Pumps are used to transfer and distribute liquids and are classified as either positive displacement or dynamic pressure pumps. Positive displacement pumps displace a fixed volume of fluid with each cycle through rotating or reciprocating components. They include piston pumps, diaphragm pumps, gear pumps, lobe pumps, screw pumps, vane pumps, and rotary plunger pumps. Dynamic pressure pumps use impellers to impart tangential force and accelerate the fluid, including centrifugal pumps, propeller pumps, and turbine pumps. Pumps have components like casings, impellers, prime movers, piping, valves and instruments and are selected based on the end-use application requirements.