CA1051408A - Valve actuator - Google Patents
Valve actuatorInfo
- Publication number
- CA1051408A CA1051408A CA270,553A CA270553A CA1051408A CA 1051408 A CA1051408 A CA 1051408A CA 270553 A CA270553 A CA 270553A CA 1051408 A CA1051408 A CA 1051408A
- Authority
- CA
- Canada
- Prior art keywords
- cylinder
- valve
- piston
- accumulator
- actuator
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16K—VALVES; TAPS; COCKS; ACTUATING-FLOATS; DEVICES FOR VENTING OR AERATING
- F16K31/00—Actuating devices; Operating means; Releasing devices
- F16K31/12—Actuating devices; Operating means; Releasing devices actuated by fluid
- F16K31/122—Actuating devices; Operating means; Releasing devices actuated by fluid the fluid acting on a piston
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- Engineering & Computer Science (AREA)
- General Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Fluid-Driven Valves (AREA)
- Supply Devices, Intensifiers, Converters, And Telemotors (AREA)
- Safety Valves (AREA)
- Actuator (AREA)
- Valve Device For Special Equipments (AREA)
- Lift Valve (AREA)
Abstract
VALVE ACTUATOR
Abstract of the Disclosure A valve actuator is capable of being mounted on a valve in alignment with a valve stem which can be moved to open and close the valve. The actuator includes a hydraulic cylinder and a piston slidably mounted within the cylinder. A piston rod is joined at a first side of the piston and extends outwardly of the cylinder toward the valve to be joined to the valve stem. A high pressure gas accumulator is mounted on the cylinder and includes a generally spherical shaped pressure wall which is intersected by the cylinder to locate an end of the cylinder within the accumulator to allow communication of the interior of the accumulator with a second side of the piston. Hydraulic oil acting on the first side of the piston opens the valve against high pressure gas within the accumulator and evacuation of the hydraulic oil allows the high pressure gas to act on the second side of the piston to rapidly close the valve.
Abstract of the Disclosure A valve actuator is capable of being mounted on a valve in alignment with a valve stem which can be moved to open and close the valve. The actuator includes a hydraulic cylinder and a piston slidably mounted within the cylinder. A piston rod is joined at a first side of the piston and extends outwardly of the cylinder toward the valve to be joined to the valve stem. A high pressure gas accumulator is mounted on the cylinder and includes a generally spherical shaped pressure wall which is intersected by the cylinder to locate an end of the cylinder within the accumulator to allow communication of the interior of the accumulator with a second side of the piston. Hydraulic oil acting on the first side of the piston opens the valve against high pressure gas within the accumulator and evacuation of the hydraulic oil allows the high pressure gas to act on the second side of the piston to rapidly close the valve.
Description
105~U8 VALVE ACTUATOR
Background of the Invention Field of the Invention - This invention relates to an actuator for a valve and, more specifically, to such an actuator which includes a hydraulic cylinder and piston arrangement in which a generally spherical shaped accumulator is mounted on the cylinder to provide a reservoir of high pressure gas for reliable closure of the valve as hydraulic pressure is relieved.
Description of the Prior Art - There have herebefore been utilized a number of means for closing large valves in the feedwater and steam systems of nuclear power plants. Because of safety and reliability requirements for these plants, the time required to close the valves within the system and the ability of the valves to safely withstand seismic shock are of real concern. While electrical motor operators have been used for reliable closure of heavy duty valves of this type in the past, the closure time required has generally made them unattractive.
It is presently felt that a valve actuator incorporating a hydraulic cylinder and gas accumulator affords the best means for rapid closure of the valve. Hydraulic oil is directed to a piston within the hydraulic cylinder to open the valve in opposition to a precharged source of high pressure gas which acts on the other side of the piston. A reservoir of ~ the high pressure gas is maintained in an accumulator to ensure a sufficient ,~ quantity is available to act on the piston to rapidly close the valve when the hydraulic pressure is relieved. While it is obvious that an ' accumulator might be provided in the form of a tank at a remote location from the valve, it is preferred to have a self-contained system. One such system presently employed for use with balanced globe valves up to 32" includes a cylinder within a cylinder configuration in which the high pressure gas is located between the cylinders. However, this configuration is not inexpensive to provide and the size and weight of ~0514~)8 the outer cylinder required to provide ample closing forces is recognized as being a significant factor to be considered in a determination of the ability of the valve to withstand seismic shock.
Additionally, although this configuration has ensured rapid closure of balanced valves in the past, its applicability for use with unbalanced gate valves is questionable. There are indications that the larger forces which would be needed to close a comparable sized gate valve would require an outer cylinder of significantly larger dimensions and weight, greatly complicating the seismic problems and space problems which must be considered in power plant design.
Summary of the Invention I' is, therefore, an object of the invention to provide a valve actuator having a hydraulic cylinder and gas accumulator configuration which is self-contained, weighs less and is less expensive to manufacture.
It is another object to provide a valve actuator of the type described which includes an accumulator having a generally spherical shaped wall which is mounted to the hydraulic cylinder.
It is a further object to provide a valve actuator of the type described in which the spherical shaped wall is intersected by the hydraulic cylinder to locate an end of the cylinder within the interior of the accumulator.
These and other objects of the invention are provided by the preferred embodiment thereof in the form of a valve actuator which is capable of being mounted on a valve in alignment with a valve stem which can be moved to open and close the valve. The actuator includes a hydraulic cylinder and a piston slidably mounted within the cylinder. A piston rod is joined at a first side of the piston and extends outwardly oF the cylinder toward the valve through an opening in a first end of the cylinder for sealed, slid-ing movement therethrough. The rod has an extended end which is capable of being joined to the valve stem. A high pressure gas accumulator is mounted on the cylinder and has a generally spherical shaped pressure wall wh;ch is intersected by the cylinder to locate a second end of the cylinder w;th;n the accumulator to allow communication of an interior of the accumulator w;th a second side of the p;ston.
Brief Description of the Drawings F
Figure 1 is a sect;onal side v;ew of a preferred valve actuator . ;ncluding various features of the invention.
Figure 2 ;s a sect;onal side view of a prior art val~e actuator.
Detailed Description of the Preferred Embodiment Although Figure 1 shows the preferred valve actuator of the present invention, it is perhaps best to first discuss the prior art actuator of Figure 2.
As seen in Figure 2, a prior art valve actuator 10 includes a hydraulic cylinder 12 with a piston 14 slidably mounted therein. A piston rod 16 is mounted at a first side 18 of the piston 14 to extend outwardly of the cylinder 12 through a hole 20 in the lower end 22 of the cylinder.
`, A sealing device 24 encircles the rod 16 at hole 20 to prevent the loss of `!'' hydraulic oil from the cylinder 12 while allowing sl;ding movement of the rod 16 therethrough. An extended end 26 of the rod 16 is joined to a valve stem 28 of a valve 30 on which the actuator 10 is mounted~
A hydraulic pump and manifold system 32 (shown in phantom) can be , of any type well known in the art which is capable of prov;ding hydraulic flùid for controlled positioning of the piston 14. An oil reservoir 34 , (also shown ;n phantom) can extend at least partially around the valve actuator 10 to provide a supply of hydraulic oil for the pump and manifold 32 when the valve is opened and a collector for hydraulic oil when the valve is closed.
To provide the positive means needed for closing the valve 30, the prior art valve actuator 10 further includes a high pressure gas cylinder 36 which encircles the cylinder 12 to completely encase it therein. The ~ 05~4~8 lower end of the gas cylinder 36 is, like the cylinder 12, sealably mounted to a flange member 38 which includes a means in the form of bolts 40 for securing the actuator 10 to the upper structure 42 of the valve 30. The upper end 44 of the cylinder 36 includes a sealed closure 46 to generally confine the gas between the flange member 38 and the end closure 46 and -to generally define a high pressure gas accumulator 48 in the space between the cylinders 36 and 12.
The end closure 46 includes a gas valve 50 for precharging the accumulator 48 to a desired, predetermined pressure when the piston 14 is in a lowered position (at the opposite end of the cylinder from the position shown in Figure 2). Since there is an access space 52 between the upper end 54 of cylinder 12 and the end closure 46, the gas is free to flow between the accumulator 48 and the upper portion of cylinder 12 to act on the second side 56 of the piston 14. A pressure transducer 58, also provided in the end closure 46, is used for monitoring the pressure of the gas.
With the piston 14 at the lower end of the cylinder 12, the piston rod 16 has acted on the stem 28 to close the valve 30. When it is desired to open the valve 30, the pump and manifold 32 are employed to pump hydraulic oil through a supply and discharge line 60 integrally formed in the flange member 38. As the hydraulic oil acts on the first side 18 of the piston 14, the rod 16 and stem 28 begin to move upwardly. The hydraulic pressure is of sufficient magnitude to overcome the precharged gas pressure in the upper portion of the cylinder 12 and the accumulator 48. The pumping of hydraulic oil is continued until the piston 14 is relocated at the upper end 54 of the cylinder 12, as shown in Figure 2, at which time the valve 30 will be in the open position. In this position, the high pressure gas will be primarily contained within the accumulator 48 and will be at a significantly higher pressure than the precharge pressure because of the 3~ decreased volume resulting from piston movement.
1051~()8 If rapid closure of the valve 30 is desired, because of a line rupture or some other operational requirement, the pump and manifold system 32 is remotely controlled to allow evacuation of the hydraulic oil from the cylinder 12 by way of the supply and discharge line 60. With resistance to piston movement removed, the high pressure gas in the accumulator 48 will act on the second side 56 of the piston 14 to rapidly close the valve.
To ensure reliable operation of the actuator 10, the piston 14 is provided a pair of piston sealing rings 62 to prevent the passage of oil and/or gas around the piston 14. As an added protection against the formation of a gas-hydraulic oil mixture, a circumferential groove 65 between the rings 62 and a drain line 66 are formed in the piston 14 and rod 16. The drain line 66 extends downwardly through the interior of the rod 16 to a discharge location below the cylinder 12 which allows access thereto for monitoring the effectiveness of the sealing rings 62.
Although the valve actuator 10 described hereinabove has provided an adequate means for rapidly closing balanced globe valves in nuclear power plants, it does include features which require serious consideration when designing a power plant. Because of the potential hazard to the general population which a nuclear power plant is said to present a number of rigid and extensive safety requirements must be met. As stated hereinabove, a valve actuator must be capable of meeting certain closure time requirements in case of dangerous line rupture. However, to ensure that a sufficient force is available to rapidly close the valve, the encircling cylindrical configuration of the prior art actuator 10 requires a relatively heavy, large structure to retain the gas at expected, high operating pressures. The weight and size of the outer cylinder significantly contribute to the total eccentric weight of a valve which is to be installed in the system. The amount of weight extending in a cantilevered fashion from the feedwater or steam line presents structural problems which must be solved when seismic -l()Sl~)8 shock requirements are considered. The double cylinder design includes a large flange member 38, in order to provide a support means for the larger diameter cylinder, which further increases the weight of the actuator.
As seen in Figure 1, a preferred valve actuator 70 of the present invention also includes a similar hydraulic cylinder 72, piston 74 and piston rod 76 configuration. A similar oil reservoir, pump and manifold system (not shown) are mounted to the actuator 70 for control of hydraulic oil into and out of a supply and discharge line 78, located at the lower end 80 of the cylinder 72. However, in the preferred embodiment, the outer cylinder has been eliminated by providing a high pressure gas accumulator 82 having a spherical shaped pressure wall 84. The pressure wall 84 includes an opening 86 therethrough having a diameter generally matching the outer diameter of the cylinder 72. Interior threads 88 of the opening 86 are -adapted to engage matching threads 90 about the outer surface 91 of the cylinder 72 for positive retention of the cylinder 72 therein. Accordingly, the spherical shaped pressure wall 84 is intersected by the cylinder 72 as it is mounted on the cylinder 72 at threads 90. So mounted, the upper end 92 of the cylinder 72 is disposed within the interior 94 of the accumulator 82 to afford free communication of the interior 94 with the upper side 96 of the piston 74. As with actuator 10, the upper end 92 of -the cylinder 72 is generally opened for free gas communication to the interior of the cylinder 72 when the piston 74 is lowered. A gas valve 98 and a pressure transducer 100 again allow precharging of the accumulator and monitoring of the gas pressure therein. A flexible metallic seal 102 at the lower end of the spherical shaped pressure wall 84 encircles the outer surface 91 of the cylinder 72 and is welded thereto to ensure retention of the high pressure gas.
Since the preferred spherical shaped pressure wall 84 only partially receives the cylinder 72 therein, the accumulator 82 does not extend to the ~30 lower end B0 of the cylinder 72. This eliminates the need for so largea flange member as 38 of the prior art actuator 10. Further, although ~C~51~(~8 the preferred actuator 70 might include a similar flange member but one having a small diameter to extend around the cylinder 72, the lower end 80 of the cylinder 72 and the upper structure 104 of the valve have been adapted to be joined by a conventional yoke lock ring 106 which is well known in the art. As a result, the preferred actuator 70 accommodates an improved mounting means while affording some reduction in weight and material.
It has also been found by the present invention that providing an accumulator with a generally spherical shape, despite the fact that it is intersected by a cylinder, affords a significantly better gas volume to overall weight ratio than can be obtained with the accumulator of the prior art configuration. It should be noted that the preferred actuator is not truly spherical because of the intersection by the hydraulic cylinder.
Further, as the diameter of the cylinder approaches the diameter of the generally spherical shaped wall, it is apparent that the exact shape of the lower half of the accumulator becomes less significant. For example, it might be preferred for manufacturing reasons to cast the hydraulic cylinder with an integrally formed upwardly flared frustrum section thereon which section would serve as the lower half of the accumulator. A preferred hemispherical upper section could be welded on the frustrum to provide an accumulator which is mounted on the cylinder and within the scope of the invention. In any case, an accumulator which includes a major portion which lies within a generally spherical surface will possess the desired strength characteristics which makes the improved gas volume to overall weight ratio possible.
To verify the advantages of the preferred actuator, a computer analysis of comparable actuator configurations for a balanced, 32" globe valve of the type mentioned hereinabove was conducted. A comparison was made of material weight (prior to machining), material costs, and manufacturing time expected. The dimensions of the cylinder 72 and the generally spherical 105~4()8 shaped pressure wall 84 and the relative amount of insertion of the cylinder 72 within the wall 84 were determined from various combinations of standard cylinder sizes and hemisphere sizes available for use in manufacturing.
Accordingly, the preferred configuration is not intended to present the optimum pressure to weight ratio design, but rather one which may be practically supplied. Nevertheless, it was found that a prior art actuator 10, including the hydraulic cylinder, piston, piston rod, etc., would require about 3,350 pounds of material and about 120 hours of time to manufacture. A
comparable valve actuator 70 incorporating the above described features of the present invention would weigh only about 1,200 pounds at a material cost which is less than half that of the actuator 10 and require only about 75 hours of manufacturing time.
With the savings of material by weight and cost each being greater than one-half and the manufacturing time being reduced by about one-third, - the preferred actuator 70 obviously represents a substantial improvement over the prior art actuator 10 while continuing to provide effective, reliable valve closure. Additionally, the aforementioned weight reduction further ensures safe operation of the valve even if the power plant were ; subjected to seismic shock forces of a higher magnitude than the prior art actuator would have been able to withstand.
With an increasing interest in the use of gate valves in nuclear power plant systems, the advantages described hereinabove become even more significant. It should initially be understood that a comparable sized, unbalanced gate valve requires only a slightly longer piston closing stroke than a balanced globe valve, but that the expected, required opening and closing forces would be greatly increased, on an order of about five times the force needed for the globe valve. For the same stroke, this increased force, in turn, requires the piston to be provided a larger diameter for the gas to be maintained at a similar pressure while still ensuring rapid closure. As a result, the hydraulic cylinder would have a diameter over twice as large as the ~05i408 embodiments shown in Figures 1 and 2 although the height would be similar.
With the cylinder having greater than twice the original volume, the volume of the accumulator would also be more than doubled to generate the same gas pressures through valve operation.
It can be seen that to employ an accumulator, as shown in Figure 2, with an outer cylinder to encircle a larger hydraulic cylinder while retain-ing the same gas pressure would significantly increase its diameter and weight requirements. Initial evaluations indicate that the outside diameter would extend well beyond the outside dimensions of the valve to make instal-lation in the system highly impractical and that the weight would make com-pliance with seismic requirements highly unlikely. In short, ~he preferred configuration makes possible the practical use of a hydraulic-gas actuator for rapid closure of some valves which would not heretofore have been possible.
While the embodiment discussed hereinabove represents the preferred valve actuator for a particular large valve utilizing available manufacturing material, it should be obvious that significant alterations may be made while remaining within the scope of the invention as claimed. It might, for example, be found that the most efficient closing pressure to weight ratio can be obtained by decreasing the amount of insertion of the hydraulic cylinder into the accumulator. On the other hand, where height limitations within a particular power plant installation dictate, the length of insertion of the hydraulic cylinder within the accumulator might approach the diameter of the accumulator. Additionally, the method employed to mount the spherical shaped pressure wall on the cylinder and the method of mounting the cylinder to the valve might be changed to any number of means well known in the valve manufacturing art. Similarly, although general manufacturing procedures and seismic considerations would presently seem to indicate otherwise, it would be possible, if desired, to mount the spherical shaped pressure wall in an eccentric manner with respect to the hydraulic cylinder.
Background of the Invention Field of the Invention - This invention relates to an actuator for a valve and, more specifically, to such an actuator which includes a hydraulic cylinder and piston arrangement in which a generally spherical shaped accumulator is mounted on the cylinder to provide a reservoir of high pressure gas for reliable closure of the valve as hydraulic pressure is relieved.
Description of the Prior Art - There have herebefore been utilized a number of means for closing large valves in the feedwater and steam systems of nuclear power plants. Because of safety and reliability requirements for these plants, the time required to close the valves within the system and the ability of the valves to safely withstand seismic shock are of real concern. While electrical motor operators have been used for reliable closure of heavy duty valves of this type in the past, the closure time required has generally made them unattractive.
It is presently felt that a valve actuator incorporating a hydraulic cylinder and gas accumulator affords the best means for rapid closure of the valve. Hydraulic oil is directed to a piston within the hydraulic cylinder to open the valve in opposition to a precharged source of high pressure gas which acts on the other side of the piston. A reservoir of ~ the high pressure gas is maintained in an accumulator to ensure a sufficient ,~ quantity is available to act on the piston to rapidly close the valve when the hydraulic pressure is relieved. While it is obvious that an ' accumulator might be provided in the form of a tank at a remote location from the valve, it is preferred to have a self-contained system. One such system presently employed for use with balanced globe valves up to 32" includes a cylinder within a cylinder configuration in which the high pressure gas is located between the cylinders. However, this configuration is not inexpensive to provide and the size and weight of ~0514~)8 the outer cylinder required to provide ample closing forces is recognized as being a significant factor to be considered in a determination of the ability of the valve to withstand seismic shock.
Additionally, although this configuration has ensured rapid closure of balanced valves in the past, its applicability for use with unbalanced gate valves is questionable. There are indications that the larger forces which would be needed to close a comparable sized gate valve would require an outer cylinder of significantly larger dimensions and weight, greatly complicating the seismic problems and space problems which must be considered in power plant design.
Summary of the Invention I' is, therefore, an object of the invention to provide a valve actuator having a hydraulic cylinder and gas accumulator configuration which is self-contained, weighs less and is less expensive to manufacture.
It is another object to provide a valve actuator of the type described which includes an accumulator having a generally spherical shaped wall which is mounted to the hydraulic cylinder.
It is a further object to provide a valve actuator of the type described in which the spherical shaped wall is intersected by the hydraulic cylinder to locate an end of the cylinder within the interior of the accumulator.
These and other objects of the invention are provided by the preferred embodiment thereof in the form of a valve actuator which is capable of being mounted on a valve in alignment with a valve stem which can be moved to open and close the valve. The actuator includes a hydraulic cylinder and a piston slidably mounted within the cylinder. A piston rod is joined at a first side of the piston and extends outwardly oF the cylinder toward the valve through an opening in a first end of the cylinder for sealed, slid-ing movement therethrough. The rod has an extended end which is capable of being joined to the valve stem. A high pressure gas accumulator is mounted on the cylinder and has a generally spherical shaped pressure wall wh;ch is intersected by the cylinder to locate a second end of the cylinder w;th;n the accumulator to allow communication of an interior of the accumulator w;th a second side of the p;ston.
Brief Description of the Drawings F
Figure 1 is a sect;onal side v;ew of a preferred valve actuator . ;ncluding various features of the invention.
Figure 2 ;s a sect;onal side view of a prior art val~e actuator.
Detailed Description of the Preferred Embodiment Although Figure 1 shows the preferred valve actuator of the present invention, it is perhaps best to first discuss the prior art actuator of Figure 2.
As seen in Figure 2, a prior art valve actuator 10 includes a hydraulic cylinder 12 with a piston 14 slidably mounted therein. A piston rod 16 is mounted at a first side 18 of the piston 14 to extend outwardly of the cylinder 12 through a hole 20 in the lower end 22 of the cylinder.
`, A sealing device 24 encircles the rod 16 at hole 20 to prevent the loss of `!'' hydraulic oil from the cylinder 12 while allowing sl;ding movement of the rod 16 therethrough. An extended end 26 of the rod 16 is joined to a valve stem 28 of a valve 30 on which the actuator 10 is mounted~
A hydraulic pump and manifold system 32 (shown in phantom) can be , of any type well known in the art which is capable of prov;ding hydraulic flùid for controlled positioning of the piston 14. An oil reservoir 34 , (also shown ;n phantom) can extend at least partially around the valve actuator 10 to provide a supply of hydraulic oil for the pump and manifold 32 when the valve is opened and a collector for hydraulic oil when the valve is closed.
To provide the positive means needed for closing the valve 30, the prior art valve actuator 10 further includes a high pressure gas cylinder 36 which encircles the cylinder 12 to completely encase it therein. The ~ 05~4~8 lower end of the gas cylinder 36 is, like the cylinder 12, sealably mounted to a flange member 38 which includes a means in the form of bolts 40 for securing the actuator 10 to the upper structure 42 of the valve 30. The upper end 44 of the cylinder 36 includes a sealed closure 46 to generally confine the gas between the flange member 38 and the end closure 46 and -to generally define a high pressure gas accumulator 48 in the space between the cylinders 36 and 12.
The end closure 46 includes a gas valve 50 for precharging the accumulator 48 to a desired, predetermined pressure when the piston 14 is in a lowered position (at the opposite end of the cylinder from the position shown in Figure 2). Since there is an access space 52 between the upper end 54 of cylinder 12 and the end closure 46, the gas is free to flow between the accumulator 48 and the upper portion of cylinder 12 to act on the second side 56 of the piston 14. A pressure transducer 58, also provided in the end closure 46, is used for monitoring the pressure of the gas.
With the piston 14 at the lower end of the cylinder 12, the piston rod 16 has acted on the stem 28 to close the valve 30. When it is desired to open the valve 30, the pump and manifold 32 are employed to pump hydraulic oil through a supply and discharge line 60 integrally formed in the flange member 38. As the hydraulic oil acts on the first side 18 of the piston 14, the rod 16 and stem 28 begin to move upwardly. The hydraulic pressure is of sufficient magnitude to overcome the precharged gas pressure in the upper portion of the cylinder 12 and the accumulator 48. The pumping of hydraulic oil is continued until the piston 14 is relocated at the upper end 54 of the cylinder 12, as shown in Figure 2, at which time the valve 30 will be in the open position. In this position, the high pressure gas will be primarily contained within the accumulator 48 and will be at a significantly higher pressure than the precharge pressure because of the 3~ decreased volume resulting from piston movement.
1051~()8 If rapid closure of the valve 30 is desired, because of a line rupture or some other operational requirement, the pump and manifold system 32 is remotely controlled to allow evacuation of the hydraulic oil from the cylinder 12 by way of the supply and discharge line 60. With resistance to piston movement removed, the high pressure gas in the accumulator 48 will act on the second side 56 of the piston 14 to rapidly close the valve.
To ensure reliable operation of the actuator 10, the piston 14 is provided a pair of piston sealing rings 62 to prevent the passage of oil and/or gas around the piston 14. As an added protection against the formation of a gas-hydraulic oil mixture, a circumferential groove 65 between the rings 62 and a drain line 66 are formed in the piston 14 and rod 16. The drain line 66 extends downwardly through the interior of the rod 16 to a discharge location below the cylinder 12 which allows access thereto for monitoring the effectiveness of the sealing rings 62.
Although the valve actuator 10 described hereinabove has provided an adequate means for rapidly closing balanced globe valves in nuclear power plants, it does include features which require serious consideration when designing a power plant. Because of the potential hazard to the general population which a nuclear power plant is said to present a number of rigid and extensive safety requirements must be met. As stated hereinabove, a valve actuator must be capable of meeting certain closure time requirements in case of dangerous line rupture. However, to ensure that a sufficient force is available to rapidly close the valve, the encircling cylindrical configuration of the prior art actuator 10 requires a relatively heavy, large structure to retain the gas at expected, high operating pressures. The weight and size of the outer cylinder significantly contribute to the total eccentric weight of a valve which is to be installed in the system. The amount of weight extending in a cantilevered fashion from the feedwater or steam line presents structural problems which must be solved when seismic -l()Sl~)8 shock requirements are considered. The double cylinder design includes a large flange member 38, in order to provide a support means for the larger diameter cylinder, which further increases the weight of the actuator.
As seen in Figure 1, a preferred valve actuator 70 of the present invention also includes a similar hydraulic cylinder 72, piston 74 and piston rod 76 configuration. A similar oil reservoir, pump and manifold system (not shown) are mounted to the actuator 70 for control of hydraulic oil into and out of a supply and discharge line 78, located at the lower end 80 of the cylinder 72. However, in the preferred embodiment, the outer cylinder has been eliminated by providing a high pressure gas accumulator 82 having a spherical shaped pressure wall 84. The pressure wall 84 includes an opening 86 therethrough having a diameter generally matching the outer diameter of the cylinder 72. Interior threads 88 of the opening 86 are -adapted to engage matching threads 90 about the outer surface 91 of the cylinder 72 for positive retention of the cylinder 72 therein. Accordingly, the spherical shaped pressure wall 84 is intersected by the cylinder 72 as it is mounted on the cylinder 72 at threads 90. So mounted, the upper end 92 of the cylinder 72 is disposed within the interior 94 of the accumulator 82 to afford free communication of the interior 94 with the upper side 96 of the piston 74. As with actuator 10, the upper end 92 of -the cylinder 72 is generally opened for free gas communication to the interior of the cylinder 72 when the piston 74 is lowered. A gas valve 98 and a pressure transducer 100 again allow precharging of the accumulator and monitoring of the gas pressure therein. A flexible metallic seal 102 at the lower end of the spherical shaped pressure wall 84 encircles the outer surface 91 of the cylinder 72 and is welded thereto to ensure retention of the high pressure gas.
Since the preferred spherical shaped pressure wall 84 only partially receives the cylinder 72 therein, the accumulator 82 does not extend to the ~30 lower end B0 of the cylinder 72. This eliminates the need for so largea flange member as 38 of the prior art actuator 10. Further, although ~C~51~(~8 the preferred actuator 70 might include a similar flange member but one having a small diameter to extend around the cylinder 72, the lower end 80 of the cylinder 72 and the upper structure 104 of the valve have been adapted to be joined by a conventional yoke lock ring 106 which is well known in the art. As a result, the preferred actuator 70 accommodates an improved mounting means while affording some reduction in weight and material.
It has also been found by the present invention that providing an accumulator with a generally spherical shape, despite the fact that it is intersected by a cylinder, affords a significantly better gas volume to overall weight ratio than can be obtained with the accumulator of the prior art configuration. It should be noted that the preferred actuator is not truly spherical because of the intersection by the hydraulic cylinder.
Further, as the diameter of the cylinder approaches the diameter of the generally spherical shaped wall, it is apparent that the exact shape of the lower half of the accumulator becomes less significant. For example, it might be preferred for manufacturing reasons to cast the hydraulic cylinder with an integrally formed upwardly flared frustrum section thereon which section would serve as the lower half of the accumulator. A preferred hemispherical upper section could be welded on the frustrum to provide an accumulator which is mounted on the cylinder and within the scope of the invention. In any case, an accumulator which includes a major portion which lies within a generally spherical surface will possess the desired strength characteristics which makes the improved gas volume to overall weight ratio possible.
To verify the advantages of the preferred actuator, a computer analysis of comparable actuator configurations for a balanced, 32" globe valve of the type mentioned hereinabove was conducted. A comparison was made of material weight (prior to machining), material costs, and manufacturing time expected. The dimensions of the cylinder 72 and the generally spherical 105~4()8 shaped pressure wall 84 and the relative amount of insertion of the cylinder 72 within the wall 84 were determined from various combinations of standard cylinder sizes and hemisphere sizes available for use in manufacturing.
Accordingly, the preferred configuration is not intended to present the optimum pressure to weight ratio design, but rather one which may be practically supplied. Nevertheless, it was found that a prior art actuator 10, including the hydraulic cylinder, piston, piston rod, etc., would require about 3,350 pounds of material and about 120 hours of time to manufacture. A
comparable valve actuator 70 incorporating the above described features of the present invention would weigh only about 1,200 pounds at a material cost which is less than half that of the actuator 10 and require only about 75 hours of manufacturing time.
With the savings of material by weight and cost each being greater than one-half and the manufacturing time being reduced by about one-third, - the preferred actuator 70 obviously represents a substantial improvement over the prior art actuator 10 while continuing to provide effective, reliable valve closure. Additionally, the aforementioned weight reduction further ensures safe operation of the valve even if the power plant were ; subjected to seismic shock forces of a higher magnitude than the prior art actuator would have been able to withstand.
With an increasing interest in the use of gate valves in nuclear power plant systems, the advantages described hereinabove become even more significant. It should initially be understood that a comparable sized, unbalanced gate valve requires only a slightly longer piston closing stroke than a balanced globe valve, but that the expected, required opening and closing forces would be greatly increased, on an order of about five times the force needed for the globe valve. For the same stroke, this increased force, in turn, requires the piston to be provided a larger diameter for the gas to be maintained at a similar pressure while still ensuring rapid closure. As a result, the hydraulic cylinder would have a diameter over twice as large as the ~05i408 embodiments shown in Figures 1 and 2 although the height would be similar.
With the cylinder having greater than twice the original volume, the volume of the accumulator would also be more than doubled to generate the same gas pressures through valve operation.
It can be seen that to employ an accumulator, as shown in Figure 2, with an outer cylinder to encircle a larger hydraulic cylinder while retain-ing the same gas pressure would significantly increase its diameter and weight requirements. Initial evaluations indicate that the outside diameter would extend well beyond the outside dimensions of the valve to make instal-lation in the system highly impractical and that the weight would make com-pliance with seismic requirements highly unlikely. In short, ~he preferred configuration makes possible the practical use of a hydraulic-gas actuator for rapid closure of some valves which would not heretofore have been possible.
While the embodiment discussed hereinabove represents the preferred valve actuator for a particular large valve utilizing available manufacturing material, it should be obvious that significant alterations may be made while remaining within the scope of the invention as claimed. It might, for example, be found that the most efficient closing pressure to weight ratio can be obtained by decreasing the amount of insertion of the hydraulic cylinder into the accumulator. On the other hand, where height limitations within a particular power plant installation dictate, the length of insertion of the hydraulic cylinder within the accumulator might approach the diameter of the accumulator. Additionally, the method employed to mount the spherical shaped pressure wall on the cylinder and the method of mounting the cylinder to the valve might be changed to any number of means well known in the valve manufacturing art. Similarly, although general manufacturing procedures and seismic considerations would presently seem to indicate otherwise, it would be possible, if desired, to mount the spherical shaped pressure wall in an eccentric manner with respect to the hydraulic cylinder.
Claims (5)
1. A valve actuator capable of being mounted on a valve in alignment with a valve stem which said stem is moved to open and close said valve, said actuator comprising:
a hydraulic cylinder;
a piston slidably mounted within said cylinder;
a piston rod joined at a first side of said piston and extending outwardly of said cylinder toward said valve through an opening in a first end of said cylinder for sealed, sliding movement therethrough, said rod having an extended end which is capable of being joined to said valve stem; and a high pressure gas accumulator mounted on said cylinder, said accumulator having a generally spherical shaped pressure wall which is intersected by said cylinder to locate a second end of said cylinder within said accumulator to allow communication of an interior of said accumulator with a second side of said piston.
a hydraulic cylinder;
a piston slidably mounted within said cylinder;
a piston rod joined at a first side of said piston and extending outwardly of said cylinder toward said valve through an opening in a first end of said cylinder for sealed, sliding movement therethrough, said rod having an extended end which is capable of being joined to said valve stem; and a high pressure gas accumulator mounted on said cylinder, said accumulator having a generally spherical shaped pressure wall which is intersected by said cylinder to locate a second end of said cylinder within said accumulator to allow communication of an interior of said accumulator with a second side of said piston.
2. The valve actuator as set forth in claim 1, where said spherical shaped pressure wall includes a threaded hole therethrough to receive a matching threaded portion of said cylinder.
3. The valve actuator as set forth in claim 1, wherein said spherical shaped pressure wall is joined to said cylinder by a circumferential weld therebetween to prevent leakage of high pressure gas from said accumulator.
4. The valve actuator as set forth in claim 1, wherein said cylinder includes a substantial portion thereof which is located outwardly of said accumulator.
5. An accumulator to provide a reservoir of high pressure gas for a valve actuator of the type which is mounted on a valve and includes a hydraulic cylinder, a piston slidably mounted within said cylinder, a piston rod mounted to a first side of said piston and extending outwardly of said cylinder to have its extended end joined to a valve stem of said valve, and means for selectively applying hydraulic fluid pressure to said first side of said piston to open said valve in opposition to said high pressure gas acting on a second side of said piston and for relieving said hydraulic fluid pressure to allow said high pressure gas to close said valve, said accumulator comprising:
a container for said high pressure gas having a generally spherical shaped pressure wall;
said wall having a hole therethrough to sealably receive said cylinder therein to locate an end of said cylinder which is remote from said valve within an interior of said container; and said end of said cylinder having an opening therethrough to allow communication of said interior of said container with said second side of said piston.
a container for said high pressure gas having a generally spherical shaped pressure wall;
said wall having a hole therethrough to sealably receive said cylinder therein to locate an end of said cylinder which is remote from said valve within an interior of said container; and said end of said cylinder having an opening therethrough to allow communication of said interior of said container with said second side of said piston.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US66378776A | 1976-03-04 | 1976-03-04 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1051408A true CA1051408A (en) | 1979-03-27 |
Family
ID=24663262
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA270,553A Expired CA1051408A (en) | 1976-03-04 | 1977-01-27 | Valve actuator |
Country Status (11)
| Country | Link |
|---|---|
| JP (1) | JPS5845627B2 (en) |
| BE (1) | BE852020A (en) |
| CA (1) | CA1051408A (en) |
| CH (1) | CH601712A5 (en) |
| DE (1) | DE2708250A1 (en) |
| ES (1) | ES456521A1 (en) |
| FR (1) | FR2343185A1 (en) |
| GB (1) | GB1566504A (en) |
| IT (1) | IT1075074B (en) |
| NL (1) | NL7702298A (en) |
| SE (1) | SE434182B (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4216703A (en) * | 1978-04-17 | 1980-08-12 | Rockwell International Corporation | Valve actuator |
| FR2547015B1 (en) * | 1983-06-06 | 1985-07-26 | Amri | ACTUATOR WITH PNEUMATIC ENERGY ACCUMULATOR, PARTICULARLY FOR TAP |
| DE19932743C2 (en) * | 1999-07-14 | 2003-10-09 | Thomas Scholzen | Control valve system with pneumatic actuator |
| GB0624436D0 (en) * | 2006-12-07 | 2007-01-17 | Stannah Lifts Ltd | Improvements in or relating to drive systems |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2943624A (en) * | 1958-04-17 | 1960-07-05 | Mavis M Alquist | Quantitative indicator for syringes |
| US2943642A (en) * | 1958-07-07 | 1960-07-05 | Cleveland Pneumatic Ind Inc | Liquid spring accumulator |
| US3122169A (en) * | 1960-05-26 | 1964-02-25 | Menasco Mfg Company | Accumulator |
| US3248879A (en) * | 1965-04-22 | 1966-05-03 | Acf Ind Inc | Constant pressure source for valves |
| FR1539749A (en) * | 1967-07-05 | 1968-09-20 | Creusot Forges Ateliers | Fluid accumulator with two pressure levels |
| FR2127281A5 (en) * | 1971-03-03 | 1972-10-13 | Ellingsen Karl | |
| US3962956A (en) * | 1974-11-19 | 1976-06-15 | Greer Hydraulics, Inc. | Hydropneumatic valve actuator |
-
1977
- 1977-01-27 GB GB329477A patent/GB1566504A/en not_active Expired
- 1977-01-27 CA CA270,553A patent/CA1051408A/en not_active Expired
- 1977-02-11 CH CH171877A patent/CH601712A5/xx not_active IP Right Cessation
- 1977-02-25 DE DE19772708250 patent/DE2708250A1/en not_active Ceased
- 1977-02-28 SE SE7702173A patent/SE434182B/en not_active IP Right Cessation
- 1977-03-01 JP JP52022129A patent/JPS5845627B2/en not_active Expired
- 1977-03-01 FR FR7705952A patent/FR2343185A1/en active Granted
- 1977-03-03 BE BE2055705A patent/BE852020A/en not_active IP Right Cessation
- 1977-03-03 NL NL7702298A patent/NL7702298A/en active Search and Examination
- 1977-03-03 IT IT2084577A patent/IT1075074B/en active
- 1977-03-04 ES ES456521A patent/ES456521A1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| BE852020A (en) | 1977-07-01 |
| GB1566504A (en) | 1980-04-30 |
| FR2343185B1 (en) | 1983-02-18 |
| FR2343185A1 (en) | 1977-09-30 |
| DE2708250A1 (en) | 1977-09-08 |
| CH601712A5 (en) | 1978-07-14 |
| IT1075074B (en) | 1985-04-22 |
| SE434182B (en) | 1984-07-09 |
| NL7702298A (en) | 1977-09-06 |
| JPS5845627B2 (en) | 1983-10-11 |
| ES456521A1 (en) | 1978-02-16 |
| JPS52107619A (en) | 1977-09-09 |
| SE7702173L (en) | 1977-09-05 |
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