aerotech777
Topic Author
Posts: 71
Joined: Sat Aug 15, 2009 3:53 pm

APU Fuel Drain Mast

Mon Jul 01, 2013 11:04 pm

Hi,

"There are two drain masts. The one just aft of the port wheel-well is shared with the hydraulic reservoir vent and is a shrouded line enclosing the APU fuel supply line, this collects any leakage of fuel into the shroud which can be drained when a stop cork is pushed up in the wheel-well. If fuel drains when the stop cork is pushed, it indicates a leak in the APU fuel line".

This is an excerpt from this link: http://www.b737.org.uk/apu.htm

a) I am wondering if this excerpt is valid for the B737 NG, the classic, or both?

b) If the B737 NG is fitted with the "stop cork" (mentioned in the excerpt), where the leakage of the fuel goes in flight if there is a leak in the APU fuel line?

c) Are other aircraft (Boeing, Airbus, Bombardier, Embraer,...) fitted with APU fuel drain mast ? Is it similar to the B737 ?

Feedback appreciated.

Regards
 
AA737-823
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RE: APU Fuel Drain Mast

Mon Jul 01, 2013 11:30 pm

I can tell you that yes, the NG has a fuel drain mast.
This "stop cork" thing is new to me- none of our 737s have it. Kind of a bizarre concept, and I question it's validity. Something like this:
"We're gonna make a provision for fuel to drain, if there's a leak, and then we're going to plug the drain hole."
!?!

Regarding other aircraft, I'm assuming it's a reg that stipulates fuel must be able to safely drain away from the line without creating undue risk of combustion...
 
yeelep
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RE: APU Fuel Drain Mast

Wed Jul 03, 2013 8:07 am

Quoting aerotech777 (Thread starter):
a) I am wondering if this excerpt is valid for the B737 NG, the classic, or both?
The Classic and I believe also the Jurassic, not installed on the NG.

Quoting aerotech777 (Thread starter):
b) If the B737 NG is fitted with the "stop cork" (mentioned in the excerpt), where the leakage of the fuel goes in flight if there is a leak in the APU fuel line?

Inflight or on the ground, leakage from the APU shroud line will exit at the drain mast.

The description of the "stop-cork" is somewhat lacking. It is part of the drain line that runs along the center keel beam in the wheel well. It is a small reservoir, say 10ml-20ml that that has a valve "stop-cork" on the bottom. It is tee'd vertically into the shroud line, so if there is a leak the reservoir will fill and once full fuel will bypass it and drain out the mast. When the valve is opened and fuel comes out, you have confirmation of a fuel leak.
 
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CALTECH
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RE: APU Fuel Drain Mast

Sun Jul 07, 2013 2:28 pm

Quoting AA737-823 (Reply 1):
This "stop cork" thing is new to me- none of our 737s have it. Kind of a bizarre concept, and I question it's validity. Something like this:
"We're gonna make a provision for fuel to drain, if there's a leak, and then we're going to plug the drain hole."
!?!

Believe it, like yeelap posted, it was there. The drain mast was a shroud around the fuel line and as the OP posted, if you opened the push valve (it was kinda like a fuel sump drain) and fuel came out, you had a fuel leak. It could contain it if the shroud filled up IIRC. Better than dumping fuel overboard with no evidence of a fuel leak.

This might be where the question came from,...about halfway down the page,.....

http://www.b737.org.uk/apu.htm
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KC135Hydraulics
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RE: APU Fuel Drain Mast

Sun Jul 07, 2013 3:58 pm

I can speak for the C-17, that after the APU shutdown sequence is initiated, the APU ALWAYS dumps a few oz of fuel on the ground once the fuel flow is stopped. It is quite normal, and as you can expect it comes from a fuel drain mast.
MSgt, USAF
KC-135R / C-17A Pneudraulic Systems Mechanic Supervisor
 
AA737-823
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RE: APU Fuel Drain Mast

Mon Jul 08, 2013 6:40 am

Quoting KC135Hydraulics (Reply 4):

I can speak for the C-17, that after the APU shutdown sequence is initiated, the APU ALWAYS dumps a few oz of fuel on the ground once the fuel flow is stopped. It is quite normal, and as you can expect it comes from a fuel drain mast.

That's an entirely different issue. Several turbine engines (the PT-6A comes to mind) puke fuel upon shutdown.

Quoting CALTECH (Reply 3):
Believe it, like yeelap posted, it was there. The drain mast was a shroud around the fuel line and as the OP posted, if you opened the push valve (it was kinda like a fuel sump drain) and fuel came out, you had a fuel leak. It could contain it if the shroud filled up IIRC. Better than dumping fuel overboard with no evidence of a fuel leak.

Weird. I'm still inclined to say ours didn't have it (removed via STC??? I dunno), because I never was aware of it.
That said, it wouldn't be the first time I learned something new!
 
yeelep
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RE: APU Fuel Drain Mast

Mon Jul 08, 2013 10:00 am

Quoting AA737-823 (Reply 5):

What model(s) are you referring to? The particular models I know of are: -700,-800,-900,-900ER do not have it. The -400 does. The -200 I believe does, though its been along time since I worked on one.

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