A gate valve has a body with a gate chamber intersected by a flow passage and a stem chamber extending from the gate chamber. A gate is carried in the gate chamber. A stem, when rotated, causes linear movement of the gate between open and closed positions. A neck on the gate extends into the stem portion of the chamber. The neck has a cylindrical outer diameter, and a seal seals the neck to the stem portion of the chamber. The stem extends into engagement with a cavity in the neck. A ball screw interface is located between the stem and the cavity of the neck.

FIELD OF THE INVENTION

This invention relates in general to gate valves for oil and gas production, and in particular to a gate valve that closes automatically in the event of loss of a control signal.

BACKGROUND OF THE INVENTION

A gate valve has a body with a central chamber that is intersected by a flow passage. A gate moves within the chamber between the open and closed positions. The gate has a hole through it that aligns with the flow passage while in the open position. The gate may be of a split type, comprising two halves or it may comprise a single slab. A stem extends into engagement with the gate for moving the gate between open and closed positions. The chamber has a central portion, which is intersected by the flow passages, and a stem portion that extends from the central portion. Typically, a seal in the stem portion of the chamber engages the stem to seal pressure within the chamber.

In one type, the stem extends into rotatable engagement with a threaded nut or sleeve secured to the gate. Rotating the stem causes the gate to move linearly. In another type, the stem does not rotate. A threaded nut sleeve mounted in the bonnet of the valve engages the stem, and when rotated, causes the stem to move linearly. The threads of the sleeves and stem may slide against each other, or they may employ balls between the grooves for reducing friction.

Gate valves may be operated manually, such as with a wheel mounted to the stem or the nut sleeve. It is also known to utilize a remote operated vehicle (ROV) to engage and rotate a stem or nut sleeve. Hydraulically powered actuators are also utilized wherein a piston moves the stem linearly without rotation. Electrical actuators are also known that employ an electrical motor and a gear train to rotate a stem or nut sleeve to cause movement of the gate.

With actuators, typically, a spring is used to return the gate to a fail-safe position if power is lost. The fail-safe position could be either an open or a closed position. In a subsea environment using a hydraulic actuator, the spring must be strong enough to overcome hydrostatic pressure when pushing the piston back, requiring accommodation of relatively high loads and adversely impacting the physical size (and weight) of the actuator accordingly.

SUMMARY OF THE INVENTION

In this invention, the gate valve has a gate with a neck formed on it with a cylindrical outer diameter. The neck extends into a cylindrical stem portion of the chamber. A seal seals around the neck to seal fluid pressure in the central portion of the chamber from the stem portion of the chamber. A rotatable member, such as a stem, extends into the stem portion of the chamber on the opposite side of the seal. The stem and the neck have an interface for effecting movement of the gate between open and closed positions in response to rotation of the stem. The seal prevents any fluid in the central portion of the chamber from contacting the interface.

Preferably the stem has an inner end extending into a cavity in the neck. The outer end of the stem preferably extends to the exterior of the body for rotation by an operator, either manual or an ROV. Preferably the stem is non-rising relative to the body and the interface comprises a ball thread device with very low friction. The neck on the gate and the seal define a pressure area that is sized to exert a force in a fail-safe direction in response to the fluid pressure in the flow line. If subsea, the pressure in the stem portion of the chamber is normally the same as the hydrostatic pressure of the sea. The pressure area is selected so that a nominal pressure differential across the neck seal will cause movement of the gate to the fail-safe position. To prevent the gate from moving to the fail-safe position during normal operation, a clutch engages the stem and prevents it from rotating. The clutch is controlled by a pilot signal from a controller, which is supplied with power, either hydraulic or electrical. Upon loss of the pilot signal, the clutch disengages, allowing the stem to rotate and the gate to move to the fail-safe position.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1, gate valve11has a body13. Body13typically comprises a flow line portion13aand a bonnet13bthat are bolted together. A gate chamber14is located in flowline portion13a.A stem chamber15in bonnet13bextends from gate chamber15, and a clutch chamber16in bonnet13bextends above stem chamber15. Gate chamber14has flat sides15athat face each other, and stem chamber15is cylindrical. Clutch chamber16may be cylindrical or other shapes and is shown larger in diameter than stem chamber15.

Referring toFIG. 2, a flow passage17extends through body13and intersects gate chamber14. A seat ring19is located at each intersection of flow passage17with gate chamber14. Seat rings19are typically metal rings having seal surfaces on their inner faces.

A gate21moves linearly within gate chamber14between the open position ofFIGS. 2 and 4and the closed position ofFIG. 1. Gate21has a hole23through it that is sized to register with flow passage17while in the open position. Gate21has oppositely facing flat faces25for sealingly engaging seat rings19. Seat rings19may be biased by springs against flat faces25. The face25that seals will be a downstream side, thus the sealing engagement depends on the direction of flow through flow passage17. Gate21comprises a single slab in this embodiment, as opposed to a split slab type gate.

Gate21has a cylindrical neck27, which is best illustrated inFIG. 3. Neck27extends upward from gate21within stem chamber15and has a cylindrical outer diameter. In this embodiment, neck27has a diameter that is approximately equal to the distance from one flat face25to the other, substantially equaling the thickness of gate21, but the diameter could differ. The width of gate21measured between its side edges is somewhat larger than the diameter of neck27in this embodiment. Neck27also has a length that is at least equal to the length of the stroke of gate21from the closed to the open position

Neck27has a stem cavity or receptacle29located within it. Stem cavity29is a cylindrical hole formed on the axis of neck27with a depth at least equal to the length of the stoke of gate21from the closed to the open position. In the preferred embodiment, the bottom of stem cavity29is located at the base of neck27. A neck seal32seals between the outer diameter of neck27and the inner diameter of stem chamber15. Seal32is preferably located within bonnet13bnear the junction of stem chamber15with gate chamber14. In this embodiment, seal32is located in an annular recess formed in stem chamber15.

A rotatable member engages neck27to cause linear movement of gate21in response to rotational movement of the rotatable member. In this embodiment, the rotatable member comprises a stem33that extends into stem cavity29of neck27. An interface device, comprising a ball screw35in this embodiment, is located between stem cavity29and stem33to provide a low friction means for translating rotary motion of stem33to linear motion of gate21and vice-versa. Ball screw35may be any conventional type having a plurality of balls located between mating helical grooves31. Fluid located in gate chamber14is sealed from ball screw35by gate neck seal32. Stem33is a non-rising type in this embodiment, thus rotates only and does not move along its axis.

Stem chamber15is preferably filled with a liquid lubricant. If gate valve11is a subsea valve, means will be employed for equalizing the pressure of the lubricant in stem chamber15with the hydrostatic pressure of the sea. For example, a passage (not shown) may lead from stem chamber15to the exterior of bonnet13bfor connection to a line leading to an accumulator (not shown). The accumulator would have a bladder in contact with sea water on one side and the lubricant on the other side to maintain the pressure of the lubricant in stem chamber15at the hydrostatic pressure of the sea.

Stem33extends through clutch chamber16and has an outer end37located on the exterior of bonnet13b.Outer end37may be configured to receive a wheel for manual rotation. Alternately, outer end37may be shaped with sides configured for engagement by an ROV (remote operated vehicle) for subsea applications. A threaded retainer39secures stem33within bonnet13b.Retainer39preferably has inner diameter seals (not shown) for sealing around stem33and outer diameter seals (not shown) for sealing to bonnet13b.

Preferably a brake or clutch41is mounted to stem33for selectively preventing rotation of stem33. In this embodiment, clutch41is located within clutch chamber16in bonnet13babove stem chamber15. Clutch chamber16may be in fluid communication with stem chamber16. Alternately, a stem seal (not shown) may be located between stem chamber15and clutch chamber16. Clutch41may be of a variety of types and is not limited to any one particular means. By way of illustration of the principle of the invention, for example, it might comprise two or more plates (not shown) with friction pads isolated from any lubricant located within clutch chamber16. One of the plates is non rotatably mounted to bonnet13bwhile the other plate is mounted to stem33for rotation therewith.

When clutch41is in the engaged position, an external force causes the plates (or other means) to engage each other to prevent rotation of stem33. The force could be supplied by a electrical solenoid, from hydraulic fluid pressure, or from other devices. In this embodiment, a controller43mounted to the exterior of valve body13provides a signal or power via a passage45to clutch41. The signal or power may be electrical in nature supplied via an electrical conductor for maintaining a solenoid in a closed position. Alternately, the clutch41could be actively engaged by hydraulic fluid pressure or power supplied through passage45from controller43. In the absence of hydraulic fluid pressure, the plate on stem33would be free to rotate. Clutch41is biased to a released position, typically by a spring, which (in the illustrative example) pushes the plates of clutch41apart from each in the absence of the signal or power from controller43. Controller43receives its power or signal from a source external to valve11, which may be subsea or at the surface.

In operation, in this example, the fail-safe position is a closed position. Alternately, the fail-safe position could be an open position. Normally, fluid pressure will exist in flow passage17(FIG. 2). Assuming that valve11is in its normally open position, gate21will be in the lower position with its hole23aligned with flow passage17, as shown inFIG. 2. Clutch41(FIG. 1) will be engaged in response to a signal or power from controller43, preventing rotation of stem33. Seat rings19will not form tight seals with either of the gate faces25. Rather, fluid pressure in passage17will also exist within gate chamber14. This fluid pressure creates a pressure differential across neck seal32that equals the difference between the hydrostatic pressure in stem chamber15and the flow line pressure in passage17, which is normally higher. Neck27has a pressure area proportional to the inner diameter of seal32. The force due to the higher fluid pressure in gate chamber14urges gate21upward toward the closed position ofFIG. 1. This upward force is resisted by a downward force due to the hydrostatic pressure in stem chamber15plus the anti-rotation force on stem33exerted by clutch41. Clutch41has sufficient energy to prevent stem33from rotating when valve11is utilized under its design conditions, thus holding gate21in the lower open position.

In the event that the signal to clutch41is lost or turned off, clutch41will release. The pressure area of neck27is calculated in this example so as to be able to move gate21to the closed position under a nominal selected pressure in flow passage17greater than the hydrostatic pressure in stem chamber15. The low torque or friction of ball screw35enables closure to occur at a relatively low pressure differential across seal32. In some cases, such as very deep subsea applications, with low pressure in flow passage17, a supplemental return spring may be needed to assist in moving gate21to the closed position. As gate21moves upward to the closed position, stem33rotates, and one of the gate faces25will sealingly engage a downstream one of the seat rings19to close valve11.

To open gate valves11from the closed position, the signal to clutch41must be absent, so that it is in a released position. Stem33is rotated either by an ROV, if subsea, or manually by a wheel if at the surface. Once open, a signal is supplied by controller43to cause clutch41to engage stem33and prevent rotation in the reverse direction.

The invention has significant advantages. The valve moves to a fail-safe position in the event that clutch holding power is lost, and thereby enables remote fail-safe operation of a mechanically actuated valve, whilst avoiding the need for relatively costly hydraulic actuators. In a subsea application, this additionally avoids the need for associated accumulation and umbilical supplies, both of which incur significant cost and technical disadvantages as water depth and step out from the shore line increase. It follows that a subsea system may be supplied in a form that requires minimal hardware (actuators and umbilical functions) in order to effect the necessary functionality, whilst requiring only simple ROV (or manual) intervention in order to restore the system to the ‘normal’ production mode of operation.

The cylindrical gate neck and its sealing engagement within the stem chamber prevent fluid from the flow line from contact with the interface between the stem and the gate. This allows a very low friction interface, such as a ball screw, to be utilized without being contaminated by contact with fluid in the flow line. The pressure area provided by the neck can be sized to provide an adequate fail-safe movement based entirely on the flowline pressure in most cases. A return spring may be unnecessary. Even if a return spring is utilized for deep water and low flow line pressures, it would be much smaller than the return springs utilized with hydraulic actuators of the prior art.

While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention.