The process which forms the basis of operation of the various control loops and equipment is illustrated in.  The water finally flows back into the sump tank T1, the heat introduced into the system being removed by a water cooler, HE1. V2 simulates a vessel used for a hazardous process reaction, demanding the use of flame proof control equipment in its immediate vicinity, thus providing a logical reason for the use of pneumatic and interfaced control equipment. Water is fed to a centrifugal pump from sump tank T1 and then to a water heater HE2 before passing into two vessels V1 and V2, mounted in series and simulating a reactor system. Four standard areas of control are presented.