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Thread locker needed on fuel line elbow?

bertschb

bertschb

Well Known Member
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I'm on page 31-08 (fuselage fuel system) where the plans call for us to "fully tighten the AN924-6D nuts on the outboard elbow fittings". The elbow is shown below. Should we use thread locker on those nuts? The plans don't mention it and there is no mention of it in the Wiki but it seems like we wouldn't want that nut to come loose.


thread locker.png
 
Use thread locker if you wish. Most likely the reason the plans don't mention it is because there aren't serious consequences if the nut loosens, it will be captured by the flare fitting nut that is attached to the bulkhead fitting.....the fuel line can't go anywhere.
 
Sam Buchanan said:
Use thread locker if you wish. Most likely the reason the plans don't mention it is because there aren't serious consequences if the nut loosens, it will be captured by the flare fitting nut that is attached to the bulkhead fitting.....the fuel line can't go anywhere.
Click to expand...
One of those builder options----just make sure the bulkhead fitting is aligned and the line nuts are tight first.
Tom
 
Thanks guys. As usual, I'm overthinking it. After connecting and tightening the valve, fuel lines and the fuel line brackets, I can see where the fuel lines 'aint gonna move even if that nut loosens.
 
Isn't that a straight thread with O-ring type fitting? I think the compression of the O-ring when you tighten the nut adds enough friction to keep the nut from turning on its own.
 
scsmith said:
Isn't that a straight thread with O-ring type fitting? I think the compression of the O-ring when you tighten the nut adds enough friction to keep the nut from turning on its own.
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No o-ring.

The elbow looks like this (the left side is what sticks out the side of the fuselage and has the nut on it (shown below):
Screenshot 2024-04-20 at 6.27.32 PM.png

The nut:
Screenshot 2024-04-20 at 6.29.23 PM.png
 
scsmith said:
Has no effect on fluid sealing.
Click to expand...
Correct. I'm a new builder (yeah, pretty obvious) and I'm used to seeing safety wire, cotter pins, locking nuts, etc. It just seemed weird to have a "regular" nut on the airplane with no means to make sure it stays put.
 
It’s a good question.
Of greater concern with bulkhead fittings is rotation. There needs to be a means of either holding the fitting while torquing the lines, an anti-rotation device or bracket, or other means of holding the fitting if you can’t reach both sides.
Or, you need a buddy.

You can, and should, check the bulkhead fitting nut at each Ci when you check the fuel line connected to it.
 
JonJay said:
It’s a good question.
Of greater concern with bulkhead fittings is rotation. There needs to be a means of either holding the fitting while torquing the lines, an anti-rotation device or bracket, or other means of holding the fitting if you can’t reach both sides.
Or, you need a buddy.

You can, and should, check the bulkhead fitting nut at each Ci when you check the fuel line connected to it.
Click to expand...
In a 14, the way the valve to fuselage lines drop down to the bulkhead fittings, one the lines are tight the bulkhead fitting wont move. Just tighten the bulkhead nut.
 
TS Flightlines said:
In a 14, the way the valve to fuselage lines drop down to the bulkhead fittings, one the lines are tight the bulkhead fitting wont move. Just tighten the bulkhead nut.
Click to expand...
“other means of holding the fitting”…
I’ve never liked using the fuel line but it’s that way in other RV’s also. My 6 included.

For the OP, since you’re a new builder, I thought I would point this out. There is an old SB for fuel line pick up tubes as there was an incident whereby the fitting rotated pulling the fuel pick up off the bottom of the tank. This led to a fuel starvation accident. The fix was a bracket to hold the fitting.
Build on and keep those questions coming.
 
bertschb said:
It's not easy asking rookie questions in this public forum. It's pretty embarrassing. But, I want to do this build correctly. I'd rather risk ridicule than my safety.
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Ya, that’s too bad. I don’t post anything until I have read what I’m saying three times through, and heaven forbid you post a picture ‘cause somebody is going to see something…..
it’s value far out weighs any embarrassment, and there are no dumb questions! ( well, I’ve seen a few, but that’s another subject, ha! )
 
bertschb said:
It's not easy asking rookie questions in this public forum. It's pretty embarrassing. But, I want to do this build correctly. I'd rather risk ridicule than my safety.
Click to expand...
Brian,
There is no reason for you to feel embarrassed. You asked a good question, and got two good answers - yes you can lock tite it, and no you don’t have to. I wonder how many learned something (besides me) from your question. I didn’t use any lock tite on my bulkhead nuts, but now thinking maybe I should. I don’t see a downside.
 
Scott Hersha said:
I didn’t use any lock tite on my bulkhead nuts, but now thinking maybe I should. I don’t see a downside.
Click to expand...
That's kind of what I was thinking. Rather than tightening the nuts a little too tight, I'd rather use some Loctite and just snug them up. I'm not worried about the fuel Iines or the elbow moving if the nut comes loose because they are held in there really well. I just don't want that nut rattling around if it loosens up.
 
I have seen straight bulkhead fittings with internal teeth locking washer, on both sides. This is more typical than locktigbt for bulkhead fitting, although we are belt and suspender”ing it anyway.
 
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