A positive displacement pump makes a liquid move by trapping a fixed amount and forcing (displacing) that trapped volume into the discharge pipe. … Liquid flows into the pumpas the cavity on the suction aspect expands and the liquid flows out from the discharge because the cavity decreases.
The most typical type among centrifugal pump may be the radial flow pump. … The primary difference between these kinds of pumps and centrifugal can be that positive displacement pumps will move fluid at the same swiftness regardless of the pressure on the 
inlet end and centrifugal pumps will not