Positive Displacement Flow meters are volume based flow rate measuring instruments. There are many types of PD meters like turbine, single rotor, bi-rotor and can be used for a multitude of applications. Since the measurement is done without using any properties of the fluid passing through the flow meter, it can be used for any type of liquid. However, if there are bubbles in the liquid air eliminators and strainers may be needed to reduce the percentage of bubbles to increase measurement accuracy.