Diaphragm pumps - also known as membrane pumps - are positive displacements pumps used in the rough vacuum range from 0,5 to 1000 mbar. A membrane (rubber, Viton or Teflon ) is moving up and down in the pump body compressing and exhausting gas coming from the inlet When the application calls for a vacuum deeper than 1mbar, a rotary vane pump is likely your best option. Rotary vane pumps rely on a rotational mechanism with very tight tolerances to generate the deeper vacuum A diaphragm pump is a hydraulically or mechanically actuated positive displacement pump that uses a combination of reciprocating action and either a flapper valve or a ball valve to transfer liquids. Diaphragm pumps are self priming and are ideal for viscous liquids.