GB2222869A

GB2222869A - Butterfly valve seat

Info

Publication number: GB2222869A
Application number: GB8918227A
Authority: GB
Inventors: David Beauchamp
Original assignee: HATTERSLEY HEATON Ltd
Current assignee: HATTERSLEY HEATON Ltd
Priority date: 1988-08-19
Filing date: 1989-08-09
Publication date: 1990-03-21
Also published as: GB8819741D0; GB8918227D0

Abstract

A butterfly valve seat comprises a metal element 7 and a P.T.F.E. element 8. Element 8 provides primary sealing and element 7 secondary sealing in the event of breakdown of the primary seal. Element 7 has a profile comprising a radial flange 7a, by which the element is locked into the valve, a seating cusp 7c, a supporting cusp 7d and a convolution 7b which mates with the P.T.F.E. seat 8 to lock it in position and which supports and energises that seal. <IMAGE>

Description

SEAT FOR A BUTTERFLY VALVE The present invention relates to a seat for a butterfly valve.

Such seats are disposed between the disc form valve member and the valve body and there are already very many well known examples.

According to the present invention, there is provided a valve seat for a butterfly valve which may comprise any novel combination of the following features: (a) The seat is made of metal.

(b) It extends from either the valve body or the valve closure member disc.

(c) It comprises an outer portion extending radially of the disc.

(d) It comprises a convolution connected to the radially extending portion.

(e) It comprises a seating cusp connected to the convolution.

(f) It comprises a supporting cusp connected to the seating cusp.

(g) The metal is Inconel (h) The seat is made of a polymer, for example, a fluoroplastic such as P.T.F.E.

(i) The seat comprises an anchoring portion, a neck portion and a seating nose.

(j) The seat comprises both metal and polymeric sections which are contiguous with each other along one face.

According to the present invention there is provided a seat for a butterfly valve comprising a metal element and a synthetic plastics material element formed to be in contact along a portion of their external surface, the metal element having a flange enabling it to be connected to the valve body or valve disc, a convolution for flexibility, a seating cusp adapted for sealing contact with the valve disc or valve body and a supporting cusp adapted to provide support for the seat on the valve body or valve disc under certain loading conditions of the valve disc.

In order that the invention may be more clearly understood, one embodiment thereof will now be described by way of example, with reference to the single figure of the accompanying drawing which shows a sectional view through part of a butterfly valve.

The valve comprises a valve body 1 defining a valve bore 2 in which a disc form valve closure member 3 is rotatably disposed. A valve seat is disposed in the valve body 1 between the body and the closure member 3 and is locked in position by means of a seat retainer 4 connected to the valve body 1 by screws 5. Sealing gaskets 6 are disposed between the retainer 4 and valve body 1. The valve seat is of complex design and construction. The design is primarily a combination seat with one element 7 in metal and a second element 8 in a polymeric material. The polymeric material provides primary sealing and the metal secondary sealing in the event of break down of the primary seal due to excess temperature, abrasion etc. Each element may be used independently with minor modification to seat retainer and/or body machining.

The metal seat profile can be broken down into four distinct geometric sections, each having identifed functions; viz a radial flange 7a, a radial arm with convolution 7b, a seating cusp 7c and a supporting cusp 7d.

The functions of these parts are as follows: Radial Flange This section is radial to the valve bore 2 and extends from the outer diameter of the seat to the commencement of the radial convolution. It provides a flat surface sandwiched betwen seat retainer 4 and body 1 through which a suitable number of the retention screws 5 pass, thereby anchoring the seat 7 to the body 1. The gaskets 6 fitting in recesses in seat retainer 4 and body 1 can be clamped either side of the seat 7 to prevent leakage to atmosphere. This radial flange, when assembled in the valve, also contributes to the clamping for the polymeric seat 8 and in so doing completes the anchoring chamber for this seat.

Radial Arm with Convolution This section commences at the onset of curvature immediately in board of the radial flange 7a and is generally radial with a single convolution extending away from the seat retainer 4.

This single convolution 7b has several critical functions:a) It provides support and flexible energisation to the polymer seat 8 whose profile accurately mates with this surface. (The polymer would normally be fluoroplastic such as P.T.F.E. which has limited memory and creep resistance. The metal seat, of the profile described, when produced in material such as Inconel 718, will be capable of support and energisation to the polymer- over the full rated pressure/temperature service conditions of the valve).

b) It mechanically locks the polymer seat 8 in position.

c) It creates a point of flexure offset from the radial arm 7a, thereby increasing the responsiveness of the seat.

Seating Cusp The seating cusp 7c is formed at the apex of a generally convex surface, generated from a centre of curvature normal to the spherical seating surface on the periphery of the disc closure member 3. This convex surface commences at the inner termination of the radial arm.

When the disc member 3 is moved to the closed position its seating periphery will therefore contact the seating cusp tangentially and interference between the two seating surfaces gives optimum sealing and valve turning effort characteristics.

Supporting Cusp The support cusp 7d is formed at the apex of a geneally convex surface generated from a centre of curvature generally normal to the seat retainer ramp angle (indicated by reference 9) and hence of opposite curvature to the seating cusp previously described. This ramp 9 on the seat retainer 4 making an angle of apporiximately 150 with a tangent drawn to the spherical seating surface of the disc 3 at its point of contact with the metal seat 7 when the disc 3 is in the closed position.

In its free state the support cusp 7d will not contact the seat retainer ramp angle 9 but as increasing seating load is generated by closure of the disc 3, the support cusp 7d will be forced into contact with the ramp angle 9 thereby increasing the stiffness of the seat 7 and hence the sealing force. Further closure load will result in the support cusp travelling up the seat retainer ramp 9 thereby maintaining sealing force.

Soft Seat Description The soft seat 8 is produced in polymer material and is an annular ring held in a generally square sectioned recess 10 created in the body and clamped into said recess by the metal seat 7.

One radial surface of the polymeric seat 8 accurately corresponds to the mating surface of the metal seat 7 whilst the other radial surface is flat for its outer half whence a reduction in section to form an inner seating nose 8a is brought about by a bevel surface. This bevel surface being opposite the recess formed by the convolution on the other surface thereby creating a neck 8b effectively dividing the seat into an outer anchoring portion Sc and an inner sealing portion 8a. The neck 8b being of reduced section allows flexing of the seating nose to occur under the influence of closure forces and/or line pressure.

The inner bore of the seat is of convex form dimensioned to interfere with the spherical seating periphery of the disc 3 when it is in the closed position.

Mode of Operation a) Pressure applied to seat retainer side of valve will cause any disc 3 deflection to be in an axial direction away from the seat retainer thereby tending to reduce interference between the seating elements 7 and 8 and the seating periphery of the disc 3. The design of seating elements 7 and 8 must therefore be capable of axial deflection to compensate for this potential disc movement. Fluid will first encounter the metal seat 7 and will apply axial forces to the radial arm with convolution 7b which will increase sealing force between seating cusp 7c and disc spherical periphery. Axial deflection of the radial arm 7b will also bring about deflection of the soft seat 8 due to the intimate contact existing between the two seating components.This deflection of the soft seat 8 will cause the seating nose Ba to pivot about the neck section 8b thereby increasing interference with the disc spherical surface. It can therefore be seen that with pressure applied in this direction both metal and soft seats operate in a pressure energized mode. An increase in pressure will therefore bring about an increase in sealing force on both seats.

b) Pressure applied from body side of valve (that is shaft side of disc 3) will cause any disc deflection to be in a generally axial direction moving towards the seat retainer 4 and thereby increasing interference between disc spherical periphery and the two seating elements 7 and 8.

Pressure will also act upon the primary soft seat 8 which in this case is supported by and energised by the metal seat 7. The metal seat will impart resilience and energisation to the soft seat 8 enabling it to effectively tolerate both temperature and pressure transients. In the event of failure or desctruction of the soft seat 8, pressure will then act directly upon the metal seat 7 moving it in an axial direction, that is the radial arm with convolution approaches the seat retainer. At the same time the support cusp 7d will move up the seat retainer ramp angle and the sealing force between the seating cusp 7c and spherical seating periphery of disc 3 will be maintained.

It will be appreciated that the above embodiment has been described by way of example only and that many variations are possible without departing from the invention.

Claims

1. A seat for a butterfly valve comprising a metal element and a synthetic plastics material element formed to be in contact along a portion of their external surface, the metal element having a flange enabling it to be connected to the valve body or valve disc, a convolution for flexibility, a seating cusp adapted for sealing contact with the valve disc or valve body and a supporting cusp adapted to provide support for the seat on the valve body or valve disc under certain loading conditions of the valve disc.

2. A seat as claimed in claim 1, in which the metal element is made of Inconel

3. A seat as claimed in claim 1 or 2, in which the synthetic plastics material element is made of a polymer.

4. A seat as claimed in claim 3, in which the polymer is a fluoroplastic.

5. A seat as claimed in claim 4, in which the fluoroplastic is polytetrafluoroethylene (P.T.F.E.).

6. A seat as claimed in any preceding claim, in which the seating and supporting cusps are adjacent each other.

7. A seat as claimed in any preceding claim, in which the synthetic plastics material element provides a seating nose.

8. A seat as claimed in claim 7, in which the synthetic plastics material element is formed with a neck about which the nose may pivot.

9. A seat for a butterfly valve substantially as hereinbefore described with reference to the accompanying drawings.

10. A butterfly valve comprising a valve seat as claimed in any preceding claim.

11. A butterfly valve as claimed in claim 10, in which the flange of the metal element extends radially of the disc of the valve and is clamped between the body of the valve and a seat retainer.

12. A butterfly valve as claimed in claim 10 or 11, in which the synthetic plastics material element comprises an anchoring portion which is held between the metal seat and the body of the valve.