comprising a body having a flowway therethrough and a closure member movable therein between positions opening and closing the flowway, an actuator having a stem including a portion connected to the closure member, a member threadedly connected to another portion of the stem and mounted for rotation without reciprocation, piston means on the one stem portion, means for supplying control fluid to the piston means for urging the one stem portion in one direction in order to move the closure member to one position and maintain it in that position as long as the control fluid is maintained at a predetermined pressure level, means for yieldably urging the one stem portion in the other direction in order to move the closure member to its other position in the event the control fluid is not so maintained, operating means mounted on the actuator for manipulation from the exterior thereof, means shiftable between a first position rotatably connecting the operating means and the member for moving the stem in said one direction only in response to manipulation of the operating means to rotate the member, and a second position rotatably disconnecting the stem and member so that the operating means is inoperative to move the stem in said one direction or resist movement of the stem in the other direction, and additional piston means automatically responsive to the supply of said control fluid to said first-mentioned piston means for shifting said shiftable means to its second position.

8. A fail safe valve of the character defined in claim 7, wherein the piston means includes a plurality of cylinders arranged about the stem, and a piston sealably slidable within each cylinder.

9. A valve of the character defined in claim 8, wherein the operating means has a shaft mounted with the actuator for rotation and reciprocation between inner and outer positions, the shiftable means comprises means carried on the shaft for rotative engagement with the member upon movement of the shaft to its inner position, and the additional piston means is mounted within the actuator for extension with respect to the bonnet in response to the supply of said control fluid to move the shaft to its outer position.

10. A valve of the character defined in claim 7, wherein the piston means includes a cylinder in the actuator and a piston on the one stem portion and sealably slidable in the cylinder.

11. A valve of the character defined in claim 10, wherein the operating means has a shaft mounted within the bonnet for rotation and reciprocation therein between inner and outer positions, the connecting and disconnecting means comprises means carried on the shaft for rotative engagement with the member upon movement of the shaft into its inner position, and said additional piston means is on the shaft.

12. In a fail safe valve actuator, a body having a stem including a portion mounted therein for reciprocation in opposite directions, without rotation, a member threadedly connected to the stem portion, means mounting the member within the body for rotation, without axial movement, operating means mounted on the body for manipulation from the exterior thereof and having a shaft mounted within the body for rotation and reciprocation between inner and outer positions in axial alignment with the stem portion, means on the shaft rotatably engageable with means on the member, upon movement of the shaft to one position, so as to permit the member to be rotated by the operating means in one direction, and rotatably disengageable therefrom, upon movement of the shaft to its other position, so that the operating means is ineffective to move the stem, and means for preventing rotation of the member in the opposite direction when the means on the shaft is rotatably engaged with means on the member, but permitting such rotation when said means on the shaft is rotatably disengaged with said means on the member.

13. A valve actuator of the character defined in claim 12, wherein one of the member and stem portion is a ball nut.

14. A valve actuator of the character defined in claim 12, including brake means on the member frictionally engageable with the body to retard rotation of the member in said opposite direction.

15. A valve actuator of the character defined in claim 13, wherein the member is the ball nut.

16. A valve actuator of the character defined in claim 12, wherein the means for preventing rotation of the member comprises a pawl mounted for reciprocation with the shaft between one position rotatably engaged with the member, when the means on the shaft is rotatably engaged therewith, and another position disengaged therefrom when the means on the shaft rotatably disengaged therefrom, when the shaft is rotatably disengaged from the member.

17. A valve actuator of the character defined in claim 12, including detent means on the body and shaft for releasably holding the shaft in its other position.

18. A valve actuator of the character defined in claim 12, wherein the member has slots formed therein, and the inner end of the shaft has dogs movable into and out of rotative engagement with the slots.

19. A valve actuator of the character defined in claim 18, including a pawl mounted for reciprocation in the body to one side of the shaft between an inner position engaged with a slot on the member and an outer position disengaged therefrom.

20. A valve actuator of the character defined in claim 19, including means yieldably urging the pawl to its inner position, and means on the shaft for moving the pawl with it to their outer positions and for permitting the yieldable urging means to move the pawl to its inner position as the shaft moves to its inner position.

21. A valve actuator of the character defined in claim 12, including means on the body for visually indicating connection or disconnection of the shaft and member automatically in response to shifting of said shaft into and out of its positions.

22. A valve actuator of the character defined in claim 12, including means on the body for moving the shaft into its position disengaged from the member automatically in response to a predetermined environmental temperature condition.

23. A valve actuator of the character defined in claim 12, including means on the body for moving the shaft to its position disengaged from the member automatically in response to a fluid pressure control signal.

24. A valve actuator of the character defined in claim 22, wherein said means includes piston means on the shaft.

25. A fail safe valve actuator, comprising a bonnet adapted to be mounted on a valve body, a stem including one portion adapted to be connected to a closure member of the valve, when the bonnet is so mounted, means mounting the one stem portion within the bonnet for reciprocation in opposite directions to move the closure member between opened and closed positions, means for yieldably urging the one stem portion in a direction to move the closure member from one position in which it may be maintained under one or more controlled conditions to its other position upon failure of such condition, operating means mounted on the bonnet for manipulation from the exterior thereof for moving another portion of the stem in the opposite direction in order to move the closure member to its one position, and means automatically responsive to a predetermined environmental temperature condition for rendering said operating means inoperative to move said other stem portion in said opposite direction upon reestablishment of said one controlled condition.

26. A fail safe valve actuator of the character defined in claim 25, wherein the operating means is also rendered inoperative in response to a predetermined fluid pressure condition.

27. A fail safe valve actuator, comprising a bonnet adapted to mount on a valve body, a stem including one portion adapted to be connected to a closure member, when the bonnet is so mounted, means mounting the one stem portion within the bonnet for reciprocation in opposite directions to move the closure member between opened and closed positions, piston means responsive to the supply of a control fluid thereto for urging the one stem portion in one direction in order to move the closure member to one position and maintain it in that position as long as the control fluid is maintained at a predetermined pressure level, means for yieldably urging the one stem portion in the other direction in order to move the closure member to its other position in the event the control fluid is not so maintained, operating means mounted on the bonnet and manipulatable from the exterior thereof for moving another portion of the stem in the one direction to move the closure member to its other position, and means automatically responsive to the failure of a predetermined environmental temperature condition for rendering said operating means inoperative to move said other stem portion in said one direction upon reestablishment of the supply of said control fluid to said piston means at said predetermined pressure level.

28. An actuator of the character defined in claim 27, wherein said means for rendering the operating means inoperative is also automatically responsive to the supply of said control fluid to said piston means.

29. A fail safe valve actuator, comprising a bonnet adapted to be mounted on a valve body, a stem including one portion adapted to be connected to a closure member, when the bonnet is so mounted, means mounting the one stem portion within the bonnet for reciprocation in opposite directions to move the closure member between open and closed positions, means for yieldably urging the one stem portion in a direction to move the closure member from one position in which it may be maintained under one or more controlled conditions to its other position upon failure of one such condition, operating means mounted on the bonnet and manipulatable from the exterior of the bonnet for manipulation into one position in which it is operative to move another portion of the stem in the other direction in order to move the closure member to its one position, and another position in which the operating means is inoperative to move said other stem portion in said other direction, and means automatically responsive to failure of a predetermined environmental temperature condition for moving said operating means from its one to its other position so that the operating means is inoperative to move the closure member to its one position upon reestablishment of said one controlled condition.

30. An actuator of the character defined in claim 29, including means automatically responsive to manipulation of the operating means for visually indicating in which position it is located.

31. A fail safe valve actuator, comprising a bonnet adapted to be mounted on a valve body, a stem including one portion adapted to be connected to a closure member, when the bonnet is so mounted, means mounting the one stem portion within the bonnet for reciprocation in opposite directions, a rotatably mounted member threadedly connected to another portion of the stem, operating means mounted on the bonnet for manipulation from the exterior thereof, means shiftable in response to manipulation of the operating means between a first position connecting the operating means and the member for moving the other stem portion on one direction only and thus to one position in response to rotation of the operating means, and a second position rotatably disconnecting the member and operating means so that the operating means is inoperative to move the other stem portion in said one direction or resist movement of the other stem portion in the other direction, spring means for yieldably urging the stem in the other direction to move the closure member from its one position to which it may be moved under one or more controlled conditions to its other position upon failure of one of those conditions, and means automatically responsive to a control signal for shifting said connecting and disconnecting means for the first to its second position so that the operating means is inoperative to move the closure member to its one position upon reestablishment of said one controlled condition.

32. An actuator of the character defined in claim 31, wherein one of the member and the other portion is a ball nut, and a means is movable into engagement with the member to prevent rotation thereof in direction to move the other stem portion in the other direction, upon shifting of the connecting and disconnecting means into rotative engagement with the member, and out of engagement therewith to permit such rotation, upon shifting of the connecting and disconnecting means out of rotative connection with the member.

33. An actuator of the character defined in claim 31, wherein the operating means has a shaft which is mounted within the bonnet for rotation and reciprocation between inner and outer positions, and said shaft has means theron for rotative engagement with the member upon movement of the operating means into one of said inner and outer positions.

34. A fail safe valve actuator, comprising a bonnet adapted to be mounted on a valve body, a stem including one portion adapted to be connected to a closure member of the valve when the bonnet is so mounted, means mounting the one stem portion within the bonnet for reciprocation in opposite directions to move the closure member between said positions, a member threadedly connected to another portion of the stem, piston means responsive to the supply of control fluid thereto for urging the other stem portion in one direction in order to move the closure member to one position and maintain it in that position as long as the control fluid is maintained at a predetermined pressure level, spring means for yieldably urging the stem in the other direction in order to move the closure member to its other position in the event the control fluid is not so maintained, operating means mounted on the bonnet for moving the other stem portion in the one direction upon manipulation from the exterior thereof, means shiftable between a first position rotatably connecting the operating means and member for moving the other stem portion in said one direction only, in response to manipulation of the operating means to rotate the nut, and a second position rotatably disconnecting the member and operating means, and additional piston means automatically responsive to the supply of said control fluid to said first-mentioned piston means for shifting said connecting and disconnecting means to its second position. so that the operating means is inoperative to move the other stem portion in said one direction, upon reestablishment of the control fluid, or resist movement thereof in said opposite direction.

35. An actuator of the character defined in claim 34, wherein the piston means includes a plurality of cylinders arranged about the other stem portion, and a piston sealably slidable within each cylinder.

36. An actuator of the character defined in claim 35, wherein the operating means has a shaft mounted within the bonnet for rotation and reciprocation between inner and outer positions, the connecting and disconnecting means comprises means carried on the shaft for rotative engagement with the other stem portion upon movement of the shaft to its inner position, and the additional piston means is mounted within the bonnet for extension with respect to the bonnet, in response to the supply of said control fluid, to move the operating means to its outer position.

37. An actuator of the character defined in claim 34, wherein the piston means includes a cylinder in the bonnet and a piston on the one stem portion and sealably slidable in the cylinder.

38. An actuator of the character defined in claim 37, wherein the operating means has a shaft mounted within the bonnet for rotation and reciprocation therein between inner and outer positions, the connecting and disconnecting means comprises means carried on the shaft for rotative engagement with the other stem portion upon movement of the shaft into its inner position, and said additional piston means is on the shaft.

39. A fail safe valve, comprising a body having a flowway therethrough and a closure member movable therein between positions opening and closing the flowway, an actuator having a stem including one portion connected to the closure member and mounted for reciprocation in opposite directions to move the closure member between said positions, spring means for yieldably urging the one stem portion in a direction to move the closure member from one position in which it may be maintained under one or more controlled conditions to its other position upon failure of one such condition, operating means mounted on the actuator and manipulatable from the exterior thereof for moving another portion of the stem in the opposite direction in order to move the closure member to its one position, and means automatically responsive to the failure of a predetermined environmental temperature condition for rendering said operating means inoperative to move said other stem portion in said one direction upon reestablishment of said one controlled condition.

40. A fail safe valve of the character defined in claim 39, wherein the controlled conditions include a predetermined fluid pressure condition, and said means for rendering the operating means inoperative is also automatically responsive to reestablishment of said fluid pressure condition.

41. A fail safe valve, comprising a body having a flowway therethrough, and a closure member movable within the flowway to open and close the valve, an actuator mounted on the body having a stem including one portion connected to the closure member, drive means connected to another portion of the stem, operating means mounted on the actuator for manipulation from the exterior thereof, means shiftable between a first position connecting the operating means and drive means to permit the closure member to be moved to one of its position, upon manipulation of said operating means, and a second position disconnecting the operating means and drive means, so that the operating means is inoperable to so move the closure member, a part reciprocable within the actuator between a first position permitting the connecting and disconnecting means to be shifted to its first position and a second position to engage and move the shiftable means to its second position, spring means yieldably urging said shiftable means toward its second position, and means mounted on the actuator for retaining said part in its first position, but being fusible in response to a predetermined environmental temperature condition to release said part for movement to its second position.

42. A fail safe valve having a flowway therethrough and a closure member movable within the flowway to open and close the valve, a reciprocable stem including one portion connected to the closure member, drive means connected to another portion of the stem in order to move the other stem portion in one direction, and thus move the closure member to one of its positions in which it may be maintained under one more controlled conditions, in response to movement of the drive means in one direction, spring means urging the other stem portion in the opposite direction to move the closure member to its other position upon loss of a controlled condition, operating means mounted on the valve for manipulation from the exterior thereof, and means shiftable in response to a control signal between a first position connecting the operating means and the drive means to permit the operating means to be manipulated in order to move the drive means in only said one direction, and a second position disconnecting the operating means and the drive means so that the operating means is inoperable to move the drive means in said one direction upon reestablishment of said controlled condition or resist movement of the drive means in the opposite direction, the connection of said drive means to the other stem portion being operable to permit the spring means to move said one stem portion in said other direction and thus move said closure member to its other position when said shiftable means is in said second position.

43. A valve of the character defined in claim 42, wherein the control signal is the failure of a controlled condition.

44. A valve of the character defined in claim 43, wherein the controlled condition is a predetermined fluid pressure level condition.

45. A valve of the character defined in claim 43, wherein controlled condition is a predetermined environmental temperature condition.

46. A valve of the character defined in claim 44, wherein the controlled condition is alternatively a predetermined environmental temperature condition.

47. A valve of the character defined in claim 42, wherein the control signal is the reestablishment of a controlled condition.

48. A valve of the character defined in claim 47, wherein the controlled condition is a predetermined fluid pressure level condition.

49. A valve of the character defined in claim 47, wherein the control signal is alternatively the failure of another controlled condition.

50. A valve of the character defined in claim 49, wherein the other controlled condition is a predetermined environmental temperature condition.

51. A valve of the character defined in claim 42, wherein the drive means is rotatable without reciprocation, and one portion of the stem is reciprocable without rotation.

52. A valve of the character defined in claim 51, wherein one of said drive means and one stem portion is a ball nut.

53. A valve of the character defined in claim 52, wherein the operating means has a shaft thereon which is reciprocable between inner and outer positions, and the shiftable means is on the shaft for rotatable connection to the drive means in one of its positions.

54. A valve of the character defined in claim 53, including means for releasably holding the shaft in the other position.

55. A valve of the character defined in claim 51, including piston means connected to the other portion of the stem, said one stem portion being held against rotation and being connected to the other stem portion for reciprocation without rotation with respect thereon, and means by which control fluid may be supplied to the piston means to move said other stem portion in said one direction.

56. A valve of the character defined in claim 55, wherein said shiftable means comprises additional piston means to which control fluid may be supplied to move it to its second position.

57. A vlave of the character defined in claim 56, wherein said operating means has a shaft which is reciprocable between inner and outer positions, the additional piston means is on the shaft for moving it to the second position in response to the supply of control fluid.

58. A fail safe valve actuator, including a bonnet adapted to be mounted on a valve body and having a stem including one portion adapted to be connected to a closure member, drive means connected to another portion of the stem, operating means mounted on the bonnet for manipulation from the exterior thereof, means shiftable between a first position connecting the operating means and drive means to permit the closure member to be moved to one of its positions, upon manipulation of said operating means in which it may be maintained under one or more controlled conditions, and a second position disconnecting the operating means and drive means, so that the operating means is inoperable to so move the closure member, and a part reciprocable within the actuator between a first position permitting the connecting and disconnecting means to be shifted to its first position and a second position to engage and move the connecting and disconnecting means to its second position, spring means yieldably urging said connecting and disconnecting means toward its second position, and means mounted on the actuator for retaining said part in its first position but being fusible in response to a predetermined environmental temperature condition to release said part for movement to its second position.

59. A fail safe valve actuator, including a bonnet adapted to be mounted on a valve body and having a stem including one portion reciprocable in the bonnet for moving a closure member of the valve between opened and closed positions in which it may be maintained under one or more controlled conditions, drive means connected to another portion of the stem in order to move the other stem portion in one direction, and thus move the closure member to one of its positions, in response to movement of the drive means in one direction, spring means urging the one stem portion in the opposite direction to move the closure member to its other position upon loss of a controlled condition, operating means mounted on the bonnet for manipulation from the exterior thereof, and means shiftable in response to a control signal between a first position connecting the operating means and the drive means to permit the operating means to be manipulated in order to move the drive means in only said one direction, and a second position disconnecting the operating means and the drive means so that the operating means is inoperable to move the drive means in said one direction upon reestablishment of said controlled condition, or resist movement of the drive means in the opposite direction, the connection of said drive means to the other stem portion being operable to permit the spring means to move the other stem portion in the opposite direction and thereby move said closure member to its other position when said shiftable means is in said second position.

60. An actuator of the character defined in claim 59, wherein the control signal is the failure of a controlled condition.

61. An actuator of the character defined in claim 60, wherein the controlled condition is a predetermined fluid pressure level condition.

62. An actuator of the character defined in claim 60, wherein the controlled condition is a predetermined environmental temperature condition.

63. An actuator of the character defined in claim 61, wherein the controlled condition is alternatively a predetermined environmental temperature condition.

64. An actuator of the character defined in claim 59, wherein the control signal is the reestablishment of a controlled condition.

65. An actuator of the character defined in claim 64, wherein the controlled condition is a predetermined fluid pressure level condition.

66. An actuator of the character defined in claim 64, wherein the control signal is alternatively the failure of another controlled condition.

67. An actuator of the character defined in claim 60, wherein the other controlled condition is a predetermined environmental temperature condition.

68. A valve of the character defined in claim 59, wherein the drive means is rotatable without reciprocation, and one portion of the stem is reciprocable without rotation.

69. A valve of the character defined in claim 68, wherein one of said drive means and one stem portion is a ball nut.

70. A valve of the character defined in claim 69, wherein the operating means has a shaft thereon which is reciprocable between inner and outer positions, and the shiftable means is on the shaft for rotatable connection to the drive means in one of its positions.

71. A valve of the character defined in claim 70, including means for releasably holding the shaft in the other position.

72. A valve of the character defined in claim 68, including piston means connected to the other portion of the stem, said one stem portion being held against rotation and being connected to the other stem portion for reciprocation without rotation with respect thereon, and means by which control fluid may be supplied to the piston means to move said other stem portion in said one direction.

73. A valve of the character defined in claim 72, wherein said shiftable means comprises additional piston means to which control fluid may be supplied to move it to its second position.

74. A valve of the character defined in claim 73, wherein said operating means has a shaft which is reciprocable between inner and outer positions, the additional piston means is on the shaft for moving it to the second position in response to the supply of control fluid.

75. A fail safe valve, comprising a valve body having a flowway therethrough, a closure member movable within the valve body between positions opening and closing the flowway, a generally cylindrical housing on the valve body, a stem on the closure member extending from the body and into the housing for longitudinal reciprocation therein, a flange on the stem, a plurality of cylinders mounted on the outer end of the housing each to one side of the stem axis, a piston sealably reciprocable with respect to each cylinder and extending into the housing for engaging the stem flange in order to move the closure member to one position in response to the supply of operating fluid to the cylinders, and spring means within the housing and compressed between the stem and housing to move the closure member to its other position upon the exhaust of operating fluid from the cylinder, the outer ends of the pistons being generally adjacent the outer ends of the cylinders in said other position of the closure member.

76. A valve of the character defined in claim 75, wherein the housing has an inner end wall through the stem sealably extends, and the cylinders extend outwardly from the outer end wall laterally to one side of the stem.

77. A valve of the character defined in claim 75, wherein the spring means surrounds the stem and is compressed between the flange and inner end of the housing.

78. A fail safe valve actuator, comprising a generally cylindrical bonnet adapted to be mounted on the body of a valve, a stem adapted to be connected to a closure member mounted in the valve body for movement between positions opening and closing a flowway through the body, means mounting the stem within the bonnet for longitudinal reciprocation therein opposite directions in order to move the closure member between said positions, a flange on the stem, a plurality of cylinders mounted on the outer end of the bonnet each to one side of the stem axis, a piston sealably reciprocable with respect to each cylinder and extending into the housing for engaging the stem flange in order to move the closure member to one position in response to the supply of operating fluid to the cylinders, and spring means within the bonnet and compressed between the stem and the bonnet to move the closure member to its other position upon the exhaust of operating fluid from the cylinder, the outer ends of the pistons being generally adjacent the outer ends of the cylinders in said other position of the closure member.

79. An actuator of the character defined in claim 78, wherein the bonnet has an end wall through which the stem is sealably extendable, and the cylinders extend outwardly from the outer end wall laterally to one side of the stem.

80. An actuator of the character defined in claim 78, wherein the spring means surrounds the stem and is compressed between the flange and the inner end of the housing.