GB2173882A

GB2173882A - Diaphragm valve

Info

Publication number: GB2173882A
Application number: GB08509251A
Authority: GB
Inventors: Rolf Jonas
Original assignee: KIM PROD Ltd; KIM PRODUCTION Ltd
Current assignee: KIM PROD Ltd; KIM PRODUCTION Ltd
Priority date: 1985-04-11
Filing date: 1985-04-11
Publication date: 1986-10-22
Also published as: GB8509251D0; GB2173882B

Abstract

A diaphragm valve for corrosive liquids comprising a thin diaphragm (4) in contact with the liquid, and a thicker backing diaphragm (5) of rubber or the like are attached to a compressor (7) by a stud bolt (13) which is secured in the compressor by a bayonet closure comprising a cross pin (14) in the top end of the stud bolt (13). During fitting of a new diaphragm the cross pin is inserted into the recess (15) through a slot (17) and rotated about an angle of 90 degrees. The backing diaphragm (5) is provided with a central aperture which facilitates exchanging the backing diaphragm only without having to withdraw the cross pin (14) out of the bolt (13), which is usually firmly retained therein by rust or dirt, by pushing the cross pin through the aperture. <IMAGE>

Description

SPECIFICATION Improvement in diaphragm valves for corrosive liquids The invention relates to diaphragm valves and more particularly to valves for fluid control of corrosive liquids.

In a diaphragm valve for fluid control of corrosive liquids such as acids or alkalis, the diaphragm is of an anticorrosive material, preferably of Teflon (RTM) polytetra-fluoroethylene) which is, in thin sheet form, sufficiently flexible to be pressed against a seat in the valve body by a closure member known as "compressor", the latter being attached to the spindle end.

Although the strength of the material is high, the Teflon diaphragm requires a backing diaphragm of a polymer, such as natural or synthetic rubber, Viton (RTM) or the like, which serves as a cushion pressing the PTFEdiaphragm evenly onto the valve seat.

The two diaphragms are in close contact and are securedby clamping both of them between the valve body and the bonnet, their position being fixed by holes in their corners coinciding with the holes in the valve body which serve to attach the bonnet to the body by through-going bolts and nuts. Connection between the Teflon diaphragm and the compressor is conventionally made by a stud bolt having it head rigidly embedded in the center of the teflon diaphragm. Its shaft is provided, at its upper end, with a transverse hole in which a cross pin is rigidly fastened, so as to protrude out of both sides of the shaft by the same length.This pin engages with the bottom end of the compressor, in a known manner, by means of a bayonet closure in the form of a central hole and a slot crossing this hole positioned in the center of the compressor, the hole being widened inside the compressor body to permit an angular displacement of the pin in order to secure it in both upward and downward direction.

The backing diaphragm of rubber-which is generally much thicker than the Teflon diaphragm-is positioned above the teflon diaphragm in close contact therewith, whereby the shaft of the stud penetrates through a cylindrical hole in its center. For closing the valve by turning the spindle, the compressor is pressed downwards onto the backing diaphragm which urges, in its turn, the Teflon diaphragm onto the valve seat, the pin in the shaft end having sufficient clearance so as not being required to transmit the force from the spindle onto the diaphragm.

A problem commonly encountered with the conventional arrangement is that the exchange of the backing diaphragm requires the withdrawal of the cross pin out of the stud shaft, a task not readily carried out in the field or on a store, since the pin is necessarily embedded in the transverse hole. The exchange is necessitated by either of two causes:-- the material of the backing diaphragm. has to be selected in accordance with the fluid passing through the valve with a view to resisting the corrosive effects as well as possible. Since the cost of the Teflon diaphragm is a multiple of that of any rubber diaphragm, it is economical to keep a limited number of teflon diaphragms and a large number of different rubber diaphragms in stock and to chose each time the suitable kind of rubber for the respective corrosive fluid.The second cause for exchanging the backing diaphragm is that this usually deteriorates much quicker than the Teflon diaphragm and requires its exchange in the field. In this case the removal and reinsertion of the cross pin is still more difficult owing to rust causing adherence of the pin to the hole, and it is, therefore, the main object of the present invention to facilitate the exchanging and positioning of a backing diaphragm by removing it from the stud bolt and by placing a replacement close to the existing Teflon diaphragm without the need of pulling the cross pin out of the stud shaft.

A preferred embodiment of the invention consists in providing each backing diaphragm with a through-going central bore corresponding in diameter to the shaft of the,stud bolt and with two through-going slots extending from the bore in opposite direction, the width and the length of each slot corresponding to the dimensions of the protruding ends of the cross pin in a manner permitting the diaphragm to be slipped over this pin without obstruction.

This is an improvement over the conventional central bore provided in the existing backing diaphragms and avoids the keeping of a large stock of assembled Teflon and backing diaphragms for every kind of corrosive fluid, since it permits easy and ready exchange.

The invention will be better understood from the following description of a preferred embodiment thereof, reference being had to the accompanying drawing, wherein Figure 1 is a part section through a diaphragm valve of the kind referred to, Figure 2 is a section through the compressor body along the line A-A of Fig. 1, Figure 3 is a section through the backing diaphragm along line B-B of Fig. 1, and Figure 4 is a plan view of another embodiment of the perforation of the packing diaphragm.

With reference to Figs. 1, 2 and 3 of the drawing, a diaphragm valve comprises a valve body 1 defining a flow passage 2, a bonnet 3 secured to the body by bolts (not visible), a Teflon diaphragm 4 and a backing diaphragm 5 both clamped at their margins between the body 1 and the bonnet 3. The body inside is shaped to form a curved valve seat 6 onto which the teflon disphragm is pressed by a compressor 7 by way of an interposed backing diaphragm, causing the closing of the flow passage 2. The compressor, in its turn, is movable in upward and downward direction by a spindle 8 privided with an enlarged head 9 at its bottom end, which engages with a recess 10 in the compressor.

The Teflon diaphragm is provided with an upwardly extending central boss 11 which firmly encloses the head 12 of a stud bolt 13.

The shaft of the stud bolt 13 penetrates through a central bore 21 in the backing diaphragm 5 into a recess 15 inside the compressor 7 and is secured therein by a pin 14 firmly fastened in a transverse bore in the top of the stud shaft. The recess, as shown in Fig. 2 consists of a central hole 16 in the bottom center of the compressor which is crossed by a slot 17 corresponding in size to the dimensions of the pin 14, this hole being enlarged in the interior of the compressor to permit angular displacement of the pin.

The arrangement as described hereinbefore is that known and applied in a conventional diaphragm valve in connection with the attachment of the diaphragm to the compressor.

The novel aspect of the invention is in respect of the backing diaphragm 5 which is of identical outer dimensions as the Teflon diaphragm 4, and is positioned between the latter and the compressor 7. Diaphragm 5 is provided with an upstanding boss 18 cooperating with a corresponding recess 19 in the bottom portion of the compressor and, in its underside, with a recess 20 cooperating with the boss 11 of the Teflon disphragm. The boss 18 is perforated by a central hole 21 of a size permitting the passage of the stud shaft 13 therethrough, and by a slot 22 crossing the hole centrally, the slot being of a size permitting the passage of the pin 14 therethrough.

The assembly of the valve components comprises the following steps:-- The backing diaphragm is placed over the Teflon diaphragm in that the shaft 13 and the pin 14 are first pushed through the perforation (21, 22) in the boss 18. The two diaphragms are now angularly displaced by turning one of them about a right angle in respect of the other, and thereafter the shaft and the pin are inserted into the recess 15 of the compressor through the hole 16 and the slot 17 in the bottom portion of the compressor, and the two diaphragms together are again rotated about a right angle so as to retain the pin in the recess and to prevent its slipping out through the slot 17. The edges of the two diaphragms are now compressed between the body 1 and the bonnet 3 by means of bolts passing through holes in the corners of all components to be assembled.

The form of the perforation (21, 22) of the boss 18 as shown in Fig. 3 is advantageous in that it provides central guidance of the shaft 13 in the hole 21, after the pin 14 has been pushed through the diaphragm into the recess 15 of the compressor. However, a similar result can be achieved by an elliptical or oblong perforation 30 as shown in Fig. 4 of the drawing. The width of the oblong perforation should correspond to the diameter of the stud shaft 13, thus performing a guiding action of the shaft in the diaphragm.

Still another embodiment comprises a circular perforation through the boss 18, of a diameter corresponding to the length of the pin 14. This perforation permits the passage of the shaft and the pin in any relative position of the two diaphragms.

It will be understood that the size and shape of the perforation in the boss 18 is not limited to the three embodiments described in the foregoing, but that, a peforation of any other shape or size must permit the passage of the pin 14 without, however, weakening the construction of the diaphragm itself.

It will be furthermore understood that the invention is not limited to the specific design of the diaphragm valve illustated in Fig. 1, but that it may be applied to any type of valve as long as connection between diaphragm and compressor is of the kind employing a stud and a pin therethrough.

Claims

CLAIMS 1. In a diaphragm valve for corrosive fluids comprising a main, thin diaphragm of an anticorrosive material such as Teflon (RTM) (polytetrafluoroethylene) and a backing diaphragm of a polymer such as rubber positioned between said main diaphragm and the compressor of said valve, wherein connection of said main diaphragm to said compressor is made by means of a stud bolt provided with a head, said head being firmly embedded in the center of said main diaphragm, and with a cross pin passing through the shaft of said stud bolt close to the end remote from said head, the improvement comprising a central perforation in the center of said backing diaphragm of a size permitting the unobstructed passage therethrough of said stud shaft and said cross pin. 2. The central perforation in said backing diaphragm in the shape of a circular hole corresponding to the diameter of said shaft of said stud and of a slot extending across said circular hole in central alignment, the size of said slot corresponding to the dimensions of said cross pin. 3. The central perforation in said backing diaphragm in the shape of an oblong of a length corresponding to the length of said cross pin and of a width corresponding to the diameter of said stud shaft. 4. The central perforation in said backing diaphragm in the shape of a circular hole of a diameter of at least the length of said cross pin. 5. The improved diaphragm valve substan tially as hereinbefore described and illustrated in the accompanying drawing. CLAIMS Amendments to the claims have been filed, and have the following effect: Claims 1-5 above have been deleted or textually amended. New or textually amended claims have been filed as follows:-

1. A diaphragm valve for corrosive fluids comprising a valve body, a bonnet secured to said valve body, a main thin, diaphragm of an anticorrosive material such as teflon (polytetrafluoroethylene) and a backing diaphragm of a polymer such as rubber clamped between the valve body and the bonnet, a compressor for actuating the diaphragms, the backing diaphragm being positioned between said main diaphragm and the compressor of said valve, wherein a connection of said main disphragm to said compressor is made by means of a stud bolt provided with a head, said head being firmly embedded in the center of said main diaphragm, and with a cross pin passing through the shaft of said stud bolt close to the remote from said head, characterised by a central perforation in the center of said backing diaphragm of a size permitting the unobstructed passage therethrough of said stud shaft and said cross pin, permitting ready exchange of said backing diaphragm.

2. A diaphragm valve as claimed in Claim 1, the central perforation in said backing diaphragm being in the shape of a circular hole corresponding to the diameter of said shaft of said stud and of a slot extending across said circular hole in central alignment, the size of said slot corresponding to the dimensions of said cross pin.

3. A diaphragm valve as claimed in Claim 1, the central perforation in said backing diaphragm being in the shape of an oblong of a length corresponding to the length of said cross pin and of a width corresponding to the diameter of said stud shaft.

4. A diaphragm valve as claimed in Claim 1, the central perforation in said backing diaphragm being in the shape of a circular hole of a diameter of at least the length of said cross pin.

5. A diaphragm valve substantially as described with reference to and as illustrated in Figs 1 to 3 of the accompanying drawings.

6. A diaphragm valve substantially as described with reference to and as illustrated in Figs. 1 to 3 modified as in Fig. 4 of the accompanying drawings.