Pneumatic pump is a double piston pump, one piston having a relatively large diameter and the other a relatively small diameter. The two pistons are connected together and fit inside two connected cylinders. The larger piston is driven by compressed air (the gas alternately driving the piston in one direction and then the other) and actuates the smaller piston, which pumps the liquid. The system acts as a pressure amplifier, as the output pressure from the pump with the smaller piston will be equal to the pressure applied to the larger piston times the ratio of the cross-sectional area of the larger piston to that of the smaller piston. It is the simplest type of pump that can be designed to provide exceedingly high pressures.