REVERSE FLOW COOLING TYPE MULTISTAGE ROOT TYPE VACUUM PUMP WITH BUILT-IN COOLING WATER PASSAGE

摘要

PURPOSE:To improve performance by a method wherein gas coming through a suction port to a housing and discharged through a delivery port is guided to an outer peripheral gas flow passage for cooling. CONSTITUTION:In a first pump section 1, gas G81 sucked with the aid of a pump is sucked as suction gas G13 through a suction port 13, and is conveyed through the motions of rotors 12A and 12B. In this case, the gas on which reverse flow compression is applied in a state that a rise in temperature is suppressed to a low value by means of gas G15 for reverse flow cooling is delivered as delivery gas G14 through a delivery port 14 to outer peripheral gas flow passages 16A and 16B. This constitution suppresses a temperature difference between the housing 11 and the rotors 12A and 12B during running to a low value, eliminates a difference in a thermal expansion amount between the housing and the rotors, and reduces an amount of gas leaking through a gap therebetween.