Patent ID: 7140846

Claim:
A vacuum pump comprising: a main pump including a pump chamber and a gas transferring body that is located in the pump chamber and an exhaust space communicating with the pump chamber, the main pump being driven by a drive source through a rotary shaft for transferring gas to the exhaust space; a check valve located downstream of the exhaust space for preventing the gas from flowing back; a sub pump connected to the exhaust space for partially exhausting the gas from the exhaust space, the sub pump being driven by the same drive source, the displacement volume of the sub pump being smaller than that of the main pump; and an exhaust passage of the sub pump communicating with a gas passage downstream of the check valve, wherein said main pump is a roots pump, the roots pump comprising: a plurality of rotary shafts located parallel to each other, wherein one of the rotary shafts is driven by the drive source of the roots pump; a plurality of the main rotors as gas transferring bodies respectively connected to the rotary shafts, the main rotors on coadjacent rotary shafts being engaged with each other; and a plurality of the main pump chambers as the pump chamber accommodating a set of the engaged main rotors, one of which has a minimum volume and communicates with the exhaust space, and wherein said sub pump is a diaphragm pump including a diaphragm, a suction valve and a discharge valve, the diaphragm being positioned such that the plane of the diaphragm intersects a hypothetical extended line of an axis of the rotary shaft being driven by the drive source of the roots pump.