A control valve for regulating the flow of compressible and non-compressible fluids in a fluid system and comprising: a control valve body having in spatial relationship a fluid inlet and a fluid outlet; Filtera movable control valve gate member between the inlet and outlet for controlling fluid flow through the control valve body; differential pressure switch means connected to spaced tappings in the control valve body for detecting abnormal fluid flow conditions therein; and means initiated by the differential pressure switch means for closing the movable gate member when abnormal fluid flow conditions prevail in said fluid system, the means including a piston-and-cylinder assembly provided with a vent to atmosphere and operatively connected to the valve gate member and adapted to be maintained in a balanced, position when the valve gate member is open by the fluid of the system under normal fluid flow conditions, a normally-closed venting valve operatively connected to said piston-and-cylinder assembly for controlling venting of said cylinder,BALANCING VALVES a pneumatic supply source, a pneumatic actuator connected to said pneumatic supply source and said venting valve for operating the latter, and an electrically-operated valve disposed between the pneumatic actuator and the pneumatic supply source and operatively connected to the differential pressure switch means to effect venting of the piston-and-cylinder assembly when abnormal fluid conditions prevail via the pneumatic actuator and venting valve to create fluid imbalance in the assembly and resulting control valve closure.

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2012-01-12

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