The mechanical booster vacuum system is mainly of use down to the 10~0.001 Torr range where it can give at least one of the following advantages:
1. Shorter evacuation time
2. Increase in pumping capacity.
3. Reduced primary pump size (a primary vacuum pump is a unit normally designed to discharge
to atmospheric pressure – termed a “backing” pump when used in conjunction with a
4. Extension of operation into a pressure range that the primary pump cannot reach.
The mechanical booster cannot discharge to atmospheric pressure and must be combined with a backing pump.
Various types of backing pump can be used.
Compression ratios of 2:1 to 10:1 are usual – the value chosen depends on the backing pressure, lower backing absolute pressure higher compression ratios.
Multi-staging of booster can provide high capacity whilst giving a further reduction in backing pump size.
Generally, pumped vapors do not condense in the booster during operation as the heat of compression more than compensates for the increase in pressure.