Patent ID: 7214036
Filing Date: 2007-05-08
Classification: F04C

Abstract:
1. A screw vacuum pump having a pair of screw rotors rotatively engaged with each other in a pump casing to discharge a gas along a longitudinal direction of the pump, each rotor having a cross section with a profile including an epitrochoid curve, a circular arc, and a pseudo-Archimedean spiral curve, wherein the pump is characterized in that: each rotor of the pair of screw rotors has a first, a second, and a third set of helical teeth, which are serially located in a longitudinal direction of each rotor, are different from each other in theoretical displacement volume, and are different from each other in type; wherein the first helical teeth of each rotor are positioned on a suction side, the third helical teeth of each rotor are located on a discharge side, and the second helical teeth of each rotor are located intermediate to the suction and discharge side; and a bypass conduit communicates with a delivery side of the pump, is connected via a first check valve to a first intermediate space defined between the first helical teeth and the second helical teeth, and is connected via a second check valve to a second intermediate space defined between the second helical teeth and the third helical teeth.