The Model DDX deluge valve is a hydraulic piston operated, mechanical type deluge valve. The valve is intended for use as a principal control valve in certain types of fire protection systems such as preaction or deluge. The valve can be reset externally after the operation. When the side chamber of the Reliable Model DDX Deluge Valve is depressed, the hydraulic supply pressure simultaneously affects the piston and pushrod assembly, as well as the underside of the clapper. The mechanical advantage of the lever multiplies the supply pressure’s resulting force pressing on the piston/pushrod, which is more than enough to maintain the clapper closed in the face of normal supply pressure spikes. The pushrod chamber pressure decreases instantly when a releasing device vents the chamber to the atmosphere through its exit.