GB731526A - Improvements in or relating to radial flow impellers - Google Patents

Abstract

731,526. Centrifugal fans and pumps. HOWDEN & CO., Ltd., J. April 18, 1952 [April 23, 1951], No. 9369/51. Class 110 (1). A centrifugal impeller comprises blades arranged between a back-plate and an annular shroud plate and backwardly inclined with respect to the direction of rotation of the impeller, each blade comprising a fixed inner portion of aerofoil profile and an outer portion slidable in guides on the back and shroud plates, means being provided to secure the outer portion in any desired position. Fig. 4 shows a construction in which each impeller blade comprises a fixed nose 12 which is welded or otherwise secured at one end to a back-plate 102 and at the other end to a shroud plate (not shown). A retractable tail 20 can be held in various extended positions by means of locking pins which are passed through selected holes 25 in the back plate 102 and are received in sockets 24. The tail 20 may slide in guide rails formed on the back plate 102 and the shroud plate, and may be fixed into position after 'adjustment by welding or riveting. It may slide alongside the nose 12 instead of within it. In the impeller blade shown in Figs; 7 and 9, the tail 20 is slidable in guide members 35, 36, consisting of angle irons or the like attached to the back plate and shroud plate. The tail 20 is moved by a screw 58 which is turned by a tool applied to its square end 63. A removable access door 64 is provided. The tail 20 is locked in the required position by, means of pins 42 which are inserted through holes 38, 39. in the guide members 35, 36 and corresponding holes in the tail 20. If the impeller is used for corrosive gases, the sliding surfaces of the tail 20 and of the guide members 35, 36 are preferably, faced with corrosion-resistant material. A mechanism for making the adjustment while the impeller is rotating comprises a member 87, Fig. 13, which is slidable on the impeller shaft 86 into any of three positions in which it is held by engagement of a spring-loaded ball 98 with one or other of three annular grooves 99. Two bevel gears 80, 82, journalled in ball-bearings, mesh with a number of bevel gears 84, each on a radially disposed shaft 73 which is connected by further gearing to the adjusting screw of one of the impeller blades: When the member 87 is moved by a link 92 from the neutral position shown into, for example, the left-hand position, it is connected to bevel gear 80 by the engagement of dog clutch teeth 88, 90. On application of brake shoe 96 to brake drum 95, the rotational speed of bevel gear 80 is reduced below that of bevel gear 82, and the resultant rotation of bevel gears 84 and shafts 73 effects adjustment of the impeller blades in one direction. Adjustment in the other direction is effected by bringing the member 87 into the right-hand position. Preferably, link 92 and brake shoe 96 are actuated by a common means, which may be mechanical, electrical or hydraulic.