GB2037954A - Forged casing for a gate valve - Google Patents

Abstract

A forged casing for a gate valve comprises a top casing part 10, which, in the completed valve, receives the means for actuating the valve wedge, and, welded to part 10, a bottom casing part comprising two symmetrical half shells 1 and 2 welded together along a weld seam 3 in the plane of the gate spindle. The half shells have seating surfaces 4, 5, and spigots 8, 9, formed therein by forging. The weld seam 3 lies on the circumference of a circle about an axis of the valve. The half shells 1 and 2 have integral formations affording, in the finished valve, opposing surfaces between which gate-guiding grooves 12 are defined. The boundaries of the surfaces 6, 7 at the base of the grooves lie on circular arcs about the same axis as that about which is described the arc on which the weld seam 3 lies. <IMAGE>

Description

SPECIFICATION Forged casing for a gate valve The invention relates to a forged casing for a gate valve, comprising: a casing bottom part embodied by two symmetrical half-shells welded together in the plane of the gate spindle and having seating surfaces and spigots forged on their lower parts; and a casing top part which receives the means actuating and associated with the valve gate.

German utility model 1,706,081 discloses a fitting of this kind wherein the casing bottom part has a forged-on cover flange to which the corresponding casing top part is adapted to be secured. German patent specification 1,114,683 discloses a construction which is easier to weld i.e., easier so far as the use of welding machines is concerned. However, this construction is more a welded construction than a forged one. In neither construction is there any guiding of the valve gate.

A gate guide can be disposed only in the top part of the casing, in which event heavy forces act on the gate spindle; alternatively, the guide strips can be welded into the casing underpart subsequently, in which event inaccuracies are likely to occur and subsequent machining may be necessary.

It is the object of the invention to provide a forged casing construction in which the problem of guiding the valve gate within the casing bottom part is solved at reduced cost or compared with known construction.

According to the invention there is provided a forged casing for a gate valve, comprising a bottom casing part embodied by two symmetrical half-shells welded together along a weld seam in the plane of the gate spindle and having seating surfaces and spigots forged on their lower parts; and a casing top part which, in the completed valve, receives the means actuating and associated with the valve gate, wherein the casing bottom part is circular in shape near the weld seam interconnecting the half-shells and the boundaries of the gate-guiding groove or grooves are integral with the half-shells and are disposed on a circular surface whose centre coincides with the centre of the circular weld seam.

A gate valve casing embodying the invention has significant advantages. The parts of each shell providing the guide groove boundary surfaces can be forged together with the respective seating surface for the valve gate, and it is then possible to finish machine, on each shell, on a lathe, in a single clamp-up, the respective welding edge and the respective boundary surface of the or each guide groove. After the two casing shells have been welded together in a simple apparatus, the casing bottom part is internally complete and can then be welded to the casing top part.

Since the valve gate guide elements are disposed in the casing bottom part, there is very little loading of the gate and the forces arising can be diverted to the casing by the shortest possible path. Only the construction according to the invention provides these advantages, which are achieved without the use of additional facilities.

An embodiment of the invention is described below by way of example with reference to the accompanying drawings, in which: Figure 1 is a view in longitudinal section of part of a gate valve casing embodying the invention, Figure 2 is a view in horizontal axial section of the valve casing of Figure 1, and Figure 3 is a cross-sectional view of the casing of Figures 1 and 2.

Referring to Figure 1, a gate valve casing includes a casing bottom part comprising two similar shells 1 and 2. The two shells 1, 2 of the casing bottom part are joined together by means of a weld seam 3 extending in a circular arc around the bottom casing part. Each shell has finish machined gate seat surfaces 4, 5 (inclined with respect to one another, since the gate in question utilises a tapering or wedge--shaped valve gate) and finish machined boundary surfaces 6,7 defining, at each side of the casing, on opposite sides of the longitudinal axis thereof, a respective gate guide groove 12. Spigots 8, 9 for connection to piping are also present. Figure 1 also shows how a casing top part (shown in chain lines) is secured to the casing bottom part by means of a weld seam 11.

The horizontal section view of Figure 2 shows how the boundaries 6, 7 for the groove 12 and the peripheral circular seam 3 are disposed in staggered planes.

As can be gathered very clearly from Figure 3, the centre of curvature of the circular arc along which seam 3 extends coincides with the centre of the circle on which the boundaries 6, 7 of the groove 12 are disposed. This feature greatly simplifies production.

In the preferred embodiment, two distinct gate guide grooves 12 are provided within the casing bottom part, one on either side of the coincident longitudinal axis of the pipe spigots 8, 9, each said guide groove being defined between a respective planar surface 6 provided by a respective integral formation in the shell 1 and a respective planar surface 7 provided by a respective integral formation in the shell 2.

The two shells 1, 2, immediately prior to being welded together, have cooperating further surfaces which, over the zone of mutual interengagement of the two shells, exhibit circular symmetry about an axis upon which said centres lie and which locate the shells with respect to one another during welding of the shells together along weld seam 3, which, as indicated above, extends in a circular arc around said axis upon which said centres lie.

The two surfaces 6 in shell 1 are co-planar, as are the two surfaces 7 in shell 2, said planar surfaces being normal to the axis upon which said centres lie, which in the preferred embodiment is parallel with, but spaced from, the axis of the spigots 8, 9.

In respect of each of the shells 1, 2, a respective circle, having its centre on the lastmentioned axis, has a circumference parts of which correspond with circular arcs on which lie edges in which the respective surfaces 6, 7 terminate in their regions furthest from the lastmentioned axis terminate, said edges, in each shell 1,2, being formed at the meeting of the respective surfaces 6, 7, with respective grooves formed in the respective shell and having the form, in each shell, of parts of a respective annulus exhibiting circular symmetry about the last-mentioned axis.

Claims (4)

1. A forged casing for a gate valve, comprising a bottom casing part embodied with two symmetrical half-shelis welded together along a weld seam in the plane of the gate spindle and having seating surfaces and spigots forged on their lower parts; and a casing top part which, in the completed valve, receives the means actuating and associated with the valve gate, wherein the casing bottom part is circular in shape near the weld seam interconnecting the half-shells and the boundaries of the gate-guiding groove or grooves are integral with the half-shells and are disposed on a circular surface whose centre coincides with the centre of the circular weld seam.

2. A forged casing for a gate valve, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.

3. A gate valve incorporating a forged casing accordiny to claim 1 or claim 2.

4. A novel feature or combination of features disclosed herein.