GB2123526A

GB2123526A - Valve member for a butterfly valve

Info

Publication number: GB2123526A
Application number: GB08309613A
Authority: GB
Inventors: George Aubrey Felton
Original assignee: AMBA TOOLS Ltd
Current assignee: AMBA TOOLS Ltd
Priority date: 1982-07-13
Filing date: 1983-04-08
Publication date: 1984-02-01
Also published as: GB8309613D0; DE3324442A1

Abstract

The valve member comprises a sealing disc (1) having opposed trunnions (2) at or adjacent one face of the disc to provide an offset axis of rotation for said disc within the valve body (5), and a load-equalising member (3) connecting the trunnions to provide, in combination with said disc, an anti-deformation arrangement which, in use, restricts flexing of said disc. Preferably the valve member is designed so that the fluid flow is towards that face of the disc opposite to said one face, in which case, said load-equalising member acts in tension. Said load-equalising member is preferably of fixed construction, e.g. a flat plate (3), and may incorporate means (7) Fig. 3, (not shown) for preloading. <IMAGE>

Description

SPECIFICATION Improved valve member for a butterfly valve In the design of valves for the control of fluids one of the most important considerations is to minimise friction losses through the valve when fully open to fluid flow. As all such losses are directly proportional to the power required to pump the fluid through the appliance it has prime economic importance.

A common type of valve used for fluid control in large pipelines is known as the butterfly type. This valve consists essentially of a pivoted disc rotatable by a shaft which obdurates a circular hole formed by a ring casing of diameter approximately equal to that of the pipeline into which the assembly is fitted. It will be apparent that when the pivoted disc member is fully open, i.e. lying along the horizontal axis of the pipeline, it's frictional resistance will be a function of the frontal area presented by the disc in this position.

It is likewise evident that the smaller the area or blockage presented, the lower will be the friction losses and it is the aim in the design of such valves to achieve a minimum blockage. However, the attainment of this desirable feature is generally inconsistent with the structural forms necessary to provide a closure member when the disc is In the closed position at 900 to the open position. At this position the disc is required to seal against pipeline pressure and to sustain the dynamic forces involved in rotating the disc.

These particular requirements are inimical to the need for a slim form of structure and call for a compromise design where the primary emphasis is structural.

An object of the invention is to provide a butterfly valve offering very low frontal area when open and adequate structural strength in the closing mode, and a minimum deflection of the sealing disc.

According to this invention, there is provided a valve member for a butterfly valve which is in the form of a sealing disc having opposed trunnions at or adjacent one face of the disc to provide an offset axis of rotation for said disc within the valve body, and a load-equalising member connecting the trunnions to provide, in combination with said disc, an anti-deformation arrangement which, in use, restricts flexing of said disc.

Preferably, the flow of fluid is towards that face of the disc opposite to said one face, in which case, said load-equalising member acts in tension.

Said load-equalising member is preferably of fixed construction, e.g. a flat plate, and may incorporate means for preloading.

It will be appreciated that the invention includes a butterfly valve fitted with such a valve member.

In order that the invention may be readily understood and further features made apparent, a butterfly valve construction in accordance therewith will now be described with reference to the accompanying drawings, in which: Figure 1 is a front elevation, with the valve member open, Figure 2 is a view similar to Figure 1 with the valve member closed, Figure 3 is a fragmentary view of a modification, and Figure 4 is a section on-the line IV--IV through the valve and blade.

Referring to the drawings, the valve member is in the form of a relatively thin flat sealing disc 1 to the rear face of which two diametrically opposed trunnions 2 are attached to provide an axis for rotation of the sealing disc 1, perpendicular to the axis X-X, as shown in Figure 1. The trunnions are in the form of a pair of spaced walls extending parallel to the direction of fluid flow, which are fixed to said rear face of the disc 1. The walls are profiled in cross-section to present a minimum resistance to flow when in the position shown in Figure 1, and preferably are shaped along their length to provide a convergingidiverging passage 8 therebetween, as shown in Figure 2, to reduce the effect of pressure losses in fluid flowing through said passage.The sealing disc 1 is rotatably mounted via shafts 4 in the valve body 5 at a position offset from an annular sealing face 6 around the periphery of the disc 1, which face is provided by a shaped annular ring of metal or plastics material e.g. such as P.T.F.E. Parallel to the disc 1 and bridging the tops of the trunnions 2 so as to be offset on the other side of the axis of rotation relative of the disc, so as to oppose the latter, is provided a load-equalising member 3 (in this case a tensioning member) comprising a thin flat plate which may, if required, be pre-tensioned e.g. using turn-buckles 7 as shown in Figure 1.

When this valve member is in the open position within a pipeline it will present a substantially thin-walled, open box-like structure to the fluid flow and hence provide minimal blockage. On the other hand, with the valve member closed, the disc 1, trunnions 2 and tensioning member 3 will act in unison to resist flexing of the disc 1 due to fluid pressure in the following manner: Uniform hydraulic pressure on the flat plate disc member will tend to induce bowing about axis X-X and corresponding deflection of the attached trunnions 2.The provision of the loadequalising member 3 by restraining deflection of the trunnions 2, provides a fixed end condition for the plate disc 1, thereby permitting the use of a much thinner plate member than is possible with the current state of the art, which is restricted to two solutions to the problem as follows:- (a) a solid lenticular blade, and (b) an eccentrically mounted thick plate.

The summated thickness of the disc 1 and loadequalising member 3 present a frontal area when open substantially less than that obtained in the present state of the art for equal loading.

In the foregoing description of the embodiment, it is assumed that the flow of fluid is towards the front, flat face of the disc. However, the arrangement as described is bi-directional, so that fluid flow could equally well be towards the rear face of the disc 1 on which the trunnions 2 are mounted. In this case it will be appreciated that the load-equalising member would act in compression (instead of tension as described above) to resist flexing of the disc 1.

The arrangement described above may be used over a large range of sizes for the valve member: however, to reduce any tendency for the loadequalising member 3 to flutter in larger applications, e.g. for valve members of 2' 0" upwards, preferably one, or more, stiffening member 9, which may be contoured to reduce pressure losses, is connected between the rear face of the disc 1 and the load-equalising member 3, as shown dotted in the Figures.

Claims

1. A valve member for a butterfly valve in the form of a sealing disc having opposed trunnions at or adjacent one face of the disc to provide an offset axis of rotation for said disc within the valve body, and a load-equalising tensioning member connecting the trunnions to provide, in combination with said disc, an anti-deformation arrangement which, in use, restricts flexing of said disc.

2. A valve member according to claim 1, designed for fluid flow which is towards that face of the disc opposite to said one face, wherein said load-equalising member is adapted to act in tension,

3. A valve member according to claim 1, or 2, wherein said load-equalising member is of fixed construction and in the form of a flat plate.

4. A valve member according to any one of claims 1 to 3, wherein the load-equalising member incorporates means for pre-loading.

5. A valve member according to any preceding claim, wherein said trunnions are in the form of a pair of spaced walls extending in the fluid flow direction which are profiled in cross-section to present minimum resistance to fluid flow with the valve member open.

6. A valve member according to claim 5, wherein the walls are shaped along their length to provide a converging/diverging passage therebetween to reduce the effect of pressure losses in fluid flowing therethrough.

7. A valve member according to any preceding claim, wherein at least one stiffening member is provided to connect said one face to an intermediate part of the load-equalising member.

8. A valve member constructed, arranged and adapted for use substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.

9. A butterfly valve incorporating a valve member according to any one of the preceding claims.