Port a of the pressure relay is connected to the delivery line so that plunger 1 exerts a force on plunger 2, which is subject to the action of spring 3. Chamber d of the pressure relay is connected to a line of constant pressure, maintained by a relief valve. In the position shown, chamber b and plunger 4 of the time relay are subject to constant pressure, because chambers d and b are connected together. Plunger 4 of the time relay, in its upper position, compresses spring 5 and contacts stop 6. If the pressure in the delivery line increases, plungers 1 and 2 are raised, chamber b of the time relay is connected through holes f and e in plunger 2 and pipeline 7 to the tank. Plunger 4 is moved downward by spring 5 and presses pin 8, which transmits a signal to the actuating mechanism. Adjustment of stop 6 sets the stroke of plunger 4 and, consequently, the required time delay.
$4301$CHP,Re$