Positive displacement pumps that use pistons to move water through an enclosed space.
In a piston pump, the first stroke of the piston creates a vacuum with the inlet valve open and the outlet valve closed. Liquid is drawn into the piston chamber (the suction phase).
As the motion of the piston reverses, the inlet valve, now under pressure, is closed and the outlet valve opens allowing the fluid contained in the piston chamber to be discharged (the compression phase).
NOTE: These pumps must not be run dry.
If cold water is introduced into the pump following a period of accidental dry running, the ceramic pistons will crack. Allow the pump to cool first.