WO2004018913A1

WO2004018913A1 - Gate valve

Info

Publication number: WO2004018913A1
Application number: PCT/GB2003/003076
Authority: WO
Inventors: Robert Hart
Original assignee: Weir Valves & Controls Uk Limited
Priority date: 2002-08-21
Filing date: 2003-07-14
Publication date: 2004-03-04
Also published as: GB0219460D0; AU2003254459A1

Abstract

A gate valve comprising a rotatably mounted plate (101) provided with an aperture (102), the gate being held in a housing (111) provided with first and second openings, the gate valve further comprising a movement compensation disk (104) rotatably mounted in a recess in the plate, and a drive disk (106) rotatably mounted over the plate to allow the plate to pass under the drive disk, the drive disk being rotatably connected to the compensation disk by a stem (105) which is displaced from the axis of rotation of the drive disk and displaced from the axis of rotation of the compensation disk, such that actuation of the drive disk will cause movement and rotation of the compensation disk which will in turn cause the plate to rotate within the housing.

Description

GATE VALVE

The present invention relates to a gate valve.

Gate valves are well known and are used to interrupt the flow of fluid through a pipe or other conduit. Typically a gate valve comprises a flat plate provided with an aperture, the plate being held in a body which allows the plate to move from a first position in which the aperture is aligned with a pipe connected to the body thereby allowing fluid to flow through the aperture, and a second position in which the aperture is displaced away from the pipe such that the plate forms a barrier in the pipe which prevents the passage of fluid through the pipe. Gate valves of this type are generally large in size compared with the diameter of the pipe to which they are connected, and often suffer from the disadvantage that the cavity in which the plate moves may become fouled by debris, or deposits which may build up within the valve.

Gate valves having rotatable elements have been proposed as replacements for conventional gate valves. Rotary gate valves have the advantage that they occupy less space, and since they do not require a cavity for a plate to move into and out of, they are less liable to fouling by debris or formation of deposits.

A rotatable gate valve is described in WO99/66237. An example of a gate valve of this type is illustrated in figure 1. Referring to figure 1, the gate valve comprises a circular plate 1 provided with an aperture 2 which passes through the plate 1. the circular plate 1 is hereafter referred to as the gate disk 1. A circular opening 3 passes partway into the gate disk 1, and holds therein a rotatably mounted disc 4. The disc 4 is provided with an eccentrically mounted stem 5. The disc 4 is referred to hereafter as a compensator wheel 4. A further disc 6 is provided with an aperture 7 which locates over the eccentrically mounted stem 5 of the compensator wheel. The further disc 6 is referred to hereafter as the drive wheel ^'6. The drive wheel 6 is provided with a centrally mounted stem 8, referred to hereafter as the drive stem. The rotatable gate, compensator wheel and drive disc are held within a cavity 10 defined by a housing 11.

The housing 11 is shown in two halves 11a, lib in figure 1 for ease of illustration. The gate disk 1 is free to rotate within a first region 10a of the cavity 10. -The drive wheel 6 is free to rotate within a second region 10b of the cavity 10. The drive stem 8 extends beyond the housing 11.

The gate disk 1 is rotated by rotating the drive stem 8. The gate is moveable to an open configuration in which the aperture 2 is aligned with apertures 12, 13 provided in the housing 10 thereby allowing flow of fluid through the housing.

It has been found that the gate valve described and illustrated in WO99/66237 has practical limitations when it is implemented. In particular, the gate valve as illustrated and described will not move from a fully closed position to a fully open position and back to a fully closed position. The gate valve becomes jammed when it approaches a fully open configuration in which the aperture 2 in the gate disk 1 overlaps fully with the apertures 12, 13 provided in the housing. If the valve is opened to this degree then it cannot be subsequently closed.

It is an object of the present invention to provide a gate valve which overcomes or substantially mitigates the above disadvantage.

According to the invention there is provided a gate valve comprising a rotatably mounted plate provided with an aperture, the gate being held in a housing provided with first and second openings, the plate being rotatable from a first orientation in which the aperture is aligned with the openings thereby allowing fluid to flow between the openings, to a second orientation in which the aperture does not overlap with the openings thereby preventing the flow of fluid between the openings, the gate valve further comprising a movement compensation disk rotatably mounted in a recess in the plate, and a drive disk rotatably mounted over the plate to allow the plate to pass under the drive disk, the drive disk being rotatably connected to the compensation disk by a stem which is displaced from the axis of rotation of the drive disk and displaced from the axis of rotation of the compensation disk, such that actuation of the drive disk will cause movement and rotation of the compensation disk which will in turn cause the plate to rotate within the housing, wherein the separation between the axis of rotation of the plate, the axis of rotation of the drive disk, the stem of the compensation disk, and the axis of rotation of the compensation disk is such that rotational force is transferred efficiently from the drive disk to the plate over the range of movement of the plate from the first orientation to the second orientation and back to the first orientation.

The gate valve may be configured such that the angle subtended by a line connecting the axis of rotation of the compensation disk and the stem of the compensation disk, and a line connecting the axis of rotation of the plate and the axis of rotation of the drive disk remains greater than 45 degrees.

The gate valve may be configured such that the angle subtended between a line connecting the axis of rotation of the plate to the axis of rotation of the compensation disk forms an angle with a curve of motion of the axis of rotation of the compensation disk, the angle being sufficiently acute that force acting along the line has a sufficiently large component in the direction of the curve of motion to overcome friction which inhibits operation of the valve, for all orientations of the plate.

The angle is preferably less than 80 degrees for all orientations of the plate, more preferably less than 71 degrees for all orientations of the plate, and most preferably less than 50 degrees for all orientations of the plate.

The gate valve may be configured such that the angle subtended between a line connecting the axis of rotation of the compensation disk to the axis of rotation of the stem, and a line connecting the axis of rotation of the stem to the axis of rotation of the drive disk, is greater than 10 degrees for all orientations of the plate. Preferably, the angle subtended between a line connecting the axis of rotation of the compensation disk to the axis of rotation of the stem, and a line connecting the axis of rotation of the stem to the axis of rotation of the drive disk, is greater than 40 degrees for all orientations of the plate.

Preferably, the transfer of rotational force from the drive disk to the plate over the range of movement of the plate is sufficiently efficient to overcome friction or other forces that may act to inhibit movement of the valve, over the range of motion of the plate from the first orientation to the second orientation and back to the first orientation.

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

Figure 1 is a perspective exploded view of a gate valve which is known from the prior art;

Figure 2 is a plan view and a cross sectional view of a gate valve which embodies the invention;

Figure 3 is a series of plan views of the gate valve of figure 2 which show the gate valve in various orientations;

Figure 4 is a plan view of the gate valve of figure 2 which shows axes of rotation of components of the gate valve;

Figure 5 is a schematic illustration of the gate valve of figure 2 as a four bar linkage ;

Figure 6 is a schematic illustration showing in steps movement of the prior art gate valve of figure 1;

Figure 7 is a schematic illustration showing in steps movement of the gate valve shown of figure 2;

Figure 8 is a schematic illustration showing in steps movement of the gate valve of figure 2 in relation to a reference line;

Figure 9 is a schematic illustration showing in steps movement of the prior art gate valve of figure 1, and illustrating the direction of action of forces; Figure 10 is a schematic illustration showing in steps movement of the gate valve of figure 2, and illustrating the direction of action of forces; and

Figure 11 is a schematic illustration showing in steps movement of a second gate valve which embodies the invention.

An embodiment of the invention is shown in figure 2. The embodiment of the invention corresponds in large part to the prior art gate valve described and illustrated in WO99/66237. However, the size and positioning of the components which comprise the gate valve are modified. The inventor has realised that the size and positioning of the components is fundamental to ensuring that the gate valve operates correctly. The relative dimensions of the embodiment shown in figure 2 are selected such that the gate valve is moveable from a fully closed configuration to a fully open configuration, and back to a fully closed configuration without jamming.

Figure 2a shows the valve in plan view, and figure 2b shows a side view of the valve with the housing shown in cross section. Referring to figures 2a and 2b, the gate valve comprises a circular plate 101 provided with an aperture 102 which passes through the plate 101. the circular plate 101 is hereafter referred to as the gate disk 101. A circular opening 103 passes partway into the gate disk 101, and holds therein a rotatably mounted disc 104 (referred to hereafter as the compensator wheel 104). The compensator wheel 104 is provided with an eccentrically mounted pin 105 (hereafter referred to as the drive pin 105). A further disc 106 is provided with an aperture 107 which locates over the eccentrically mounted stem 105 of the compensator wheel. The further disc 106 is referred to hereafter as the drive wheel 106. The drive wheel 106 is provided with a centrally mounted stem 108, hereafter referred to as the drive stem. The gate disk 101, compensator wheel 104 and drive wheel 106 are held within a cavity 110 defined by a housing 111.

The housing 111 is shown in two halves Ilia, 111b in figure 2b for ease of illustration. The gate disk 101 is free to rotate within a first region 110a of the cavity 110. The drive wheel 106 is free to rotate within a second region 110b of the cavity 110. The drive stem 108 extends beyond the housing 111. The gate disk 101 is rotated by rotating the drive stem 108. In contrast to the prior art, and due to the selection of appropriate component sizes and locations (described below), the gate is moveable between a fully open configuration and a fully closed configuration without jamming. In the open configuration, the aperture 102 is aligned with apertures 112, 113 provided in the housing 110 thereby allowing flow of fluid through the housing. In the closed configuration the aperture 102 has no overlap with the apertures 112, 113 thereby preventing the flow of fluid through the valve.

The operation of the valve is shown in stages in figure 3. Beginning at figure 3a the valve is in a fully closed configuration. The valve moves through progressively more open configurations shown in figures 3b, 3c and 3d to the fully open configuration shown in figure 3e. The valve then moves through progressively more closed configurations show in figures 3f, 3g and 3h to the fully closed configuration shown in figure 3a.

The gate valve may be considered to be a system comprising four linkages, i.e. connections between four points of rotation. Referring to figure 4, the four points of rotation are the axis of rotation G of the gate disk 101, the axis of rotation C of the compensator wheel 104, the axis of rotation P of the drive pin 105 and the axis of rotation S of the drive stem 108. The gate disk 101 is constrained to rotate within the housing, and cannot be displaced. For this reason the axis of rotation G of the gate disk 101 is fixed. Similarly, the drive stem 108 is constrained by the housing to rotate about a fixed axis S. The pivot point P of the drive pin 105 will move relative to the gate disk 101 and the drive stem 108. The pivot point C of the compensator wheel 104 will move relative to the gate disk 101 and the drive stem 108.

Figure 5 shows schematically the gate valve of figure 2 as a four bar linkage. The axis of rotation G of the gate disk is fixed, and this is represented by showing the axis as being mounted on a stationary rod Rj. Similarly, the axis of rotation S of the drive stem is fixed, as represented by showing the axis as being mounted on a stationary rod R₂. The pivot points C and P are free to move in the plane of the figure, although the directions in which they may move is restricted. For example, pivot point C is constrained to move along a curve defined by rotation of the linkage GC. Similarly, pivot point P is constrained to move along a curve defined by rotation along the linkage PS.

The lengths of the linkages are fixed. The inventor has realised that the relative dimensions of the linkages are very important since the selection of the lengths of the linkages determines whether or not the valve may be opened and closed without jamming One set of linkage lengths which has been found to work correctly is as follows:

SG = 3.5, GC = 2.007, CP = 1.4 and PS = 2.1875

The lengths are relative lengths, and may be factored to any required size. The gate valve shown in figures 2 to 4 has relative dimensions that correspond to this set of linkage lengths (as does the four bar linkage of figure 5).

The inventor has determined the relative linkage lengths on the basis of an understanding of the operation of the linkages, and in particular an understanding of why the arrangement illustrated in W99/66237 does not move fully between the open and closed configurations. This is illustrated in figures 6 and 7.

Figure 6 is a schematic illustration which shows linkages, as measured by the inventor, of the prior art gate valve shown in figure 1 (the linkages are measured for the same components and in the same manner as described above for the gate valve of figure 4). The ratio of lengths of the linkages of the prior art gate valve are as follows:

SG = 3.5, GC = 3.608, CP = 2.625 and PS = 2.474 During movement of the gate valve the axis of rotation G of the gate disk 101 and the axis of rotation S of the drive stem 108 are fixed. The axis of rotation C of the compensator wheel 104 moves through an arc shown diagrammatically in figure 4 by curve C_c. The axis of rotation P of the drive pin 105 moves through an arc shown diagrammatically in figure 4 by curve P_p.

In a first position the compensator C and drive pin P together with the drive stem S are aligned. This corresponds to the valve being in a closed configuration.

The drive stem S is rotated in an anticlockwise direction. This movement draws the drive pin P downwards along the curve P_p. The drive pin P is constrained to move along the curve P_p because the distance between the drive pin P and the drive stem S is fixed. Since the distance between the drive pin P and the compensator C is fixed, the compensator is constrained to move along the curve C_c. The compensator is drawn upwards along the curve C_c by the movement of the drive pin P.

A series of positions of the drive pin P together with corresponding positions of the compensator C are shown in figure 6. It can be seen that the movement of the drive pin along the arc P_p continues until the drive stem S has been rotated anticlockwise through almost 90 degrees. The movement of the drive pin in turn draws the compensator C along the curve C_c in a clockwise direction though 90 degrees. The drive pin P finishes in a final position PF and the compensator C finishes in a final position CF. When the compensator C is in the final position CF, this corresponds to the valve being in the fully open position, as shown in figure 6e.

Although figure 6 shows schematically movement of the gate valve from the fully closed to the fully open position, in practice the gate valve will be susceptible to jamming. The reason why the valve is susceptible to jamming may be understood with reference to figure 6.

When the compensator C begins to move from the fully closed configuration (i.e. the left hand side of figure 6), the line of action of the force acting on the compensator C is positive. The line of action is shown by the linkage CP which extends between the drive pin P and the. compensator C. The sign of the line of action is determined relative to the vertical in figure 6; the line of action is positive when the linkage slopes to the left of the vertical, and is negative when the linkage slopes to the right of the vertical.

For a small movement of the valve from a fully closed configuration to a slightly open configuration, for example to position C₄, the line of action of the force acting on the compensator remains positive. Since the line of action of the force is positive, rotational force is transferred smoothly by the linkage CP to the compensator C, and the compensator C moves along the curve C_c.

For a large movement of the valve towards the fully open configuration, the line of action of the force acting on the compensator C changes from positive to negative. This occurs as the compensator C moves from position C₆ to C₉, as can be seen by referring to the vertical dotted line V which is shown in figure 6 for reference. Once the line of action goes negative, rotational force is not transferred smoothly by the linkage CP to the compensator C, and the compensator becomes susceptible to jamming during operation of the valve.

Jamming of the valve is unacceptable in practice, since the valve would need to be dismantled and forced back to the closed configuration, interrupting any process that was being controlled by the valve. The inventor has realised that jamming of the valve may be avoided by changing the relative lengths of the linkages so that the line of action always remains positive for every position of the compensator C. This- is achieved by reducing the separation between the drive stem S and the drive pin P, and increasing the separation between the compensator C and the drive pin P.

As previously indicated, one set of linkage lengths which has been found to provide a valve which works correctly is as follows:

SG = 3.5, GC = 2.007, CP = 1.4 and PS = 2.1875 Figure 7 shows linkages of a rotating gate valve which correspond to these ratios. For a small movement of the valve from a fully closed configuration to a slightly open configuration, for example to position C₄, the line of action of the force acting on the compensator remains positive, and rotational force is transferred smoothly by the linkage CP to the compensator C.

For a larger movement of the valve towards the fully open configuration, it can be seen that there is no point at which the line of action becomes negative. Instead, the line of action is always positive with the result that rotational force is transferred smoothly by the linkage CP to the compensator C over the entire range of motion of the compensator C. This means that the valve may be moved from the fully closed configuration to the fully open configuration, and back to the fully closed configuration without the valve jamming.

It is noted that defining the line of action in relation to the orientation of the valve provides an incomplete definition of the orientation of the line of action. For this reason an alternative figure, figure 8 is used to show the definition without reference to the orientation of the valve. Referring to figure 8, the linkage SG between the gate G and the drive stem S defines the horizontal. Since the positions of the gate G and drive stem S do not change during operation of the valve, this provides a fixed line of reference. Since the horizontal has been defined, the direction of the line of action may be defined with reference to the horizontal. The valve will open and close without jamming provided that the angle θ subtended between the linkage CP and the horizontal does not fall below 45°. It will be seen that this definition corresponds to that described in figure 7, since the linkage SG between the gate G and the drive stem S in figure 5 is 45° from the horizontal.

An alternative way of considering the effect of modifying the lengths of the linkages which comprise the valve is to consider the components of force which act along the linkages and act along the curves C_c and P_p. Referring to figure 9, which shows the prior art valve that is susceptible to jamming, the linkage CP may be thought of as a rod which is pivotally connected to the curve C_c and the curve P_p. The linkage PS may similarly be thought of as a rod which is pivotally connected to the curve P_p and to the rod CP. The linkages CP and PS are both horizontal when the valve is in the closed configuration. The linkage PS is driven to rotate in an anticlockwise direction by rotation of the drive stem S. This draws the linkage CP downwards along the curve P_p, causing the linkage to CP to be drawn in a clockwise direction along the curve C_c. In terms of components of force, force acts in the direction shown by arrow F, i.e. along the linkage CP. This is illustrated at position C₂. The force has a component F_p which is perpendicular to the curve C_c, and a component F_c which is parallel to the curve C_c. Since the parallel component is substantial, the compensator C moves in the clockwise direction along the curve C_c. The smooth transfer of force continues whilst the angle between the linkage CP and the curve C_c remains sufficiently acute (for example the angle at point C₆ is 78 degrees). This is equivalent to saying that the rotational force is transferred smoothly to the compensator (the expression used above when describing the line of action).

It can be seen that the parallel component F_c of the force will gradually be reduced as the compensator moves along the curve C_c. This is because the linkage CP moves ever closer to being perpendicular to the curve C_c. By the time the linkage CP reaches position C₉ for example it can be seen that the parallel component F_c of the force is very small. This is because the angle subtended between the linkage CP and the curve C_c is large (approximately 83 degrees), so that almost all of the force F acts perpendicular to the curve C_c. Although it might be considered that in a theoretical system of linkages this small parallel component of force might be enough to move the compensator C, in a practical implementation of the valve there will be friction between the components, and the small parallel component of force will not be enough to overcome the friction. The valve will therefore become jammed.

Figure 10 shows linkages for the valve which has been found to operate without jamming. It can be seen that at position C₂ the size of the parallel component F_c of the force is similar to that shown in figure 9. However, at position C₉ the size of the parallel component F_c of the force is several times greater than the parallel component F_c of the force shown in figure 9. The angle subtended between the linkage CP and the curve C_c never becomes larger than 50 degrees. This means that rotational force is transferred smoothly to the compensator over the full range of operation of the valve. The parallel component of force is always sufficiently large to overcome friction, and the valve opens and closes smoothly without jamming.

A further alternative way of considering the effect of modifying the lengths of the linkages which comprise the valve is to consider the angle subtended between the linkage CP and the linkage PS. Rotational force is to be transferred from the linkage PS to the linkage CP such that the compensator C is caused to move along the curve C_c. In order to transfer the rotational force efficiently there should be a significant angle between the linkage CP and the linkage PS. It can be seen in figure 9 that the angle θ between the linkage CP and the linkage PS is large initially but becomes very small when the compensator C moves towards the fully open position, so that rotational force cannot be transferred to the compensator efficiently. In contrast, in figure 10 the angle θ between the linkage CP and the linkage PS remains significant for all positions of the compensator C (the angle is never less than 40 degrees), thereby allowing the efficient transfer of rotational force to the compensator C. Jamming of the valve is thus avoided.

Although three different theoretical approaches have been used to consider the effect of changing the lengths of linkages of the valve, it will be appreciated that the approaches are unified by the fact that they all indicate that the valve will function correctly when rotational force input at the drive stem S is transferred efficiently to the compensator C. The efficiency of the transfer must be such that the transferred force is sufficiently strong to overcome friction and any other forces that may act to inhibit movement of the valve.

Valves constructed according to other ratios of linkage lengths have been found to open and close without jamming. These are:

Although the described embodiment of the invention provides 90 degrees angular movement of the gate disk 101 for 90 degrees rotation of the drive stem 108, there may be instances in which the gate disk is not required to move through 90 degrees in order to fully open the valve. This can be understood with reference to figure 3. In figure 3, 90 degrees rotation of the drive stem S causes 90 degrees rotation of the compensator wheel S, and 90 degrees rotation of the gate disk G. The angular gate rotation required in order to fully open the valve (i.e. to obtain full overlap of the aperture 112 and the gate aperture 102) is dependent upon the diameter of the apertures 102, 112 relative to the diameter of the gate disk 101. It can be seen from figure 3 that if the diameter of the apertures 102, 112 was halved then the angular movement of the gate disk 101 required to fully open and close the valve would be significantly less than 90 degrees.

The inventor has constructed a valve which has relative linkage lengths selected such that rotation of the drive stem S though 90 degrees moves the gate disk G through 78 degrees. A four bar linkage illustrating this valve is shown in figure 11. The diameter of the apertures (not shown) relative to the diameter of the gate disk is selected such that movement of the gate disk G through 78 degrees is sufficient to move the valve from a fully closed configuration to a fully open configuration. The relative lengths of the linkages for this valve are as follows: SG = 3.5, GC = 3.608, CP = 2.875 and PS = 2.2241.

It can be seen in figure 11 that the line of action remains positive for all configurations of the valve. The angle subtended between the linkage CP and the curve C_c never becomes larger than 71 degrees. The angle θ between the linkage CP and the linkage PS remains greater than 10 degrees for all positions of the compensator C.

Claims

1. A gate valve comprising a rotatably mounted plate provided with an aperture, the gate being held in a housing provided with first and second openings, the plate being rotatable from a first orientation in which the aperture is aligned with the openings thereby allowing fluid to flow between the openings, to a second orientation in which the aperture does not overlap with the openings thereby preventing the flow of fluid between the openings, the gate valve further comprising a movement compensation disk rotatably mounted in a recess in the plate, and a drive disk rotatably mounted over the plate to allow the plate to pass under the drive disk, the drive disk being rotatably connected to the compensation disk by a stem which is displaced from the axis of rotation of the drive disk and displaced from the axis of rotation of the compensation disk, such that actuation of the drive disk will cause movement and rotation of the compensation disk which will in turn cause the plate to rotate within the housing, wherein the separation between the axis of rotation of the plate, the axis of rotation of the drive disk, the stem of the compensation disk, and the axis of rotation of the compensation disk is such that rotational force is transferred efficiently from the drive disk to the plate over the range of movement of the plate from the first orientation to the second orientation and back to the first orientation.

2. A gate valve according to claim 1, wherein the angle subtended by a line connecting the axis of rotation of the compensation disk and the stem of the compensation disk, and a line connecting the axis of rotation of the plate and the axis of rotation of the drive disk remains greater than 45 degrees.

3. A gate valve according to claim 1 or claim 2, wherein the angle subtended between a line connecting the axis of rotation of the plate to the axis of rotation of the compensation disk forms an angle with a curve of motion of the axis of rotation of the compensation disk, the angle being sufficiently acute that force acting along the line has a sufficiently large component in the direction of the curve of motion to overcome friction which inhibits operation of the valve, for all orientations of the plate.

4. A gate valve according to claim 3, wherein the angle is less than 80 degrees for all orientations of the plate.

5. A gate valve according to claim 4, wherein the angle is less than 71 degrees for all orientations of the plate.

6. A gate valve according to claim 4, wherein the angle is less than 50 degrees for all orientations of the plate.

7. A gate valve according to any preceding claim, wherein the angle subtended between a line connecting the axis of rotation of the compensation disk to the axis of rotation of the stem, and a line connecting the axis of rotation of the stem to the axis of rotation of the drive disk, is greater than 10 degrees for all orientations of the plate.

8. A gate valve according to claim 7, wherein the angle subtended between a line connecting the axis of rotation of the compensation disk to the axis of rotation of the stem, and a line connecting the axis of rotation of the stem to the axis of rotation of the drive disk, is greater than 40 degrees for all orientations of the plate.

9. A gate valve according to any preceding claim, wherein the transfer of rotational force from the drive disk to the plate over the range of movement of the plate is sufficiently efficient to overcome friction or other forces that may act to inhibit movement of the valve, over the range of motion of the plate from the first orientation to the second orientation and back to the first orientation.