GB2170886A

GB2170886A - Butterfly valves

Info

Publication number: GB2170886A
Application number: GB08603360A
Authority: GB
Inventors: Edward Sagar Fort
Original assignee: Fort Valve Engineering Ltd
Current assignee: Fort Valve Engineering Ltd
Priority date: 1985-02-12
Filing date: 1986-02-11
Publication date: 1986-08-13
Also published as: DE3603998A1; GB8603360D0; FR2577295A1; JPS61189369A; FR2577295B1; GB8503504D0

Abstract

A butterfly valve comprises a housing (1), an annular valve seat (7) within the housing (1), and a flap member (25) which comprises an annular valve face (27) and is pivotally mounted within the housing (1) so as to be pivotable in use, between a first position in which the valve is open and a second position in which the annular valve face (27) co-operates with the annular valve seat (7) and the valve is closed, wherein at least that portion of the flap member (25) which lies within the annular valve seat (7) defines a spherical segment. The pivot axis (15) is offset both from the plane of the annular valve face (27) and from the centre of the flap member (25). <IMAGE>

Description

SPECIFICATION Improvements in and relating to butterfly valves The present invention relates to a butterfly valve.

A known butterfly valve comprises a flap member which is secured to a spindle and which is journalled in a housing for pivotal movement between open and closed positions. The flap member takes the form of a circular plate whose outer edge or an area adjacent thereto, forms an annular valve face which is co-operable with an annular valve seat in the housing. The plane of the plate is usually off-set from the axis of the spindle.

The advantage of such a valve is that it is axially compact and the plate being relatively thin offers only a relatively smail flow restriction. It is also less expensive to manufacture than other types of valve, for example a ball valve.

The traditional application of butterfly valves is in process plant where the low flow restriction is of importance. Their short axial length has led to their use in the field of container tanks where space restrictions are severe. The present invention is primarilly intended for use on a container tank. The discharge orifices of such tanks are frequently provided with two valves in series and a butterfly valve is frequently placed downstream of say a main foot operated valve.

When such container tanks are used to hold congealing cargoes, the butterfly valve is prone to becoming jammed closed by cargo which has become trapped between the two valves and has congealed-usually as a result of cooling. The operator is apt to try and force open the butterfly valve by applying a load in excess of that which the valve can withstand. Frequently, this results in the handle or the spindle or both becoming bent or twisted to such a degree that the valve becomes inoperable.

If the two valves were operated in the correct sequence the problem should not occur, but in practice, the butterfly valve may be closed before the main valve. As a result, if the tank has not been completely emptied, a pocket of liquid is trapped between the two valves and as it cools it becomes very hard.

The tank itself can be heated to liquify the contents for discharge, but such heating is not applied to the discharge valves. Thus, when a further discharge is required the solid slug of material up to the flap of the butterfly valve prevents the flap from being pivoted in an opening direction.

The present invention aims to overcome the problem of jamming of butterfly valves by congealed cargoes and thereby avoid damage to the valves.

According to the present invention there is provided a butterfly valve comprising a flap member secured to a spindle and journalled in a housing for pivotal movement in an opening and closing direction upon rotation of the spindle and having a valve face which is cooperable with a valve seat in the housing when the flap member is in its closed position, and wherein the flap member is in the form of a spherical segment.

Preferably, the valve face is formed on the surface of the spherical segment. The plane of the annular valve face is off-set from the axis of the spindle. For this purpose the spherical segment carries a first mounting bracket for engaging with the actuating spindle, and a second mounting bracket for co-operating engagement with a pivot pin disposed coaxially with the spindle. Thus, on opening of the valve, the valve face of the flap member lies off-set from the central axis of the discharge orifice and whilst the flap member according to the invention reduces the discharge area by approximately 25% by comparison with the size of conventional butterfly valve, this is not detrimental in the majority of container tank applications. Of course, a larger diameter valve may be provided to compensate for the loss of discharge area caused by the spherical segment.

It will be appreciated that the spherical segment does not prevent the slug from forming but ensures that the shape of the slug is such that it will not prevent the valve from opening.

Thus, the radius of the spherical segment is at least as large as half the maximum diameter of the flap member as measured in the plane of the valve face. To provide a further improvement, and so avoid the outer edge of the flap member wiping the entire surface of the slug during the opening movement the axis of symmetry of the flap member is offset from the axis of the spindle by a small amount. Thus, on opening of the valve, the edge of the flap member describes an arc which moves further away from the surface of the congealed cargo. For example, considering the spindle to be vertical it is off-set transversely from the vertical axis of symmetry of the valve member by for example 1/16 inch or 2 mm.

The present invention will now be described further hereinafter, by way of example only, with reference to the accompanying drawings; in which: Figure 1 is a cross-sectional side elevation of the valve in accordance with the present invention; and Figure 2 is an end elevation of the valve of Figure 1 looking in the direction of arrow 2, the right hand side showing the open position of the closure member.

Referring to the drawings of Figures 1 and 2 there is shown a butterfly valve according to the present invention. The assembly comprises a housing 1 which is essentially annular having an internal bore 5 and three equispaced counter bored holes 3. The assembly has an annular valve seat 7 which in the illustrated embodiment is a separate component and is held in position by an annular locating plate 9. The locating plate 9 is secured in position by two self-locking pins 11 received in the bores 3. The arrangement permits the use of an appropriate material for the valve seat. The housing has a tubular projection 13 which receives a spindle 15. The spindle passes through a bore in the wall of the annular member and has a splined end 17. The axis of the spindle is parallel to but off-set from the diameter of the internal bore 5.The spindle is provided with seals 19,21 to prevent leakage of fluid from within the housing by way of the spindle. Located opposite to the spindle and coaxial therewith is a pivot pin 23 which is received screw threadingly in a bore in the housing. The pivot pin is likewise sealed to prevent leakage.

A flap member 25 is provided to act as a valve closure member, which in the closed position co-operates with the annular valve seat 7. The flap member is in the form of a spherical segment and has an annular valve face 27 formed on or by the spherical surface thereof.

Projecting from the flap member 25 are two mounting brackets 29,31. Conveniently, these are welded to the spherical segment. The bracket 29 has a splined bore to receive the splined end 17 of the spindle 15, whilst the bracket 31 has a bore receiving a bearing bush 33 which in turn is received on the end of the pivot pin 23. Thus, the flap member is journalled for rotation on the pivot pin 23 and is moved by rotation of the spindle 15. A handle 35 is received on an opposite splined end of the spindle 15.

The tubular projection 13 has an end flange 37 to which is bolted a closure plate 39. The closure plate has two detents therein disposed 90 apart and which serve as location points for a spring loaded plunger 41 carried by the handle 35. Thus, the valve is located in the open and closed positions and can only be moved from one to the other by first releasing the plunger 41.

The radius S of the spherical segment is at least as large as the radius D of the flap member at its maximum diameter in the plane of the annular valve face. Furthermore, the axis of the spindle 1 5 about which the flap member is pivotable is off-set by an amount X from the centre of the valve member. The valve member is itself concentric with the internal bore 5. Thus, on opening, the edge 43 only wipes the slug for a short distance since the flap then moves away from the hard slug.

In practice an off-set of the order of 1/16 inch or 2 mm is sufficient.

The part spherical shape on the upstream side of the flap member 25 ensures that if any slug of solid material is formed, it will not prevent the valve from opening and therefore the possibility of damage being done to the valve on opening by this obstruction is eliminated. Furthermore, although discharge cannot take place, the open valve allows access for a steam line to act directly on the solid slug to effect the melting of it. The position of the valve member when in its open position is indicated by the shaded portion in Figure 2.

The valve housing is conveniently positioned downstream of a main valve in the discharge line. The illustrated embodiement does not have any mounting flanges and is intended to be clamped in position between the mounting flanges of an upstream and downstream component. By this means the axial length can be kept to the minimum.

Claims

1. A butterfly valve comprising a housing, an annular valve seat within the housing, and a flap member which comprises an annular valve face and is pivotally mounted within the housing so as to be pivotable in use, between a first position in which the valve is open and a second position in which the annular valve face cooperates with the annular valve seat and the valve is closed, wherein at least that portion of the flap member which lies within the annular valve seat defines a spherical segment.

2. A butterfly valve according to claim 1, wherein the annular valve face is formed by a portion of the surface of said spherical segment.

3. A butterfly valve according to claim 1 or 2, wherein the plane of the annular valve face is offset from the axis of rotation about which the flap member is pivotable between said first and second positions.

4. A butterfly valve according to claim 3, wherein the flap member comprises first and second mounting means which engage respectively, with a valve actuating spindle and a pivot pin disposed co-axially with the valve actuating spindle.

5. A butterfly valve according to any preceding claim, wherein the radius of a sphere defined by said spherical segment is at least as large as the radius of the flap member at its maximum in the plane of the annular valve seat.

6. A butterfly valve according to any preceding claim, wherein the axis of rotation about which the flap member is pivotable between said first and second positions is offset by a predetermined amount from the centre of the flap member.

7. A butterfly valve according to any preceding claim, wherein releasable securing means are provided to prevent the flap member from being moved between said first and second positions unless the releasable securing means is first released.

8. A butterfly valve substantially as herein before described with reference to the accompanying drawings.