ABSTRACT
The gas flow theory enables to determine gas flows in stationary flow regimes, that is, under the conditions when the gas flow regimes are invariable along the entire length of the tube and independent of the time. The pumping performance of a vacuum system depends on the effective pumping speed that is determined by the pumping speed at the inlet of a pump and the conductance of the tube through which the gas is evacuated. It also depends on the pressures of the pumped volume and at the pump inlet, as these parameters determine the gas flow regime; the nature of the pumped gas; the pumping method; and the number of pumps integrated into the pumping unit. At low vacuum, the gas can be pumped under viscous laminar conditions. Under molecular flow conditions, the gas flows from secondary gas sources become significant and they may dominate in the gas load.
