Patent ID: 7500381

Claim:
A trace gas leak detector comprising: a test port to receive a sample containing a trace gas, the test port connected to a test line; a mass spectrometer to detect the trace gas, the mass spectrometer having an inlet; a high vacuum pump having an inlet port coupled to the inlet of the mass spectrometer, the high vacuum pump having an exhaust port; and a forepump having a main inlet, at least one intermediate inlet connected to a working volume of the forepump, and an exhaust, the main inlet coupled to the exhaust port of the high vacuum pump, the intermediate inlet controllably connected to the test line, wherein the intermediate inlet operates at an intermediate pressure and wherein the forepump is of a type that permits location of the intermediate inlet at a range of intermediate pressures between the main inlet and the exhaust, a location of the intermediate inlet and the corresponding intermediate pressure being selectable according to an expected test line pressure in a particular application, the forepump selected from the group consisting of a scroll vacuum pump and a screw vacuum pump.