Abstract: A valve for pressurized, liquid sprinkler systems which is adapted for flow esting of the valve without activating the sprinkler system. The valve is constructed with a valve body having a fluid inlet and a fluid outlet connected by a flow passage. The fluid inlet is provided with a supply of pressurized fire extinguishing medium. A cylinder is positioned in the flow passage with a piston slidingly mounted in the cylinder so as to form a chamber with the cylinder. The chamber is pressurized by a sensor-controlled fluid pressure line and controls the position of the piston in the cylinder to open or close the inlet. Pressure in the chamber positions the piston so as to close the fluid inlet. A stem is mounted in the outlet so as to project into the flow passage and through the cylinder to the piston. The stem is attached to the piston on a first end and provided on the other end with a stem extension which projects out of the outlet to a position external to the valve.