Air-operated diaphragm pumps are unique in that they are actuated with a compressed air and not a motor. The air pressure actuates diaphragms or bellows, and their reciprocating motion creates the pumping action. Due to this design, these pumps can pump a wide range of working fluids, from chemicals to food products of variable viscosity, and can run dry indefinitely. This quality comes down to the fact that there are no dynamic seals and that the flow rate is maximally adjustable (0% to 100%) based on air pressure. This allows for purity and durability for a wide variety of pumping situations. In Image 1, you can see the most common type of air-operated diaphragm pump (duplex) and its inner workings.
For more information on air-operated pumps, refer to HI standard, Air-Operated Pumps for Nomenclature, Definitions, Application, and Operation (ANSI/HI 10.1-10.5) at www.pumps.org.