Double Acting Pump Demonstration - continued.

Piston Movement Left to Right

Suction Port A: Open
Suction Port B: Closed
Discharge Port C: Closed
Discharge Port D: Open

Piston Movement Right to Left

Suction Port A: Closed
Suction Port B: Open
Discharge Port C: Open
Discharge Port D: Closed

Notice that irrespective of piston movement, a set of suction and discharge ports is always open. Therefore there is a continuous discharge from the pump.