knoll Screw pumpOperate using two counter-rotating screw rotors that are carefully designed to rotate "toward each other." This traps the gas in the space between the rotor "screws." As the screw rotates, this trapped volume decreases, which not only compresses the gas, but also moves it toward the exhaust port.

In the first case (Figures 2, 3), mechanical bearings support the rotor at both ends. The cantilever design (Figure 4) solution supports the rotor at the high pressure end, and the rotor can be cooled internally. The motor drives two rotors through gears. The gears and bearings are lubricated but separated from the pumping mechanism (" vacuum generator ") by a shaft seal or labyrinth seal, so compression is oil-free. There is no mechanical contact between the rotor and the pump housing, so mechanical wear is zero. To keep the installed power low, modern pumps are driven by electronic inverters and rotate more slowly in a pressure range close to atmospheric pressure. Some versions use a so-called blowdown valve instead to keep the speed constant even under high pressure. Cooling is usually done by water.