Vacuum pumps
AssigneeThe BOC Group, Inc.
InventorMichael Henry North
Life of this patent
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Abstract
A vacuum pump having a screw mechanism and comprising two externally threaded rotors mounted on respective shafts in a pump body and adapted for counter-rotation therein with intermeshing of the rotor threads with close tolerances between the threads and internal surfaces of the pump body in order that gas may be pumped from a pump inlet to a pump outlet by action of the rotor threads, the root diameter of each rotor increases and the thread diameter of each rotor decreases in a direction from the pump inlet to the pump outlet, and wherein the pitch of the rotor threads decreases in a direction from the pump inlet to the pump outlet.
Claims8
A vacuum pump having a screw mechanism and comprising two externally threaded rotors each one comprising one piece and mounted on respective shafts in a pump body and adapted for counter-rotation therein with intermeshing of the rotor threads with close tolerances between the threads and internal surfaces of the pump body in order that gas may be pumped from a pump inlet to a pump outlet by action of the rotor threads, the root diameter of each rotor increases and the thread diameter of each rotor decreases in a direction from the pump inlet to the pump outlet, and wherein a first one of the rotors has a first set of threads having a constant pitch and a second set of threads with a varying pitch less than the constant pitch.
Dependencies are inferred from the claim text.