A positive displacement pump moves a fluid by repeatedly enclosing a fixed volume, with the aid of seals or valves, and moving it mechanically through the system. The pumping action is cyclic and can be driven by pistons, screws, gears, lobes, diaphragms or vanes. There are two main types: reciprocating and rotary.A positive displacement pump makes a fluid move by trapping a fixed amount and forcing (displacing) that trapped volume into the discharge pipe. Some positive displacement pumps use an expanding cavity on the suction side and a decreasing cavity on the discharge side.
The centrifugal pumps work on the centrifugal action of rotating impeller to push the fluid. ... The main difference between the centrifugal pumps and positive displacement pump is that positive displacement pumps moves fluid at the same speed regardless of the pressure on the inlet end and centrifugal pumps will not.
Positive Displacement pumps are commonly used for pumping high viscosity fluids such as oil, paints, resins or foodstuffs. They are preferred in any application where accurate dosing or high pressure output is required.