Jump to content

Bleed Air Switch


Great Above
 Share

Recommended Posts

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 models

with GTC, there was only "ON" giving maximum pressure from engines (75 to 85psi)

 

Edited by pjvr99
Link to comment
Share on other sites

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.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...