ABSTRACT
This chapter is concerned with the prevention of overloading high-vacuum pumps and the resulting adverse effects or malfunctions. High-vacuum pumps, like other compressors, have basic limitations in regard to the maximum pressure difference and maximum mass flow rates that they can produce. Because high-vacuum pumps are usually made to discharge into another pump, their tolerable discharge pressure must be associated with the characteristics of the backing pump. The traditional plot of pumping speed versus inlet pressure often produces conceptual confusion with regard to the cause of pumping speed reduction at the end of the constant speed section. Popular opinion ascribes the reduction to the arrival of viscous flow at the inlet of the high-vacuum pump. In a high-vacuum pump, this power is a very minor part of the total power. In a vapor jet pump, most of the power is consumed in reboiling the motive fluid after condensation.
