Example: In the case of a diffusion pump having a pumping speed of
400 l/s the effective pumping speed is 50 % of the value stated in the
catalog when using a shell baffle. The max. permissible backing pressure is
2 · 10-1 mbar. The pumping speed required as a minimum for the backing
pump depends on the intake pressure pA according to equation 2.41a.
At an intake pressure of pA = 1 · 10-2 mbar the pumping speed for the high
vacuum pump as stated in the catalog is about 100 l/s, subsequently 50 %
of this is 50 l/s. Therefore the pumping speed of the backing pump must