It is well known in the petroleum industry that gate valves are required for use in the piping at various locations and in particular in piping known in the industry as a christmas tree located at a drilling location. The gate valve opens and closes to contain pressure within the well bore. It is also well known in the industry that wireline is used to lower tools of various types into the well bore in an oil or gas well through the bore of the safety valve in the upper master valve of the christmas tree. It is necessary therefore to attach an actuator to the safety valve, which may be of the gate valve type, that will provide the forces necessary to move the valve between the open and closed positions by application or removal of a pressurized fluid. In a typical application the valve would incorporate a reverse-acting gate in a conventional manner which would be moved to the open position by application of a pressurized fluid through the inlet port to the top of the actuator piston. Upon removal of the pressure applied to the inlet port, the safety valve would move to the closed position due to the force developed by valve body pressure acting on the area of the valve stem. The actuator design in the prior art incorporates a linear force storage device which assists in closing and is capable of closing the valve when valve body pressure is not present. This type of operation is conventional in safety valves. On occasion, however, wireline may be extending through the safety valve because of tools of various types that have been lowered into the well bore. It may be necessary to close the valve with sufficient force to cut the wireline. The additional factor in wireline cutting actuators is that the closing force must be sufficient not only to close the valve when valve body pressure is absent, but also to provide the additional force to cause the valve gate to shear through any wireline that is in the valve bore at the time of closing.
Wireline cutting actuators to perform this function are common in the industry. In most cases, the design force at the wire cutting position is over eight thousand pounds. Traditionally, this force has been developed by large coil springs, cams, helical springs, spring washers or other type devices.
The prior art devices have a number of disadvantages. First, they must be very large to accommodate the size of springs that are necessary to develop the force that must be present to cut wirelines. Thus, they are very heavy and very large. In addition, the force generated by the metal springs is in proportion to the size and weight. Thus, there is a limit to the force that can be generated inasmuch as the size of the actuator is a factor to be considered in the use of the devices at the wellhead. Further, in order to have a predetermined force necessary to close the valves without any well pressure, there must be a predetermined compression built into the springs which creates a hazard condition when disassembling and handling the valves. Also, it is difficult to provide a variable and adjustable closing force with the use of metal springs. Further, there is no way to indicate the force units available in such a device. One simply has to know from the construction and the age of the device how much force it can provide.
The present invention overcomes the disadvantages of the prior art by providing an actuator which utilizes a gas spring. Thus, a variable and adjustable closing force can be provided. In addition, a pressure gauge can be utilized to indicate the force units available. This gas spring valve actuator can generate a higher force for the same size unit than metal springs can provide. It is of small size and weight and is so constructed as to provide safety in disassembly and handling thereof.
The force generating element is a gas compression device commonly known as a gas spring. Gas springs have been used in large metal presses to separate the die heads. As far as is known, gas springs have not been used in valve actuators prior to the present invention. The novel concept uses a concentric, annular gas spring design that fits around the valve stem to create a uniform force in a minimum size envelope. The gas spring can develop the high forces required in a smaller package than that which must be used with standard springs.
The gas spring includes concentric, annular cylinders with a first stationary body member that has pressure seals which engage with the internal bore of a second movable annular spring body member. An integral gas charging device allows the injection and pressurization of gas trapped in the concentric annular cylinders. Pressure in the annular cylinders forces the first body member and piston in a direction to exert force on top of the valve bonnet and the gas spring housing to exert force on the actuator piston and gate valve stem urging the stem to move the sealing element of the gate valve to the closed position. The integral gas charging device connects to the interior of the second body member of the gas spring by a sealed connection. The side force generated by the gas charge pressure acting on this connection is balanced by a connection of equal size on the opposite side of the second body member. This design counteracts all side forces developed at the pressure ports.
The force of the gas spring depends upon pressure trapped in the spring cylinder created by the first and second spring body members. By having an integral charging device, the pressure can be changed, thus changing the closing force without changing any parts or disassembling the actuator. Thus, a variable and adjustable closing spring force can be provided.
Further, the integral charging device for the gas spring may include a pressure gauge that will constantly indicate the pressure trapped inside the gas spring cylinder. Since the areas exposed to pressure are constant, the pressure is in a direct relationship with force and the gauge may be calibrated in force units available. In this way, the actuator can be checked regularly for available closing force without disassembly.
In addition, the gas spring can produce forces in excess of that available with other types of conventional metal springs in the same overall size outer housing. The smaller size and weight are important in applications on wellheads on offshore oil and gas production platforms. This becomes an advantage in installation in maintenance, especially on high density production platforms.
The actuator is designed to prevent disassembly of the actuator without first removing all fluid pressure from the actuator. The gas spring in the subject invention contributes to safety over conventional spring designs. The gas spring must be depressurized prior to removal from the actuator housing. The integral charging device must be removed before the gas spring body members can be removed from the housing. To do this requires that the gas spring be partially compressed for removal of the integral charging device. Compression of the gas spring cannot be readily accomplished without removal of the gas charge, thus removing the spring force. Once the gas charge is removed, there are no retained forces. Also, since the gas spring is charged after installation, there is no requirement for the compression of springs and the use of special tools during assembly as with conventional mechanical springs.
Further, the gas spring lends itself inherently to a variety of operating procedures. The actuator may be used as a spring return actuator to the outward or closed position. By simply connecting the gas spring integral pressurizing device to a second fluid pressure source, the actuator becomes a "double acting" actuator that may be powered in either direction by application of fluid pressure to the appropriate chamber while venting fluid pressure from the opposite chamber. A third way in which the actuator may be used is as a spring return to the inward or open position by simply charging the actuator chamber above the piston with the gas charge and admitting the pressurized actuating fluid to the gas spring integral charging device. This simply reverses the operation of the actuator.
Due to the attachment of the outer actuator housing to the valve bonnet by the use of a retaining ring, the outer housing may be rotated to any convenient position to align a window therein for the gas spring position indication. The fluid connection to the actuator is made through the top center of the outer actuator housing which allows the actuator supply pressure inlet to remain fixed.
The unit is also safe and easy to disassemble. On removal of pressure from the actuator by disconnection of the actuator pressure inlet piping from a fluid connection port on the top of the actuator housing, a square positioning ring at the bottom of the actuator housing may be snapped out of its position. The fluid connection port is designed so that it is necessary that it be pushed inwardly and rotated to engage a slot in the piston head to commence disassembly of the valve. The fluid connection port cannot be pushed inwardly while pressure is maintained in the actuator, thus making disassembly under pressure virtually impossible. The actuator housing can then be pushed downwardly. A retainer ring may then be removed from a groove in the actuator housing. Rotation of the piston by turning the inlet connection on top of the housing (which is now locked to the piston) will unthread the piston from its stem, thus allowing the actuator to move outwardly from the bonnet. Bearings are located between the piston and the top of the gas spring to provide easier rotation of the stem without rotating the gas spring. The gas spring may retain the gas charge and remain pressurized because it can only extend to the limit of a retainer ring between the first gas spring body member and the second gas spring body member. Once this point of spring extension is reached, all force from the gas spring is internally retained and the piston may be fully unthreaded from the valve stem allowing removal of the actuator assembly from the bonnet of the valve. The actuator assembly may be reinstalled on the bonnet in the reverse procedure without changing the gas spring setting or the charge.
In addition, a slot is provided in the side of the actuator housing to reveal the position of the first gas spring body member which is relative to the position of the valve. Position indicating switches, such as microswitches, may be adapted to this area for remote position indication. The downstop position of the actuator is dependent upon the relative location of a downstop nut on the valve stem. This may easily be adjusted for the proper valve stroke prior to or after the assembly of the actuator to the bonnet.
Thus, it is an object of the present invention to provide a gas spring actuator.
It is also an object of the present invention to provide a gas spring actuator which has a variable and adjustable closing force.
It is still another object of the present invention to provide an indication of actual closing force with the use of a pressure gauge that will constantly indicate the pressure trapped inside the gas spring.
It is still another object of the present invention to provide a gas spring which can produce forces in excess of that available with other types of conventional metal springs in the same overall size housing.
It is also an object of the present invention to provide a gas spring which has smaller size and weight than comparable size valve actuators utilizing metal springs.
It is yet another object of the present invention to provide a gas spring actuator that is safe to disassemble and handle because it cannot be disassembled without first removing fluid pressure from the gas spring.
It is also an object of the present invention to provide a gas spring actuator that can be used as a spring return actuator to either close or open a valve.
It is yet another object of the present invention to provide a gas spring actuator that can be used as a "double acting" actuator that may be powered in either direction.
It is still another object of the present invention to provide a gas spring actuator that has a visual position indicating window through which the position of the gas spring can be noted and which can be moved to any convenient position by rotating the housing to align the window for position indication.
It is yet another object of the present invention to provide visual position indication and position indicating switches that may be used to indicate the gas spring position at a remote location.
It is also an object of the present invention to provide a downstop position adjustment to adjust the proper valve stroke.