Diaphragm pump (membrane pump) is an oil-free vacuum pump that is used for obtaining #prevacuum of about 0.5 mbar. The pumping in this device is based on the movement of the membrane. As the membrane is pulled down, the volume of the chamber increases, causing a drop of pressure and gas enters the chamber through the inlet. Next, the inlet is closed, outlet opened and the membrane pushed up. This causes the volume of the chamber to decrease and pressure to increase. So the gas is forced to leave the system through the outlet.