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|Fig. 11-6 An air starter motor.|
11. The starter turbine is rotated by air taken from an external ground supply, an auxiliary power unit (A.P.U.) or as a cross-feed from a running engine. The air supply to the starter is controlled by an elec- trically operated control and pressure reducing valve that is opened when an engine start is selected and is automatically closed at a predetermined starter speed. The clutch also automatically disengages as the engine accelerates up to idling r.p.m. and the rotation of the starter ceases. A typical air starting system is shown in fig. 11-7.
|Fig. 11-7 An air starting system.|
13. Some turbo-jet engines are not fitted with starter motors, but use air impingement onto the turbine blades as a means of rotating the engine. The air is obtained from an external source, or from an engine that is running, and is directed through non-return valves and nozzles onto the turbine blades. A typical method of air impingement starting is shown in fig. 11-8.
|Fig. 11-8 Air impingement starting.|