Abstract: A pressure relief valve for relieving excess pressure in a fluid distribution system comprising a valve body having an inlet port and an outlet port in communication with an interior of the valve body. The inlet port is connectable to the fluid distribution system. A valve member within the interior of the valve body is movable between a closed position to prevent fluid flow through the body and an open position to permit fluid flow. The valve member is exposed to a first opening force exerted directly by the pressure in the fluid distribution system. There is a movable piston/diaphragm member co-operating with the valve member such that the piston/diaphragm is exposed to the pressure in the fluid distribution system to provide a second opening force for the valve member. A biasing system exerts a default closing force to move the valve member to the closed position. The closing force is set to be equivalent to a pre-selected pressure in the fluid distribution system.

Abstract: The invention provides a pilot valve apparatus for use in an automatic fluid control system for maintaining pressure downstream from a main control valve between two setpoints irrespective of flow changes through the main control valve. The pilot valve has a flexible pilot diaphragm which moves with a moveable pilot valve member to cooperate with a fixed pilot valve member to control fluid flow through the pilot valve apparatus. The pilot valve controls control pressure acting on the main control valve. An actuator apparatus connected to a body of the pilot valve apparatus has a moveable actuator partition which is exposed to a pressure differential signal reflecting flow through the main control valve. A resilient connector cooperates with the actuator partition and the pilot diaphragm to permit limited relative movement therebetween, and to transfer resilient force to the pilot diaphragm resulting from movement of the actuator partition.