When purged with compressed air, liquid within the downpipe is displaced by air pressure equal to the hydrostatic force of liquid in the tank. If carefully regulated at a low rate of flow, air pressure will constantly maintain equilibrium against the force of the liquid. Output is proportional to liquid depth and can be transmitted as an electronic 4-20 mA signal or pneumatically as a direct 1:1 pressure signal. LiquiSeal D/P purge control is a fully integrated air purge regulator and level transmitter. Operation is based on the control regulating a continuous 1 cfh (cubic foot per hour) flow of compressed air into the tank downpipe. An internal differential pressure sensor element converts resulting pressure into a 4-20 mAdc two wire signal. APPLICATION NOTE: Available in all-pneumatic configurations for hazardous area service.