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Title:
A GATE FOR A GATE VALVE
Document Type and Number:
WIPO Patent Application WO/2013/158029
Kind Code:
A1
Abstract:
A gate (202) for a gate valve (200), a gate valve (200), and a method of assembling a gate valve (200) are provided. The gate (202) comprises a central plate (234) configured to be driven between an open position and a closed position by a stem (206) of the gate valve (200); a first side plate (232a) disposed adjacent to the central plate (234) on an upstream side of a fluid flow; and a second side plate (232b) disposed adjacent to the central plate (234) on a downstream side of the fluid flow; wherein the central plate (234) and the second side plate (232b) are configured to block the fluid flow in the closed position such that a contact pressure between the central plate (234) and the second side plate (232b) is greater than a working pressure of the valve (200).

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Inventors:
KUSWANTORO, Eko (Taman Duta Mas, Cluster 6 No. 26,Batam Centre, Batam Island, Indonesia, 29463, ID)
-, Suwar (Perum GMP, Blk A1/23Tanjung Sengkuang, Batu Ampar,,Batam Island, Indonesia, 29432, ID)
Application Number:
SG2012/000136
Publication Date:
October 24, 2013
Filing Date:
April 18, 2012
Export Citation:
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Assignee:
AKER SOLUTIONS PTE LTD (77 Science Park Drive, #04-01/07 Cintech III,Singapore Science Park, Singapore 6, 11825, SG)
KUSWANTORO, Eko (Taman Duta Mas, Cluster 6 No. 26,Batam Centre, Batam Island, Indonesia, 29463, ID)
-, Suwar (Perum GMP, Blk A1/23Tanjung Sengkuang, Batu Ampar,,Batam Island, Indonesia, 29432, ID)
International Classes:
F16K3/02; F16K3/18; F16K39/04
Foreign References:
US20090256099A1
DE102006053373B3
US4678008A
JP2001032951A
JPH0468262U
Other References:
None
Attorney, Agent or Firm:
SPRUSON & FERGUSON (ASIA) PTE LTD. (PO Box 1531, Robinson Road Post Office, Singapore 1, 90303, SG)
Download PDF:
Claims:
CLAIMS

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

a central plate configured to be driven between an open position and a closed position by a stem of the gate valve;

a first side plate disposed adjacent to the central plate on an upstream side of a fluid flow; and a second side plate disposed adjacent to the central plate on a downstream side of the fluid flow;

wherein the central plate and the second side plate are configured to block the fluid flow in the closed position such that a contact pressure between the central plate and the second side plate is greater than a working pressure of the valve.

2. The gate as claimed in claim 1 , wherein the first side plate comprises a first contact hole, and the central plate comprises a first protrusion of a first cross-sectional area such that, in the closed position, an upstream pressure of the fluid flow acts on the first cross-sectional area .

3. The gate as claimed in claim 2, wherein the second side plate comprises a second contact hole of a second cross-sectional area smaller than the first cross-sectional area, and the central plate further comprises a second protrusion equal to the first protrusion and configured to sealingly abut the second contact hole in the closed position.

4. The gate as claimed in claim 2 or 3, wherein the first cross-sectional area is determined based on the maximum torque exerted on the stem and a coefficient of friction between the central plate and the second side plate.

5. The gate as claimed in claim 4, wherein the second cross-sectional area is determined based on the first cross-sectional area and a working pressure of the valve.

6. The gate as claimed in any one of the preceding claims, wherein the central plate is configured to drive the side plates between the open and closed positions.

7. The gate as claimed in claim 6, wherein the central plate comprises a catch configured to engage with respective recesses disposed on the side plates for driving the side plates between the open and closed positions.

1.4

8. The gate as claimed in claim 7, wherein the catch engages a first surface of the recesses for driving the side plates from the open position to the closed position, and engages a second surface of the recesses for driving the side plates from the closed position to the open position.

9. A gate valve comprising:

a housing defining first and second cylindrical sections and a gate cavity between the first and second cylindrical sections; and

a gate as claimed in any one of claims 1 to 8 disposed in the gate cavity.

10. The gate valve as claimed in claim 9, further comprising:

a first seat mounted to the first cylindrical section and adjacent to the first side plate; and a second seat mounted to the second cylindrical section and adjacent to the second side plate.

11. The gate valve as claimed in claim 10, further comprising sealing means disposed between respective seats and the housing.

12. The gate valve as claimed in any one of claims 9 to 1 1 , further comprising a rotation member coupled to the stem for rotating the stem.

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

providing a housing defining first and second cylindrical sections and a gate cavity between the first and second cylindrical sections; and

assembling a gate as claimed in any one of claims 1 to 8 in the gate cavity.

14. The method as claimed in claim 13, further comprising the following steps prior to assembling the gate:

mounting a first seat to the first cylindrical section and adjacent to the first side plate; and mounting a second seat to the second cylindrical section and adjacent to the second side plate.

15. The method as claimed in claim 14, further comprising attaching sealing means between respective seats and the housing.

16. The method as claimed in any one of claims 13 to 15, further comprising coupling a rotation member to the stem for rotating the stem.

Description:
A GATE FOR A GATE VALVE

FIELD OF INVENTION

The present invention relates broadly to a gate for a gate valve, to a gate valve, 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. in chemical or petroleum-related operations. Figure 1 a shows a cut-away perspective view of a conventional slab gate valve 100. The gate valve 100 includes a housing 112 defining hollow cylindrical sections 114a, 114b and a gate cavity 116. A rectangular gate 102, which includes a through hole 103 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 1 14a, 114b and the gate cavity 116 such that the seats 104a, 104b are on either side of, and adjacent to, the gate 102. Sealing means is usually provided between the seats 104a, 104b and the housing 112.

As described below with respect to Figures 1 b-1 e, in the position shown in Figure 1 a, the gate 102 may be moveable upward or downward, to allow or prevent the flow of a fluid, respectively. Typically, the gate 102 is driven by a stem 106, which includes threads 107 that engage with the gate 102. The stem 106, which is rotatable about its axis, is attached to a rotation member 108 having a handle 110 which can be gripped by a human operator. By turning the rotation member 108 with the help of the handle 1 10 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. Figures 1 b-1e show cross-sectional views illustrating an operation of the gate valve 100 of Figure 1 a. In Figure 1 b, the gate 102 is raised to the highest level such that the through hole 103 is aligned with the seats 104a, 104b and the cylindrical sections 1 14a, 114b. In other words, the gate valve 100 is fully open and permits the flow of a fluid, e.g. from right to left. Some fluid may flow into the gate cavity 116 through gaps between the gate 102 and seats 104a, 104b. In Figure 1c, the gate 102 is partially lowered and the flow is constricted to only a part of the through hole 103. In Figure 1d, the flow is almost completely blocked, as the through hole 103 is completely out of alignment with the cylindrical sections 114a, 114b. Instead, a solid portion 105 of the gate 102 interfaces with the seats 104a, 104b and starts sealing off the flow. For a flow from right to left, some of the fluid may still enter the cavity 116 through gaps between the gate 102 and seat 104a, but is not able to escape downstream as the pressure from the flow seals off any gap between the gate 102 and seat 104b. In Figure 1e, the gate 102 is completely lowered, i.e. the gate valve 100 is fully closed. Metal-to-metal sealing between the seat 102 and gate 104b is provided by the fluid pressure acting on the solid portion 105.

To open the gate valve 100, a torque provided to the rotation member 108 must overcome the frictional force on the gate 102 caused by the fluid pressure. As this pressure acts over a substantially large part of the solid section 105 that directly faces the flow and the frictional force is equal to the product of the contact area and pressure, the frictional force may be significantly high. As a result, the torque required to initiate valve opening may be too high for one-man operation. In other words, it is difficult to use the gate valve 100 in many applications.

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

SUMMARY

In accordance with a first aspect of the present invention, there is provided a gate for a gate valve, the gate comprising a central plate configured to be driven between an open position and a closed position by a stem of the gate valve; a first side plate disposed adjacent to the central plate on an upstream side of a fluid flow; and a second side plate disposed adjacent to the central plate on a downstream side of the fluid flow; wherein the central plate and the second side plate are configured to block the fluid flow in the closed position such that a contact pressure between the central plate and the second side plate is greater than a working pressure of the valve.

The first side plate may comprise a first contact hole, and the central plate may comprise a first protrusion of a first cross-sectional area such that, in the closed position, an upstream pressure of the fluid flow may act on the first cross-sectional area.

The second side plate may comprise a second contact hole of a second cross-sectional area smaller than the first cross-sectional area, and the central plate may further comprise a second protrusion equal to the first protrusion and configured to sealingly abut the second contact hole in the closed position.

The first cross-sectional area may be determined based on the maximum torque exerted on the stem and a coefficient of friction between the central plate and the second side plate.

The second cross-sectional area may be determined based on the first cross-sectional area and a working pressure of the valve.

The central plate may be configured to drive the side plates between the open and closed positions.

The central plate may comprise a catch configured to engage with respective recesses disposed on the side plates for driving the side plates between the open and closed positions. The catch may engage a first surface of the recesses for driving the side plates from the open position to the closed position, and may engage a second surface of the recesses for driving the side plates from the closed position to the open position.

In accordance with a second aspect of the present invention, there is provided a gate valve comprising a housing defining first and second cylindrical sections and a gate cavity between the first and second cylindrical sections; and a gate as defined in the first aspect disposed in the gate cavity. The gate valve may further comprise a first seat mounted to the first cylindrical section and adjacent to the first side plate; and a second seat mounted to the second cylindrical section and adjacent to the second side plate. The gate valve may further comprise sealing means disposed between respective seats and the housing.

The gate valve may further comprise a rotation member coupled to the stem for rotating the stem.

In accordance with a third aspect of the present invention, there is provided a method for assembling a gate valve, the method comprising the steps of providing a housing defining first and second cylindrical sections and a gate cavity between the first and second cylindrical sections; and assembling a gate as defined in the first aspect in the gate cavity.

The method may further comprise the following steps prior to assembling the gate:

mounting a first seat to the first cylindrical section and adjacent to the first side plate; and mounting a second seat to the second cylindrical section and adjacent to the second side plate.

The method may further comprise attaching sealing means between respective seats and the housing.

The method may further comprise coupling a rotation member to the stem for rotating the stem.

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 1 b shows a cross-sectional view of the conventional gate valve of Figure 1 a at a fully open position. Figure 1c shows a cross-sectional view of the conventional gate valve of Figure 1 a at a partially closed position.

Figure 1d shows a cross-sectional view of the conventional gate valve of Figure 1 a at an almost fully closed position.

Figure 1e shows a cross-sectional view of the conventional gate valve of Figure 1 a at a fully closed position.

Figure 2a shows a partial cut-away perspective view of a gate valve according to an example embodiment.

Figure 2b shows a cross-sectional view of the gate valve of Figure 2a, taken horizontally about the axis of the cylindrical sections after the gate is fully lowered, according to an example embodiment. Figure 3a shows a cross-sectional view of the gate valve of Figure 2a, taken vertically about the axis of the cylindrical sections, at a "fully open" position according to an example embodiment.

Figure 3b shows the cross-sectional view of the gate valve of Figure 3a, at a "partially closed" position, according to an example embodiment.

Figure 3c shows the cross-sectional view of the gate valve of Figure 3a, at an "almost fully closed" position, according to an example embodiment.

Figure 3d shows the cross-sectional view of the gate valve of Figure 3a, at a "fully closed" position, according to an example embodiment.

Figure 3e shows the cross-sectional view of the gate valve of Figure 3a as the gate is about to be opened position according to an example embodiment. DETAILED DESCRIPTION

Figure 2a shows a partial cut-away perspective view of a gate valve 200 according to an example embodiment. The gate valve 200 includes a housing 212 defining hollow cylindrical sections 214a, 214b and a gate cavity 216. An internal diameter Dp of the cylindrical sections 214a, 214b is normally matched with the internal diameter of the pipe (not shown). In some example implementations, the internal diameter Dp may be about 2 VI 6 inches (5.28 cm). The housing 212 may further include mounting members 218a, 218b at respective ends of the cylindrical sections 214a, 214b for connecting the gate valve 200 to respective pipe ends (not shown).

In the position shown in Figure 2a, a gate 202 disposed in the gate cavity 216 may be moveable upward or downward, to allow or prevent the flow of a fluid, in particular a liquid, respectively. Typically, the gate 202 is driven by a stem 206, which includes threads 207 that engage with the gate 202. The stem 206, which is rotatable about its axis, is attached to a rotation member 208 having a handle 210 which can be gripped by a human operator. By turning the rotation member 208 with the help of the handle 210 in one direction, e.g. clockwise, the gate 202 may be moved downward to block the flow. Conversely, by turning the rotation member 208 in the opposite direction, e.g. anticlockwise, the gate 202 may be moved upward to allow the flow.

As described, the housing 212, and the driving mechanism comprising the rotation member 208 and stem 206, of the gate vale 200 are the same as those of the conventional gate valve. 00 of Figure 1. In other words, the existing gate valves can be retrofitted with components of the gate valve 200, as described in detail below, without having to replace the existing housing and the driving mechanism. This may help to reduce replacement costs. Additionally, as the driving mechanism is unchanged, the actions to be performed by the human operator remain unchanged. No re-training of the human operator may be required.

Referring to Figure 2a, the gate 202 includes a through hole 203. In example embodiments, the diameter of the through hole 203 are equal to the internal diameter Dp of the cylindrical sections 214a, 214b. Seats 204a, 204b, which may be collars fitted to the internal surface of the cylindrical sections 214a, 214b, may be disposed in the interfaces between the cylindrical sections 214a, 214b and the gate cavity 216. For example, for a fluid flow from right to left, the seat 204a is adjacent to the gate 202 on the upstream (right) side of the flow (thus also referred to as the upstream seat), while the seat 204b is adjacent to the gate 202 on the downstream (left) side of the flow (thus also referred to as the downstream seat).

Figure 2b shows a cross-sectional view of the gate valve 200 of Figure 2a, taken horizontally about the axis of the cylindrical sections 214a, 214b (Figure 2a) after the gate 202 is fully lowered (i.e. the gate valve 200 is closed) according to an example embodiment. As can be seen in Figure 2b, the gate 202 comprises a central plate 234 and two side plates 232a, 232b, each adjacent to one side of the central plate 234. For example, for a fluid flow from right to left in Figure 2b, the side plate 232a is adjacent to the central plate 234 on the upstream (right) side of the flow (thus also referred to as the upstream side plate), while the side plate 232b is adjacent to the central plate 234 on the downstream (left) side of the flow (thus also referred to as the downstream side plate). Each of the central plate 234 and side plates 232a, 232b includes a respective hole section 312, 310a, 310b (Figure 3a) of diameter Dp that makes up the through hole 203. In addition, the side plates 232a, 232b each includes a contact hole 236a, 236b of a diameter d, respectively. The diameter d of the contact holes 236a, 236b is much smaller than the internal diameter Dp of the cylindrical sections 214a, 214b. In some example implementations, the ratio of d/Dp is equal to about 0.1936. It will be appreciated that different ratios may be used in alternate embodiments, depending on actual operational requirements. Further, the position of the contact holes 236a, 236b is selected, e.g. based on the depth of the gate cavity 216 and the position of the cylindrical sections 214a, 214b, such that when the gate valve 200 is fully closed, the contact holes 236a, 236b share the same axis as the cylindrical sections 214a, 214b.

As can be seen in Figure 2b, the central plate 234 includes a threaded hole 240 for engaging with the threads 207 of the stem 206 (Figure 2a). A gap 237a exists between the central plate 234 and the side plate 232a, while a gap 237b exists between the central plate 234 and the side plate 232b. In preferred embodiments, the central plate 234 further includes protrusions (also known as noses) 238a, 238b in the gaps 237a, 237b respectively. The size of the protrusions 238a, 238b is slightly larger than that of the contact holes 236a, 236b. Sizes of the holes 236a, 236b and the protrusions 238a, 238b may be selected such that the contact pressure (also referred to as the bearing stress) at the bearing area between the central plate 234 and the downstream side plate 232b due to the upstream pressure pushing the protrusion 238a facing the upstream is larger than the working pressure of the valve, as will be described in detail below. The position of the protrusions 238a, 238b is selected, e.g. based on the depth of the gate cavity 216 and position of the cylindrical sections 214a, 214b, such that when the gate valve 200 is fully closed, the protrusion 238b sealingly abuts the contact hole 236b for blocking the fluid flow. In example embodiments, sealing means in the form of primary U-seals 222a, 222b and backup radial seals 224a, 224b, are provided between the seats 204a, 204b and the housing 212. The seals 222a, 222b, 224a, 224b are typically metal seals and help to prevent fluid leakage after the gate valve 200 has been closed. It will be appreciated that other materials may be used for the seals 222a, 222b, 224a, 224b.

With reference to Figures 3a-3e, an example operation of the gate valve 200 of Figure 2a is now described. Here, the numerals that have been used in Figures 2a-2b are re-used to indicate the respective elements already described.

Figure 3a shows a cross-sectional view of the gate valve 200 of Figure 2a, taken vertically about the axis of the cylindrical sections 214a, 214b, at a "fully open" position according to an example embodiment. In Figure 3a, the gate 202 is raised to the highest level such that the through hole 203 is aligned with the seats 204a, 204b and the cylindrical sections 214a, 214b, thus forming a substantially linear channel that permits the flow of a fluid, e.g. from right to left, as illustrated by arrow 314. Some fluid may flow into the gate cavity 216 through gaps 237a, 237b between the gate 202 and seats 204a, 204b. Additionally, the side plates 232a, 232b of the gate 202 each includes a rectangular recess

302a, 302b disposed on respective inner surfaces 304a, 304b which are adjacent to the gaps 237a, 237b (Figure 2b). The central plate 234 of the gate 202 includes a catch 306 configured to engage with the recesses 302a, 302b. In the position shown in Figure 3a, the catch 306 contacts upper surfaces 308a, 308b of the recesses 302a, 302b such that a hole section 312 on the central plate 234 is aligned with hole sections 310a, 310b on the side plates 232a, 232b respectively. The catch 306 and recesses 302a, 302b also help to maintain the position of the side plates 232a, 232b relative to the seats 204a, 204b. For example, if the gate valve 200 is deployed in the orientation shown in Figure 3a, the side plates 232a, 232b are prevented from dropping, under the effect of gravity, into the cavity 216. In the implementation shown in Figure 3a, the recesses 302a, 302b and the catch 306 are disposed at respective bottom ends of the side plates 232a, 232b and central plate 234. However, it will be appreciated that different catching mechanisms and positions may be used in alternate embodiments.

From the position shown in Figure 3a, the stem 206 may be rotated about its axis to drive the central plate 234 downward. Figure 3b shows the cross-sectional view of the gate valve 200 of Figure 3a, at a "partially closed" position according to an example embodiment. As the central plate 234 is driven downward, the catch 306 contacts lower surfaces 318a, 318b of the recesses 302a, 302b such that the side plates 232a, 232b are also driven downward together with the central plate 234. In the position shown in Figure 3b, the flow path, as shown by arrow 316, is progressively restricted.

As the gate 202 comprising the central plate 234 and side plates 232a, 232b is driven further downward the flow path is further narrowed and eventually closed. Figure 3c shows the cross-sectional view of the gate valve 200 of Figure 3a, at an "almost fully closed" position according to an example embodiment. Here, the flow path has been blocked as each of the hole sections 310a, 310b, 312 are totally out of alignment with the cylindrical section 214a, 214b and seats 204a, 204b. For the fluid flow from right to left, the fluid pressure acting on the upstream side plate 232a may cause some gaps between the upstream side plate 232a and the upstream seat 204a, and some fluid may flow into the cavity 216 as a result. However, the same fluid pressure is transferred onto the central plate 234 and downstream side plate 232b such that metal-to-metal sealing is effected and the fluid is prevented from flowing onto the downstream seat 204b and cylindrical section 214b downstream. For example, the protrusion 238b sealingly abuts the contact hole 236b. In addition, the downstream side plate 232b presses against the seat 204b such that the interface 322 therebetween is sealed. It will be appreciated that the protrusion 238b seals only the downstream contact hole 236b, while the upstream contact hole 236a is not sealed in the position shown on Figure 3c. There is an upstream pressure on the front and at the back of the upstream side plate 232b, causing the pressure at the contact area between the central plate 234 and the upstream side plate 232a to be equal to the upstream pressure. Further, sealing between the seat 204b and the housing 212 is provided by the primary U-seal 222b and back-up radial seal 224b (Figure 2b). As a result, the fluid flow is effectively stopped at this point. Figure 3d shows the cross-sectional view of the gate valve 200 of Figure 3a, at a "fully closed" position according to an example embodiment. At this point, the gate 202 is fully lowered and contacts a bottom surface 320 of the cavity 216. The rotation member 208 (Figure 2a) may be locked to prevent an accidental rotation of the stem 206 (Figure 2). The catch 306 still contacts the lower surfaces 318a, 318b of the recesses 302a, 302b. The side plates 232a, 232b are thus secured in place and prevented from accidental vertical movement.

Further, in the "fully closed" position shown in Figure 3d, the fluid is still sealed from flowing onto the seat 204b downstream, as described above with respect to Figure 3c. The axis of the contact holes 236a, 236b is aligned with the axis of the cylindrical sections 214a, 214b and seats 204a, 204b. The fluid flow impinges onto the protrusion 238a of the central plate 234 that is adjacent to the contact hole 236a and facing the upstream flow. In other words, the contact area of the central plate 234 that is subject to the fluid pressure P is equal to the size of the protrusion 238a. The upstream side plate 232a effectively floats, as there is fluid pressure at the back and in the front of the upstream side plate 232a, resulting in jio net pressure. The pressure in the cavity 216 comes from the fluid that has entered the cavity 216 through the gaps between the upstream seat 204a and the upstream side plate 232a. There are gaps between the upstream seat 204a and the upstream side plate 232a because the net force working to the upstream seat 204a pushes the upstream seat 204a to the upstream direction. The frictional force F r acting on the central plate 234 due to the flow can be calculated as:

where F is the horizontal force by the upstream fluid on the protrusion 238a and transferred onto the protrusion 238b, D is the diameter of the protrusion 238a and μ 0 is the coefficient of friction between the central plate 234 and the downstream side plate 232b.

As the diameter D of the protrusion 238a is smaller than the diameter Dp of the through hole 203, the net frictional force on the central plate 234 in the example embodiments is significantly reduced compared to existing gate valves where the contact area is equal size of the through hole 203 (as is the case in Figure 1e). This is based on the assumption that the pressure P remains constant in Equation (1). In actual implementations, as the diameter d of the contact hole 236a is smaller than the diameter Dp of the seat 204a, based on Bernouli's principle, the fluid pressure actually decreases in the contact hole 236a, making the frictional force F r even lower.

When the gate valve 200 is to be opened, the rotation member 208 (Figure 2a) may be unlocked (if necessary) for rotating the stem 206 (Figure 2a), and the gate 202 is driven upward. In the example embodiments, the central plate 234 of the gate 202 is driven upward first, before pulling the side plates 232a, 232b upward with it. Figure 3e shows the cross-sectional view of the gate valve 200 of Figure 3a as the gate 202 is about to be opened position according to an example embodiment. As shown in Figure 3e, the catch 306 of the central plate 234 moves a short distance first upward before engaging with the upper surfaces 308a, 308b of the recesses 302a, 302b. During this initialization, since only the central plate 234 moves perpendicularly relative to the fluid flow, the frictional force that has to be overcome is the force F r of Equation (1). Thus, the gate valve 200 of the example embodiments may require a significantly lower torque for the initial opening, compared to existing gate valves. Additionally, as the central plate 234 moves upward, the contact hole 236b is no longer sealed by the protrusion 238b, and the fluid starts to flow to the seat 204b downstream. This may further lower the torque required for turning the stem 206 as the central plate 234 and side plates 232a, 232b are effectively suspended by the fluid pressure. Thus, the gate valve 200 may be operated by just one person, resulting in simpler and more cost-effective operations.

In some implementations, the maximum torque T that can be provided by one operator is known, and the lever-arm R of the rotation member 208 (Figure 2a) is known. Thus the force F a applied at the handle 210 (Figure 2a) can be calculated as:

F a = T / R (2)

The load Q acting on the stem 206 (Figure 2a) can be calculated based on the following equation:

F = Q x — x— (3 where p is the lead of the threads 207 (Figure 2a), μ is the coefficient of friction, and r is the pitch radius of the threads 207. In the ' example embodiments, the load Q is equal to the frictional force F r between the central plate 234 and the downstream side plate 232a. Thus, by combining with Equation (1) and knowing the working pressure, the size of the protrusions 238a, 238b, i.e. the diameter D, can be calculated.

Further, the effective annular area between the central plate 234 and the downstream side plate 232b on which the horizontal force F (Equation (1)) acts is equal to the difference between area of the protrusion 238b and the contact hole 236b, i.e. — (D 2 - d 2 ). Thus, the contact or sealing pressure P' between the central plate 234 and the downstream side plate 232b can be calculated as: * (D> - d*) ~ * (D* - d> ) ~ ( D2 - d2 )

4 · 4

Using Equation (4), the size of the contact holes 236a, 236b, i.e. the diameter d, can be determined such that the contact pressure P' is greater than the working pressure of the valve 200, i.e. the maximum allowable pressure in the valve 200. For example, the working pressure may be about 15,000 pounds per square inch (103.5 MPa) in some implementations. As the valve 200 may be deployed in different orientations or configuration, the contact pressure P' is typically about 5 times larger than the working pressure of the valve 200, to account for external factors such as gravity. The diameter d of the contact holes 236a, 236b may be calculated accordingly based on Equation (4).

A gate valve according to example embodiments may be assembled as follows. At a first step, a housing defining first and second cylindrical sections and a gate cavity between the first and second cylindrical sections provided. At the next step, first and seats are disposed at the interfaces between the housing and the first and second cylindrical sections respectively. Next, a gate as described above is assembled in the gate cavity. In some implementations, the gate may be assembled separately in a prior step. Moreover, after the gate has been assembled, the driving mechanism may be coupled and the cavity closed, e.g. by fasteners. The assembly process may be applied in a production floor, or as an on-site refurbishment. 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. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.