the actual volume of fluid put out by a pump divided by the volume displaced by a piston or pistons (or other device) in the pump. Volumetric efficiency is usually expressed as a percentage. For example, if the pump pistons displace 300 cu in. But the fluid put out by the pump is 290 cu in., Then the volumetric efficiency of the pump is about 97 percent. Pumps are seldom 100 percent efficient.
