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Cryosorption Pumping at 77°K from Atmospheric Pressure to 10-7 Torr

Two types of cryosorption pumps with pumping speeds for air of 60 liters/sec (1.5 kg Zeolite 5A, 1/16'' pellets) and 165 liters/sec (4.5 kg Zeolite 5A, 1/16'' pellets) have been constructed in laboratory. A 10 liter vacuum system, evacuated by two cryosorption pumps (1.5 kg Zeolite each) was used to establish the optimum activation conditions. The final pressures and the residual gas compositions for various activation conditions are discussed. Our results demonstrate that final pressures in the 10-7 Torr range can be attained (after a one-stage pre-evacuation from 760 to approx 1 Torr by means of another cryosorption pump) if (a) the chilled pump is saturated with air prior to the activation process, (b) the vacuum system is rinsed effectively by the gas desorbed during the activation process, and (c) activation temperatures <150°C are applied.