A GATE VALVE ASSEMBLY

The present invention relates to a gate valve assembly and more particularly, but not exclusively, to a small-bore gate valve assembly for use in sub-sea applications in the gas and oil industry.

Gate valves are commonly used in the gas and oil industry to isolate fluid pipelines in sub-sea well christmas tree valve blocks. They comprise a sliding valve gate that is moved to open or close the fluid line and an actuating spindle connected to the gate. Rotation of the spindle is converted into linear sliding movement of the valve in order to operate the valve. A conventional gate valve requires multiple rotations of the actuating spindle to move the gate from open to closed positions and vice versa.

Small-bore gate valves used in the branch lines of sub-sea trees lend themselves to actuation by ROVs. An example of a gate valve assembly of this kind described above is disclosed in our international patent application WO 2004/003411. The valve assembly has a rotary spindle for operating the gate valve and a mechanism for converting the rotary movement into a linear sliding movement of the gate. The direction of movement of the gate is transverse to the axis of rotation of the spindle.

Ia gate valves of this kind a stem sealing arrangement provides a barrier between the fluid being transported in the pipeline and the environment in which the valve is located, hi order to effect linear movement of the gate valve it is necessary to overcome three principal forces: a friction force between the valve and its seats; a friction force between the stem seal and the stem, which is dependent oh the diameter of the stem; and a stem ejection force imparted by the fluid being transported on one end the stem. For small-bore gate valves (i.e. those having a bore diameter of less than around 1.5 inches (3.81cm)) the relatively small size of gate means that it is the stem ejection force that is the more significant of the three forces and such valve assemblies tend to be disproportionately larger and more expensive than larger gate valves.

It is an object of the present invention to obviate or mitigate the aforesaid or other disadvantages. It is also an object to provide for a valve assembly in which effect of the stem ejection force on valve operation is obviated or mitigated.

According to the present invention there is provided a gate valve assembly comprising a valve body with a fluid conduit therethrough, a valve gate mounted in

said fluid conduit for movement in a direction transverse to said conduit between an open position whereby fluid can flow through said conduit and a closed position whereby the gate blocks said conduit and fluid flow is prevented, a stem slidable in a stem bore in the valve body and connected to said gate, the stem being slidable to move the gate between the open and closed positions, a first chamber defined between a first end of the stem and the valve body, the first chamber being sealed by a first seal between said first end of the stem and the stem bore, a second chamber defined between a second end of the stem and the valve body, a second chamber being sealed by a seal between said second end of the stem and the stem bore, a passage extending through the stem and interconnecting the first and second chambers so that, in use, the fluid pressure in each chamber is substantially equalised, first actuating means for moving the stem in a first direction so as to move the gate between the open and closed positions and second actuating means for moving the stem in the opposite direction, wherein the first actuating means is a third chamber sealed between a working surface of the stem and the stem bore and a port that is connectable to a soiirce of control fluid.

The provision of the passage through the stem allows the fluid pressure acting on each end of the stem to be equalised and therefore for the stem ejection force to be counteracted.

The third chamber may be defined by a radial clearance between part of the stem and part of the stem bore.

The stem preferably comprises a central portion flanked by first and second outer portions that respectively define said first and second ends, the central portion being of greater diameter than the outer portions. The stem bore may have a corresponding central portion that receives the central portion of the stem and is flanked by outer first and second bore portions that each have a diameter less than that of the central portion of the stem bore. The central portion of the stem is shorter in length than the central portion of the stem bore so as to permit relative translating movement.

The stem may be stepped between the central portion and either of the first and second portions so as to define said working surface, the surface being in the form of

an annular face that extends in a plane substantially perpendicular to the plane occupied by the axis of the stem.

The second actuator may be a biasing member, such as a spring or the like, that may extend between the stem and a wall of the valve body. The stem may have a counterbore in which the biasing member is received.

The spring is designed to bias the gate to an open or closed position and the spring force is pre-selected to overcome at least part of the friction forces between the gate and any surroundings and those between the stem and any seals.

The second actuator may, alternatively or in addition, be a fourth chamber defined between the stem and the body on an opposite end of the stem to the third chamber, the fourth chamber being sealed between a working surface of the stem and the stem bore, and a port that is connectable to a source of control fluid. Hydraulic control fluid may thus be selectively injected under pressure into the third or fourth chambers to control the position of the stem and therefore the gate. hi one embodiment the diameters of the first and second outer portions of the stem may not be not equal so that the stem acts as a differential piston with the fluid acting at each end of the stem with equal pressure applying unequal forces and thus moving the stem and gate in a predetermined direction. This force applied by virtue of the differential piston can be applied in addition to the spring force so as to assist in overcoming friction forces.

There may be provided a rotary actuator for effecting movement of the gate between said open and closed positions, and a connection between the rotary actuator and the gate for converting rotational movement of the actuator into a translation movement of the gate. The rotary actuator is intended for use as an override actuator and may be operated manually or by a ROV.

The direction of movement of the gate may be substantially perpendicular to the axis of rotation of the actuator.

The connection between the rotary actuator and the gate may configured to move the gate member from open to closed positions or vice versa in response to a predetermined angle of rotation of the actuator which predetermined angle may be 90, 180 or 270 degrees.

The rotary actuator may be provided with a position indicator from which it can be identified whether the valve is open or closed. A stop may be provided to prevent rotation of the actuator beyond a predetermined angle which may be, for example, 90, 180 or 270 degrees. The rotary actuator may have a radially extending member for abutment with the stop.

The connection between the rotary actuator and the gate may be in the form of an eccentrically mounted member on said actuator and a slot associated with said stem, the eccentrically mounted member being received in said slot.

The passage may extend through the central portion of the stem and one of said first and second outer portions.

The passage may extend between an end of the second outer portion of the stem and an annular surface defined by a stepped transition between the central portion and the first outer portion

The gate may comprise a sliding member with a bore therethrough, the bore being aligned with the flow conduit when the gate is in the open position and offset from the conduit when in the closed position.

A specific embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a longitudinal sectioned view through a gate valve assembly in accordance with the present invention and with the valve shown in an open position;

Figures 2 to 4 are diagrammatic representations of the valve assembly of figure 1 illustrating movement of the valve gate member and rotation of a rotary override spindle; and

Figure 5 is a side view of the valve assembly of figure 1, the assembly having been rotated through ninety degrees;

Figure 6 is a plan view of the assembly of figure 5; and

Figure 7 is a plan view of the valve assembly shown fitted with an indicator plate.

Referring now to the figure 1 of the drawings, the exemplary sub-sea gate valve assembly comprises a multiple part housing 1 defining a fluid flow passage 2

that is interrupted by a valve chamber 3 and in which there is disposed a slidable valve gate 4 that serves to open or close the flow passage 2.

The valve gate 4 is connected to an end of a stem 5 that is slidably received in a stem bore 6 and which extends in a direction perpendicular to the flow passage 2, along the majority of valve body. The stem 5 is designed to reciprocate along its central longitudinal axis in the stem bore 6 so as to move the gate 4 relative to the passage 2. .

A spindle bore 7 penetrates the housing 1 in a direction parallel to the fluid flow passage 2 and intersects the stem bore 6 at a location spaced from the valve chamber 3. The spindle bore 7 receives a rotary spindle assembly 8 that engages with the stem 5 and serves as an override actuator by which the valve can be opened or closed manually or by a remote controlled device such as a ROV.

The housing 1 comprises a valve body 10, an actuator body 11, a valve bonnet 12 that separates the bodies, and a cylindrical end cap 13. The valve body 10 defines the valve chamber 3 and the fluid flow passage 2, whereas the actuator body 11 defines the intersection between the stem bore 6 and the spindle bore 7. The bonnet 12 simply defines part of the stem bore 6 that connects with the valve chamber 3. The end cap 13 houses the end of the stem 5 opposite the valve gate 4, seals to the actuator body and is retained there by a collar 14. These various parts of the housing are connected together by four stud bolts 15 and are provided with an interfacing seals 16, 17, and 18.

In addition to the parts of the housing described above, the actuator body 11 supports a bearing housing 19 with an internal bore that defines a continuation of the spindle bore 7 and receives an upper portion of the spindle assembly 8 that will be described in more detail below.

The valve gate 4 comprises a generally rectangular member with a bore 20 therethrough. Two annular seats 21 support the gate 4 and are received in annular recesses in the chamber 3. The seats 21 are penetrated by interior bores 22 that correspond in diameter to that of the fluid passage 2 and therefore effectively extend the fluid passage 2 across the chamber 3. Annular seals 23 seal the seats to the valve housing 1.

In figure 1 the valve gate 4 is shown in an open position whereby its bore 20 is in coaxial register with the fluid flow passage 2 and the seat bores 22. Sliding movement of the gate 4 to the right in figure 1 in a direction perpendicular to the longitudinal axis of the fluid passage 2 moves the bore 20 in the gate 4 out of register with the flow passage 2 so that the gate the flow of fluid through the passage and the valve is closed. The sliding movement of the valve gate 4 is driven by the reciprocating stem 5, the gate 4 being secured to an end of the stem by a cylindrical connection 24 of T-shaped cross-section. The stem 5 is generally cylindrical in shape and is stepped so as to define a central portion 25 of enlarged diameter that is flanked by first and second outer portions 26, 27 of slightly reduced diameter. In a corresponding configuration the stem bore 6 is stepped with a central portion 28 having an internal diameter marginally greater than the outside diameter of the central portion 25 of the stem 5 but longer in length to allow reciprocal movement of the stem 5 in the bore 6.

The first outer portion 26 of the stem is sealed to the stem bore 6 by packing seals 29 that are received in annular grooves on the inside surfaces of the end cap 13, whereas the second outer portion 27 of the stem 5 is similarly sealed by packing seals 30 received in annular grooves in the actuator body 11 and the bonnet 12.

One end of the valve housing 1 the cylindrical end cap 13 houses the first outer portion 26 of the stem 5 and is sealed thereto by means of an annular sliding packing seal 31 that is disposed in a circumferential groove defined in the stem 5. This seal is a spring-energised U-cup seal of known configuration and is the primary packing seal with seals 29 serving as a back-up. A similar seal 31a is provided at the other end of the stem and serves to seal the stem bore 6 from the valve chamber 3.

A clearance between an end wall 32 of the cap 13 and the stem 5 serves to define a variable volume fluid chamber 33, the purpose of which will become clear. The first outer portion 26 of the stem 5 has a counterbore 34 (shown in dotted line in figure 1) therethrough that extends into part of the central portion 25 of the stem 5. This counterbore provides a seat for a compression spring 35 (represented in dotted line in figure 1) that is disposed coaxially in the stem bore 6 and the fluid chamber 33 and extends between the end wall 32 of the cylindrical end cap 13 and an end wall of

the counterbore 34. In use, the spring 35 urges the stem 5 towards the valve chamber 3 so as to move the gate 4 out of alignment with the flow passage 2 and to close the valve.

The stem 5 is connected to the spindle assembly 8 at an upper surface of the central portion 25, which is recessed. At the bottom of the recess there is a transverse slot 36 for receipt of a crank pin 37 having an outer roller bearing 37a and which is eccentrically mounted on the end of the spindle assembly 8. The slot 36 and pin 37 operate in the manner of a scotch yoke mechanism. In an alternative design the crank pin may be in the form of a sliding block.

The spindle assembly 8 has an inner spindle 38 that extends into the bore of the bearing housing 19 and interfaces with the stem recess, and an outer spindle 39 that extends out of the housing 19 and is connected to the inner spindle 38. Both spindles 38, 39 are prevented from moving in an axial direction, the outer by a radially outward extending flange 40 that is flanked by a first set of bearings 41 that serve to support the spindle assembly 8 in rotation. The upper end of the outer stem 39 projects from the cover housing and terminates in a spindle 42 of square cross-section. Such a spindle 42 is intended for connection to an extension rod (not shown) of the kind that is designed to interface with a ROV panel and enable actuation of the stem assembly 8 by the ROV, The inner stem 38 is supported for rotation in a concentric sleeve bearing 43 and terminates in the crank pin 37.

The spindle assembly 8 is sealed by a seal set around the inner spindle and is retained in the bearing housing 19 by four capped screws 56 (shown in figure 6 only).

In operation, the valve chamber 3 will be flooded with the fluid that flows in the flow passage 2 and, ordinarily, would apply a force to the stem 5 in a direction counter to the force applied by the spring 35. However, in the present invention there is provided a pressure balance passage 45 (represented in dotted line) in a radially outer part of the stem 5 that interconnects the valve chamber 3 with the fluid chamber 33 defined by the end cap 13. The pressure balance passage 45 extends through the second outer portion 27 and the central portion 25 of the stem 5 and emerges at a step 46 defined between the central portion 25 and the first outer portion 26 of the stem 3. The fluid thus flows from the valve chamber 3 via the passage 45 and into the spring

chamber 35. It will be understood that with fluid present at both its ends, the stem 5 operates like a hydraulic piston. In one embodiment of the invention the effective diameters 0A and 0B of the ends of the stem 5 are equal so that the forces applied by the same fluid pressure on each end of the piston are equal. In this instance the piston is in balance and there is no stem ejection force. With such an arrangement the only variable force that acts counter to the spring force is that provided by the friction between the gate valve 4 and seats 21 and provided between the packing seals 29, 30 and stem 5.

In an alternative embodiment the effective diameter 0B may be greater than 0A in which case the stem operates as a differential piston and is urged towards the valve chamber 3 as the fluid pressure in the respective chambers 3, 33 is equal. The piston arrangement is configured so that the force that urges the stem 5 in this direction is sufficient to overcome the gate to seat friction and thus move the gate 4 to the closed position. When there is only low or no fluid pressure in the chambers 3, 33 the spring force dominates and serves to move the gate 4 to the closed position. Thus the differential piston areas offered by the stem 5 can be configured to allow the valve to close without spring assistance when the fluid reaches a certain pressure.

Since the central portion 25 of the stem 5 is shorter in length than the central portion of the stem bore 6, there is a working chamber 47 defined between the two. External hydraulic control fluid can be supplied under pressure to this working chamber 47 via a supply port 48 through the valve body in order to move the stem. The fluid in the chamber 47 is sealed against egression by an annular seal 49 disposed in an annular groove in the circumferential surface central portion 25 and by the stem packing seals 30. Since the fluid pressure acts on the radially extending annular face 50 provided by the stepped transition between the central 25 and second outer portion 27 of the stem 5 it urges the stem in the direction against the spring force. When the pressure of the fluid is such that the force exceeds the spring force and any force provided by virtue of the fluid pressure acting on the differential piston form of the stem 5, the stem 5 and therefore the valve gate 4 move in a direction towards the end cap 13 to the position shown in figure 1 thereby opening the valve.

The diagram of figure 2 shows the valve gate 4 out of register with the fluid passage 2 and therefore the valve is closed. In order to open the valve, hydraulic fluid is injected into the working chamber 47 via the port 48 so as to urge the stem 5 in the direction towards the end cap 13. This movement causes the edge of the slot 36 to bear against the crank pin 37 in a camming action such that the inner spindle 38 and spindle assembly 8 rotate about their axes in the direction indicated by the arrow. The stem 5 carries the valve gate 4 with it and so the bore 20 is moved to the left and into communication with the fluid passage 2. Rotation of the stem assembly 8 is restricted to 180° by virtue of the engagement of a pin 60, which extends perpendicularly from the spindle 42, with stops 61, 62, as is shown in figure 6. When the pin is in contact with one of the stops 61, 62 the valve gate 4 is at the limit of its travel and is either in the open position as shown in figure 1 and 4 or the closed position shown in figure 2. An intermediate position is illustrated in figure 3. In order to close the valve, the hydraulic fluid pressure in the working chamber 47 is released so that the forces provided by the compression spring 35 and the fluid pressure on the differential piston configuration dominate and move the stem 5 to the right and back to the position shown in figure 2. The movement of the stem 5 and spindle assembly 8 is thus reversed.

In the embodiment of figure 7, the pin 60 is replaced with a stop plate 70 that is carried by the spindle 42 for rotation with the assembly 8. The plate 70 is formed from a circular disc that is cut-away to defined two radial edges 71 for engagement with the stop pin 61. The interaction of the stop pin 61 and the plate 70 restrict the rotational movement of the stem assembly 8. In the position shown in figure 7, one of the edges 71 engages the stop pin 61 to prevent further rotation of the stem assembly in the anticlockwise direction. In this position the valve is open. The upper surface of the bearing housing 19 is labelled with status indicators OPEN and CLOSED at diametrically opposite locations. When the valve is in the open position as shown in figure 7, the plate conceals the CLOSED label (this is shown in faint lettering in the figure to aid understanding) but not the OPEN label and vice-versa when the valve is closed. This enables the status of the valve to be monitored by easily.

The spindle assembly 8 is used as an override actuator to effect valve opening or closure in the absence of a hydraulic control fluid, whereby rotation of the spindle assembly effects sliding movement of the stem 5 and valve gate 4 via the scotch yoke mechanism. The half turn movement required to move the valve between the open and closed positions makes it easy to operate and particularly suitable for actuation by a ROV.

It is to be understood that the connection between the spindle assembly 8 and the stem 5 may take any appropriate form that provides conversion from rotational movement to translating movement and provides the potential for the gate to be moved from open to closed positions or vice versa in 180° of rotation of the spindle assembly. In other embodiments of the valve assembly the connection may be configured to provide for movement of the gate between the open and closed position in response to 90° or 270° rotation of the spindle assembly. One example of an alternative mechanism is described in WO 2004/003411 in relation to figure 7. The roller bearing of the crank pin 37 may take the form of a plain bearing or a rectangular slider bearing.

In an alternative embodiment, the hydraulic control fluid is supplied to both sides of the central portion 25 of the stem 5 so that it serves as a double-acting piston arrangement. For this purpose, an additional port 55 is provided in the body to supply control fluid to a second working chamber on the other side of the piston. It will be appreciated that the shape of the stem 5 or stem bore 6 would have to be modified to accommodate a second working chamber. In such an embodiment hydraulic control fluid can be supplied under pressure to the second chamber to urge the stem 5 towards the valve chamber 3 so that the gate 4 is moved from the open to the closed position, rather than relying on the spring force and a differential piston arrangement to achieve this.

In all embodiments the relationship between the rotation of the stem assembly 8 and the motion of the valve gate 4 is designed to be non-linear such that there is a higher mechanical advantage at the beginning of the stroke when the friction between the gate and the seats is at its highest.

It will be appreciated that numerous modifications to the above described design may be made without departing from the scope of the invention as defined in the appended claims. For example, the valve assembly may be used to control the flow of fluid through any flow line. Moreover, the transverse slot 36 may be of any appropriate form. Furthermore, it is to be understood that the arrangement of the valve assembly may be configured so that the spring 35, and any force applied by virtue of fluid acting on the differential piston surfaces of the stem, serve to bias the stem and valve gate to a normally open position.