A turbomolecular pump (TMP) is a multi-stage axial‑flow turbine in which high speed rotating blades provide compression by increasing the probability of gas molecules moving in the pumping direction. The turbomolecular pump is optimised for molecular flow conditions and requires a suitably sized two stage rotary vane pump or an oil free scroll pump to exhaust to atmosphere.

A compound molecular pump (CMP) is based on the concept of combining bladed turbomolecular stages with molecular drag stages on the same rotor. This design allows:

• High critical foreline pressures (typically up to 10 mbar)

• Options to use smaller backing pumps or dry diaphragm backing pumps