Patent ID: 9617998
Date: 2017-04-11
CPC Classifications: F04C

Claim:
1. A Roots-type blower comprising: a housing defining first and second transversely overlapping cylindrical chambers, the housing comprising a first end wall and a second end wall, and the housing defining at least one inlet port in the first end wall and at least one outlet port at an intersection of the first and second chambers, adjacent the second end wall; first and second meshed, lobed rotors disposed, respectively, in the first and second cylindrical chambers, each rotor including a plurality of lobes, each lobe having first and second axially facing end surfaces sealingly cooperating with the first and second end walls, respectively, and a top land sealingly cooperating with a respective cylindrical chamber, each lobe having its first and second axially facing end surfaces defining a twist angle of at least 90°, and each lobe defining a helix angle; a plurality of control volumes for transfer of fluid from the at least one inlet port to the at least one outlet port, each control volume being defined by a pair of adjacent lobes on one of the rotors, and at least one of the cylindrical chambers, the first end wall, or the second end wall; a leakage mechanism for effecting a leakage of fluid between adjacent control volumes, the leakage mechanism including blowholes formed within the cylindrical chambers in connection with meshing of the lobes of the first and second rotors; and an additional leakage mechanism comprising at least two individual backflow slots provided on each side of a center line of the housing, each backflow slot extending through a wall of the housing for effecting a leakage of fluid from downstream of the at least one outlet port into a control volume prior to traversal of boundaries of the at least one outlet port by the top land of a lead lobe of the control volume, wherein the individual backflow slots on either side of the center line are arranged along a slot axis having a slot axis angle to a longitudinal direction of the housing, and wherein the slot axis angle is smaller than the helix angle of the lobes, such that the individual backflow slots along each slot axis sequentially enable a fluid flow passage to a control volume as the top land of the lead lobe of the control volume progressively traverses the slot axis.