| 摘要 |
A rotary vacuum pump having a low vacuum stage and a high vacuum stage, each stage including a stator body having a bore and a rotor mounted eccentrically in the bore to form a cavity between the stator body and the rotor, the rotor of each stage having two vanes slideably positioned in diametrically opposed slots in the rotor which in use of the pump are substantially in contact with an inner wall of the stator body during rotation of the rotor, and the stator body of each stage having an inlet and an outlet to allow, in use of the pump, fluid being pumped to enter into and be expelled from the cavity by means of the rotating vanes, wherein: i) means are provided to enable oil to be injected in to the low vacuum stage and, when required, in to the high vacuum stage also, and ii) means are provided to allow differential flow rates (including zero) of ballast gas to the low vacuum stage, for example in an amount in excess of ten percent of the overall vacuum pump capacity (which equates to the capacity of the high vacuum stage) thereby having an ability to operate as a one stage or as a two stage pump. <IMAGE> |
