GB2042682A - Improvements in or Relating to Gate Valves - Google Patents

Abstract

This invention relates to tapered gate valves with gates having a resilient coating. A gate has a tapered portion (11) formed by two converging faces (12) merging into a portion (13) of constant thickness, and the valve passage is formed with tapered faces such that in the closed position the tapered faces (12) on the gate are engageable with the tapered faces in the valve passage & the peripheral face of the untapered portion (13) of the gate is of arcuate shape engageable with a correspondingly contoured portion of the periphery of the valve passage. The angle of taper of the gate is large enough to prevent rubbing of the gate faces against the faces on the valve body while keeping the thickness of the gate small. This has also the effect of reducing the unbalanced hydrodynamic force tending to close a partly open valve. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Gate Valves The subject of this invention is a gate valve i.e.

a valve which has a body formed with a passage for fluid and a gate movable across the passage.

The invention has particular reference to valves of the type in which the gate is covered with a resilient coating usually a rubber coating so that it can seal against the "as cast" surface in the valve body.

Gate valves incorporating gates partially or wholly encased in coatings of resilient material are already known. To provide a proper seal the gate is usually tapered and is engageable by wedge action with a correspondingly tapered seat provided within the valve body. To guide the gate into its sealing position and to resist the force of the fluid passing through the valve while the gate is being moved it is customary to provide means arranged to guide and support the gate as it moves across the passage to close or open the valve. For the purpose of closing and opening the gate it is customary to provide a screw-threaded shaft passing through a non-rotating nut, one end of the shaft entraining the gate and the other end in valves arranged for manual operation carrying a wheel for rotation by an operator.

In designing valves of the type aforementioned account must be taken of several conflicting requirements. In a valve to be operated by hand the valve must not require too much force to open or close it despote the fact that a gate valve tends to be self-closing because when the gate in being moved to the open or closed position is in any intermediate position between closed and fully open (in which the area of the passage through the valve at the position below the gate is less than the full area of the passage) the fluid velocity below the partly open gate increases producing a Bernouilli effect which results in a local reduction in pressure below the gate. As the top of the partly open gate is exposed to the full fluid pressure there is an unbalanced force causing the gate to tend to move towards the lower pressure zone, i.e. towards the closed position.This unbalanced force is small at large valve openings but becomes appreciable when the gate is close to the closed position. While this effect assists the operator when he is closing the valve it operates against him when he is opening the valve. The situation can be aggravated by another consideration and that is that to reduce abrasion of the resilient coating when the gate is being forced against its seat the wedge angle of the gate should be as great as possible. A large angle, however, requires a thick gate and the thicker the gate the greater the area exposed to the pressure of the fluid when the valve is partly open. A thick gate thus increases the force opposing opening of the gate. A thick gate also introduces another difficulty. For convenience the length of the valve body should be as short as possible and valves are usually made to standard lengths.A thick gate requires that the chamber in which it is housed when the valve is closed should be correspondingly large in an axial direction. This reduces the space between the housing of the chamber and the flanges at the ends of the valve body provided for connecting the valve to adjacent pipe sections. A reduced space between the chamber housing and the flanges makes it difficult to insert the nuts to be fitted to the ends of the bolts customarily used to connect the valve to the adjacent pipe sections. It is also desirable to provide some form of stop to prevent the coated gate from being forced with too great effort against its seat yet which cannot act as a collector of debris. An'y debris on the stop surface prevents the gate from being able to reach the closed position.

It is an object of the present invention to provide a construction of gate valve which minimizes the extra closing force generated in partly open positions of the gate and wear of the resilient coating on the gate, and which prevents overstressing of the resilient coating when the gate reaches the closed position and which facilitates the provision of adequate room between the housing of the chamber and the end flanges for fitting the holding nuts.

A gate valve according to the invention incorporates a valve body formed with a passage extending through the body and with a chamber on one side of the passage communicating with the passage, said chamber having a maximum dimension in a direction transversely of the axis of the passage greater than the diameter of the passage and being continued part-way across the passage so that the passage intersects the chamber at one end of the chamber and the wall of the passage is discontinuous at the junction of the passage and the chamber, the walls of the chamber defining the dimension of the chamber in the direction of the axis of the passage being convergent where they intersect the passage so that opposite inclined faces are presented by the valve body, said faces facing one another across the gap where the wall of the passage is discontinuous and the walls of the chamber which define the width of the chamber being convergent at the ends adjacent the passage and meeting tangentially the wall of the passage at opposite ends of an arcuate portion of the wall of the passage opposite the chamber, a gate having a tapered portion formed by two opposite convergent faces the angle between which substantially matches the angle between said inclined faces in the valve body, said tapered portion of the gate merging into a non-tapered portion bounded by a peripheral face which has a contour presenting two mutually inclined portions connected by an arcuate portion to which they are tangent, the angle between the two inclined portions being substantially equal to the angle between said tangential portions of the side walls of the chamber and the arcuate portion being of substantially the same radius as the radius of the passage, the gate being formed to engage guide means in the side walls of the chamber, and means for moving the gate along the guide means between two extreme positions in one of which the gate is retracted and lies within the chamber clear of the passage and in the other of which it projects across the passage with the convergent faces of the gate engaging said inclined faces presented by the valve body, said mutually inclined portions of the peripheral surface of the gate engaging said tangential portions of the side walls of the chamber and the arcuate portion of the peripheral surface of the gate engaging the arcuate portion of the passage.

The gate may be a composite body formed of a metallic casting encased in a resilient coating which may be of rubber or of a rubber-like material. Where the gate has a coating of resilient material all the surfaces of the valve body and the gate casting may be left in the "as cast" condition.

The guide means may comprise fins presented by the gate engaging grooves formed in the side walls of the chamber or fins presented by the side walls of the chamber engaging grooves formed in the gate.

At the points where the walls defining the width of the chamber become convergent the converging surfaces function as abutments at the points where the wall surfaces abruptiy change direction to become convergent, said abutments being engageable by the gate when the gate is closed. The gate is thus prevented from being forced too far down by the application of excessive force on the gate-closing mechanism and the surfaces being inclined, there is no accumulation of debris.

A practical embodiment of the invention is illustrated in the accompanying drawings in which Fig. 1 is a longitudinal section of a valve body, Fig.

2 is a half transverse section through the line 22 in Fig. 1, Fig. 3 is a half plane view looking into the entrance to the chamber from the outside of the valve body, Fig. 4 is a view looking on the face of the gate and Fig. 5 is a side view of the gate.

The gate illustrated is a composite body formed of a metallic casting encased in a resilient coating.

In the drawings 1 denotes a valve body formed with a passage 2 extending through the body and 3 denotes a chamber disposed on one side of the passage 2 and continuing part-way across the passage 2 so that the passage 2 intersects the chamber 3 at one end of the chamber 3, so that the wall of the passage is discontinuous i.e. there is a gap 3A at the position where the chamber opens into the passage. The maximum dimension of the chamber 3 measured in a direction transversely of the axis of the passage 2 is greater than the diameter of the passage 2.At the intersection of the passage 2 and the chamber 3 the portions of the walls 4 of the chamber 3 defining the dimension of the chamber 3 in the direction of the axis of the passage 2 are convergent in the direction towards the portion of the passage 2 so that opposite inclined faces 4A are presented by the valve body 1 facing one another across the gap 3A. The walls 5 defining the width of the chamber 3 are formed with grooves 6 and at the end of the chamber adjacent the passage 2 converge to form portions 7 which meet tangentially an arcuate portion 8 of the wall of the passage 2 opposite the chamber 3. The grooves 6 run in a direction towards the passage 2 and terminate at the convergent portions 7 of the walls 5. 9 denotes flanges at the ends of the valve passage for connecting the valve body 1 to adjoining lengths of pipe.

10 denotes a gate having a tapered portion 11 formed by two convergent faces 12 the angle between which substantially matches the angLe between the opposite inclined faces 4A and a non-convergent portion 13 into which the convergent faces 12 merge. The non-convergent portion 1 3 is bounded by a peripheral face 14 which has a contour presenting two mutually inclined portions 1 5 connected by an arcuate portion 1 6 to which they are tangent, the angle between the portions 1 5 being substantially the same as the angle between the convergent portions 7 of the walls 5 and the radius of the arcuate portion 1 6 being substantially the same as the radius of the passage 2.The gate presents two fins 17 which, when the gate 10 is in place in the body 1, engage the grooves 6 in the body 1.

The gate 10 is formed with an undercut groove 1 8 for attachment of the gate to the mechanism which when bolted to the end of the chamber remote from the passage 2 is operative to retract the gate 10 into the chamber 3 or advance the gate 10 across the passage 2 whereby to close the passage 2. The gate 10 incorporates a flexible coating. When the gate is advanced across the passage 2 to close the valve the convergent faces 12 on the gate engage the inclined faces 4A on the valve body 1, the mutually inclined portions 1 5 of the peripheral face 14 of the gate 10 engage the convergent portions of the chamber walls 5 and the arcuate portion 1 6 of the face 14 engages the arcuate portion 8 of the passage 2.

The gate when closed thus provides a fluid-tight barrier across the passage 2. In the closed position of the valve the fins 1 5 come against abutments constituted by the convergent portions 7 at the ends of the grooves 6 and thus further movement of the gate cannot take place so that excessive pressure cannot be generated between the sealing surfaces on the gate and on the valve body. Excessive pressure here causes wear on the resilient coating of the gate. Because the tapered portion 11 of the gate takes up little more than half the sealing surface of the gate and the remaining portion 13 is non-convergent, also because single fins project from the gate instead of the customary grooves formed in the gate, the gate can be made thinner in the axial direction than is possible in the customary valve even while allowing for an angle between the convergent faces 11 of the gate sufficient to prevent excessive rubbing between them and the inclined faces 4A of the valve body while providing the non-convergent portion 13 with adequate strength.This makes it possible to use a chamber 3 the extent of which measured in the direction of the axis of the passage 2 is small compared with the standard length of body allowed for each size of valve so that there is plenty of room between the chamber 3 and the flanges for the addition of the customary fixing bolts through the flanges.

The thinness of the gate reduces the projected area of the top end of the gate within the chamber 3 and as the chamber 3 is open to the full pressure of the fluid on the high pressure side of the gate when the gate is partly open the force required to open the valve against the force resulting from the Bernouilli effect trying to close it is kept to a minimum since the self-closing effort of the valve is a function of the pressure on the top end of the gate and the area on which that pressure operates. This makes it easier for an operator to open the valve since it is against a reduced self-closing force that he has to open the valve.

While a gate formed with grooves engaging projecting films on the body as the guide means may be slightly thicker than the gate specifically described above, the increase in thickness is not sufficient to detract to a serious extent from the advantages provided by the valve according to the invention.

Claims (9)

Claims

1. A gate valve incorporating a valve body formed with a passage extending through the body and with a chamber on one side of the passage communicating with the passage, said chamber having a maximum dimension in a direction transversely of the axis of the passage greater than the diameter of the passage and being continued part-way across the passage so that the passage intersects the chamber at one end of the chamber and the wall of the passage is discontinuous at the junction of the passage and the chamber, the walls of the chamber defining the dimension of the chamber in the direction of the axis of the passage being convergent where they intersect the passage so that opposite inclined faces are presented by the valve body, said faces facing one another across the gap where the wall of the passage is discontinuous and the walls of the chamber which define the width of the chamber being convergent at the ends adjacent the passage and meeting tangentially the wall of the passage at opposite ends of an arcuate portion of the wall of the passage opposite the chamber, a gate having a tapered portion formed by two opposite convergent faces the angle between which substantially matches the angle between said inclined faces in the valve body, said tapered portion of the gate merging into a non-tapered portion bounded by a peripheral face which has a contour presenting two mutually inclined portions connected by an arcuate portion to which they are tangent, the angle between the two inclined portions being substantially equal to the angle between said tangential portions of the side walls of the chamber and the arcuate portion being of substantially the same radius as the radius of the passage, the gate being formed to engage guide means in the side walls of the chamber, and means for moving the gate along the guide means between two extreme positions in one of which the gate is retracted and lies within the chamber clear of the passage and in the other of which it projects across the passage with the convergent faces of the gate engaging said inclined faces presented by the valve body, said mutually inclined portions of the peripheral surface of the gate engaging said tangential portions of the side walls of the chamber and the arcuate portion of the peripheral surface of the gate engaging the arcuate portion of the passage.

2. A gate valve as claimed in claim 1 in which the gate is a composite body formed of a metallic casting encased in a resilient coating.

3. A gate valve as claimed in claim 2 in which the resilient coating is of rubber-like material.

4. A gate valve as claimed in claim 2 in which the surfaces of the valve body and the gate casting are left in the "as cast" condition.

5. A gate valve as claimed in claim 1 in which the guide means is constituted by fins presented by the gate engaging grooves formed in the side walls of the chamber.

6. A gate valve as claimed in claim 1 in which the guide means is constituted by fins presented by the side walls of the chamber engaging grooves formed in the gate.

7. A gate valve as claimed in claim 5 in which at the points where the walls defining the width of the chamber become convergent the converging surfaces function as abutments at the ends of the grooves in said walls, said abutments being engageable by the fins on the gate when the gate is closed.

8. A gate valve substantially as described with reference to the accompanying drawings and as claimed in claim 1.

9. A gate for a gate valve substantially as described with reference to the accompanying drawings and as claimed in claim 1 or claim 2.