The major advantage of the diaphragm pump is that the pumping chamber is totally sealed and therefore does not require a sliding seal between moving parts.  Vacuum and pressure is produced by the flexing of the diaphragm back and forth in the chamber.  The reciprocating action is created by an eccentric driven connecting rod under the diaphragm.  The pumps can handle corrosive gases and vapours when the correct materials are specified and are completely oil-free which makes them ideal for use in applications where contamination cannot be tolerated.