P/00/00 I I Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT ORIGINAL Name of Applicant: APEX VALVES LIMITED Actual Inventors: David Gordon Arthur CRICHTON and Philip Michael WEIR Address for service in Australia: Newnham & Co PO Box 1325, Crows Nest New South Wales 2065, Australia Ph: 0064-27-231 6702 Fax: 0064-9-414 6012 Invention Title: A PRESSURE CONTROL VALVE The following statement is a full description of this invention. including the best method of performing it known to us: Pauapp 2 This invention relates to a liquid pressure limiting valve and morc particularly to a valve for limiting the pressure in a water main as typically reticulated to a building. Often it is the case that the pressure in a water main or similar conduit needs to be controlled within upper and lower pressures. Typically this compensation or adjustment needs to take 5 place between an upstream or originating substantially constant mains pressure and a downstream or "draw-off' related pressure that may fluciuate from moment to moment depending upon the extent of "draw-off'. Typically such valves are "factory-set" with a threshold or desired outlet pressure achieved with an appropriately adjusted and set compression spring against which a water pressure operated piston or plunger operates to open 10 and close the valve. It is considered desirable that such a valve is sensitive to the pressure changes acting thereon and a first object of this invention is to provide such a valve. Also many such water control valves include a resilient seal or seat such as a washer against which a rigid port forming valve rim impinges to close the valve. It follows the seals or seats tend to wear with usage and replacement is necessary. Thus from both a manufacturing and servicing, 15 particularly seal replacement, view point a cost effective valve siructure is important and another object of this invention is to provide such a valve. A further object is to provide the public with a useful choice. According to a first embodiment of this invention there is provided a liquid pressure limiting valve comprising a housing having an inlet to and an outlet from an interior chamber thereof, 20 the interior chamber containing a valve port forming member fixed therein and an associated valve seal supporting pressure plate reciprocally and sealingly mounted between the port forming member and a cap fixed into the outlet, a chamber formed between the cap and the pressure plate, the pressure plate incorporating first and second pressure platen surfaces, the 3 first being of larger area than the second and being presented to the outlet and the second being presented to the inlet via a passage extending through the seal and the pressure plate to join the chamber to the inlet whereby the pressures in the outlet and the inlet tend to move the pressure plate to close the valve, a compression spring mounted to resist the closing movement 5 of the pressure plate and being set to maintain the valve open up to a prescribed pressure at the outlet. According to a second embodiment of this invention there is provided a liquid pressure limiting valve as described in the preceding paragraph wherein the seal comprises an "0-ring". According to a third embodiment of this invention there is provided a liquid pressure limiting 10 valve as described in either of the two immediately preceding paragraphs wherein the valve seal seats within a rebate formed in a section of the wall of the pressure plate defining the passage adjacent the port. According to a fourth embodiment of this invention there is provided a liquid pressure limiting valve as described in the third embodiment wherein a seal-compression sleeve is mounted in 15 the passage to distort the seal to stand proud of the associated end of the wall forming the passage. According to a fifth embodiment of this invention there is provided a liquid pressure limiting valve including a pressure plate mounted between an inlet and an outlet thereof and including platen surfaces presented to each of the inlet and outlet as to be reciprocally operated therein 20 against a compression spring tending to close the valve as to tend to open the valve dependent upon the pressure differential between the inlet and outlet, the valve including an annular shaped replaceable valve seal with the flow passage through the valve being about the outer 4 periphery thereof and the pressure plate being presented to the inlet via a passage that includes the bore of the seal characterised in that the seal is formed by a conventional "O"-ring. In further describing the invention reference is made to the accompanying drawings of a preferred embodiment wherein; 5 Fig 1 is a longitudinal section view of the valve in a closed mode, and Fig 2 is a longitudinal section view of the valve in an open mode. A valve includes an housing preferably consisting of two detachably joined parts, the fxst housing part forming an inlet 1 and the second housing part an outlet 8 to and from respectively of an interior of the housing 1,8. A port forming member 13 that includes a 10 valve rim 13a and a pressure plate 11 carrying an associated valve seat or seal 4 are mounted within the interior, the port forming member 13 being adjacent the inlet 1 as to be, in use, upstream of the pressure plate 11. Preferably port forming member 13 is clamped in position between the abutting sections of the housing members 1, 8 with a seal 2 provided between itself and the port forming member 1. The pressure plate 11 preferably comprises a pair of 15 generally cylindrically configured sections being an inner section 1 lb and an outer section 1 la. Outer section 1 la is spaced concentrically outward, such as by radially disposed ribs (not depicted) of inner section 11 b, to form a water passage l ie between the two sections 11, 11 b. Plate 11 is sealingly and slidingly mounted, such as by "O"-seal 7, between a cap 9 (which is fixed, by clip 10, into the outlet 8) and the wall of the outlet 8 (via seal 5). 20 As described in more detail below the inner end of the cap 9 is rebated to form, a chamber 14 which is connected to inlet 1. Displacement of plate 11 is dependent upon the differential of the liquid pressures between the outlet 8 and the inlet 1. To that end pressure plate 11 includes 5 a first platen face or area II c exposed to the pressure at the outlet 8 and a second and smaller platen face or area I1d exposed to the pressure at the inlet 1. The pressure at the outlet 8 acts on the plate 11 against a compression spring 12 and in so doing tends to close the valve. The compression of spring compression 12 is set to maintain the valve open up to a pre-set 5 specified pressure at the outlet 8. Preferably the outer section 1 Ia of pressure plate 11 includes an inner end reduced diameter section 11 f that seals (via seal 3) against port forming member 13 and creates an annular void between itself and the wall of outlet housing part 8 in which spring 12 is retained. A valve seat or seal 4 is mounted on the inner section 11 b of pressure plate 11 to open and 10 close, with movement of pressure plate 11, against rim 13a. The flow path through the valve is through the bore of port member 13, radially outward about seal 4 and then through passage 1Ie formed through pressure plate 11 and a similarly formed passage 9a through cap 9. Seal 4 includes a ccntral aperturc tiereirough that conjoins with a bore 6a forming a passage betwccn the inlet 1 and chamber 14 as described in more detail below. Thus the pressure at 15 the inlet 1 acts on the platen face 11d of the pressure plate 11 to also tend to close the valve and thereby displaces the pressure plate 11 to compensate for any changes in the inlet pressure. Preferably seal 4 is formed by an "O-ring" and preferably to that end a rebate 14 is formed in the end section adjacent the port rim 13a of the wall of the pressure plate 11 defining a bore 20 11 g of the plate 11. The rebate 14 is preferably dimensioned to provide that a suitable sized standard "O-ring" when seated therein stands proud of the associated end on the inner section 11 b. Preferably the "O'-ring also extends marginally into the bore 11 g and a cylindrical tight fitting sleeve 6, that includes bore 6a, is mounted in bore 11 g to compress the seal radially 6 mitward and thus distort the "O"-ring to stand proud as aforesaid. Preferably slccvc 6 also includes an outer annular lip 6b at the end thereof associated with the seal 4 that tends to retain the seal 4 in the rebate 14. Use of a standard readily available "O"-ring as the seal 4 reduces manufacturing costs and simplifies replacement when required.