Vacuum pumps are used to reduce the gas pressure in a certain volume and thus the gas density
Consequently consider the gas particles need to be removed from the volume. Basically differentiation is made between two classes of vacuum pumps:
a) Vacuum pumps where – via one or several compression stages – the gas particles are removed from the volume which is to be pumped and ejected into the atmosphere (compression pumps). The gas particles are pumped by means of displacement or pulse transfer.
b) Vacuum pumps where the gas particles which are to be removed condense on or are bonded by other means (e.g. chemically) to a solid surface, which often is part of the boundary forming volume itself.
A classification which is more in line with the state-of-the-art and practical applications makes a difference between the following types of pumps, of which the first three classes belong to the compression pumps and where the two remaining classes belong to the condensation and getter pumps:
- Pumps which operate with periodically increasing and decreasing pump chamber volumes (rotary vane and rotary plunger pumps; also trochoid pumps)
- Pumps which transport quantities of gas from the low pressure side to the high pressure side without changing the volume of the pumping chamber (Roots pumps, turbomolecular pumps)
- Pumps where the pumping effect is based mainly on the diffusion of gases into a gas-free high speed vapor jet (vapor pumps)
- Pumps which pump vapors by means of condensation (condensers) and pumps which pump permanent gases by way of condensation at very low temperatures (cryopumps)
- Pumps which bond or incorporate gases by adsorption or absorption to surfaces which are substantially free of gases (sorption pumps). A survey on these classes of vacuum pumps is given in the diagram of Table 2.1.
Table 2.1 Classification of vacuum pumps