Abstract:
A rotary valve is opened and closed with a combination incremental rachet mechanism and a continuous motor mechanism. Two separate control circuits are used for opening and closing the valve. When the opening or closing circuit is energized alone, the valve is incrementally opened or closed by the ratchet respectively. When the opening circuit is energized and the closing circuit is subsequently energized, the valve is continuously opened by the motor. Likewise, when the closing circuit is energized and the opening circuit is subsequently energized, the valve is continuously closed by the motor.

Description:
This application claims priority from provisional application 60/038,792 which was filed on Feb. 21, 1997. 
    
    
     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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, like reference numbers are used to describe like elements: 
     FIG. 1 is a fluid schematic for a rotary output actuator; 
     FIG. 2 is a fluid schematic for the actuator wherein fluid pressure is provided through the clockwise supply line to induce incremental clockwise rotation of the output shaft; 
     FIG. 3 is a fluid schematic for the actuator wherein fluid pressure is provided through the counterclockwise supply line to induce incremental counterclockwise rotation of the output shaft; 
     FIG. 4 is a fluid schematic for the actuator wherein fluid pressure is provided through the clockwise supply line in the first of two steps to induce continuous clockwise rotation of the output shaft; 
     FIG. 5 is a fluid schematic for the actuator wherein fluid pressure is maintained in the clockwise supply line, and is supplemented by fluid pressure provided through the counterclockwise supply line in the second of two steps to induce continuous clockwise rotation of the output shaft; 
     FIG. 6 is a fluid schematic for the actuator wherein fluid pressure is provided through the counterclockwise supply line in the first of two steps to induce continuous counterclockwise rotation of the output shaft; and 
     FIG. 7 is a fluid schematic for the actuator wherein fluid pressure is maintained in the counterclockwise supply line, and is supplemented by fluid pressure provided through the clockwise supply line in the second of two steps to induce continuous counterclockwise rotation of the output shaft. 
    
    
     DETAILED DESCRIPTION 
     The present invention is described in detail in the following with reference to the accompanying figures. 
     FIG. 1 illustrates a fluid flow schematic for the rotary output actuator in a normal, non-pressurized condition. The actuator is “powered,” i.e., pressurized, either hydraulically or pneumatically, but is described below in terms of hydraulic fluid pressure. The clockwise portion of the circuit  10  is depicted with its cylinder and valves in the upper portion of the schematic. The counterclockwise portion of the circuit  22  is depicted with its cylinder and valves in the lower portion of the schematic. The pilot valves are all in their default positions, and the rams of both hydraulic cylinders  14 ,  26  are in their respective retracted positions. 
     FIG. 2 shows the operation of the actuator when a pressure pulse is provided through clockwise hydraulic fluid supply line  12  to the clockwise portion of the circuit  10 . Fluid pressure in the clockwise line  12  passes through the clockwise cylinder pilot valve  16  to extend the ram of clockwise hydraulic cylinder  14  towards its extended position. The extension of the ram induces one incremental clockwise rotation via a ratcheting means that results in approximately one-eighth of a clockwise revolution of the actuator output shaft. 
     The pressurized fluid in the clockwise line  12  is also delivered through the network of fluid flow lines to the counterclockwise cylinder pilot valve  28  which shifts the valve  28  to its “block” position. The pressurized fluid is further delivered through counterclockwise motor pilot valve  30  to clockwise motor pilot valve  18  which shifts the valve  18  to its “flow through” position. Depressurization of line  12  causes all pilot valves to return to their normal positions under their own return spring action. The hydraulic fluid in the fluid flow network is exhausted back out of line  12 . The results of these actions will be discussed further below. 
     FIG. 3 shows the operation of the actuator when a pressure pulse is provided through counterclockwise hydraulic fluid supply line  24  to the counterclockwise portion of the circuit  22 . Fluid pressure in the counterclockwise line  24  passes through a counterclockwise cylinder pilot valve  28  to extend the ram of counterclockwise hydraulic cylinder  26  towards its extended position. The extension of the ram induces one incremental counterclockwise rotation via a ratcheting means that is equal to approximately one-eighth of a revolution of the actuator output shaft. 
     The pressurized fluid in the counterclockwise line  24  is also delivered through the network of fluid flow lines to clockwise cylinder pilot valve  16  which shifts the valve  16  to its “block” position. The pressurized fluid is further delivered through the clockwise motor pilot valve  18  to the counterclockwise motor pilot valve  30  shifting the valve  30  to its “flow through” position. Depressurization of line  24  causes all pilot valves to return to their normal positions under their own return spring action. The hydraulic fluid in the fluid flow network is exhausted back out of line  24 . The results of these actions will also be discussed further below. 
     FIGS. 4 and 5 illustrate the two-step sequence required for continuous clockwise rotation of the actuator output shaft. As shown in FIG. 4, the first step of the sequence is applying a pressure pulse to the clockwise line  12  results in identical consequences described above for FIG.  2 . Thus, the ram of clockwise hydraulic cylinder  14  is moved to its extended position, inducing one incremental clockwise rotation of the actuator output shaft. Additionally, the counterclockwise pilot valve  28  is shifted to its “block” position, and the clockwise cylinder pilot valve  18  is shifted to its “flow through” position. 
     As shown in FIG. 5, the second step of the sequence is maintaining the pressure in the clockwise hydraulic line  12  while pressure is applied to the counterclockwise line  24 . Pressurization of the counter clockwise line  24  causes clockwise cylinder pilot valve  16  to shift to its “block” position, thereby allowing the biasing spring on the ram of the clockwise cylinder  14  to return the ram to its retracted position and exhaust the fluid pressure back out through valve  16  to the piston exhaust port  36 . 
     The pressure from the counterclockwise line  24  is further delivered through clockwise motor pilot valve  18  to clockwise motor drive pilot valve  20 . It moves the valve  20  to its “flow through” position. This allows the fluid pressure to pass through the valve  20  and to the hydraulic motor  34 . The fluid pressure energizes the motor and continuously drives the actuator output shaft via a gear assembly in a clockwise direction. This actuator continues until the shaft reaches its mechanical limit or the pressure is removed from either the counterclockwise line  24  or the clockwise line  12 . The fluid passing through the hydraulic motor  34  also passes through counterclockwise motor drive pilot valve  32  and out the motor exhaust port  38 . 
     FIGS. 6 and 7 illustrate the two-step sequence required for continuous counterclockwise rotation of the actuator output shaft. As shown in FIG. 6, the first step of the sequence is applying a pressure pulse to the counterclockwise hydraulic line  24  to produce the identical results described above for FIG.  3 . Thus, the ram of the counterclockwise cylinder  26  is moved to its extended position, inducing one incremental counterclockwise rotation of the actuator output shaft. The hydraulic clockwise pilot valve  16  is shifted to its “block” position, and the counterclockwise motor pilot valve  30  is shifted to its “flow through” position. 
     FIG. 7 shows step two of the sequence, where the pressure is maintained in the counterclockwise line  24  while pressure is then applied to the clockwise line  12 . Pressurization of the clockwise line  12  causes counterclockwise cylinder pilot valve  28  to shift to its “block” position, thereby allowing the biasing spring on the ram of the counterclockwise cylinder  12  to return the ram to its retracted position and exhaust the fluid pressure back out through the counterclockwise cylinder pilot valve  28  and to the piston exhaust port  36 . 
     The pressure from the clockwise line  12  is further delivered through counterclockwise motor pilot valve  30  to counterclockwise motor drive pilot valve  32 . It moves the valve  32  to its “flow through” position. This allows the fluid pressure to pass through the valve  32  and to the hydraulic motor  34 . The fluid pressure energizes the motor and continuously drives the actuator output shaft in a counterclockwise direction. The actuator continues until the shaft reaches its mechanical limit or the pressure is removed from either the clockwise supply line  12  or the counterclockwise line  24 . The fluid passing through the hydraulic motor  34  also passes through the clockwise motor drive pilot valve  20  and out the motor exhaust port  38 . 
     In an alternative embodiment, the cylinder pilot valves  16  and  28  may be omitted if the ratchet action of fluid-powered cylinders  14  and  26  is acceptable while the hydraulic motor  34  is powered for continuous rotation of the output shaft. 
     Although exemplary embodiments have been shown and described, those skilled in the art will recognize that other embodiments fall within the spirit and scope of the invention. Accordingly, the invention is not limited to the disclosed embodiments, but rather is defined solely be the scope of the appended claims.