GB2084296A - Improvements relating to flap valves - Google Patents

Abstract

A flap valve has a composite flap comprising a hinged gate (5) and a sealing disc (4) spring mounted on and guided by the gate. When closed the rim (19) of the disc seals against a matching part-spherical surface (17), on the interior of the valve body (1, 2), being urged there by spring bias. The disc is movable relative to the gate from outside the valve body (to unseat from the sealing surfaces (17)) by means of a linkage (6, 7, 10), one of whose elements passes co-axially through a journal (12) on which the gate hinges. A rotatable and axially movable shaft (15) couples independently to the journal and to the co-axial link (10) to govern the unseating of the disc and the rotation of the flap. <IMAGE>

Description

SPECIFICATION Improvements relating to flap valves The invention relates to flap valves. Such valves have a valve body and a hinged flap therein operable from outside the body to move between open and closed positions.

One known type of flap valve has a flap around whose edge there is an elastic seal which, in the closed position, is pressed against a fixed sealing face in the valve body. In some versions an eccentric disposition of the flap axis in relation to the pipe axis achieves a wedge-like clamping action of the sealing faces to improve the sealing effect. However, this is limited since it depends solely on the mechanical closing force with which the two sealing faces are pressed together. At high pressures or high temperatures, stress deformations or heat expansion in the body and in the flap assembly can impair the seal.

In another known flap valve a sealing ring fixed on the flap rim co-operates with an elastic, hollow sealing member on the valve body. In the closed position this sealing member is pressed against the sealing ring, either by being inflated by an outside pressure medium or by means of the pressure inherent in the medium sealed off within it. This type of flap valve is complicated, susceptible to breakdown and, as a result of the use of elastic materials, suitable only for limited pressures and temperatures.

In a further known flap valve there is again a sealing ring fixed on the flap rim, while a sealing ring in the valve body is movable, being urgeable by an outside pressure medium against the sealing ring on the flap rim. Generally, ring pistons or annular spring elements are used in such cases and are accommodated in the body of the valve.

Flap valves of this type require movable sealing elements for the body sealing ring, with accurately sized precision components whose functioning can be adversely affected by stress deformation and heat expansion at high pressures or at high temperatures. The scope of use of such flap valves is therefore limited.

The present aim is to provide a flap valve which is suitable for high temperatures and which is so constructed that a reliable sealing action is achieved at high pressures. The components of the flap valve should be largely insensitive both to stress deformation and also to heat expansion, while operation of the valve should be readily possible with no outside pressure media or other aids.

According to the present invention there is provided a flap valve having a valve body and a hinged flap therein operable from outside the body to move between open and closed positions, wherein the flap comprises a journalled gate and a rigid sealing member carried thereby for cooperating with an interior sealing surface of the valve body in the valve closed position, the sealing member being guided by and spring biased in relation to the gate so that it is urged into its sealing position, and wherein a linkage extends co-axially through one of the gate journals and is coupled to the sealing member whereby the sealing member can be moved relative to the gate from the exterior of the valve body.

Preferably the flap hinge axis extends centrally across the valve body. The sealing surface may be a section of a sphere centred on this axis, and the sealing member may be a disc whose rim cooperates with that sealing surface.

Conveniently the sealing member has a distributed array of parallel guide pins which enter apertures in the gate. These pins may have heads which co-operate with the gate to act as stops to the spring biased movement of the sealing member This spring bias may be provided by coil springs or stacks of spring plates or washers surrounding the pins.

Preferably, the linkage includes a bellcrank lever mounted on the gate with one arm hingedly coupled to the centre of the sealing member and with the other arm to a rod which extends through said one journal. Such a linkage will not materially restrict the passage through the valve when the flap is open.

Said one journal may form a connection between the gate and a co-axial shaft for rotating the gate. In this case, the shaft may be axially movable as well as rotatable and have a sliding dog coupling to said one journal and a pivotal connection to the linkage. Axial movement of the shaft will generate said relative movement of the sealing member.

A second sealing surface may be provided in the valve body, opposite the first one, and the flap will then be movable to bring the sealing member into co-operation with this second surface. Thus, the valve can work in the same way whatever the direction of the intended flow through it.

The linkage may be coupled to the sealing member through a spring loaded valve member which normally blocks a pressure compensating passage through said sealing member. Actuation of the linkage to unseat the sealing member will first move the valve member to open the passage and will then move the sealing member. Thus there is a restricted flow of fluid first tending to equalise the pressure, easing the task of unseating the flap against the fluid flow. Conveniently, with a disc shaped sealing member, the disc is the head of a mushroom-shaped member whose stem houses the compensating valve.

For a better understanding of the invention one embodiment will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is an axial section on the line I-I of Figure 2 through a flap valve in the closed position; Figure 2 is a cross-section through the flap valve on the line Il-li of Figure 1; Figure 3 is a cross-section on the line Ill-Ill of Figure 1, and Figure 4 is a sectional view of a pressure compensating valve in the area D of Figure 1, on an enlarged scale.

The flap valve has a main body 1 with an integrally formed, flanged projection for coupling to pipework at one end, on the left as seen in Figure 1. At the other end there is a separately formed flanged coupling piece 2 which is firmly secured and sealed to the valve body 1. A cap 3 on one side of the body 1 houses controls for the flap, which comprises a sealing disc 4 mounted on a pivoted gate 5. The disc 4 is the domed head of a mushroom-shaped member whose stem freely extends through an aperture in the centre of the gate 5 to be coupled by a hinged link 6 to one arm of a bellcrank lever 7. This is pivoted at 8 on the gate 5 and the end of its other arm has a pivotal connection 9 to the end of a rod 10 which extends laterally through the side of the valve body into the cap 3.The gate 5 hinges on journals 11 and 12, whose common axis extends centrally across the valve body. The journal 12 is centrally bored freely to receive the rod 10, and at its inner end it is keyed to the gate 5 and at its outer end to a dog 1 3. The latter couples to another dog 14 keyed to the end of a shaft 1 5 which extends through packing 1 6 to the exterior of the cap 3. The rod 10 is connected to the inner end of the shaft 1 5 so that as the shaft is moved axially (which is permitted by the engagement of the dogs 13 and 14) the bellcrank lever 7 is operated. When the shaft 1 5 is rotated, the entire flap pivots about the common axis of journals 11 and 12.

The interior of the valve body 1 has, at the root of the flanged coupling portion, a sealing surface 17 which is a section of a sphere centred on the meet of the flap hinge axis and the longitudinal axis of the body 1. A similar surface 1 8 is provided on the interior of the coupling piece 2. The disc 4 has an accurately formcd rim 1 9 with a matching part spherical surface which, in the position shown in Figure 1, seals against the surface 19 and which, if the flap is turned through 1800,will cooperate similarly with the surface 1 8. It is not always necessary to have a completely reversible valve, and only one such surface may be provided.

The disc 4 is urged away from the gate 5 and into sealing engagement with surface 1 7 or 1 8 by compression springs 20 which surround guide pins 21 evenly distributed around the axis of the disc. Three such pins are shown, but there could be more, and instead of coil spings there might be stacks of dished washers.

An alternative arrangement is shown in Figure 4, where the stem of the "mushroom" is hollow and houses a valve with a stepped stem 22 and a head 23, the stem being surrounded by a single coil spring under compression between the head and a cap 24 through which the narrower portion of the stem extends. The latter is coupled to the link 6. This will be referred to in more detail later.

Referring to the Figure 1 position of the flap, if the intended flow in the pipeline is from left to right, the valve is held closed by the springs 20, acting in opposition to the pressure of fluid over the face of the disc. At a predetermined level this pressure will prevail, and the rim 19 will become unseated as the disc is pressed back against the springs.

If the pressure is acting in the opposite direction with the intended flow from right to left, there will be more positive closure as the fluid will be aiding the springs. By providing the two sealing surfaces 17 and 18, one can always have the valve operating in this mode, whatever the intended direction of flow.

In order to open the valve, the shaft 1 5 is withdrawn a short distance, thus turning the bellcrank lever 7 to pull the disc 4 away from the sealing surface 17 and further compressing the springs 20. The shaft 1 5 is then rotated through 900, and axially released again to allow the springs to push the disc 4 away from the gate 5.

End stops on the pins 21 prevent excessive movement in this direction and keep the disc captive to the gate. Alternatively, the flap might be turned through 1 BOo, and upon axial return of the shaft 1 5 the disc will seal against the surface 18.

To close the valve or return it to the original position, the reverse movements are applied.

It will be seen that, in the closed position and with pressure acting on the concave side of the disc 4, effectively only that disc and the valve body 1 are loaded. All the other components, in particular the journals, the shaft 1 5 and the gate 5 remain unloaded. Furthermore, the shape of the disc 4 and of the valve body, and their cooperating sealing portions which are part spherical, all retain considerable stability of shape even at high pressures, and the sealing will not be materially affected by heat expansion or slight movement of the disc 4 relative to the valve body 1. The sealing effect and durability of the flap valve are restricted only by the strength of the body and the flange bolts. It is thus a construction which is particularly suited for valves in large pipelines operating at high pressures and temperatures.

However, in order to break the seal when the pressure is on the concave side of the disc, the linkage from the shaft 1 5 has to overcome both the springs 20 and the fluid pressure. It must therefore be constructed to cope with considerable forces; but if the pressure is excessive then there must be some means for reducing the differential between opposite sides of the disc 4 before attempting to open the valve.

Such pressure equalisation could be achieved by bypass lines and auxiliary valves, but a preferred solution is offered by Figure 4.

The valve head 23 of Figure 4 seats against a central aperture in the disc 4, and if withdrawn opens that aperture to an angled bleed passage leading from the concave side of the disc.

Operation of the shaft 15 to pull the link 6 unseats the valve head 23 and thus opens a duct between opposite sides of the disc 4. After a time, therefore, the differential pressure will reduce.

Further pulling movement on the link 6 will bring the shoulder of the valve stem 22 against the cap 24 and will unseat the disc 4. The full opening movement can then be carried out as described above.

Claims (14)

1. A flap valve having a valve body and a hinged flap therein operable from outside the body to move between open and closed positions, wherein the flap comprises a journalled gate and a rigid sealing member carried thereby for co-operating with an interior sealing surface of the valve body in the valve closed position, the sealing member being guided by and spring biased in relatiion to the gate so that it is urged into its sealing position, and wherein a linkage extends co-axially through one of the gate journals and is coupled to the sealing member whereby the sealing member can be moved relative to the gate from the exterior of the valve body.

2. A flap valve as claimed in Claim 1 , wherein the flap hinge axis extends centrally across the valve body.

3. A flap valve as claimed in Claim 2, wherein the sealing surface is a section of a sphere centred on the flap hinge axis and the sealing member is a disc whose rim co-operates with the sealing surface.

4. A flap valve as claimed in Claim 1, 2 or 3, wherein the sealing member has a distributed array of parallel guide pins which enter apertures in the gate.

5. A flap valve as claimed in Claim 4, wherein the pins have heads which co-operafe with the gate to act as stops to the spring biased movement of the sealing member.

6. A flap valve as claimed in Claim 4 or 5, wherein the spring bias is provided by springs surrounding said pins.

7. A flap valve as claimed in Claim 4 or 5, wherein the spring bias is provided by stacks of spring plates or washers surrounding said pins.

8. A flap valve as claimed in any preceding claim, wherein the linkage includes a bellcrank lever mounted on the gate with one arm hingedly coupled to the centre of the sealing member and with the other arm to a rod which extends through said one journal.

9. A flap valve as claimed in any preceding claim, wherein said one journal forms a connection between the gate and a co-axial shaft for rotating the gate.

10. A flap valve as claimed in Claim 9, wherein the shaft is axially movable as weli as rotatable and has a sliding dog coupling to said one journal and a pivotal connection to said linkage, axial movement of the shaft generating said relative movement of the sealing member.

11. A flap valve as claimed in any preceding claim, wherein a second sealing surface is provided in the valve body, opposite the first one, and the flap is movable to bring the sealing member into co-operation with this second surface.

12. A flap valve as claimed in any preceding claim, wherein the linkage is coupled to the sealing member through a spring-loaded valve member which normally blocks a pressure compensating passage through said sealing member, actuation of the linkage to unseat the sealing member first moving the valve member to open said passage and then moving the sealing member.

13. A flap valve as claimed in Claim 12 as appendant to Claim 3, wherein the disc is the head of a mushroom shaped member whose stem houses the valve member.

14. A flap valve substantially as hereinbefore described with reference to Figures 1 to 3 or those Figures as modified by Figure 4 of the accompanying drawings.