When a pressure is developed, air enters through hole 1 and raises piston 2 in a transparent cylinder of plexiglas. At the end of the piston stroke, rubber insert 4 closes the hole in cover 5 leading to the atmosphere. The side surfaces of the piston are painted red. By watching the piston, the operator can tell when he has air under pressure. When hole 1 is connected to the atmosphere, piston 2 drops to its lower position by gravity. This indicator is employed on the pneumatic control panels of complex control systems and has the same function as a signal lamp in an automatic electrical system.
$3723$SHP,M$