GB464844A - Improvements in or relating to the control of centrifugal fans, pumps and the like - Google Patents

Abstract

464,844. Centrifugal fans. DAVIDSON & CO., Ltd., and WHITMORE, J. Oct. 30, 1935, No. 29990. [Class 110 (i)] A centrifugal fan is regulated, at all loads under the maximum, by the division of the entering air into two controllable portions ; one passes through the main inlet and the other through a secondary inlet which gives the air a rotary flow in the direction of rotation of the fan impeller. The fan shown has an impeller 2 working in the casing 1 provided with a tangential outlet 4 and main inlet 5. An annular chamber 8 is formed by a casing 7 round the main inlet 5, from which it is separated by a system of stationary vanes 6. This vaned space forms the secondary inlet and gives the entering air a whirling motion. The effective area of the main inlet 5 is varied by two dampers 9 which can be moved inwards or outwards together by means of a right and left-handed screw 11 rotated by a handle 13. Each damper may consist of two relatively movable plates of substantially crescent shape, one plate being arranged to move faster than the other by means of screw threads of different pitches. The chamber 8 may be situated partly inside the fan casing 1 so that the vanes 6 are within that casing, or the vanes may project at an angle into the casing 1 as shown in Fig. 5. The outer ends of the dampers are made to cover the openings to the chamber 8 between the shields 20, when the dampers are in their outermost position to give full access to the main entry 5 under full load conditions. The dampers may be actuated by levers operated by a screwthreaded rod, or by two endless belts 23, 23a, Fig. 7, round pulleys 19, 22 of different diameters. Semi-cylindrical shields 25, Fig. 10, may be attached to extensions on the dampers to diminish the quantity of air passing between the vanes when the main inlet 5 is closed. These shields 25, may have extensions 28 to prevent air from passing through the space behind'the shields 20 to the secondary inlet. When the fan is under full load the dampers 9 are open to the fullest extent thereby closing the secondary inlet so that all air enters by the main inlet 5. When the fan is under partial load the dampers are moved inwards, so that air enters the secondary inlet between the vanes and joins the main stream and imparts a rotary motion to it. A damper 14 in the fan outlet 4 provides for further volume regulation.