As show in the operating scheme, the liquid flowing inside the PD flowmeter pushes the rotor on the right , which is in condition of unbalanced pressure, to rotate clockwise; contemporarly the rotor on the left, being driven by the timing gears , is forced to rotate counterclockwise.
After a 90 degrees rotation, the rotors are in a reciprocal position when compared to the initial one and therefore it is the rotor on the left which, pushed from the liquid, rotates counterclockwise driving, through the timing gears, the rotor on the right. During the operating cycles the volumes which are generated between the rotors and the components of the measuring chamber determine the "base volume" of the instrument .A complete rotors' rotation generates four "base volumes". By transmitting the number of rotors' rotations to the register the volume flown through the PD flowmeters is displayed.
