What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Torque value for -6 fuel line jamb nut in stainless steel?

Desert Rat

Well Known Member
For the main fuel line firewall passthrough I'm replacing the aluminum fitting with stainless.

Does anybody know the torque value to be used on a AN833-6j jamb nut on a AN942-6j elbow?

I can find the value for both aluminum and steel, but suspect that stainless is probably somewhere between the two. Can anybody confirm one way or the other?

Thanks
 
Terry,

I'm not sure about your AN numbers. They seem wrong. I think you mean AN924-6J for the bulkhead nut. I actually have this same configuration for my fuel line passing through the firewall. I haven't installed that fitting yet though. It's amazing how the simplest things can become a big investigation. The only reference I could find for bulkhead nuts is MS33515. In the applicable chart it doesn't seem to reference the material at all.
 
Logical opinion

I'm working on brake lines and bulkhead fittings etc and was also wondering about torque value for the AN-924 nuts. AC43.13 Table 9-2 gives torque values for the AN-818 nuts, these are the same thread as the AN-924. Note the torque is dependent on the tubing material, not the nut material. I'd be comfortable torquing the AN-924 to the same value as the AN-818s on that fitting.
 
I don't think an AN818 and an AN924 are good to compare. One is just a threaded connection the other is creating a seal with a flare. MS33515 has the appropriate torque for the AN924. I just used these values for my fuel vent line bulkhead fittings. The bulkhead fitting torque is quite a bit higher than the B nut torque.

In the absence of any other spec for the AN924 torque I would probably just use the values in MS33515 for the steel as well as the aluminum fittings.
 
I don't think an AN818 and an AN924 are good to compare. One is just a threaded connection the other is creating a seal with a flare. MS33515 has the appropriate torque for the AN924. I just used these values for my fuel vent line bulkhead fittings. The bulkhead fitting torque is quite a bit higher than the B nut torque.

In the absence of any other spec for the AN924 torque I would probably just use the values in MS33515 for the steel as well as the aluminum fittings.

Where did you obtain MS33515? I haven't come across it before but should get a copy.
 
Ray- you're right, I transposed the numbers in my original post.

I've looked at that spec as well, but it's unclear as to the material callout. common sense would seem to indicate that you should be able to torque a stainless jamb nut higher than an aluminum one, but stainless is typically not as robust as black steel and I don't want to overdo it.

The reason for my question is that I went with the gudntite method for the initial fit and when I was fitting the boost pump plumbing in the cabin floor I discovered that it still pretty easy to turn from the cabin side. I definitely don't want that thing turning or working loose after it's in service.
 
Ray---good find on the spec! On the firewall, I use 2 stainless washers, then tight and some more. Yes, I like stainless bulkhead fittings in the firewall, and yes, I like the nuts tight.

I've heard of guys sealing the fitting with 3M Firebarrier 2000. Probably not a bad idea, I'll defer to Dan Horton and his firewall barrier tests.

Tom
 
Back
Top