How piston pumps work
In a piston pump, the first stroke of the piston creates a vacuum, opens an inlet valve, closes the outlet valve and draws fluid 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). Piston pumps can also be double acting with inlet and outlet valves on both sides of the piston. While the piston is in suction on one side, it is in compression on the other. More complex, radial versions are often used in industrial applications.