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.
Vacuum can be understood as space from where matter (for example air) has been removed. It naturally exists in outer space but for certain applications, like materials characterization techniques, it needs to be achieved artificially. The desired level of vacuum is obtained with the help of a suitable vacuum pump. For example low vacuum (low quality vacuum with higher pressure) can be generated with a diffusion pump, scroll compressor pump, rotary vane pump, diaphragm pump or a sorption pump. High vacuum (high quality vacuum with very low pressures) however, can be obtained with high vacuum pumps such as the turbomolecular pump, ion pump, titanium sublimation pump and cryopump. The level of vacuum is measured with devices called vacuum gauges (vacuum meters) like the thermocouple gauge, pirani gauge, penning ionization gauge and the quadrupole mass spectrometer (analyzer). The working principle of vacuum pumps and vacuum gauges is explained with 3D animations in the video lecture above.