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Operation <br />The Reliable Model DDX-LP Dry Pipe Valve System is shown <br />in both the closed and open position in Figure 1. In the closed <br />position, pneumatic pressure acts on the actuator preventing <br />release of hydraulic pressure from the pushrod chamber. The <br />supply water pressure acts simultaneously on the underside of <br />the clapper and on the pushrod through the pushrod chamber <br />restricted inlet. The resultant force on the pushrod is multiplied <br />by the mechanical advantage of the lever and acts to hold the <br />clapper closed against normal pressure surges in the water <br />supply. When a sprinkler operates, the loss of pneumatic <br />pressure in the sprinkler system causes the diaphragm <br />and seal in the actuator to move away from the water seat <br />allowing the release of water from the pushrod chamber. <br />Since water cannot be replenished through the inlet restriction <br />as rapidly as it is vented, the pushrod chamber pressure <br />falls instantaneously. When the pushrod chamber pressure <br />approaches approximately one-third of the supply pressure, <br />the upward force of the water pressure acting beneath the <br />clapper overcomes the force applied to the lever, opening <br />the clapper. Water then flows through the Model DDX-LP Dry <br />Pipe Valve into the system piping and into the alarm outlet <br />activating the alarm device(s). Once the clapper has opened, <br />the lever acts as a latch preventing the clapper from returning <br />to the closed position. <br />Section View of Model DDX-LP Dry Valve with Clapper in Open, Closed, and Latched Positions <br />DDX VALVE CLAPPER IN "OPEN," "CLOSED," AND <br />"LATCHED" POSITIONS <br />TO SYSTEM <br />LEVER <br />PUSH ROD <br />PUSH ROD <br />CHAMBER <br />OUTLET <br />RESTRICTION <br />PUSH ROD <br />CHAMBER <br />INLET <br />WEEP HOLE <br />EXTERNAL <br />RESET HINGE <br />CLAPPERIN <br />4"OPEN' POSITION <br />O CLAPPERIN <br />"LATCHED" POSITION <br />CLAPPERIN <br />"CLOSED" POSITION <br />ALARM PORT <br />TEST PORT <br />REAR VIEW OF MODEL DDX VALVE <br />PUSH ROD <br />CHAMBER <br />4 "— DRAIN PORT <br />FROM SUPPLY PUSH INWARD AND ROTATE KNOB CLOCKWISE (AS VIEWED FROM REAR) <br />saercoin TO RESET CLAPPER. NOTE: PUSH ROD CHAMBER MUST BE VENTED TO DRAIN. <br />Bulletin 338 Reliably Page 2 of 7 <br />June 2021 www.reliablesprinkler.com <br />