A differential pressure type mass flow meter, is composed of compound pipes in parallel with two branch pipe lines of equal size, a constant flow pump, two differential manometers and flow controlling valves.
Both of the branch pipe lines I, II have two straight portions of equal diameters and the differential manometers measure the pressure differences of each of the straight portions of both branches.
The liquid to be measured flows in the pipe line and then is divided into two branches. The flow rate in branch pipe I is so controlled that the pressures at the straight portion of upstream sides are equal to each other. A constant volume flow rate is sent by the pump from the pipe line II to the pipe line I, then the difference of pressures at the straight portions of the two pipe linesis proportional to the mass flow rate.