Safety switch esp. for three-phase electric water heater - is activated by plunger movement consequent on excessive difference between pressures on opposite faces of diaphragm

摘要

The switch has a differential pressure transducer (10) which contains two chambers (12,13) sepd. by a diaphragm (11) sealed around its edge between the two halves (15,16) of the housing. A water pipe (17) leads through the lower half (16) into the upper chamber (12) in which a disc (20) holding the centre of the diaphragm flat carries a plunger (21) operating a double-snap spring contact arrangement in the heating current circuit. Pressure exceeding 30 atmos. drives another plunger (25) to operate a microswitch (31) energising an electromagnet in the safety circuit. The same result is produced by overheating of a bimetallic switch mechanism. ADVANTAGE - Compact and easily mfd. structure affords greater safety in disconnection of power in event of excessive pressure.