Pilot operated valve with pressure relief

In a pilot-operated diaphragm valve comprising a valve body having a flow path therethrough, the latter having an inlet and an outlet, said valve body having a main valve seat within said flow path and diaphragm valve means sealably mounted within said valve body for movement between an open position in which said diaphragm valve means is clear of said main valve seat thereby to permit the flow of fluid through said flow path and a closed position in which said diaphragm valve means sealably engages said main valve seat thereby to block the flow of fluid through said flow path, said valve body further having a chamber therewithin in which said diaphragm valve means is received as it moves between its closed and open positions, a fluid supply passage for communication between said flow path upstream from said main valve seat and said chamber thereby to supply pressurized fluid to said chamber, fluid pressure within said chamber acting to hold said diaphragm valve means in one of its stated positions, a pilot passage for communication between said chamber and said flow path downstream from said main valve seat, said pilot passage including a pilot valve seat, a pilot valve member movable relative to said pilot valve seat between an open position in which said pilot valve member permits the flow of fluid from said chamber to said pilot passage and a closed position in which said pilot valve member is in sealing engagement with said pilot valve seat thereby to block the flow of fluid from said chamber via said pilot passage, said pilot valve seat and said pilot passage being sized relative to said fluid supply passage so that when said pilot valve member is open, fluid pressure within said chamber is below the pressure of the fluid in said flow passage on the inlet side of said main valve seat, the side of said diaphragm valve means in communication with said chamber having a cross-sectional area larger than the opposite face of the diaphragm valve means exposed to fluid pressure in said flow path on the downstream side of said main valve seat when said diaphragm valve means is in its closed position and being of substantially the same cross sectional area when said diaphragm valve means is open, a spring engagable with said pilot valve member thereby to bias the latter toward its closed position, and selectively actuable means for effecting movement of said pilot valve between its opened and closed positions so that with said pilot valve open, fluid pressure within said chamber is less than the fluid pressure within said flow path whereby the fluid pressure within the flow path maintains said diaphragm valve means in one of its stated positions and so with the pilot valve member closed fluid pressure within said chamber increases so as to positively hold the diaphragm valve means in another of its said positions, wherein the improvement comprises:

• said pilot passage having a first portion between said chamber and said pilot valve seat and a second portion between said pilot valve seat and said flow path downstream from said main valve seat, said pilot valve member having an area of sufficient size exposed to fluid pressure within said first portion of said pilot passage when said pilot valve member is in its closed position so as to overcome the bias of said spring forcing said pilot valve member toward its closed position and to overcome the fluid pressure forces acting on said pilot valve member via said second portion of said pilot passage upon the pressure differential of said fluid between said inlet and outlet of said pilot operated diaphragm valve exceeding a predetermined value thereby to cause the pilot valve member to open which in turn effects movement of said diaphragm valve means from its said one to its said other position.

A pilot operated valve which automatically opens upon the pressure differential across said valve exceeding a predetermined limit, said pilot operated valve having a flow path therethrough including an inlet and an outlet, a main valve seat constituting a portion of said flow path and a main valve member movable relative to said main valve seat between an open position in which flow of fluid occurs through said flow path and a closed position in which said main valve member sealing cooperates with said main valve seat thereby to block the flow of fluid through said flow path, a space receiving said main valve member, a passage permitting fluid from the upstream side of said main valve seat to enter said space and to act on said main valve members to at least in part aid in maintaining said main valve in its closed position, a pilot valve passage providing communication between said space and said flow path downstream from said main valve seat, said pilot passage including a pilot valve seat and a pilot valve member movable between a closed position cooperable with said pilot valve seat so as to block the flow of fluid from said space whereby said main valve is maintained in its closed position and an open position in which fluid within said space is exhausted to said flow path downstream from said main valve seat at a rate faster than fluid enters said space thereby to permit opening of said main valve, said pilot valve member being biased toward its closed position by a spring, said pilot passage having a first portion between said space and said pilot valve seat and a second portion between said pilot valve seat and said flow path downstream from said valve seat, said pilot valve member having an area of sufficient size exposed to fluid pressure within said first portion of said pilot passage when said pilot valve member is in its closed position so as to overcome the bias of said spring forcing said pilot valve member toward its closed position upon the pressure differential of said fluid between said space and said flow passage downstream from said valve seat exceeding a predetermined level thereby to cause said pilot valve member to open which in turn effects movement of said main valve means from its said closed position to its said open position.