Control of a two-stage vacuum pump

摘要

An oil-free two-stage vacuum pump is disclosed, which comprises a first and a second pump stage (200A,200B) coupled for series driving. The first and second pump stages have their discharge spaces (56,57) capable of being communicated with each other via a bypass passage. The bypass passage is provided with a pressure control valve (125) to be closed when the pressure in it becomes lower than a predetermined pressure. The second pump stage does not withdraw compressed gas under pressure higher than the atmospheric pressure, and is free from heat generation that might result from excessive compression. <IMAGE>