GB2215813A - Valves - Google Patents

Abstract

A solid seat element for a ball valve is formed between a seat face and a backing zone (8, 9 respectively) with an annular relief zone (10) such as to permit at least some localised toroidal bending of the seat element to compensate for minor asymmetry of the ball (1) and/or its rotation. <IMAGE>

Description

Improvements in and relating to valves This invention relates to fluid valves and in particular to ball valves in which the active element is a ball having a passageway therethrough. In use, the ball is 0 turned through 90 to progressively occlude, or open the passageway. Fluid sealing around the ball is usually effected by providing annular seals against which the ball seats. These seals are often biassed against the valve, by fluid pressure or spring pressure, or by both.

As the ball may not be perfectly spherical, and/or it may not rotate about its true axis, it is essential for a leak-free seal to provide valve seats having at least a degree of resilience/conformability. This is often accomplished by making the seat from composite plastics or elastomeric materials. However, such materials are not acceptable for use in certain environments, for example where the fluid passing through the valve is corrosive, abrasive or otherwise aggressive. In such circumstances it is usual to fit a solid seat, in the form of a machined annulus of metal. Whilst this may solve the immediate problem, it rarely leads to a satisfactory seal, due to the factors mentioned earlier, even where spring and/or fluid pressure biassing forces are applied to hold the seat against the ball.

According to the present invention an annular solid valve seat element has a seat face zone and a backing zone remote from the seat face zone, and an annular relief zone intermediate said zones such as to permit at least some localised toroidal bending of the seat element in the vicinity of the relief zone.

Preferably the localised toroidal bending is sufficient to allow the seat face zone to conform to the local surface parameters of a valve ball against which it is, in use, to seal.

Preferably the annular relief zone is in the form of a U-shaped notch; this may be formed internally of the seat element or externally, or both. The latter is preferred in order to enable the desired localised toroidal bending to relect distortion in more than one direction (referred to the cross section of the seat element.) Other notch profiles may be employed; multiple relief zones may be provided to confer added localised conformability and/or resilience. It will be appreciated that there is considerable scope for choice of relief zone profile without departing from the principle of the invention.

In order that the latter be better understood, preferred embodiments of it will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic view (in section) illustrating a conventional solid seat in place against a valve ball, Figure 2 is a similar view, but this time showing a valve seat element according to the invention, Figure 3 is an enlargement of the circled part of -Figure 2, and Figures 4a,4b illustrate variations on the relief zone profile shown in Figures 2 and 3. Like parts bear like reference numerals in all four figures.

In Figure 1, a valve ball 1 has a central fluid passageway 2. An annular solid metal valve seat 3 is held with its seat face zone 8 against the face of the ball by springs 4, the latter acting against a seat backing zone 9. In operation, the ball is rotated about axis A-A to present the passageway 2 to a pipeline (not shown in detail but designated 5). The springs 4 are carried in a recess 6 in the main body of the valve, only a very small part of which is shown, designated 7.

It will be readily apparent that in the event of the axis A-A being only slightly out of alignment, or the ball being only slightly out-of-round, it will not be possible to achieve the substantially leak-free seal which is required in any applications. The machined seat face zone 8 of the solid seat element will simply not sit cleanly against the ball surface.

In Figures 2 and 3, the seat face zone 8 and the backing zone 9 are connected by an annular relief zone 10 in the form of a U-shaped notch machined into the annulus from its radially-inward facing surface 11. Referring now to Figure 3, the annular relief zone serves to permit localised toroidal bending of the seat element about an axis normal to the plane of the figures. This is shown (in exaggerated form) in Figure 3, simply for purposes of illustration. In practice, only a small amount of toroidal bending is needed to achieve proper sealing engagement of the seat face zone 8 against the ball 1.

More significantly, the anount of bending needed can reflect the precise, localised distortion which is to be compensated, since in practical terms, the errors will necessarily be very small if the valve is to be commercially-useful/acceptable.

Figure 4a shows a U-shaped notch 12 machined from the radially-outward facing surface 13 of the seat element.

In this configuration, the toroidal bending will be most easily effected in the opposite direction to that of Figure 3. Figure 4b illustrates an embodiment combining the features of Figures 3 and 4a. In this case two, generally oppositely-directed notches 10,12 are provided, for increased conformability. It will be appreciated that the exact notch profile and/or number of notches is a matter of choice according to circumstances such as fluid pressure, seat element material properties and the like.

Claims (7)

1. An annular solid valve seat element for a ball valve, the element having a seat face zone and a backing zone remote from said seat face zone, and an annular relief zone intermediate said zones such as to permit at least some localised torodial bending of the seat element in the vicinity of the relief zone.

2. A seat element according to Claim 1 wherein said toroidal bending is sufficient to allow the seat face zone to conform to the local surface parameters of a ball valve against which it is, in use, to seal.

3. A seat element according to Claim 1 or 2 in which the annular relief zone is constituted by a notch formed internally or externally of the seat element annulus, or both.

4. A seat element according to any preceding claim provided with a plurality of notches.

5. A seat element according to Claim 3 or Claim 4 wherein the notch or notches are generally U-shaped.

6. A ball valve provided with an annular solid valve seat element according to any preceding claim, or as illustrated by Figures 2-4 of the accompanying drawings.

7. A valve seat element substantially as described with reference to and illustrated by Figures 2-4-of the accompanying figures.