ABSTRACT
Dry vacuum pumps are vacuum devices with new technological concepts, which are developed due to the industrial demands. The dry cylinder piston pumps are suited to produce clean, dry, oil-free vacuum in low-vacuum regions and to back up turbomolecular pumps. Dry rotary vane pumps are designed with multiple vanes. The dry multivane pumps operate at high pressure where the gas load is very large. Diaphragm pumps do not pump water vapors and other condensable gases because they are positive displacement pumps working on the principle of periodic increasing and reducing their operational volumes. The mechanism of Roots pumps was invented and patented by brothers Philander Higley Roots and Francis Marion Roots in 1860. Single-stage Roots pumps do not operate against atmospheric pressure. The trilobed pumps have segmented rotors. The mechanical concept of rotary claw vacuum pumps is used in gas compressors. Rotor screws can be designed with rectangular thread profiles or with variable screw pitch along the pumping path.
