This device is used to maintain cell pressure constant fora long duration and the system can be used in place of conventional constant pressure system using mercury pots where certain minimum heights are required. Problems like deaeration of pump, leakage of mercury etc. is eliminated in this system . This unit is smaller in volume and can be used in mobile laboratory also. This can maintain pressure in the cell upto 20kg/cm sq. Pressure is maintained constant in the system by a balancing calibrated weights on a spindle against a column of oil, operating under constant feedback.