Fluid handling – Processes
Reexamination Certificate
1998-02-20
2001-10-16
Walton, George L. (Department: 3753)
Fluid handling
Processes
C060S483000, C251S058000
Reexamination Certificate
active
06302128
ABSTRACT:
TECHNICAL FIELD
The present invention relates to valve actuators, and more particularly to bi-directional rotary output actuators having ratchet-type output advances.
BACKGROUND OF THE INVENTION
Actuators with rotary ratchet advances are used to accurately position the trim of control or injection valves known as “choke valves” in the oil field industry. Choke valves are used to restrict or stop the flow of process fluids and are typically designed to handle highly abrasive fluids. A choke valve placed on a well head, for example, may be used to control the flow of well bore fluids in cooperation with a gate valve that is used as a safety shut-off valve which can rapidly stop the flow of the well bore fluids. A choke valve is often used in such applications to minimize, the flowrate of the highly abrasive well bore fluids before the gate valve is closed and exposed to the fluids, because at full flow the abrasive fluids might damage the sealing capabilities of the gate valve.
In a typical subsea wellhead installation, the choke valve is replaceable subsea, but the gate valve can only be replaced by retrieving the wellhead to the surface. Thus, it is important to protect the gate valve during emergency shutdown operations so to avoid retrieving the wellhead to repair any damage.
Conventional choke valve ratchet actuators require about ten seconds per pressure pulse to rotate the actuator output shaft one increment, which is approximately one-eighth of a six pitch revolution. Thus, with a two inch travel valve stem, a choke valve actuator can take as long as sixteen minutes to move the valve trim between the fully opened and the fully closed positions. With ratchet actuators, if you loose electrical power, hydraulic power, or the electrical position feedback device fails, you can count the hydraulic pulses to get to a known position. Conventional gate valves, on the other hand, can move between fully opened and closed positions in as little as ten seconds. As a result, a gate valve must often be used in emergency shut-down conditions to stop the flow of well bore fluids before the choke valve can minimize the flowrate of the well bore fluids. This results in possible damage to the gate valve and the need to retrieve the subsea wellhead.
It is known in the industry to use continuous-operation actuators with choke valves. These actuators can move the valve between fully opened and closed positions in approximately thirty seconds. However, these continuous-operation actuators cannot accurately position the trim of the choke valve to desired settings between the opened and closed positions. Accurate trim settings are required, for example, when the pressure drop across the choke valve is very high, because small variations in the valve trim can result in large changes in the flowrate of the well bore fluids.
SUMMARY OF THE INVENTION
In some aspects, the invention relates to an apparatus for controlling a rotary valve which comprises a hydraulic opening piston which activates an opening ratchet for incrementally opening the valve; a hydraulic closing piston which activates a closing ratchet for incrementally closing the valve; a hydraulic drive motor arranged to continuously open or close the valve; and a hydraulic control circuit connected to the hydraulic opening piston, the hydraulic closing piston, and the hydraulic drive motor; the hydraulic control circuit having a first hydraulic supply line, a second hydraulic supply line, two piston control valves, two drive motor control valves and two drive motor activation valves; wherein when the first hydraulic supply line is pressurized alone; the first piston control valve activates one of the pistons, the second piston control valve disengages the other piston, and the first drive motor control valve is opened; wherein when the first hydraulic supply line is pressurized and the second hydraulic supply line is subsequently pressurized; the first piston control valve disengages the previously activated piston, and the first drive motor activation valve engages and activates the drive motor; wherein when the second hydraulic supply line is pressurized alone; the second piston control valve activates one of the pistons, the first piston control valve disengages the other piston, and the second drive motor control valve is opened; and wherein when the second hydraulic supply line is pressurized and the first hydraulic supply line is subsequently pressurized; the second piston control valve disengages the previously activated piston, and the second drive motor activation valve engages and activates the drive motor.
In an alternative embodiment, an invention relates to an apparatus for controlling a rotary valve which comprises means for incrementally opening the valve with an opening ratchet piston; means for incrementally closing the valve with a closing ratchet piston; means for continuously opening and closing the valve with a drive motor; means for controlling the opening and closing of the valve with two hydraulic supply lines.
In an alternative embodiment the invention relates to a method for controlling a rotary valve using a hydraulic control circuit connected to the hydraulic opening piston, the hydraulic closing piston, and the hydraulic drive motor; the hydraulic control circuit having a first hydraulic supply line, a second hydraulic supply line, two piston control valves, two drive motor control valves and two drive motor activation valves comprising: pressurizing the first hydraulic supply alone; wherein the first piston control valve activates one of the pistons, wherein the second piston control valve disengages the other piston, and wherein the first drive motor control valve is opened; pressurizing the first hydraulic supply line and subsequently pressurizing the second hydraulic supply line; wherein the first piston control valve disengages the previously activated piston, and wherein the first drive motor activation valve engages and activates the drive motor.
In an alternative embodiment the invention relates to a method for controlling a rotary valve using a hydraulic control circuit connected to the hydraulic opening piston, the hydraulic closing piston, and the hydraulic drive motor; the hydraulic control circuit having a first hydraulic supply line, a second hydraulic supply line, two piston control valves, two drive motor control valves and two drive motor activation valves comprising pressurizing the second hydraulic supply alone; wherein the second piston control valve activates one of the pistons, wherein the first piston control valve disengages the other piston, and wherein the second drive motor control valve is opened; and pressurizing the second hydraulic supply line and the subsequently pressurizing the first hydraulic supply line; wherein the second piston control valve disengages the previously activated piston, and wherein the second drive motor activation valve engages and activates the drive motor.
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Hydril Company
Rosenthal & Osha L.L.P.
Walton George L.
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