A comparison of Centrifugal and Positive Displacement Pumps

Priming
Centrifugal pumps need to be primed separately.  The priming can be manual or through a separate priming arrangments

Positive displacement pumps are self priming as they develop a low pressure which can draw the fluid inside.

Flow Rate
Centrifugal Pumps have a flow rate which is dependent on the discharge pressure

Positive Displacement pumps have a constant flow rate regardless of the pressure

Viscous Fluids
Centrifugal pumps cannot handle viscous fluids due to increased friction between the impeller and the liquid.

Positive displacement pumps can handle viscous fluids.

Efficiency
Centrifugal pumps have lower efficiency as the viscosity increases

Positive displacement pumps have high efficiency as the viscosity increases

Method of operation
Centrifugal pumps build pressure by imparting velocity to the liquid and then converting it into pressure.

Positive displacement pumps develop pressure by drawing a fixed amount of liquid and pressurizing it.