ABSTRACT
"Diffusion" pumps are vapor jet pumps or vapor ejector pumps designed for pumping rarefied gases in the high-vacuum range of pressures. The only justification for calling them diffusion pumps is due to the observation that the molecules of the pumped gas penetrate some distance into the vapor jet in a manner resembling diffusion of one gas into another. The vapor is produced in the boiler and is expanded through a nozzle achieving a high velocity. At the bottom of the cylinder is the boiler where the pumping fluid is placed. There is an electrical heater at the bottom of the pump with sufficient power to evaporate the pumping fluid and maintain desired pressure in the boiler. Tolerable forepressure of a pump is the maximum permissible pressure at the foreline. The tolerable forepressure for various gases is approximately the same as far as the complete collapse of vapor jet (last stage) is concerned.
