Generalize: Gas recirculating cooled roots vacuum pump consists of a pair of rotors, pump housing , cooler, etc.  Cooled air from the both sides of the pump housing enters into the pump chamber for cooling the rotors in order to avoid the pump overheating without any effect on its pumping performance. Performance of pumping rate, noise and vibration are significantly improved than two-lobe pumps. The rotors of gas-cooled Roots pump take the involute profile, and rotate without contact and keep a constant gap in-between. Due to this special and patented structure, gas-cooled Roots pump can maintain the long-term reliable operation in high pressure differential and high compression ratio. Gas-cooled vacuum pump can be used alone or in series, or combined with other vacuum pumps to achieve higher vacuum and meet kinds of requirements.