Steam pipeline working principle of the pneumatic valve to relieve stress

principle is very simple. In fact, the spring scale.
don't know is to ask mechanical or electronic. From the beginning of the machine first.
pressure-relief devices will have a first probe, one end of the probe with a spring to resist, probe into one end of the pipe and at the other end of the pressure-relief device is sealed, when air pressure is greater than the jacking force of spring, connected to the exhaust system on the raft back to be opened. Began to stress, when the pressure less than the jacking force of spring, recovery. The principle of electronic is the same, different is to open the pneumatic valve by touch point contact. Also can adjust the size of the air pressure.
principle is in different position of the spring contraction device contact switch. When touch point contact, through magnetic coil on pneumatic valves, and institutions on pneumatic valves, pneumatic valves open, and then to reduce pressure. When spring after for open contact, magnetic coil power, closed, pneumatic valve shut off.