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Air
Page 38
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operated fan drive
• A cone type clutch actuated by air pressure is a feature of a fan drive, produced by Dynair Ltd., Dunkirk Mills. Woodchester, Stroud, that will be seen fitted to the engines of a number of vehicles at Earls Court. Versions of the drive are available for various types of application, including direct mounting on the fan or crankshaft and installation remote from the engine, as for example at the end of a shaft driven from an auxiliary gearbox. While two separate forms of clutch drive cater for direct and shaft drive, the same principle of clutch operation is applicable to both types.
Engagement by air pressure is preferred to disengagement on the score that the fan is operating for only about 10 per cent of the total running time of the vehicle. The working parts are not, therefore, operating under load for 90 per cent of the running time.
A wax thermostat is incorporated in a special Dynair air-control valve located in the top or bottom hose, the thermostat being adjusted accordingly. The thermostat opens the valve at the pre-set temperature and air is fed to a piston in the clutch mechanism, the clutch being designed to transmit 8 hp per 1,000 rpm. By employing a cone that has three engagement faces it has been possible to reduce the size of the unit to about 3fin. Air is derived from the brake-system reservoir and maximum air consumption is approximately 0.00041b of air per engagement. Bolts in the casing can be used to lock the drive in the event of fan-drive or control-valve failure.