GB887100A - Centrifugal fans - Google Patents

Abstract

887,100. Centrifugal fans. WESTING- HOUSE ELECTRIC CORPORATION. Jan. 25, 1960 [Jan. 29, 1959], No. 2585/60. Class 110 (1). Centrifugal fan blades 24, Fig. 1, of aerofoil form are inclined backwardly with respect to the direction of rotation and mounted between a front plate of an impeller and a back plate 20 (or the centre plate in the case of a doubleinlet impeller). A strip 25 of spring metal having a bent-over end 26 is riveted to the pressure face of each blade near the trailing end and can be placed manually into an alternative position in which it lies flush with the pressure face, with the end 26 extending behind the trailing end of the blade. In this alternative position of the strips 25 the fan develops its normal pressure and volume. When the strips 25 are in the position shown, they deflect the flow forwardly in the direction of rotation to increase the capacity of the fan by up to 30% with a slight loss of efficiency. In the blade shown in Fig. 8, a strip 25E is riveted to the suction face of the blade with its bent-over end 26E projecting beyond the pressure face of the blade to increase the capacity. Alternative holes for pins 39 are provided to give a fully retracted position in which the end 26E does not project beyond the pressure face, the pressure then being normal; and an intermediate position in which an intermediate pressure increase is obtained. In a modification, the pins 39 are omitted and the strip 25E has two positions only, the second position being obtained by bracing the end 26E against the suction face of the blade. In a further modification, infinite variation between the two limits is obtained by means of an adjusting screw threaded into the blade and bearing against the strip 25E. An alternative construction comprises a strip, without a bent-over end, riveted to the pressure face of the blade and retractable against its own springiness by means of an adjusting screw into a position flush against the pressure face. In Fig. 7 a strip 29 extending through the pressure and suction faces of the blade has slots 28 to receive adjustment screws 30 whereby the extent of its projection beyond the pressure face can be varied. Specification 841,164 is referred to.