Powder Coupling Fan Drive
Page 48
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PROTOTYPES of a fan coupling have been produced by Powder Couplings Ltd., Airedale Works, Hunslet Road, Leeds, which represent a new approach to the technical problem of providing variable fan drive. Based on the company's well-known Permadryve powder coupling, the system incorporates a thermostat in the cylinder head which energizes a brake pad to immobilize the fan at lower temperatures with a resultant saving in fan h.p. and improved regulation of coolant temperature.
It will be recalled that the coupling essentially comprises a housing and a corrugated rotor and that the housing contains a " flow-charge " of spherical steel shot (of about 0-0l in. diameter) which locks the housing to the rotor under the action of centrifugal force above a critical speed. In its application to fan drives an extension of the rotor carries the belt pulley and the fan is mounted on the housing, which is braked by the thermostatically operated pad. The steel shot tends to move outwardf under centrifugal force and form a sulk transmission medium between the rotoi and casing at higher speeds, but wher the casing is locked by the brake the sho is retained in the centre of the housini and exerts negligible drag. It is claimei that the drive is 100 per cent efficien when the fan has been accelerated to : speed corresponding to that of the inpu drive.