Great Above Posted August 22, 2015 Share Posted August 22, 2015 Hi pls can some one explain what placing the bleed air switch to override does during engine start. Quote Link to comment Share on other sites More sharing options...
pjvr99 Posted August 22, 2015 Share Posted August 22, 2015 (edited) in "ON" position air pressure is regulated to 40psi (similar to APU delivery pressure),whereas "OVERRIDE" is 70psi, giving your a faster cooler start. On older B & E modelswith GTC, there was only "ON" giving maximum pressure from engines (75 to 85psi) Edited August 22, 2015 by pjvr99 Quote Link to comment Share on other sites More sharing options...
Lkuest Posted August 22, 2015 Share Posted August 22, 2015 Hi pls can some one explain what placing the bleed air switch to override does during engine start.The starter control valve regulates at around 39 psi, so you'd think there would be no difference between "on" and "Override" at the starter. There is, however, a difference at the starter control valve itself. It has to do with the "rise rate" of air pressure, which allows smooth and prompt engagement of the starter clutch at just the correct starter turbine RPM. Basically, the full 70+ psi opens the starter control valve more quickly. If the valve opens too slowly, and the starter turbine is allowed to spin up to an RPM too high before the force from the air forces clutch engagement. The starter control valve can be adjusted, though, to tune the rise rate to the desired manifold pressure. There are Lockheed service news bulletins that touch on it a bit, likeV13No1, V17No3, and V24No4, but I'm struggling to remember if there is one that addresses "on" vs "Override" specifically. I could swear there is one though, it just escapes me at the moment. Quote Link to comment Share on other sites More sharing options...
Great Above Posted August 23, 2015 Author Share Posted August 23, 2015 Thank you LKuest, really appreciate. Quote Link to comment Share on other sites More sharing options...
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