Patent GB-1045219-A (GB)
Title: Centrifugal gas or liquid pump
IPC: F04D17/16
Filed: 1964-11-10
Abstract: 1,045,219. Centrifugal gas and liquid pumps. K. D. McMAHAN. Nov. 10, 1964 [Dec. 20, 1963] No. 45843/64. Heading F1C. [Also in Division H2] In a centrifugal gas or liquid pump adjacent passages of a number of volute passages extending around and axially of the impeller have an axial overlap substantially greater than the radial overlap. A single stage blower is shown but the blower may be used in series to form a multi-stage assembly or have a number of stages mounted on a single shaft. The total area of radial overlap of adjacent volute passages 51, expressed as a percentage of the area of the cylindrical surface having the mean diameter and axial width of receiver 45, may be between zero and 15 to 25 %. The total area of axial overlap, expressed as a percentage of the circumferential area between the periphery of the impeller back plate 40 and the wall of the casing part 16, is preferably above 75 %. The addition of the percentage axial and radial overlaps must exceed 75 % and preferably should total 100 % or more, and the ratio of axial overlap to radial overlap must be greater than 2, preferably 4À5 or more. The dead space between radially outer wall 53 and the casing serves for accommodating variations in design. The radial clearance between cut-offs 50 and the discharge ends 43 of the impeller blades 42 is preferably 3 % of the impeller diameter. To reduce noise developed at the cutoffs 50 the angle # between the ends of the upstream edges of each cut off is at least 20 degrees and the ratio of the angle # to the angle # between adjacent impeller blades is at least 1 but preferably less than 2. Moreover, the ratio of the number of impeller blades (nineteen) to cut-offs (five) is a mixed number. The casing parts 16, 17, 18 may be moulded from plastics and are secured together by screws 27 passing through threaded spacers 28 to bosses on casing 17, and screws 56, 58 and vanes 52. The wall 53 of each passage 51 merges with the casing and an inner wall 55 merges with a housing 20 for the driving motor 11. An outlet elbow 60 of each passage 51 has an overextended outer bend 63 to counteract the tendency of the stream, due to centrifugal force, to crowd at the outer bend. A protuberance 62 on the inner bend 61 aids in preventing the stream from breaking away from the bend 61. The casing part 18 has a concentric protuberance 65 and an overextended elbow 64 associated with an overextended and optional guide vane 66, to direct the streams over a curved surface 67 to a common outlet 68. The elbow 64 may be dispensed with and the elbows 60 arranged to direct the streams at any angle between an axial and radial inward direction. Holes (not shown) in a motor support 22 permit free circulation of cooling air or gas around the motor windings 31. To permit manufacture of the blower with different performances, using the same housing and the same basic impeller, the outer diameter of the latter may be reduced in steps. The blower may be mounted in an aperture in a metal panel (not shown) to deliver in either axial direction, by a number of bolts carrying stout washers with tongues engaging the appropriate set of crescent-shaped recesses 77, 77a, or a continuous groove in casing parts 16, 17. In a modification, Fig. 9 (not shown), the impeller peripheral discharge is frustoconical and the cut-offs are inclined to provide constant radial clearance to the discharge ends of the impeller blades. Further, the motor housing has been eliminated to conserve radial space, reduce weight and provide maximum ventilation of the motor.