An adjustable pressure controlled valve, comprising: a housing with a cavity therein; an inlet passage leading to said cavity and an outlet, passage leading from said cavity in said housing; said housing having a valve seat interposed between said inlet passage and said outlet passage; a valve member (255, 257) mounted in said cavity and operably interposed between said inlet passage and said outlet passage of said housing, said valve member having a valve surface for seating on said valve seat when in a closed position and movable from said valve seat to an open position; a first resilient biasing member mounted in said housing for exerting an opening bias force on said valve member, (255, 257) to move said valve member (255, 257) to said open position; a second resilient biasing member mounted on an opposite side of said valve member (255, 257) for exerting a closing bias force on said valve member (255, 257) to move said valve member (255, 257) to said closed position; said closing biasing force of said second resilient biasing member being less than said opening biasing force of said first resilient biasing member; a cap member being inserted in a bore a pre-set axial amount to seat and pre-compress said second resilient biasing member a pre-set amount between said cap member and said valve member (255, 257), said cap member being affixed in place such that said closing bias force of said second resilient biasing member is adjustably pre-set by said cap member; said valve member (255, 257) being biased to the closed position by a pneumatic pressure in a control chamber formed in part by said bore and when pneumatic pressure in said pneumatic pressure control chamber is over a pre-determined amount, its closing bias force in addition to the closing bias force of said second resilient biasing member overcomes the opening bias force of said first resilient biasing member to close said valve member (255, 257); and said control chamber being in communication with a pneumatic pressure control source via a vent through cap, passing from said control chamber to an external side of said housing. a housing with a cavity therein; an inlet passage leading to said cavity and an outlet, passage leading from said cavity in said housing; said housing having a valve seat interposed between said inlet passage and said outlet passage; a valve member (255, 257) mounted in said cavity and operably interposed between said inlet passage and said outlet passage of said housing, said valve member having a valve surface for seating on said valve seat when in a closed position and movable from said valve seat to an open position; a first resilient biasing member mounted in said housing for exerting an opening bias force on said valve member, (255, 257) to move said valve member (255, 257) to said open position; a second resilient biasing member mounted on an opposite side of said valve member (255, 257) for exerting a closing bias force on said valve member (255, 257) to move said valve member (255, 257) to said closed position; said closing biasing force of said second resilient biasing member being less than said opening biasing force of said first resilient biasing member; a cap member being inserted in a bore a pre-set axial amount to seat and pre-compress said second resilient biasing member a pre-set amount between said cap member and said valve member (255, 257), said cap member being affixed in place such that said closing bias force of said second resilient biasing member is adjustably pre-set by said cap member; said valve member (255, 257) being biased to the closed position by a pneumatic pressure in a control chamber formed in part by said bore and when pneumatic pressure in said pneumatic pressure control chamber is over a pre-determined amount, its closing bias force in addition to the closing bias force of said second resilient biasing member overcomes the opening bias force of said first resilient biasing member to close said valve member (255, 257); and said control chamber being in communication with a pneumatic pressure control source via a vent through cap, passing from said control chamber to an external side of said housing.