Patent ID: 7850434

Claim:
Differentially pumped vacuum system comprising first, second and third pressure chambers; and a pumping arrangement attached thereto for evacuating the first, second, and third pressure chambers, the pumping arrangement comprising first and second compound pumps each comprising at least a first inlet, a second inlet, a first pumping section and a second pumping section downstream from the first pumping section, the sections being arranged such that fluid entering the first or second compound pump from the first inlet passes through the first and second pumping sections and fluid entering the aforementioned pump from the second inlet passes through, of said sections, only the second section, wherein the second inlet of the first compound pump and the first inlet of the second compound pump are attached to an outlet or respective outlets from the second pressure chamber in a manner that fluid in the second pressure chamber is drawn out through the second inlet of the first compound pump and the first inlet of the second compound pump, instead of through the first inlet of the first compound pump or the second inlet of the second compound pump, so that, in use, the first compound pump evacuates the second pressure chamber in parallel with the second compound pump.