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.
The sorption pump is an oil-free #prevacuum pump that is based on the adsorption of gases on cold surfaces. The colder the surface, the more efficient the pumping is! Therefore liquid nitrogen with a temperature less than 77 degrees Kelvin is used for cooling the adsorber. The adsorber is a porous zeolite with a very large surface area as the pores have a diameter in the range of a few nanometers (or less). If the pump is full, then it needs to be renewed by degassing, which is basically heating the adsorber so that the gas can remove the pump through the outlet.
Rotary Vane Pump is an oil-based vacuum pump, that can be used to obtain #prevacuum or even medium vacuum (depending on the system). In this device the rotor and vane(s) are in the housing, that is filled with oil. When the gas enters the chamber through the inlet, it gets trapped in the oil and is transported through the working chamber with the help of the rotor and vane(s) to the outlet, where the gas exits the system. The oil acts as a lubricant and also allows the pumping of some corrosive gases, as it protects the metal to some degree. Although this pump is quite fast and efficient for obtaining pre vacuum, it also may contaminate the vacuum system with oil. Therefore the use of oil traps is highly recommended.
Scroll pump (scroll compressor) is an oil-free vacuum pump used for obtaining #prevacuum with a level of 0.1 mbar. The #scrollpump is based on two scrolls, that are placed insede the working chamber. One of these scrolls is fixed and the other one mobile. Once the gas enters the system through the inlet, it gets carried to the outlet in the middle by the mobile orbiting scroll. This is possible due to the fact that during the mobile scrolls movement a wide gap is locally kept between the two scrolls and the gap moves to the middle, carrying the gas in it. As the volume of the gap decreases at the outlet, the gas is pushed out of the system. Due to wear the orbiting scroll needs to be replaced about twice a year.