GB2181820A - Butterfly valves - Google Patents

Abstract

In a butterfly valve in which the valve disc (6) is secured to a unitary operating shaft (10), in order to minimize the machining required to centralise the disc in the fluid flow channel, the axial position of the shaft is set by a retaining pin (18) which engages tangentially in an annular groove (21) provided in the shaft. The retaining pin is housed in a stepped through-bore (20) which is sealed at one end by a gasket (25) for a seal retaining ring (8) and at it other end, in use, by a pipe flange gasket. <IMAGE>

Description

SPECIFICATION Bufterfly valves This invention relates to butterfly valves of the kind comprising a housing, a circular fluid flow channel in the housing, a circular disc mounted in the channel on an operating shaft for rotation with the shaft between an open position in which the disc lies substantially parallel to the channel axis and a closed position in which the periphery of the disc sealingly engages with a sealing surface which encircles the channel. Such a valve will hereinafter be referred to as a 'valve of the kind set forth'.

With a valve of the kind set forth it is desirable to ensure that the disc does not move relative to the housing in the axial direction of the operating shaft, to keep the disc and sealing surface substantially concentric, and thereby assist in maintaining an effective sealing engagement between the disc and the housing sealing surface.

The axial movement can be limited by thrust washers which are located on the shaft between respective machined surfaces on the disc and on the housing, at diametrically opposite sides of the disc. However, this arrangement involves costly machining of two surfaces on the valve disc and two surfaces on the valve housing.

According to the invention in a butterfly valve of the kind set forth, the operating shaft extends across the channel and is journalled in the housing on opposite sides of the channel, and the shaft is held against axial movement relative to the housing by a retaining member which engages with a circumferentially extending cutout in the shaft, the retaining member being located in the housing against movement relative thereto in the axial direction of the shaft.

The cutout is preferably an annular groove in the shaft, which can be machined relatively cheaply.

The retaining member is preferably a pin, and the pin is preferably arranged to extend in a substantially tangential direction of the shaft.

When the pin extends tangentially of the shaft the cutout in the shaft is preferably deeper than the radius of the pin, and the walls of the cutout which resist the axial forces on the shaft by engagement with the pin are preferably substantially parallel walls extending in planes normal to the axis of the shaft, so as to avoid a wedging engagement with the pin.

The retaining member is preferably housed in a bore of the housing of which one end lies in a face of the housing against which a seal retaining ring for a seal assembly carried by the housing is clamped in use, the seal retaining ring thereby preventing in use the retaining member from leaving said bore through said open end of the bore. Also, this arrangement can enable a gasket provided primarily for sealing the retaining ring to the housing to seal the end of the bore.

When the retaining member is a tangentially extending pin, the bore for the pin may be a stepped through-bore, the step providing an abutment for the inner end of the pin, and the smaller diameter part of the bore permitting a pin removal tool to be inserted therein.

On rare occasions it is possible for a valve shaft to break, under abnormal torsional load conditions. In order to minimise the risk of a broken shaft end being ejected from the housing under high fluid pressure forces, we prefer to arrange the design such that the shaft will break, if at all, at a location inboard of the retaining member, the retaining member cooperating with that end portion of the shaft which is closer to the valve actuator in use to prevent that end portion from being ejected.

This can be arranged, for example, by ensuring that the cross-sectional area of the shaft where the disc is secured by a pin to the shaft is less than that of the shaft at the retaining member. The opposite end portion of the shaft is preferably journalled in a blind bore in the housing.

A butterfly valve is accordance with the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is an end view of the valve, looking from the right in Fig. 2, the right hand half being sectioned vertically on the line 1-1; Figure 2 is a side elevation of the valve, with the lower half of the housing sectioned on the line 2-2 of Fig. 1; Figure 3 is a section on the line 3-3 of Fig.

1 on a larger scale; and Figure 4 is a section on the line 4-4 of Fig.

3 but of a modification.

With reference to Figs. 1 and 2, the butterfly valve comprises an annular valve housing 1 with integral bosses 2, 3, a unitary operating shaft 4 to which is secured by a pair of pins 5 a valve disc 6, and an annular seal assembly 7 clamped against the valve housing by a retaining ring 8. The seal assembly 7 encircles the circular fluid flow channel 8 through the housing 1 and co-operates in known manner with the part-spherical peripheral surface 9 of the disc 6.

The unitary operating shaft 4 extends across the channel 8, with its axis offset slightly, in well known manner, from a vertical diameter of the channel. The upper end portion of the shaft 1 as viewed in Figs. 1 and 2, is journalled in a through-bore 10 which extends through the upper boss 3, and the upper extremity 11 of the shaft projects from the housing for connection in use to a handle or suitable actuator mounted on housing lugs 12. The shaft bore 10 is sealed at its upper end by a suitable packing in a stuffing box 13. At its lower end 15 the shaft is journalled in a blind bore 14 in lower boss 2.

In order to obtain an effective sealing action between the disc 6 and seal assembly 7 the disc in its closed position should be positioned concentric to the seal assembly 7, and in conventional valves employing a unitary shaft it is the practice to machine accurately the upper end and lower surfaces 16 of the disc structure, and the adjacent surfaces 17 of the housing, thrust washers of appropriate thickness being positioned between the surfaces 16 and 17 in such a valve to centralise the disc. In the illustrated valve, on the other hand, the disc is centralised in the axial direction of the shaft by a retaining pin 18 which, as shown in Fig. 3, is fitted in the larger diameter portion 19 of a stepped through-bore 20 in the housing, the bore 20 conveniently extending parallel to the axis of the fluid flow channel.The pin 18 engages tangentially in an annular recess 21 in the upper portion of the shaft, sufficient clearance being provided to permit the shaft 11 to turn freely with respect to the housing 1.

In the embodiment of Fig. 3 the cross-sectional shape of the recess 21 is part-spherical corresponding to the shape of the pin 18, but in Fig. 4 a modification is shown in which the equivalent recess 21' has parallel upper and lower walls 22 which extend in planes transverse to the axis of shaft 10, the base 23 of the recess being semi-circular in crosssection. The modified shape of the recess 21' enables the axis of pin 18 to be positioned inboard of the outer surface 24 of the shaft 11 so that the pin 18 is engageable only with the transverse walls 22 to restrict movement of the shaft. This avoids any wedging action between the shaft 11 and pin 18 which might otherwise produce resistance to turning of the shaft.

The bore 20 for the retaining pin 18 at its larger diameter end breaks into the end face 25 against which the root of the seal assembly 7 is held by retaining ring 8. An annular gasket 26 which is provided primarily to seal the radially outer part of the seal assembly 7 to the housing covers the open end of bore portion 19 and thereby seals that end of the bore 20 from atmosphere. This is important since, as will be appreciated, the pin bore 20 is inboard of the stuffing box 13.

The smaller diameter portion 27 of bore 20 breaks at its outer end into the annular face 28 against which in use a pipe flange gasket is clamped to seal the valve housing 1 to an adjacent pipe end. It is preferred that the bore 20 be made a through-bore to enable the pin 18 to be removed if required by insertion of an appropriate tool into the smaller bore portion 27. The dimensions of the retaining pin 18 are chosen such that the pin is a tight fit in bore portion 19 and abuts at its inner end with the shoulder 29, defined between bore portions 19 and 27, when its outer end is flush with face.

It will be appreciated that the valve described requires very little machining, only the provision of recess 21 and pin bore 20, to achieve correct positioning of the valve disc, compared with the machining previously required.

It is desirable to try to ensure that in the unlikely event of the shaft 10 breaking, the broken shaft end is not propelled out of the housing by fluid pressure forces. Since the lower end 15 is in a blind bore 14 there is no difficulty with that end. By arranging that the weakest portion of the shaft 10 is inboard of the recess 21 it is ensured that no portion of the shaft can be forced out of the housing in the event of shaft breakage.

Claims (9)

1. A butterfly valve of the kind set forth, in which the operating shaft extends across the channel and is journalled in the housing on opposite sides of the channel, and the shaft is held against axial movement relative to the housing by a retaining member which engages with a circumferentially extending cutout in the shaft, the retaining member being located in the housing against movement relative thereto in the axial direction of the shaft.

2. A valve as claimed in Claim 1 in which the cutout is an annular groove in the shaft.

3. A valve as claimed in Claim 1 or Claim 2 in which the retaining member is a pin.

4. A valve as claimed in Claim 3 in which the pin extends in a substantially tangential direction of the shaft.

5. A valve as claimed in Claim 4 in which the cutout in the shaft is deeper than the radius of the pin, and the walls of the cutout which resist the axial forces on the shaft by engagement with the pin are substantially parallel walls extending in planes normal to the axis of the shaft.

6. A valve as claimed in any of Claims 3 to 5 in which the bore for the pin is a stepped through-bore, the step providing an abutment for the inner end of the pin, and the smaller diameter part of the bore permitting a pin removal tool to be inserted therein.

7. A valve as claimed in any of the preceding claims in which the retaining member is housed in a bore of the housing of which one end lies in a face of the housing against which a seal retaining ring for a seal assembly carried by the housing is clamped in use, the seal retaining ring thereby preventing in use the retaining member from leaving said bore through said open end of the bore.

8. A butterfly valve substantially as described with reference to Figs. 1 to 3 of the accompanying drawings.

9. A valve as claimed in Claim 8 but modified substantially as described with reference to Fig. 4 of the accompanying drawings.