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NATOPS1

45 PSI for engine start

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Some say we reduce the manifold air pressure PSI to less than 45 to allow the engine bleed air regulator valve to "open" (thinks the manifold air pressure is less than 50 PSI)

And some say it is so the starter control valve can open (against less pressure)...

I make no claim to either. I know our book says if you get NO propeller rotation to reduce the air pressure to less than 45 PSI and try to restart...

I know the manifold pressure will be less than "50 PSI" but I also know the starter control valve is subjected to "less" air pressure....

Thoughts?

References????

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Some say we reduce the manifold air pressure PSI to less than 45 to allow the engine bleed air regulator valve to "open" (thinks the manifold air pressure is less than 50 PSI)

And some say it is so the starter control valve can open (against less pressure)...

I make no claim to either. I know our book says if you get NO propeller rotation to reduce the air pressure to less than 45 PSI and try to restart...

I know the manifold pressure will be less than "50 PSI" but I also know the starter control valve is subjected to "less" air pressure....

Thoughts?

References????

Natops, are you ok? This must be your most disjointed posting

ever:-) However, it seems the question refers to starting with an

engine at normal ground idle.

It is possible that high air pressure upstream of the valve could

jam the solenoid. Several years ago I had an engine that was very

slow to start. After a few minutes, we realized the scoop anti-

icing valve was open. We replaced the scoop valve only to have no

rotation when the starter was pressed. Several rapid pushes of the

button got the engine turning, but another attempt failed.

On a whim my colleague opened the scoop valve, and pushed the

starter button - rotation! Result was no rotation with 40psi,

but 35psi was no problem.

Don't know of any T.O. or checklist references, though.....

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Natops, are you ok? This must be your most disjointed posting

ever:-) .....

Guess not.... I think I lost a few line of my orginal post...

If you try to start an engine and get NO rotation (STOP START)

"We" "check" and make sure we have power (Start valve open light will press to test)

and we have air to the starter (we see a defelction in the air pressure gauge (gage) when the regulator valve is placed to override)

But... we have a NOTE that tells us to reduce the bleed air manifold press to less than 45 PSI and attempt a restart...

The question is......

Some say we reduce the manifold air pressure PSI to less than 45 to allow the engine bleed air regulator valve to "open"

and some say it is so the starter control valve can open (against less pressure)...

Does anyone have any thoughts on this subject?

Does anyone have any references on the subject?

I have had an engine /prop that would not rotate unless I used low press air and I'm sure it was due to the starter control valve not opening aginist "higher" air pressure (it was #1 eng)... Reduce the air press engine rotates and starts...

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I've heard of this happening a few times, but as I don't get to the line

very often, I don't have hands-on experience there - just the one time

described in the cell. Maybe the valve bushings get corroded or worn

out, and gets pushed out of position with the higher pressure. Maybe

the solenoid is weak and can't release against the higher pressure.

GTC aircraft don't (normally) have the modulating engine bleed-air

valves, either open or closed, while the APU birds have the ON/OVERRIDE

type valves which regulate 45 and 75psi. Engines at NGI generally put

out 78 to 85 psi, so to go less than 45psi would mean starting off

the APU/GTC or placing the engine(s) in LSGI.

My guess would be that the mechanicals of the valve are worn out - time

for a replacement. As a further thought on this subject, I would be on the

look-out for slow-closing/valve staying open after starter release .....

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To my understanding this pressure reducing to 45psi will help only if one solenoid (solenoid B) of the Engine Bleed Air Regulator and Shutoff Valve is malfunctioning in which the valve is behaving as in “ONâ€â€ position, therefore when the main manifold is higher than 45psi the valve tends to go to the close position preventing a sufficient amount of air to enter.

By reducing the pressure manifold to 45 the valve will tends to take the full open position especially during engine start thus making start possible.

Note:

In Override position both solenoid should be energized. (Valve fully opened)

In ON position: solenoid (A) energized, solenoid (B) deenergized. (Valve modulate to maintain 50 ±7 psi)

In Off position: Both solenoids deenergized. (Valve closed).

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To my understanding this pressure reducing to 45psi will help only if one solenoid (solenoid B) of the Engine Bleed Air Regulator and Shutoff Valve is malfunctioning in which the valve is behaving as in “ON”” position, therefore when the main manifold is higher than 45psi the valve tends to go to the close position preventing a sufficient amount of air to enter.

By reducing the pressure manifold to 45 the valve will tends to take the full open position especially during engine start thus making start possible.

Note:

In Override position both solenoid should be energized. (Valve fully opened)

In ON position: solenoid (A) energized, solenoid (B) deenergized. (Valve modulate to maintain 50 ±7 psi)

In Off position: Both solenoids deenergized. (Valve closed).

I agree with the technical data solenoid (A) and (B) and the "reason" but would you try low press air to see if the engine will rotate?

I have had a start control valve that would not open with high pressure air so, I would...

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