Diaphragm valves for corrosive liquids

A backing diaphragm (5) in a diaphragm valve for corrosive liquids is perforated by a centrally positioned, oblong hole. As known to the art a diaphragm valve for corrosive liquids contains a thin Teflon-diaphragm in contact with the liquid, and a thicker backing diaphragm of rubber or the like serving as a cushion. Both diaphragms are in close contact and are attached to a compressor by a stud bolt which is secured in the compressor by a bayonet closure comprising a cross pin in the top end of the stud bolt which is enclosed in a recess inside the compressor. In a known manner, during fitting of a new backing diaphragm the cross pin is inserted into the recess through a slot and rotated about an angle of 90 degrees. The oblong hole facilitates exchanging the backing diaphragm only without having to withdraw the cross pin out of the bolt, which is usually firmly retained therein by rust or dirt, by pushing the cross pin through the oblong hole and inserting it into the compressor. The diaphragms are subsequently clamped between the valve body and the bonnet.

BACKGROUND OF THE INVENTION 
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. polytetrafluoro ethylene [PTFE] manufactured by E. I. du Pont 
de Nemours and Co., Wilmington DL) 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 or the like, which serves as a cushion pressing 
the PTFE-diaphragm evenly onto the valve seat. 
The two diaphragms are in close contact and are secured by 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 its 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. 
SUMMARY OF THE INVENTION 
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 
in a store, since the pin is necessarily solidly 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.RTM. 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 diaphragm usually deteriorates much 
quicker than the teflon diaphragm, requiring its replacement in the field. 
In this case the removal and re-insertion 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. 
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
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.RTM. and backing diaphragms for every kind of corrosive 
fluid, since it permits easy and ready exchange.

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.RTM. diaphragm 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 provided with an enlarged head 9 at its bottom end, which 
engages with a recess 10 in the compressor. 
The Teflon.RTM. 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 pin14 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.RTM. 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 diaphragm. 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 21 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 are 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 perforation 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 illustrated 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.