US3752041A - Fail-safe actuator - Google Patents

Abstract

A fail safe actuator includes a fluid-operated vane motor, a control valve means connected between a fluid source and one side of the motor, a bypass conduit connected between opposite sides of the motor including a restrictive orifice, and a storage tank cooperating to return the motor to its starting position upon failure.

Description

United States Patent Smith Aug. 14, 1973 [5 FAIL-SAFE ACTUATOR 2,820,434 1/1958 Otto 91/166 2,856,222 10/1958 Gossett et a1. 91/165 X [75] 5mm, cmcmnat" Ohm 2,937,845 5/1960 La Rocque et a1. l37/625.65 x 3 Assignee; xomox Corporation Cincinnati 3,554,096 1/1971 DeJager 92/125 Ohio 3,577,831 5/1971 Brmkrnan 91/416 [22] Filed: 1971 Primary Examiner-Irwin C. Cohen [21] Appi. No.: 204,990 Attorney-J. Warren Kinney, Jr.

[52] US. Cl 91/416, 251/25, 251/59 [57] ABSTRACT I. FlSb F16k i izld of Search 1 65 166 2 51 A ail Safe actuator includes a fluid-operated vane mo- 2 5 tor, a control valve means connected between a fluid source and one side of the motor, a bypass conduit con- [56] References Chad nected between opposite sides of the motor including a restrictive orifice, and a storage tank cooperating to UNITED STATES PATENTS return the motor to its starting position upon failure. 204,914 6/1878 Prince. Jr 91/416 X 214,603 4/1879 Westinghouse, Jr 91/416 X 2 Claims, 2 Drawing Figures Patented Aug. 14, 1973 3,752,041

3 WAY,SPR|NG RETURN, SOL: ENOID VALVE M/VE/VTUR RUSSELL G. SMITH FAIL-SAFE ACTUATOR BACKGROUND OF THE INVENTION The present invention springs from earlier efforts to automatically restore the valving member of a valve to a home position, upon the occurrence of a condition or particular contingency such as a power failure, pressure drop, or other change of conditions which might produce an element of danger or loss if the valve were permitted to remain open.

By way of example, when an actuator such as disclosed in U. S. Pat. No. 3,554,096 was used to move the valving member of a valve between full open and full closed positions, the swinging piston or vane of the actuator would be oscillated within its housing through an arc of about 90, by the force of pressure media under pressure admitted at one side or the other of the piston. Under normal operating conditions the piston would be returned tov its initial position in which the valving member would be closed, by introducing fluid media behind the piston from a pressure line incident to exhausting pressure media from the other side of the piston.

The present invention is directed to the use of a chamber or tank which at all times is in free, open communication with one side of the piston of an actuator, and wherein said chamber or tank also is always in restricted, open communication with the other side of the piston.

When pressure media is applied to the piston removing it away from its home position, the piston immediately moves to the opposite end of the stroke as it is an open communication with the source of pressure. Meanwhile, the pressure media is simultaneously bled through the orifice into the comparatively large tank so that a fully balanced pressure condition results on opposite sides of the piston after it has been shifted to the end of its actuating movement.

The piston will remain at the end of a stroke so long as pressure media under line pressure is maintained against it. However, whenever the line pressure is intentionally exhausted, the piston will be immediately and automatically shifted to its home position because the opposite side of the piston is immediately exhausted because of its open communication with pressure source while pressure stored in the tank bleeds slowly through the orifice so that a fully balanced pressure condition again results on opposite sides of the piston after it has been shifted to its"home position."

Usually a 3-way spring return solenoid valve is used for controlling the flow of fluid media under line pressure to the inlet side of the piston housing for providing means of exhausting the fluid media in event of electric power failure or pressure failure.

By utilizing such a valve a foolproof, fail-safe actuator is provided, since if the electric power should fail even though the line pressure media remains constant the line pressure to the inlet side of the piston will be exhaused and the piston will be promptly returned to its home position" for automatically closing the valve with which it is associated.

The subject device offers the following advantages over actuators of the type in which fluid media under line pressure is selectively applied to one or the other sides of a piston:

1. No check valves are required.

2. Considerable external piping is eliminated.

3. A pilot valve is eliminated.

The subject device offers the following important advantages over prior art spring return fail safe actuators:

l. About percent of the total force applied to the piston is available and useful for moving the piston to its home position as compared to 33 percent avail able on spring-return actuators.

2. There is no possibility of spring failure due to breakage, spring set or corrosion of the spring.

SUMMARY OF THE INVENTION A double-acting fluid motor is employed, having a piston shaft fixed to the piston and to the stem of a valve or other device to be actuated, so that the piston shaft when moved from one limit of travel to another, will rotate the stem and any components connected thereto. Air pressure from a suitable primary source is used for driving the piston in one direction, whereas air from an auxiliary tank kept charged by the primary source, is made automatically available to drive the piston in the opposite direction whenever pressure at the primary source is discontinued, or fails to maintain a biased posture of the piston.

The elements employed for achieving the above objective are a simple orifice unit, two standard tubes, and a tank, all of these components being readily conductive of compressed fluid such as air, without liklihood of clogging, deteriorating, or requiring maintenance attention such as may be experienced with the use of check valves and spring-biased control devices.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of the improved failsafe actuator shown applied by way of example, to a fluidcontrolling plug-type valve.

FIG. 2 is a plan view of the device of the invention and its connection with a source of compressed air.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawing, pipe 6 may be considered a suitable' primary source of compressed air, usually of a substantially constant nature, but subject to the practical possibilities of interruption or complete failure. At 8 is indicated generally a conventional three-way spring return solenoid valve for controlling flow of pressured air through pipe 6 to a feed tube 10 supplying the actuator of the present invention.

Valve 8, which is properly considered a control valve, includes an electrical coil or solenoid which, when energized, holds the valve open to permit a continuous flow of air from source 6 to feed tube 10. Any interruption of electric current to the coil or solenoid of the control valve, results in closing of the valve usually by means of a spring built into the valve structure, for automatically terminating the flow of air to feed tube 10 and exhausting fluid media from tube 10.

From the foregoing, it will be understood that either a mechanical failure or an electrical failure will deprive the feed tube 10 of compressed air.

At 12 is indicated a fluid motor or actuator comprising a chambered housing 14 in which is movable a vane or piston 16 mounted securely upon a shaft 18 which may project in opposite directions from the piston chamber 20. One end 22 of shaft 18 is shaped to accommodate a tool for externally rotating the shaft. The opposite end of shaft 18 is axially aligned with and coupled to the operating stem 24 of a rotary plug, not shown, which forms part of a plug-type service valves generally denoted 26.

Service valve 26 is adapted to control a flow of gas or liquid through a pipe system 28 and will often be quite large and heavy. The fluid passing through valve 26 may be of a hazardous or corrosive nature, possibly requiring careful and prompt full closing of the service valve under abnormal or hazardous circumstances which may arise while the valve is open.

One abnormality with which the present invention is concerned, is that of a failure of air pressure to valve 8 and feed tube 10, or an electrical failure resulting in solenoid de-energization and resultant closing of control valve 8. However, a deliberate shut-down of air pressure, or a deliberate interruption of solenoid current, may be resorted to for effecting full and prompt closing of valve 26, as will be explained hereinafter.

With further reference to the drawing, the piston chamber 20 is seen to have a first port 30 and a second port 32 located at opposite ends of the chamber, whereby compressed air entering at port 30, for example, will drive the piston 16 from the full line first position of FIG. 2 to the second position indicated by bro ken lines. Conversely, air directed into the port 32 will drive the piston from the broken line position to the full line position shown. The full line and broken line positions of FIG. 2 represent the two limits of travel of piston 16. As will be understood, one of the ports mentioned will necessarily exhaust while the other feeds air to the piston chamber.

The piston 16 sweeps an inner arcuate wall 34 of the actuator housing, and to minimize loss of power the piston may carry sealing gaskets such as 36, all as explained in the U. S. Pat. No. 3,554,096.

Feed tube leading from control valve 8 is connected to port 30, and port 30 has connection also with an air chamber, storage tank or reservoir 37 by way of a bypass tube 38. An orifice unit 40, located between port 30 and tank 37, limits the rate at which pressured air will enter the tank by way of tube 38. If desired, the orifice unit may be adjustable as to its flow constriction; however, in practice, the rate of flow may be preset at a calculated value.

The interior of air storage tank 37 is connected by means of tube 42 to port 32, to permit a free rapid flow of air between the tank and that portion of chamber which communicates with port 32. The flow through tube 42 is unrestricted at all times.

In the present example, service valve 26 is operative or closed when piston 16 is disposed in the home position," adjacent to port 30. When piston 16 is disposed in the biased position, as depicted by broken lines in FIG. 2, the service valve 26 is open. The piston is adapted to move through an arc of about 90.

OPERATION OF THE DEVICE By closing an electric switch in circuit with the solenoid of valve 8, said valve will open to direct air under pressure from a source such as 6, through feed tube 10 and port 30 for moving the piston 16 to the biased position depicted by the broken lines. The service valve 26 will thereby be opened, and will remain open as long as pressured fluid is supplied through port 30 from source 6.

Pressured fluid, such as air, simultaneously is supplied to orifice tube or bypass 38, and flows at a greatly reduced rate into tank 37 through orifice 40, to fill the tank to full line pressure in a matter of 5 to 10 seconds, as well as the tube 42, and that portion of chamber 20 which is in communication with port 32. Thus, following an initial burst of air entering the actuator chamber at 30 to drive the piston to the biased position near port 32, the air pressure becomes equalized at both faces of the piston, as well as within tank 37, under pressure equal to the source pressure. The piston therefore remains biased, with service valve 26 in an open position, as long as pressure remains equalized in the system. Equalization may occur in a short period of time, perhaps between 5 and 10 seconds, depending upon the size of orifice 40.

In the event of a sudden air pressure failure at tube 10, the air stored in tank 37 will immediately enter the piston chamber through tube 42 and port 32, to swing the piston to the home position for closing the service valve 26. The piston in so moving will enforce an exhaust of air through port 30 and a suitable exhaust port such as 44.

The aforesaid automatic operation of the actuator for closing valve 26, may result from a break in pipe 6, tubes 10 or 38, or elsewhere in the system resulting in a sudden imbalance of pressure at opposite faces of the piston. The actuator may also be activated by either an accidental or a deliberate breaking of the solenoid circuit of valve 8. If desired, a selectively operable switch may be incorporated in the solenoid valve circuit, enabling an attendant to initiate discretionary closing and opening of the service valve.

It should be understood that the actuator may, if desired, utilize a conventional reciprocating piston in lieu of the swing type piston illustrated in FIG. 2.

What is claimed is:

1. A fail-safe actuator for moving a rotary stem of a plug-type service valve, to dispose the plug to operative and inoperative positions, and comprising in combination: a fluid motor including a housing having a chamber presenting an arcuate inner wall surface, and an oscillatable vane having equal opposed areas movable within the chamber and against said wall surface between one limit of travel near one end of the arcuate inner wall surface and a second limit of travel near the other end of the arcuate inner wall surface; a rockable rotary shaft supported by said housing and connected with said vane for movement with said vane, said shaft coupled to said valve stem for corresponding movement of said stem with said shaft; a first port in fluid communicative relationship with the housing chamber at one end thereof on one side of the vane; a second port in fluid communicative relationship with the housing chamber on the other side of the vane, a first conduit connected with said first port and with a source of fluid pressure, a control valve controlling a flow of pressurized fluid from said fluid source to said first port of the chamber, for driving the vane from its said one limit of travel to its second limit of travel; an external storage tank for pressurized fluid, an external bypass conduit connected with said storage tank and in communication with said first port; a restricted flow orifice in said bypass conduit including a means for adjusting said restricted orifice for bypassing into the storage tank a portion of the pressurized fluid supplied to said first port through the control valve, said orifice providrespective limits of travel.

2. The combination as defined by claim 1, wherein the control valve includes spring means for biasing said control valve toward closed position, and electromagnetic means for opening said valve against the resistance of said spring means, said spring means providing a dominant force for closing the control valve whenever the electromagnetic means is deenergized.

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Claims (2)

1. A fail-safe actuator for moving a rotary stem of a plug-type service valve, to dispose the plug to operative and inoperative positions, and comprising in combination: a fluid motor including a housing having a chamber presenting an arcuate inner wall surface, and an oscillatable vane having equal opposed areas movable within the chamber and against said wall surface between one limit of travel near one end of the arcuate inner wall surface and a second limit of travel near the other end of the arcuate inner wall surface; a rockable rotary shaft supported by said housing and connected with said vane for movement with said vane, said shaft coupled to said valve stem for corresponding movement of said stem with said shaft; a first port in fluid communicative relationship with the housing chamber at one end thereof on one side of the vane; a second port in fluid communicative relationship with the housing chamber on the other side of the vane, a first conduit connected with said first port and with a source of fluid pressure, a control valve controlling a flow of pressurized fluid from said fluid source to said first port of the chamber, for driving the vane from its said one limit of travel to its second limit of travel; an external storage tank for pressurized fluid, an external bypass conduit connected with said storage tank and in communication with said first port; a restricted flow orifice in said bypass conduit including a means for adjusting said restricted orifice for bypassing into the storage tank a portion of the pressurized fluid supplied to said first port through the control valve, said orifice providing for two-way movement of fluid therethrough at a limited flow rate, and an external second conduit connected with said storage tank and with said second port and in open, free communication therewith to supply fluid pressure from said storage tank to said chamber to return the vane to its said one limit of travel upon occurrence of failure of fluid pressure at said first port, said restricted bypass conduit, said storage tank, and said first and second conduits resulting in equalization of fluid pressure on opposite sides of said piston at its respective limits of travel.

2. The combination as defined by claim 1, wherein the control valve includes spring means for biasing said control valve toward closed position, and electromagnetic means for opening said valve against the resistance of said spring means, said spring means providing a dominant force for closing the control valve whenever the electromagnetic means is deenergized.

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