A diaphragm pump (or Membrane pump) is a positive displacement pump that uses a combination of the reciprocating action of a rubber, thermoplastic or teflon diaphragm and suitable non-return check valves to pump.
They are also used as low-grade vacuum pumps. These pumps are quiet, cheap and have no moving parts in the airstream. This allows them to be used without added lubrication in contact with the air.