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A safety relief system for a valve in a vent or a main flowline. The safety relief system utilizes a main actuator (24) utilized primarily for a positive pressure condition and a vacuum actuator (96) in axial alignment with the main actuator (24) utilized exclusively for a negative pressure conditio

A safety relief system for a valve in a vent or a main flowline. The safety relief system utilizes a main actuator (24) utilized primarily for a positive pressure condition and a vacuum actuator (96) in axial alignment with the main actuator (24) utilized exclusively for a negative pressure condition. The main valve member (18) has a stem (22) which extends within both actuators (24, 96) and diaphragms (26, 100) are connected to the stem (22) for movement of the valve member (18).

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In a safety relief system for a tank having a main flowline connected to the tank and a control valve in the main flowline adapted to open under a predetermined negative fluid pressure within the tank to permit a flow of fluid to the tank and to open under a predetermined positive fluid pressure wit

In a safety relief system for a tank having a main flowline connected to the tank and a control valve in the main flowline adapted to open under a predetermined negative fluid pressure within the tank to permit a flow of fluid to the tank and to open under a predetermined positive fluid pressure within the tank to permit a flow of fluid from the tank, the control valve having a valve member in the flowline movable between open and closed positions and a longitudinally extending valve stem secured to said valve member for movement therewith; improved means for actuating said control valve under both negative and positive fluid pressures within said tank comprising axially aligned first and second diaphragm actuators receiving said stem and in axial alignment with said valve member and stem; said first diaphragm actuator including a body and a diaphragm within the body connected to said valve stem for defining a fluid chamber therein on the outer side of said diaphragm opposite said valve member, means in fluid communication with said fluid chamber and responsive to upstream fluid pressures in said main flowline for effecting movement of said diaphragm and associated movement of said valve member between open and closed positions in response to changes in said upstream and downstream fluid pressures; and said second diaphragm actuator connected to said valve stem outwardly of said first diaphragm actuator including a body and a second diaphragm within the body defining a vacuum fluid chamber therein on the outer side of said second diaphragm, said stem being connected to said second diaphragm for longitudinal movement relative to said second diaphragm in one direction of travel and for longitudinal movement with said second diaphragm in an opposite direction of travel, means in fluid communication with said vacuum fluid chamber on said outer side of said second diaphragm and responsive to a negative fluid pressure in said main flowline for effecting movement of said second diaphragm in said opposite direction of travel, said second diaphragm being operatively connected to said stem for moving said stem therewith for opening of said valve member under said negative fluid pressure.