GB898002A - Improvements relating to extraction fans - Google Patents

Abstract

898,002. Ventilators. SILAVENT, Ltd. June 12, 1959 [March 12, 1958], No. 7978/58. Class 137 [Also in Groups XXVI and XXXV] The shaft carrying the impeller of an extraction fan and the rotor of the electric driving motor can slide axially between a rest position in which the inlet to the fan casing is obstructed by the central part of the impeller disc and the rotor is axially displaced from the centre of the stator field, and an operating position in which the rotor is at or nearer the centre of the field and the inlet is more open. The fan casing 5 is fixed to a wall 31 with the inlet pipe 11 leading from a water-closet pan or other space from which air is to be extracted. The air is discharged through openings 19. The driving motor is bolted to a circular plate 14 which is mounted on the fan casing by means of a shock-absorbing tyre-shaped rubber ring 16 and a clamping ring 17. When the motor is switched off, the shaft 2 slides downwards in its bearings 20, 21 under gravity until the motor rotor 3 meets a stop surface 22. Alternatively or in addition, the shaft may be spring-loaded into this position. A central, preferably spheric cal, portion 23 of the fan impeller then obturates the flared inlet 12 to reduce back draught up the inlet pipe 11. Preferably, a small annular clearance is left between the portion 23 and the inlet 12 to lessen the danger of them being frozen together in cold weather. For the same reason, electrical heating elements may be embedded in the inlet 12 and connected in series or parallel with the motor. If complete sealing of the inlet is required, the portion 23 may engage a carbon ring mounted on the end of a resilient bellows at the inlet. When the motor is energized, the rotor 3 is attracted towards the centre of the stator field to bring the shaft and impeller into the operative position shown. This movement may be limited by an adjustable thrust pad (not shown) against which the shaft abuts in the operative position, adjustment of the thrust pad varying the capacity of the fan partly by throttling the inlet aperture and partly by displacing the rotor relative to the stator, thereby reducing the motor speed. According to the Provisional Specification, movement of the rotor into the operative position may be assisted by a solenoid connected in series with the motor. For the purpose of varying the capacity of the fan, the movement may be adjusted by adjusting the position of the rotor on the shaft. The movement may be effected manually instead of automatically. Instead of the central portion of the impeller, a separate obturating surface mounted on the shaft may be used. Alternatively, the axial movement of the shaft may operate a valve in the inlet.