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Title:
A STEM FOR A GATE VALVE
Document Type and Number:
WIPO Patent Application WO/2014/120081
Kind Code:
A1
Abstract:
A stem for a gate valve, a gate valve, a method of assembling a stem in a gate valve, a method of fabricating the stem, and a method of assembling a gate valve are provided. The stem comprises a rotatable first stem section; and a rotatable second stem section separable from the first stem section and configured to engage with a gate of the gate valve for moving the gate between closed and open positions; wherein, in a disengaged state, the first stem section is rotatably free from the second stem section, and wherein, in an engaged state, the first stem section is rotatably coupled to the second stem section such that the second stem section is rotatable together with the first stem section for moving the gate between the closed and open positions.

Inventors:
KUSWANTORO EKO (ID)
WICAKSONO AKIP (ID)
Application Number:
SG2013/000037
Publication Date:
August 07, 2014
Filing Date:
January 30, 2013
Export Citation:
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Assignee:
AKER SOLUTIONS SINGAPORE PTE LTD (SG)
International Classes:
F16K3/02; F16K41/02
Foreign References:
US20060118750A12006-06-08
US20080083892A12008-04-10
Attorney, Agent or Firm:
SPRUSON & FERGUSON (ASIA) PTE LTD (Robinson Road Post Office, Singapore 1, SG)
Download PDF:
Claims:
CLAIMS

1. A stem for a gate valve, the stem comprising:

a rotatable first stem section; and

a rotatable second stem section separable from the first stem section and configured to engage with a gate of the gate valve for moving the gate between closed and open positions;

wherein, in a disengaged state, the first stem section is rotatably free from the second stem section, and

wherein, in an engaged state, the first stem section is rotatably coupled to the second stem section such that the second stem section is rotatable together with the first stem section for moving the gate between the closed and open positions. 2. The stem as claimed in claim 1 , wherein, in the disengaged state, the first stem section is rotatably coupled to a packing gland of the gate valve such that the packing gland is rotatable together with the first stem section for releasably tightening and compressing onto a stem seal. ~ 3. The stem as claimed in claim 2, wherein, in the engaged state, the first and second stem sections are rotatably free of the packing gland.

4. The stem as claimed in claim 2 or 3, wherein the first stem section comprises an engaging end having plurality of keys protruding in a radial direction.

5. The stem as claimed in claim 4, wherein the plurality of keys are spaced uniformly about a circumference of the engaging end. 6. The stem as claimed in claim 4 or 5, wherein each of the plurality of keys is radially depressible onto a respective biasing means.

7. The stem as claimed in any one of claims 4 to 6, wherein the second stem section comprises a blind hole for receiving the engaging end, the blind hole having a plurality of grooves configured to engage with respective protruding keys, thereby rotatably coupling the first stem section to the second stem section in the engaged state.

8. The stem as claimed in claim 6, wherein, in the disengaged state, the protruding keys are configured to engage with respective grooves disposed in a central bore portion of the packing gland proximate to the engaging end, thereby rotatably coupling the first stem section to the packing gland.

9. The stem as claimed in claim 7, wherein the protruding keys are further configured to overcome a flange disposed after the grooves in the central bore of the packing gland, for transiting from the disengaged state to the engaged state.

10. A gate valve comprising:

a body defining a gate cavity;

a gate disposed in the gate cavity, said gate being movable between a closed position to block a fluid flow and an open position to allow the fluid flow; and

a stem comprising:

a rotatable first stem section; and

a rotatable second stem section separable from the first stem section and configured to engage with the gate for moving the gate between closed and open positions;

wherein, in a disengaged state, the first stem section is rotatably free from the second stem section, and

wherein, in an engaged state, the first stem section is rotatably coupled to the second stem section such that the second stem section is rotatable together with the first stem section for moving the gate between the closed and open positions.

11. The gate valve as claimed in claim 10, wherein, in the disengaged state, the first stem section is rotatably coupled to a packing gland of the gate valve such that the packing gland is rotatable together with the first stem section for releasably tightening and compressing onto a stem seal.

12. The gate valve as claimed in claim 10 or 11 , wherein the gate comprises:

a central plate configured to engage with the second stem section; and a first and a second side plate each disposed on a respective side of the central plate relative to the fluid flow;

wherein the first and second side plates are configured to be driven by the central plate.

13. A method of assembling a stem in a gate valve, the method comprising the step of:

connecting a rotatable first stem section to a hand wheel of the gate valve; connecting a rotatable second stem section to a gate of the gate valve, the second stem section initially being disengaged from the first stem section such that the first stem section is rotatably free from the second stem section; and

driving the first stem section to engage with the second stem section, whereby the first stem section is rotatably coupled to the second stem section.

14. The method as claimed in claim 13, wherein connecting the first stem section to the hand wheel comprises:

mounting the first stem section to a stem adapter rotatably coupled to the hand wheel; and

supporting the stem adapter at an internal flange of a bonnet cap of the gate valve.

15. The method as claimed in claim 3 or 14, wherein connecting the second stem section to the gate comprises engaging threads disposed on the second stem section with corresponding threads disposed on a gate nut of the gate.

16. The method as claimed in claim 14, wherein driving the first stem section to engage with the second stem section comprises:

initially rotating the hand wheel through a first amount, while the first stem section is disengaged from the second stem section, to tighten a packing gland rotatably coupled to the first stem section, such that the packing gland compresses onto a stem seal; and rotating the bonnet cap, after the packing gland is tightened to a predetermined amount, such that the bonnet cap advances downward together with the first stem section to dislodge the first stem section from the packing gland and to engage the first stem section with the second stem section.

17. The method as claimed in claim 16, wherein initially rotating the hand wheel further comprises:

supporting the bonnet cap such that the first stem section rotates without advancing when the hand wheel is rotated through the first amount.

18. The method as claimed in claim 16 or -17, wherein rotating the bonnet cap further comprises abutting the bonnet cap on the packing gland to secure the packing gland after the packing gland is tightened to the predetermined amount.

19. The method as claimed in any one of claims 13 to 18, wherein engaging the first stem section with the second stem section comprises mating a plurality of keys disposed on the first stem section with corresponding slots disposed on the second stem section.

20. A method of fabricating the stem as claimed in any one of claims 1 to 9.

21. A method of assembling a gate valve, the method comprising the steps of:

providing a body defining a gate cavity;

mounting a gate in the gate cavity, said gate being movable between a closed position to block a fluid or gas flow and an open position to allow the fluid or gas flow; and

connecting the gate to a hand wheel using a stem such that the gate is driven between closed and open positions by the hand wheel, the stem comprising:

a rotatable first stem section; and

a rotatable second stem section separable from the first stem section and configured to engage with the gate for moving the gate between the closed and open positions; wherein, in a disengaged state, the first stem section is rotatably free from the second stem section, and

wherein, in an engaged state, the first stem section is rotatably coupled to the second stem section such that the second stem section is rotatabie together with the first stem section for moving the gate between the closed and open positions.

Description:
A STEM FOR A GATE VALVE

FIELD OF INVENTION

The present invention relates broadly to a stem for a gate valve, to a gate valve, to a method of assembling a stem in a gate valve, to a method of fabricating a stem, and to a method of assembling a gate valve.

BACKGROUND

Gate valves are usually used in pipe systems to allow or prevent the flow of fluids (e.g. liquids or gases), e.g. in chemical or petroleum-related operations. Figure 1a shows a cut-away perspective view of a conventional slab gate valve 100. The gate valve 100 includes a housing 1 2 defining hollow cylindrical sections 1 14a, 114b and a gate cavity 16. A rectangular gate 102, which includes a through hole 03 on a solid body, is disposed in the gate cavity 116. The diameter of the through hole 103 is equal to the internal diameter of the cylindrical sections 114a, 114b, which in turn, is normally matched with the internal diameter of the pipe (not shown). For example, the diameter may be about 2 1/16 inches (5.28 cm), and the working pressure of the pipe may be about 10,000 pounds per square inch (69 MPa). Seats 104a, 104b are disposed in the interfaces between the cylindrical sections 114a, 1 14b and the gate cavity 116 such that the seats 104a, 104b are on either side of, and adjacent to, the gate 02. Sealing means is usually provided between the seats 104a, 104b and the housing 1 12.

In the position shown in Figure a, the gate 102 is closed and may be moved upward to allow the flow of a fluid (liquid or gas). Similarly, from an open position, the gate 102 may be moved downward to the position in Figure 1a to block the flow of a fluid (liquid or gas). Typically, the gate 102 is driven by a continuous stem 106, which includes threads 107 that engage with a gate nut of the gate 102. The stem 106, which is rotatable about its axis, is attached to a rotation member 108, e.g. a hand wheel, having a handle 10 which can be gripped by a human operator. By turning the rotation member 108 with the help of the handle 110 in one direction, e.g. clockwise, the gate 102 may be moved downward to block the flow. Conversely, by turning the rotation member 108 in the opposite direction, e.g. anticlockwise, the gate 102 may be moved upward to allow the flow.

Figure 1 b shows a cross-sectional view of a top portion 130 of a conventional gate valve similar to the gate valve 100 shown in Figure 1a. A packing gland 118 is disposed between the stem 106 (also shown in Figure a) and a bonnet 120, which is secured to the housing 112 (Figure 1a). As can be seen in Figure 1b, in such a conventional gate valve, the packing gland 1 8 has outer threads 119 which engage with inner threads 121 of the bonnet 120. The internal portion of the packing gland 1 18 is in the form of a hollow cylinder, allowing the stem 106 to rotate freely therewithin. Conventionally, in order to tighten the packing gland 118, a socket (not shown) is used to turn the packing gland 1 18 until it compresses onto a seal 124, thereby "energising" the seal 124 which helps to prevent fluid (liquid or gas) leakage. However, this is tedious because a bonnet cap 122 must first be removed before the packing gland 118 can be accessed by the socket. Also, there may be potential safety issues when removing the bonnet cap 22 due to pressure build-up within the gate valve.

A need therefore exists to provide a gate valve that seeks to address at least one of the above problems.

SUMMARY

According to a first aspect of the present invention, there is provided a stem for a gate valve, the stem comprising a rotatable first stem section; and a rotatable second stem section separable from the first stem section and configured to engage with a gate of the gate valve for moving the gate between closed and open positions; wherein, in a disengaged state, the first stem section is rotatably free from the second stem section, and wherein, in an engaged state, the first stem section is rotatably coupled to the second stem section such that the second stem section is rotatable together with the first stem section for moving the gate between the closed and open positions. In the disengaged state, the first stem section may be rotatably coupled to a packing gland of the gate valve such that the packing gland may be rotatable together with the first stem section for releasably tightening and compressing onto a stem seal. -

In the engaged state, the first and second stem sections may be rotatably free of the packing gland. The first stem section may comprise an engaging end having plurality of keys protruding in a radial direction.

The plurality of keys may be spaced uniformly about a circumference of the engaging end.

Each of the plurality of keys may be radially depressible onto a respective biasing means.

The second stem section may comprise a blind hole for receiving the engaging end, the blind hole having a plurality of grooves configured to engage with respective protruding keys, thereby rotatably coupling the first stem section to the second stem section in the engaged state.

In the disengaged state, the protruding keys may be configured to engage with respective grooves disposed in a central bore portion of the packing gland proximate to the engaging end, thereby rotatably coupling the first stem section to the packing gland.

The protruding keys may be further configured to overcome a flange disposed after the grooves in the central bore of the packing gland, for transiting from the disengaged state to the engaged state.

According to a second aspect of the present invention, there is provided gate valve comprising a body defining a gate cavity; a gate disposed in the gate cavity, said gate being movable between a closed position to block a fluid flow and an open position to allow the fluid flow; and a stem comprising: a rotatable first stem section; and a rotatable second stem section separable from the first stem section and configured to engage with the gate for moving the gate between closed and open positions; wherein, in a disengaged state, the first stem section is rotatably free from the second stem section, and wherein, in an engaged state, the first stem section is rotatably coupled to the second stem section such that the second stem section is rotatable together with the first stem section for moving the gate between the closed and open positions.

In the disengaged state, the first stem section may be rotatably coupled to a packing gland of the gate valve such that the packing gland may be rotatable together with the first stem section for releasably tightening and compressing onto a stem seal.

The gate may comprise a central plate configured to engage with the second stem section; and a first and a second side plate each disposed on a respective side of the central plate relative to the fluid flow; wherein the first and second side plates are configured to be driven by the central plate.

According to a third aspect of the present invention, there is provided a method of assembling a stem in a gate valve, the method comprising the step of connecting a rotatable first stem section to a hand wheel of the gate valve; connecting a rotatable second stem section to a gate of the gate valve, the second stem section initially being disengaged from the first stem section such that the first stem section is rotatably free from the second stem section; and driving the first stem section to engage with the second stem section, whereby the first stem section is rotatably coupled to the second stem section.

Connecting the first stem section to the hand wheel may comprise mounting the first stem section to a stem adapter rotatably coupled to the hand wheel; and supporting the stem adapter at an internal flange of a bonnet cap of the gate valve.

Connecting the second stem section to the gate may comprise engaging threads disposed on the second stem section with corresponding threads disposed on a gate nut of the gate. Driving the first stem section to engage with the second stem section may comprise initially rotating the hand wheel through a first amount, while the first stem section is disengaged from the second stem section, to tighten a packing gland rotatably coupled to the first stem section, such that the packing gland compresses onto a stem seal; and rotating the bonnet cap, after the packing gland is tightened to a predetermined amount, such that the bonnet cap advances downward together with the first stem section to dislodge the first stem section from the packing gland and to engage the first stem section with the second stem section.

Initially rotating the hand wheel may further comprise supporting the bonnet cap such that the first stem section rotates without advancing when the hand wheel is rotated through the first amount. Rotating the bonnet cap may further comprise abutting the bonnet cap on the packing gland to secure the packing gland after the packing gland is tightened to the predetermined amount.

Engaging the first stem section with the second stem section may comprise mating a plurality of keys disposed on the first stem section with corresponding slots disposed on the second stem section.

According to a fourth aspect of the present invention, there is provided a method of fabricating the stem as defined in the first aspect.

According to a fifth aspect of the present invention, there is provided a method of assembling a gate valve, the method comprising the steps of providing a body defining a gate cavity; mounting a gate in the gate cavity, said gate being movable between a closed position to block a fluid or gas flow and an open position to allow the fluid or gas flow; and connecting the gate to a hand wheel using a stem such that the gate is driven between closed and open positions by the hand wheel, the stem comprising: a rotatable first stem section; and a rotatable second stem section separable from the first stem section and configured to engage with the gate for moving the gate between the closed and open positions; wherein, in a disengaged state, the first stem section is rotatably free from the second stem section, and wherein, in an engaged state, the first stem section is rotatably coupled to the second stem section such that the second stem section is rotatable together with the first stem section for moving the gate between the closed and open positions.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which:

Figure 1 a shows a cut-away perspective view of a conventional slab gate valve. Figure 1b shows a cross-sectional view of a top portion of a conventional gate valve similar to the gate valve shown in Figure 1a.

Figure 2a shows a perspective view of a first stem section according to an example embodiment.

Figure 2b shows a top view of the first stem section of Figure 2a.

Figure 2c shows a cross-sectional view of the first stem section about the line AA in Figure 2b.

Figure 3a shows a perspective view of a second stem section according to an example embodiment.

Figure 3b shows a top view of the second stem section of Figure 3a.

Figure 3c shows a cross-sectional view of the second stem section about the line B-B in Figure 3b.

Figure 4a shows a perspective view of packing gland according to an example embodiment. Figure 4b shows a top view of the packing gland of Figure 4a.

Figure 4c shows a cross-sectional view of the packing gland about the line C-C in Figure 4b.

Figure 5a shows a sectional view of a gate valve employing the first and second stem sections and the packing gland according to an example embodiment. Figure 5b shows a sectional view of the gate valve of Figure 5a in an open position.

Figure 5c shows an enlarged view of a detail A in Figure 5b. Figure 6a shows a partial cut-away perspective view illustrating a top portion of the gate valve of Figure 5a according to an example embodiment.

Figure 6b shows an exploded perspective view illustrating the components in Figure 6a.

Figure 6c shows a sectional view of the top portion shown in Figure 6a when the packing gland is being tightened.

Figure 7 shows a flow chart illustrating a method of assembling a stem in a gate valve according to an example embodiment.

Figure 8 shows a flow chart illustrating a method of assembling a gate valve according to an example embodiment.

DETAILED DESCRIPTION

Example embodiments provide a gate stem that is made up of an upper portion and a lower portion, for use in a gate valve. The upper portion is connected to a hand wheel of the gate valve, and has spring-loaded keys adjacent to its bottom end. One end of the lower portion has a blind hole / cavity to receive and engage with the spring-loaded keys of the upper portion, and the other end has screw threads to engage with a gate nut (similar to the screw threads in a conventional stem). Once engaged, the upper and lower portions can function to translate a rotation of the hand wheel into up/down movement of the gate in the gate valve.

Figure 2a shows a perspective view of a first stem section (herein interchangeably referred to as the upper stem member) 200 according to an example embodiment. Figure 2b shows a top view of the first stem section 200 of Figure 2a. Figure 2c shows a cross-sectional view of the first stem section 200 about the line AA in Figure 2b.

The first stem section 200 has an elongated solid body 202 with a cylindrical upper end 210, a cylindrical lower end 220 of a smaller diameter than the upper end, and a step 204 therebetween. A key hole 206 perpendicular to a longitudinal axis of the first stem section 200 is disposed at the upper end 210, for mounting the first stem section 200 to a stem adapter, as will be described below. A plurality of keys 208, which protrude in a radial direction relative to the longitudinal axis, are disposed at the lower end 220 (herein also referred to as the engaging end). Each of the keys 208 is mounted to respective biasing means, e.g. coil springs 212 as shown in Figure 2c, such that each of the keys 208 is radially depressible. For example, the keys 208 may retract into respective holes 214 when depressed, thereby allowing the engaging end 220 to pass a protuberance such as a flange. Additionally, in a preferred implementation, each of the keys 208 includes leading and trailing edges 216, 218 disposed at an angle with respect to the longitudinal axis. The slanted leading and trailing edges can assist the engaging end 220 to overcome the protuberance in both forward and backward directions. In other implementations, e.g. where a one-way lock is desired, the angle of the trailing edge may be changed accordingly.

In an expanded state as shown in Figures 2a and 2c, the spring-loaded keys 208 can engage with corresponding slots or grooves of another part for transferring torque and rotational movement, as will be appreciated by a person skilled in the art. In a preferred implementation, the keys 208 are spaced uniformly about a circumference of the lower end 220, e.g. the keys 208 are separated at equal distances from each other. This can help to distribute the torque to be transferred evenly, and facilitate quick engagement of the keys and the corresponding slots or grooves. While four keys 208 are used in the first stem section 200, it will be appreciated that different numbers of keys may be used in alternate embodiments.

Figure 3a shows a perspective view of a second stem section (herein interchangeably referred to as lower stem member) 300 according to an example embodiment. Figure 3b shows a top view of the second stem section 300 of Figure 3a. Figure 3c shows a cross-sectional view of the second stem section 300 about the line B-B in Figure 3b.

The second stem section 300 has an elongated rigid body 302 with a substantially cylindrical upper end 310, a cylindrical lower end 320 having threads 306 thereon, and a step 304 therebetween. The step 304 allows the second stem section 300 to rest and rotate on a set of bearings, as will be apparent below. The threaded lower end 320 is configured to engage with a respective threaded hole of a gate nut of a gate (not shown), such that a rotational movement of the second stem section 300 can be transmitted to the gate, e.g. to lift or to lower the gate.

A blind hole / cavity 308 is formed on a top surface 312 of the upper end 310, and is configured to receive and engage with the spring-loaded keys 208 of the first stem section 200 (Figure 2a). For example, as can be seen in Figure 3b, the blind hole / cavity 308 includes four grooves or slots 314 corresponding to the four protruded keys 208 on the first stem section 200 (Figure 2a). The depth of the blind hole / cavity 308 may be calculated based on the position of the keys 208 on the first stem section 200, e.g. such that the keys 208 can be fully inserted in the blind hole / cavity 308 when the first and second stem sections 200, 300 engage. In the engaged state, the first stem section 200 (Figure 2a) is rotatably coupled to the second stem section 300 such that the first and second stem sections 200, 300 can rotate together like a continuous stem. As will be appreciated by a person skilled in the art, the number of slots 314 and their relative positions, as well as the depth of the blind hole / cavity 308 may be adjusted depending on the configuration of the keys 208. In addition, in example embodiments, when the first stem section 200 (Figure 2a) is disengaged from the second stem section 300 (Figure 3a), the first stem section 200 can be used to tighten a packing gland (also known as a stuffing box), which then compresses onto and energises a seal disposed between the stem sections 200, 300 and a bonnet.

Figure 4a shows a perspective view of packing gland 400 according to an example embodiment. Figure 4b shows a top view of the packing gland 400 of Figure 4a. Figure 4c shows a cross-sectional view of the packing gland 400 about the line C-C in Figure 4b.

The packing gland 400 is adapted to be rotatably coupled to the first stem section 200 when the first stem section 200 is disengaged from the second stem section 300, and to allow the first and second stem sections 200, 300 to rotate freely when the first and second stem sections 200, 300 are engaged. In addition, the packing gland 400 allows the first stem section 200 to transit between the disengaged and engaged states with respect to the second stem section 300. For example, as shown in Figures 4a-4c, the packing gland 400 is in the form of a cylindrical body having a central bore 402 extending through the length of the packing gland 400. The bore 402 includes an upper portion 410 which has a cross-sectional area substantially identical to the cross-sectional area of the blind hole / cavity 308 of the second stem section 300 (Figure 3a). Thus, the packing gland 400 can be rotatably coupled to the first stem section 200 (Figure 2a) in the same way as the second stem section 300. The length of the upper portion 410 may be calculated such that the packing gland 400 is still rotatably coupled to the first stem section 200 when fully tightened. A lower portion 420 of the bore 402 is shaped like a cylindrical tube and is able accommodate the top end 310 (Figure 3a) of the second stem section 300 therewithin. Further, the bore 402 defines a protuberance or flange 414 between the upper portion 4 0 and the lower portion 420. The flange 4 4 has slanted leading and trailing edges which allow the first stem section 200 to transit between engaged and disengaged states relative to the second stem section 300. Typically, when the engaging end 210 (Figure 2a) of first stem section 200 is further inserted into the bore 402, the flange 414 can depress the spring-loaded keys 208 (Figure 2a), thereby allowing the keys 208 to be dislodged from the corresponding grooves or slots of the upper portion 410. After the engaging end 210 passes the flange 414, the engaging end 210 can engage with the blind hole 308 of the second stem member 300.

Moreover, the packing gland 400 includes threads 406 on an outer surface 404 for engaging with corresponding internal threads on a bonnet (not shown). In use, when the first stem section 200 is rotatably coupled to the packing gland 400, a rotation of the first stem section 200 (as driven by a hand wheel) can be transferred to the packing gland 400, causing the packing gland 400 to tighten or loosen, depending on the direction of rotation. For example, a clockwise rotation may cause the packing gland 400 to tighten until its lower surface 412 compresses onto a stem seal (not shown). As a result, the seal may become energised and effect sealing. After the seal has been fully energised, e.g. after a predetermined torque value has been reached when rotating the hand wheel, rotating the bonnet cap 530 (Figure 5a) (so that it moves down) causes the upper stem member 200 to move down to engage with the lower stem member 300, as will be described in detail below. It would be appreciated by persons skilled in the art that the predetermined torque value may vary depending on factors such as the valve size. Example values may be obtained from valve specifications.

The first and second stem sections 200, 300 together with the packing gland 400 as described above with respect to Figures 2-4 can be used in a gate valve, including an existing gate valve. Figure 5a shows a sectional view of a gate valve 500 employing the first and second stem sections 200, 300 and the packing gland 400 according to an example embodiment. In Figure 5a, the gate valve 500 is in a closed position. Figure 5b shows a sectional view of the gate valve 500 of Figure 5a in an open position. Figure 5c shows an enlarged view of a detail A in Figure 5b illustrating the engagement between the first and second stem sections 200, 300.

The gate valve 500 includes a body 502, which defines a gate cavity 504. A moveable gate 506 is disposed in the gate cavity 504. In the example embodiment, the gate 506 comprises a central plate 510 and side plates 512, 514 disposed on either side of the central plate 510. The side plates 512, 514 (also known as floating plates) can be driven by the central plate 510. In alternate embodiments, the gate 506 may be in different forms, for example, a single block. As can be seen in Figures 5a-5c, the central plate 510 includes a threaded gate nut 508 that engages with the threaded lower end 320 (Figure 3a) of the second stem section 300. The first stem section 200 is connected to a hand wheel 516 via a stem adapter 518. Further, as shown more clearly in Figure 5c, the first stem section 200 is rotatably coupled to the second stem section 300, as the spring-loaded keys 208 (Figures 2a, 5c) engage with corresponding slots 314 (Figure 3b). Thus, a rotational movement of the hand wheel 516 is translated into up/down movement of the gate 506, since the gate 506 abuts seats 520 and is thereby prevented from rotating. In Figures 5a-5b, the packing gland 400 is fully tightened, and a bonnet cap 530 is securely fastened to the valve body 502 at the bonnet 540. The process of tightening the packing gland 400 and fastening the bonnet cap 530 is now described with reference to Figures 6a-6c. Figure 6a shows partial cut-away perspective view illustrating a top portion 600 of the gate valve 500 of Figure 5a according to an example embodiment. Figure 6b shows an exploded perspective view illustrating the components in Figure 6a. Figure 6c shows a sectional view of the top portion of Figure 6a when the packing gland 400 (Figure 4a) is being tightened.

The top portion 600 includes a rigid bonnet 540 (Figure 5a), a bonnet cap 530 (Figure 5a) releasably fastened to the bonnet 540, a hand wheel 516 (Figure 5a), a stem 604 which can be driven by the hand wheel 516, and a packing gland 400 disposed between the bonnet 540 and the stem 604. As described above and shown in Figure 6b, the stem 604 in the example embodiments includes the first stem section 200 having depressible keys 208 actuated by springs 212, and the separate second stem section 300. In the assembled state as shown in Figure 6a, the first stem section 200 is in an engaged state with the second stem section 300, an a set of bearings 610 is disposed between the first and second stem members 200, 300. In an example implementation, the second stem section 300 sits on a set of bearings 606, which are supported by a lower stem retaining ring 608. Also shown in Figures 6a-6b are a stem adapter 518 (Figure 5a) for connecting the first stem section 200 to the hand wheel 516. The stem adapter 518 is supported by, and rotatable relative to the bonnet cap 530, e.g. with the help of bearings 612, 614.

The bonnet 540 can be considered a part of the body 502 of the gate valve 500 (Figure 5a), and is typically secured to the main housing of the gate valve 500 by fastening means, e.g. bolts inserted into holes 616. Here, the bonnet 540 includes a body portion 618, and a neck portion 620 contiguous with the body portion 618. For example, the body portion 618 and the neck portion 620 are made from the same piece of material, e.g. steel. The body portion 618 and the neck portion 620 of the bonnet 540 define a first hollow passage 622 (Figure 6b) through their common central axis. The neck portion 620 includes threads on both its internal surface 624 and its external surface 626, for engaging with threads disposed on the packing gland 500 and the bonnet cap 530 respectively. The neck portion 620 further include a plurality of holes 628 configured to receive respective retaining pins or screws 630, for supporting the bonnet cap 530 such that the first stem section 200 rotates without advancing when the hand wheel 516 is initially rotated through a first amount to tighten the packing gland 400, as will be described in detail below.

The bonnet cap 530 has a cylindrical shape and defines a second hollow passage 632 (Figure 6b) through its central axis. The second central passage 632 has threads at its lower end 634 for engaging with the corresponding threads on the external surface 626 of the neck portion 620 of the bonnet 540. In the assembled state as shown in Figure 6a, the second central passage 632 is coaxial with the first central passage 622. The bonnet cap 530 also includes a plurality of holes 636 to receive the retaining pins or screws 630 such that the bonnet cap 530 can be securely fastened to the bonnet 540 after the bonnet cap 530 has been tightened, as will be described in detail below. Also shown in Figures 6a-6b is retention means (also known as a nipple) 638 to cover a hole 640 on the bonnet cap 204 through which a lubricant may be injected.

With reference to Figure 6b, the assembly of the above components of the top portion 600 according to an example implementation is now described. First, the lower stem member 300 is inserted into the first central passage 622 from the bottom of the bonnet 540 until a flange 642 on the lower stem member 300 abuts a step (not shown) within the first central passage 622, thereby preventing the lower stem member 300 from further insertion. Bearings 606 and lower stem retaining ring 608 are then inserted. The lower stem retaining ring 608 has threads on its external surface which engage with corresponding threads on the internal surface of the central passage 622, thereby supporting the member 300 while allowing the lower stem member 300 to rotate about its axis.

The bonnet 540 together with the lower stem member 300 are then securely mounted to the main housing of the gate valve 500 (Figure 5a), e.g. by bolts inserted into holes 616. In this step, the threaded lower end 320 (Figure 3a) of the lower stem member 300 engages with the threaded gate nut 508 (Figure 5a). Next, the set of bearings 610 is disposed in a cavity/depression 308 (Figure 3a) of the lower stem member 300, and a stem seal 644 is disposed in the gap between the lower stem member 300 and the internal surface of the first central passage 622 to provide fluid (liquid or gas) sealing. The packing gland 400 having threads 406 on its outer surface 404 (Figure 4a) is then disposed above the stem seal 644. In the example embodiment, the threads 406 may engage with corresponding threads on the internal surface of the central passage 622; however, the packing gland 400 need not be fully tightened at this stage. Next, the retaining pins or screws 630 are inserted to the respective tapped holes 628 at the neck portion 620 of the bonnet 540, thereby preventing the bonnet cap 530 from rotating downward (i.e. tightening) when assembled to the bonnet 540 and the hand wheel 516 is initially rotated. As shown in Figure 6c, the bonnet cap 530 is supported by the screws 630.

Separately, the remaining components are assembled to the bonnet cap 530. In this step, the upper stem member 200 is mounted to the stem adapter 5 8 using e.g. a dowel pin 646 such that the upper stem member 200 is rotatably fixed to the stem adapter 518. The stem adapter 518 is also rotatably fixed to the hand wheel 516 using a rotating pin 648. It will be appreciated that other fixing means, e.g. key and groove, may be used to fix these rotating components relative to each other. The stem adapter 518 and with the upper stem member 200 are then inserted into the second central passage 632 from the top, together with bearings 612 and 614. As shown in Figure 6a, the stem adapter 518 is supported (e.g. held horizontally) by an internal flange 650 of the bonnet cap 530, and is rotatable about its axis with the help of the bearings 612, 614. An upper stem retaining ring 652 is then attached to secure the stem adapter 518 in a similar manner as the lower stem retaining ring 608 secures the lower stem member 300, e.g. by having threads on the outer surface of the upper stem retaining ring 652 engage with corresponding threads on the internal surface of the second central passage 632. A hand wheel nameplate 654 and a hand wheel retaining pin 656 are also attached in a manner known in the art.

Next, the bonnet cap 530, together with the assembled components, is. mounted to the bonnet 540 such that the bonnet cap 530 sits on the retaining pins or screw 630. At this point, the spring-loaded keys 208 of the upper stem member 200 are disengaged from the matching cavity/depression 308 of the lower stem member 300, and the upper stem member 200 can rotate freely of the second stem member 300. Rather, the spring-loaded keys 208 of the upper stem member 200 are engaged with the upper portion 410 of the central bore 402 of the packing gland 400 (Figure 4a).

To join the upper and lower stem members 200, 300 and complete the assembly, the hand wheel 516 is initially turned through a first amount. The packing gland 400 is caused to rotate and tighten onto the seal 644 disposed below it (see Figure 6c). Thus, the seal 644 can be compressed/"energised" to effect sealing even as the bonnet cap 530 is in place. The upper stem member 200 rotates without advancing (e.g. stays level) during this initial rotation, period, since the upper stem member 200 is supported by the bonnet cap 530, which, in turn, is supported by the retaining pins or screws 630.

Once the packing gland 400 has compressed onto the stem seal 644 at a desired amount, the retaining pins or screws 630 are removed from the holes 628. The bonnet cap 530, which has a knurled outer surface to improve grip, is then rotated, and advances downward until it abuts the packing gland 400. The retaining screws 630 are then fastened into tapped holes 636 on the bonnet cap 530 to lock the bonnet cap 530 in place. During this further rotation by the bonnet cap 530, the upper stem member 200, together with the stem adapter 518, also advances downward in tandem since both the upper stem member 200 and the stem adapter 518 are constrained in the axial direction of the bonnet cap 530 by the flange 650 and the upper stem retaining ring 652. As a result, the spring- loaded keys 208 (Figure 2a) are caused to compress and overcome the flange 414 inside bore 402 of the packing gland 400 as the upper stem member 200 advances downward. After the spring-loaded keys 208 pass the flange 414, they engage with the cavity/depression 308 of the lower stem member 300. In the engaged state, the upper and lower stem members 200, 300 can rotate together like a continuous stem, and are rotatably free from the packing gland 400 and the bonnet cap 530. Thereafter, the gate 506 can be operated normally by turning the hand wheel 516 for raising/lowering.

In situations where the first and second stem sections 200, 300 need to be separated after assembly, the steps can be carried out in a reversed order. For example, the retaining screws 630 may be removed and the bonnet cap 530 loosened. The upper stem member 200 can be dislodged from the lower stem member 300 by rotating the bonnet cap 530, e.g. in the opposite direction, so that the upper stem member 200 moves upward together with the bonnet cap 530. After the spring loaded keys 208 are already inside the slots of the packing gland 400, the packing gland 400 can also be loosened by rotating the handwheel 516 in the opposite direction.

Figure 7 shows a flow chart 700 illustrating a method of assembling a stem in a gate valve according to an example embodiment. At step 702, a rotatable first stem section is connected to a hand wheel of the gate valve. At step 704, a rotatable second stem section is connected to a gate of the gate valve, the second stem section initially being disengaged from the first stem section such that the first stem section is rotatably free from the second stem section. At step 706, the first stem section is driven to engage with the second stem section, whereby the first stem section is rotatably coupled to the second stem section.

Figure 8 shows a flow chart 800 illustrating a method of assembling a gate valve according to an example embodiment. At step 800, a body defining a gate cavity is provided. At step 802, a gate is mounted in the gate cavity, the gate being movable between a closed position to block a fluid flow and an open position to allow the fluid flow. At step 806, the gate is connected to a hand wheel using a stem such that the gate is driven between closed and open positions by the hand wheel. In a preferred implementation, the stem comprises a rotatable first stem section; and a rotatable second stem section separable from the first stem section and configured to engage with the gate for moving the gate between the closed and open positions; wherein, in a disengaged state, the first stem section is rotatably free from the second stem section, and wherein, in an engaged state, the first stem section is rotatably coupled to the second stem section such that the second stem section is rotatable for moving the gate between the closed and open positions.

It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. For example, in the above example embodiments, the gate valve and the various components are described relative to a horizontal fluid flow and a top- mounted hand wheel. However, other directions and/or positions may be used in alternate embodiments. Also, the sizes of the components may be adjusted depending on the actual usage requirements. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.