Patent GB-737785-A (GB)
Title: Improvements in or relating to centrifugal fans or blowers
IPC: F04D29/28
Filed: 1952-07-31
Abstract: 737,785. Centrifugal fans. AIR CONTROL INSTALLATIONS, Ltd., and REEVES, H. C. Oct. 30, 1953 [July 31, 1952], No. 19427/52. Class 110 (1). A centrifugal fan or blower comprises blades adjustably mounted on an impeller so as to pivot about a pivot pin which lies within the thickness of the blade and is disposed substantially parallel to the axis of rotation of the impeller, the pivot axis being disposed at or near the centre, of gravity of the blade. Fig. 1 shows a number of different blades, blade 16 being straight and the others curved. Blades 13, 14, 15, 16, 17 and 18 are each pivoted at the centre of gravity on a bolt 22 which passes through the back plate 11 and the shroud plate of the impeller. After the blade has been adjusted to the required angular position, the bolt 22 is tightened to clamp it between the back and shroud plates. Blade 19 is freely pivoted in trunnions 32 and has a slotted sector 29 which is engaged by a stud and a clamping nut 31. In this case, in the absence of bolts 22, the back and shroud plates are clamped together by bolts 33. Blade 20 has a circular plate 34 having holes 35 which are in vernier relation with threaded holes in the back plate 11. A securing bolt is passed through a selected pair of holes to hold the blade at the required angle. In the impeller shown in Fig. 3, the back and shroud plates are held together by fixed blades 36 welded thereto. Adjustable blades 37, which may be more numerous than the blades 36, are each pivoted, preferably at the centre of gravity, on a spindle 38 and connected at 39 to a connecting rod 40 which is connected at 41 to a sleeve 42 which is freely journalled on the impeller shaft 43. The blades are adjusted in unison while the fan is running by an electric motor 46 which is carried on the impeller and rotates the sleeve by means of a worm 47 and worm-wheel 44, the latter being integral with the sleeve 42. The arrangements shown in Figs. 1 and 3 may be applied to a double inlet impeller comprising two shroud plates disposed on opposite sides of a central plate, with blades between each shroud plate and the central plate. Some of the blades, for example alternate ones, may be fixed. The double inlet impeller shown in Fig. 5 comprises two annular plates 49, 50 clamped on either side of rings 51, 52 and carried by two hub portions 55. Half shafts 58, 59 are journalled in bearings 60, 61 respectively. Bearing 60 has an internally threaded extension 64 which is engaged by a threaded plug 65. A spindle 62 is slidably keyed to the shaft 59 and rotatably connected to the plug 65 by means of a ballbearing 67. Each pair of blades 79 is carried by a spindle 77 which is connected by a crank 76 and connecting rod 74 to one arm 72 of a bell-crank, the other arm 70 of which engages a groove 69 formed in an enlargement 68 of the spindle 62. Thus, by rotating a hand wheel 66, spindle 62 may be moved longitudinally to adjust the blades 79 while the impeller is running. Cooling air enters through holes 82 and passes along the hollow shaft 58 and through holes 53, 54. The circulation of the cooling air may be assisted by an auxiliary fan. According to the Provisional Specification, the inner part of a blade may be fixed to the rotor while the outer part is adjustable about an axis disposed adjacent the fixed inner part so that no appreciable gap is produced when the adjustable part is moved.