This invention relates to a diaphragm valve, that is to say a valve in which a closure diaphragm is secured to a valve body and is movable by an operating mechanism into engagement with a seat defined by the valve body in order to close the valve to fluid flow.

Conventionally, the diaphragm of a diaphragm valve has a peripheral zone of substantially uniform thickness which is compressed between the valve body and a bonnet assembly which is itself secured to the valve body by suitable means, for example fastening bolts. With such an arrangement, the periphery of the diaphragm is visible between the body and the bonnet, and whilst this can be useful, for example in identifying the grade of elastomer from which the diaphragm is made, the fact that the diaphragm is visible is aesthetically not pleasing and can give rise to misgivings as to the capability of the diaphragm to form a reliable seal under all conditions. Further, because of the elastomeric nature of the diaphragm the presence of the diaphragm between the body and the bonnet means that the body retaining fasteners cannot be tightened hard down. They should, ideally, be set to a specified torque, but accurate setting of the torque is not always carried out, especially when valve diaphragms are changed by service personnel not familiar with the torque requirements of the particular valve and diaphragm in

question.

According to one aspect of the present invention there is provided a diaphragm valve comprising: a valve body defining a diaphragm opening and a valve seat; a valve bonnet secured to the valve body; a diaphragm closing the diaphragm opening, the peripheral zone of the diaphragm being compressed between the valve body and the valve bonnet to maintain the diaphragm in sealing engagement with the valve body around the diaphragm opening; and an operating mechanism for moving the diaphragm into sealing engagement with the valve seat to close the valve to fluid flow and away from the valve seat to open the valve to fluid flow, wherein the peripheral zone of the diaphragm comprises a relatively thick radially inner portion and a relatively thin radially outer portion both of which are compressed between the valve body and the valve bonnet, at least one of the valve body and the valve bonnet being stepped to accommodate the changes in thickness of the diaphragm.

With an embodiment of diaphragm valve according to the present invention only the relatively thin radially outer portion of the diaphragm is visible between the valve body and the bonnet, and because this portion can be made very thin the problems of aesthetic appearance and confidence referred to above are obviated. Further, if the tolerances of the various components are carefully controlled the fastenings which secure the valve bonnet to the valve body may be tightened hard to compress the relatively thin radially outer portion of the diaphragm, and when the fastenings are fully tightened in this manner the radially inner relatively thick portion of the diaphragm will be correctly compressed for proper working of the valve.

In a particularly preferred embodiment of the invention the relatively thin radially outer portion of the

diaphragm comprises a relatively thin web of elastomeric material which is moulded with one or more raised beads to form a sealing bead in the region of the relatively thin portion of the diaphragm. Such a sealing bead provides an effective secondary seal against leakage of line fluid between the valve bonnet and the body.

The invention will be better understood from the following description of a preferred embodiment thereof, given by way of example only, reference being had to the accompanying drawings in which:

Figure 1 shows, in axial cross-section, a preferred embodiment of the invention;

Figure 2 is a top plan view of the valve of Figure 1 ;

Figures 3 and 4 are respectively a top plan view and a bottom plan view of a diaphragm for use in the valve of Figure 1 ;

Figure 5 is a side view of the diaphragm of Figures 3 and 4;

Figure 6 is a cross-section on the line A-A of Figure 3; and

Figure 7 is a cross-section on the line B-B of Figure 3.

Referring to the drawings, the diaphragm valve 1 comprises a valve body 2 having a flow passage 3 and a diaphragm opening 4. A valve bonnet 5 is secured to the valve body by means of threaded fasteners 6. The peripheral zone 10 of a diaphragm 7 is compressed between the valve body 2 and the valve bonnet 5 to maintain the diaphragm in sealing engagement with the valve body around the diaphragm opening 4. An operating mechanism 8 is provided for moving the diaphragm into sealing contact with a valve seat 9 provided on the valve body to close the valve to fluid flow.

Referring particularly to Figures 3-7 the

diaphragm 7 is a rubber moulding which may optionally incorporate reinforcing fabric. As an alternative to a rubber moulding the diaphragm may be of a composite nature, having for example a PTFE facing and an elastomeric rubber backing. The peripheral zone 10 of the diaphragm which, in use, is compressed between the valve body and the valve bonnet comprises a relatively thick radially inner region 11 and a relatively thin radially outer region 12. The thickness of the radially inner region 11 substantially corresponds to the thickness of the diaphragm over the regions thereof which flex in use.

Both the upper and lower faces of the relatively thin radially outer region 12 are formed with raised beads 13 having the form shown in the drawings. Each raised bead on the upper surface overlies a raised bead formed on the lower surface with the result that the raised beads together form thickened regions of the relatively thin radially outer portion similar in nature to 0-ring seals. The lower face of the bonnet 5 is formed with a step 14 to accommodate the change of thickness of the diaphragm.

The operating mechanism 8 is of the rising handwheel type - that is to say as the handwheel is rotated to move the diaphragm from its closed position in engagement with the seat 9 towards it fully open position, the handwheel itself moves away from the body to expose progressively more of an indicator sleeve 15 provided for the purpose of giving a visual indication that the valve is open.

In assembling the above described valve the fasteners 6 may be tightened fully home to compress the relatively thin radially outer portion 12 of the diaphragm between the bonnet 5 and the valve body 2. If the fasteners 6 are fully tightened the size of the step 14 is such that the relatively thick radially inner portion of

the diaphragm will be correctly compressed between the valve body 2 and the bonnet 5.

In the illustrated embodiment of the invention, as the handwheel is moved to compress the diaphragm 7 against the valve seat 9 the under face 16 of the handwheel will engage the upper surface 17 of the bonnet to prevent further compression of the diaphragm. By this means, over tightening of the valve is prevented.

Although the invention has been described with particular reference to a rising handwheel valve it will be appreciated that the invention is of general applicability to a wide range of diaphragm valves including those having other forms of operating mechanism.