Demonstration - continued.

Notice that the incoming liquid, trapped inside the pump body, cannot go back or stay in place. It has to move to the discharge side of the pump. The pump moves the liquid in a positive sense - the incoming liquid is forced to move to the discharge side. This is the reason such pumps are called "Positive Displacement Pumps."

Reciprocating pumps are manufactured in hundreds of configurations. Many have multiple piston and cylinder assemblies. The fundamental principles, however, are the same.

The configuration shown here is known as single-acting. That means that liquid is pumped out of the pump ONLY during the discharge stroke. During the suction stroke, there is no discharge from the pump - as the pump is busy drawing in the liquid during this stroke.