Valves and valve actuation – With means for blocking or disabling actuator – Fluid pressure biased latch
Reexamination Certificate
1999-12-22
2001-03-27
Shaver, Kevin (Department: 3754)
Valves and valve actuation
With means for blocking or disabling actuator
Fluid pressure biased latch
C251S327000
Reexamination Certificate
active
06206338
ABSTRACT:
TECHNICAL FIELD
This invention relates to a hydraulic actuator for controlling the operation of a valve which is designed to actuate automatically and remain in position upon the loss of control pressure.
BACKGROUND ART
Gate and other sliding stem valves used in fluid flow control are opened and closed by inserting an obstruction or fluid control device into the flow. These valves are operated by a valve actuator employing a variety of methods, including manual actuation, diaphragm-type actuation, and hydraulic actuation. The actuator is usually mounted to the valve and provides the reciprocating linear motion required to open, close, and position the flow control device within the valve.
In the case of a hydraulic actuator, a hydraulic control feed is used to actuate the valve. A control feed line provides hydraulic pressure which actuates a piston in the actuator. As the piston moves, it opens and closes the valve. Generally, opening or closing the valve requires a high control feed pressure. When the desired degree of open or closed is reached, the control line can be locked-in to maintain the pressure. When there is a sudden drop in control feed line pressure, such as due to a failure in the feed line, the valve position is no longer locked-in. Depending on the configuration of the valve and the pressure in the flow line, the valve will tend to fail either in a fully open or a fully closed position. A pressure differential across the flow control device causes an ejection force tending to move the flow control device upward. Most prior art actuators compensate for this by forcing the flow control device either to it upper most position or down to its lower most position, thus fully opening or closing the valve. However, in some situations it is desirable for the valve to resist the ejection force and remain at the degree of open or closed it had been before the loss of control feed pressure.
It is therefore desirable to provide a hydraulic actuator that fails as-is, thus remaining in a given position in the event of a drop in control line pressure. It is also desirable that the actuator be compact and reliable and resist ejection force.
SUMMARY OF THE INVENTION
The present invention is directed toward a valve actuator that fails as-is. The valve is opened and closed by sliding a stem between two positions. The valve actuator has a housing for joining to the valve. An actuator piston is carried within the housing and adapted to couple to the valve stem. The actuator piston can reciprocate within the cylinder housing to slide the stem between the two positions. An elongate gripper shaft extends from the actuator piston. A gripping member is carried within the housing and is moveable between an engaged position, restraining movement of the gripper shaft in one direction, and a disengaged position, allowing movement of the gripper shaft in both directions. A spring member is mounted in the housing in engagement with the gripping member and urges the gripping member into the engaged position. A release piston is reciprocatingly carried in the housing for moving the gripping member to the disengaged position. A hydraulic passage extends from the actuator piston to the release piston to move the release piston to place the gripping member in the disengaged position when hydraulic fluid pressure exists at the actuator piston.
A locking ring with a tapered inner surface is carried within the upper housing. The gripping member is carried in the locking ring and the tapered inner surface that is adapted to force the gripping member inward into engagement with the gripper shaft when the spring member are moves the gripping member to the engaged position. Preferably, the gripping member comprises a collet member having collet fingers, each with a tapered outer surface adapted to engage and slid against the tapered inner surface of the locking ring. The release piston has a central protruding portion that extends into the locking ring and into abutment with the gripping member. The release piston is located on one side of the gripping member while the actuator piston is located on the opposite side. Preferably, the spring member is carried within the locking ring. The gripping shaft is grooved and the gripping member has mating grooves.
REFERENCES:
patent: 3941141 (1976-03-01), Robert
patent: 4052995 (1977-10-01), Ellison
patent: 4522370 (1985-06-01), Noack et al.
patent: 5190106 (1993-03-01), Johnston
Blair Richard
Otteman Timothy J.
Trail Len Albert
ABB Vetco Gray Inc.
Bonderer David A.
Bracewell & Patterson
Bradley James E.
Shaver Kevin
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