GB2516094A

GB2516094A - Valve

Info

Publication number: GB2516094A
Application number: GB1312457.3A
Authority: GB
Inventors: Mark Breese
Original assignee: SEV GLOCON Ltd
Current assignee: SEV GLOCON Ltd
Priority date: 2013-07-11
Filing date: 2013-07-11
Publication date: 2015-01-14
Anticipated expiration: 2033-07-11
Also published as: GB201312457D0; GB2516094B

Abstract

A butterfly valve comprises a valve member 12 supported for angular movement relative to a valve seat (14, Fig. 1) about a pivot axis 18, the valve member 12 having a peripheral edge defining a sealing surface and a sealing line 12b. The sealing line 12b lies upon the surface of a notional sphere 12a and the pivot axis 18 is parallel to and offset from a plane of the valve member 12 and offset from a diameter of the valve seat 14 in a first direction. The valve seat 14 takes the form of a truncated cone 28 of circular cross-section, the notional apex 26 of the truncated cone 28 being eccentric to the valve seat. A notional line 26a passes through the apex 26 and extends parallel to the axis 24 of the valve seat 14 and is offset from the axis 24 of the valve seat in the first direction. A first part of the truncated cone 28 is tangential to the notional sphere 12a, and a second part of the truncated cone 28 is not tangential to the notional sphere 12a.

Description

VALVE

This invention relates to a valve for use in controlling the flow of a fluid along a passage, and in particular to a butterfly valve suitable for such use.

Butterfly valves are well known and typically comprise a valve member of generally disc shaped form supported for angular movement about an axis of rotation which extends across a flow passage of generally circular cross section. The valve member is adapted so as to be movable between a closed position in which it substantially closes the flow passage, and a fully open position in which it forms a minimum obstruction to fluid flow along the flow passage. A compliant seat is typically formed about the passage for cooperation with the valve member so that a substantially fluid tight seal is formed between the valve member and the seat, closing the passage, when the valve member occupies its closed position.

It is desirable for butterfly valves to require only a relatively low input torque to drive the valve member between its open and closed positions, to experience only relatively low levels of wear and so of long operating life) to include limit stops which are engaged when the valve occupies its closed position, and for the valve to form only a small restriction to fluid flow along the passage when in its fully open position.

With an arrangement of the type outlined hereinbefore, the forces which must be applied to move the valve member in either the opening or the closing direction when the valve member is close to its fully closed position are high, largely due to the interference between the valve member and the seat. In order to reduce these loadings, it is known to offset the axis of rotation of the valve member from the plane of the valve member, altering the path of movement of the valve member to reduce sliding of the valve member against the seat and so reduce the torque required to move the valve member. However, the wear that occurs between the valve member and the seat in a simple single offset valve of this type can be undesirably high.

Double offset valves in which the axis of rotation is not only shifted from the plane of the valve member, but is also shifted from a diameter of the valve member are also known. In such valves, the sealing face of the valve member is typically of part spherical form. The corresponding face of the associated seal may take a range of forms designed to interfere with the valve member. In one example, the seat is of truncated conical form, the cone angle of which is selected to minimize wear between the valve member and the seal. This is achieved by arranging for the cone of the seat to be tangential to the sphere of the valve member about substantially the entire periphery of the seat and valve member. Whilst such valves are advantageous in that both wear and the torque required for operation are reduced, the truncated conical form of the valve seat and part spherical form of the valve member are such that no physical stop is formed preventing over travel of the valve member when moving to its closed position. In order to counter the risk of the valve member overshooting beyond the closed position, and the consequent partial reopening of the valve and accompanying leakage at a time when the valve is intended to be closed, it has been necessary to incorporate limit stops in the mechanism used to drive the valve member for movement. Whilst such stops may serve to prevent over travel of the valve member, they increase the complexity of the drive mechanism. Furthermore, inaccuracies in the setting of the stops associated with the drive mechanism may still result in over-or under-travel when the valve member is being moved towards its closed position.

So-called triple offset valves are known in which not only is the axis of rotation of the valve member shifted as set out hereinbefore, but also the shape of the valve seat is modified to take the form of a slice taken from a notional cone orientated or angled such that the apex of the cone lies at or adjacent an edge of the passage. Such offsetting of the apex of the cone results in the engagement of at least part of the valve member with the seat being such that the valve member buts up against the seat, forming a face seal therewith. As a consequence, the engagement between the valve member and the seat serves as a stop, preventing over travel of the valve member. Furthermore, sliding movement between the valve member and the seat is significantly reduced, thus wear of the valve member and seat is much reduced.

Whilst such triple offset valves are advantageous, they do have the disadvantage that the valve member and seat are not of circular form as the seat takes the form of a slice of a cone, the slice being angled to the axis of the cone. Rather than being of circular form) they are of generally elliptical form. In order to accommodate the elliptical valve member and seat within the passage, it is necessary for parts of the flow passage to be blocked. The flow permitted when the valve is fully open is thus more restricted than may be desirable. Furthermore, the manufacture of the valve is of increased complexity.

Attempts have been made to compensate for the elliptical form of the valve member of a triple offset valve, for example by manufacture of the valve member in the form of a slice from a notional cone of elliptical, rather than circular, cross-section, the shape of the cone being chosen such that the slice is of substantially circular shape. The process for designing such valves is complex.

The present invention relates to an alternative design of valve, designed using an alternative methodology, of a form similar to the triple offset valve but in which the valve member and seat are of substantially circular shape.

According to the present invention there is provided a valve comprising a valve member supported for angular movement relative to a valve seat about a pivot axis, the valve member having a peripheral edge defining a sealing surface and a sealing line, the sealing line lying upon a notional sphere, the pivot axis being parallel to and offset from a plane of the valve member and offset from a diameter of the valve seat in a first direction, the valve seat taking the form of a truncated cone of circular cross-section, the notional apex of the truncated cone being eccentric to the seat, a notional line passing through the apex and extending parallel to the axis of the seat being offset from the axis of the seat in the said first direction, wherein a first part of the truncated cone is tangential to the notional sphere, and a second part of the truncated cone is not tangential to the notional sphere.

The first part of the truncated cone preferably includes a part closer to the notional line than it is to the axis of the valve seat, and the second part of the truncated cone preferably including a part thereof close to the axis of the seat than it is to the notional line.

Such an arrangement is advantageous in that wear of the valve member and seal is relatively low, at least part of the valve member forming a face seal rather than a sliding seal with the valve seat.

Furthermore, engagement between the valve member and the valve seat may serve as a stop limiting movement of the valve member and so reducing the risk of over travel of the valve member. The accuracy with which the valve can be operated is thus enhanced.

As the valve member and valve seat are both of substantially circular form, the valve, when open, can permit fluid flow along the associated passage forming only a relatively small restriction to flow. Furthermore, as the valve member and seat are of generally circular form, manufacture of the valve is considerably simplified.

According to another aspect of the invention there is provided a method of designing a valve of the type described hereinbefore, the method comprising the steps of deriving a notional sphere, a sealing line of a valve member lying upon the notional sphere, deriving a first notional cone which lies tangential to the notional sphere at the position of the sealing line, identifying a point on a sidewall of the first notional cone, deriving a second notional cone having a base coextensive with the base of the first notional cone and an apex at the said point, and using part of the second notional cone to define the shape of a valve seat.

As the apex of the second notional cone lies upon the sidewall of the first notional cone, and the first notional cone is tangential to the notional sphere, it will be appreciated that the valve seat includes a first part which is tangential to the notional sphere and a second part which is not tangential to the notional sphere.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic view illustrating a double offset valve; Figure 2 is a diagrammatic representation illustrating a triple offset valve; Figures 3a, 3b and 3c are views illustrating the design methodology of an embodiment of the invention.

Referring firstly to Figure 1, a double offset butterfly valve 10 is illustrated which comprises a valve member 12 supported for angular movement relative to a valve seat 14 located within a passage 16. The valve member 12 is of generally circular, disc-like form and has an outer periphery defining a sealing surface. A sealing line 12b lies upon the sealing surface, the sealing line 12b also lying upon the surface of a notional sphere 12a. The sealing line extends vertically, in the orientation illustrated, perpendicularly to the axis of the passage.

The valve member 12 is supported for angular movement about a pivot axis 18. The pivot axis lies parallel to, but spaced or offset from, a plane of the valve member 12, and is also offset from a diameter of the valve seat 14. These offsets are denoted as offset a and offset b, respectively, in Figure 1.

The valve seat 14 is of truncated conical form, lying upon the surface of a notional cone 14b which is tangential to the notional sphere 12a at the position of the valve member 12. The notional sphere 12a and notional cone 14a are both aligned with the axis of valve seat 14 and valve member 12, and so the apex of the notional cone 14a lines upon the axis of the valve seat 14 and valve member 12.

As described hereinbefore, in use, an appropriate drive mechanism is used to drive the valve member 12 for movement about the pivot axis 18. Such movement drives the valve member 12 for movement between its closed position (as shown) in which it bears and seals against the valve seat 14 and so closes the passage 16, and a fully open position.

Whilst a double offset valve has the advantages outlined hereinbefore compared to a traditional butterfly valve, it has the disadvantage that a mechanical stop is required to limit movement of the valve member 12 to ensure that the valve member 12 is correctly located when the valve is required to be closed.

Furthermore, in order to achieve full sealing, it is necessary for the valve seat and/or valve member to be of a resilient material. The use of a full metal seat and valve member is thus not possible where a perfect seal is required, although such are used where a degree of leakage is permitted.

Figure 2 illustrates a triple offset valve. In Figure 2, like reference numerals are used to denote parts similar or the same as those of the double offset valve of Figure 1. In the arrangement of Figure 2 it will be seen that the notional cone 14a is rotated or tilted such that the apex thereof, instead of lying on the axis of the valve member 12 and valve seat 14, is situated adjacent the wall of the passage 16. As a consequence, part of the valve seat 14 lies substantially parallel to the side wall of the passage 16 and another part thereof may be angled relatively steeply thereto.

In use, as the valve member 12 is moved towards its closed position, it will be appreciated that the peripheral surface of the valve member 12 moves into contact with and abuts the adjacent valve seat 14. The positive engagement between the valve member 12 and the valve seat 14 serves to define a stop, limiting further movement of the valve member 12.

As described hereinbefore, whilst such an arrangement forms a positive stop, it has the disadvantage that the valve member 12 and valve seat are not of generally circular form but rather are of generally elliptical form. This arises from the fact that the valve seat is not defined by a slice of the notional cone perpendicular to the axis thereof, but rather is tilted relative thereto. The elliptical form of the valve seat 14 and valve member 12 in this arrangement results in the formation of undesirable flow restrictions and also results in manufacture of the valve being relatively complex.

In accordance with an embodiment of the invention, as shown in Figures 3a to 3c, a butterfly valve of relatively simple form comprises a valve member 12 having an outer periphery defining a sealing surface. A sealing line 12b is defined upon the sealing surface. The sealing line 12b lies upon the surface of a notional sphere 12 and is of generally circular cross-sectional shape. The valve member 12, like that of Figure 1, is supported for angular movement about a pivot axis 18 which is offset both from a plane of the valve member 12 and from a diameter thereof. A suitable drive mechanism (not shown) is used to drive the valve member 12 for movement about its axis.

The valve member 12 is arranged to engage a valve seat 14 located within a passage 16 to control fluid flow along the passage 16. To derive the shape of the valve seat 14, a first notional cone 20 is derived, the first notional cone 20 lying tangential to the notional sphere 12a at the point at which the first notional cone 20 meets the sealing line 12b of the valve member 12. The first notional cone 20 is thus of circular cross section and has an apex 22 lying upon an axis 24 of the valve member 12 and valve seat 14. The cone 20 is thus a right circular cone.

As shown in Figure 3b, a point 26 lying upon a sidewall of the first notional cone 20 is identified. A second notional cone 28 is then derived, the base of which is coextensive with that of the first notional cone 20 and the point 26 forms the apex of the second notional cone 28. It will be appreciated that the second notional cone 28 can be regarded as a cone of circular cross-section with the axis of the cone tilted relative the axis of the first notional cone. In other words, the second notional cone 28 is an oblique circular cone whereas, as mentioned above, the first notional cone 20 is a right circular cone. The apex of the second notional cone 28 is eccentric to the seat, a notional line 26a passing through the apex and extending parallel to the axis 24 of the seat being offset from the axis 24 of the seat. As illustrated, the direction in which the notional line 26a is offset from the axis 24 is the same as the direction of offset b by which the pivot axis 18 is offset from the diameter of the valve seat 14.

The valve seat 14 is manufactured such that the seat surface thereof is of truncated conical form, lying upon the surface of the second notional cone 28. Consequently, the valve seat 14 includes a first part 14b lying upon a part of the second notional cone 28 which is tangential to the notional sphere, and so also lies upon part of the first notional cone 20, and a second part 14c lying upon a part of the second notional cone 28 which not tangential to the notional sphere 12a. The first part 14b of the valve seat 14 includes a part closer to the notional line than it is to the axis of the valve seat, and the second part 14c includes a part thereof closer to the axis of the seat than it is to the notional line.

It will be appreciated that the butterfly valve of this design is advantageous in that face sealing of the sealing surface at the periphery of the valve member 12 and valve seat 14 occurs) with the result that wear is limited, and the abutting of the valve member 12 with the valve seat 14 results in the formation of a positive stop limiting movement of the valve member 12. Furthermore, as the second notional cone 28 is a circular cone, the valve seat 14 and the valve member 12 are both of generally circular shape with the result that minimal restrictions to fluid flow are formed when the valve is fully open, and manufacture of the valve is simplified. The face sealing allows the use of a full metal valve seat and valve member, if desired, whilst achieving a perfect seal.

Whilst one embodiment of the invention is described herein, it will be appreciated that a number of modifications and alterations to the arrangement may be made without departing from the scope of the invention as defined by the appended claims.

Claims

CLAIMS: 1. A valve comprising a valve member supported for angular movement relative to a valve seat about a pivot axis) the valve member having a peripheral edge defining a sealing surface and a sealing line, the sealing line lying upon the surface of a notional sphere, the pivot axis being parallel to and offset from a plane of the valve member and offset from a diameter of the valve seat in a first direction, the valve seat taking the form of a truncated cone of circular cross-section, the notional apex of the truncated cone being eccentric to the seat, a notional line passing through the apex and extending parallel to the axis of the seat being offset from the axis of the seat in the said first direction) wherein a first part of the truncated cone is tangential to the notional sphere) and a second part of the truncated cone is not tangential to the notional sphere.
2. A valve according to Claim 1) wherein the first part of the truncated cone includes a part closer to the notional line than it is to the axis of the valve seat.
3. A valve according to Claim 2, wherein the second part of the truncated cone includes a part thereof closer to the axis of the seat than it is to the notional line.
4. A valve according to any of the preceding claims) wherein the valve seat is perpendicular to the notional line.
5. A method of designing a valve of the type described hereinbefore, the method comprising the steps of deriving a notional sphere) a sealing line of a valve member lying upon the notional sphere, deriving a first notional cone which lies tangential to the notional sphere at the position of the sealing line) identifying a point on a sidewall of the first notional cone, deriving a second notional cone having a base coextensive with the base of the first notional cone and an apex at the said point, and using part of the second notional cone to define the shape of a valve seat.