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  #1  
Old 03-13-2011, 12:59 PM
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rv8ch rv8ch is online now
 
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Default Mixing Steel and Aluminum AN fittings?

Hi,

I would like to use steel fittings FWF wherever I can, particularly the bulkhead fitting for the fuel line. However, the hose that comes with the FWF kit has an aluminum "nut" on it. Anyone know if this will cause issues?

Thanks,
Mickey
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  #2  
Old 03-13-2011, 01:15 PM
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L.Adamson L.Adamson is offline
 
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It's not a problem. Steel fittings, such as the one for a constant speed prop oil line will thread into the engine's aluminum casing.

L.Adamson --- RV6A
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  #3  
Old 03-13-2011, 05:14 PM
DesertFlier DesertFlier is offline
 
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I was taught not to mix steel and aluminum fittings. They will thread together just fine. The problem is getting them apart after years of dissimilar metal corrosion. I would suggest either using an aluminum bulkhead fitting, or changing the female end of the line to steel to match the bulkhead fitting.

Threading steel fittings in to aluminum castings is different. Normally those are a non-flared pipe thread fitting, and are coated with pipe dope before installation. The dope not only acts to seal the threads, but also inhibits corrosion. In contrast, flared AN fittings are threaded together dry.
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  #4  
Old 03-13-2011, 05:35 PM
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L.Adamson L.Adamson is offline
 
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Quote:
Originally Posted by DesertFlier View Post
I was taught not to mix steel and aluminum fittings. They will thread together just fine. The problem is getting them apart after years of dissimilar metal corrosion. I would suggest either using an aluminum bulkhead fitting, or changing the female end of the line to steel to match the bulkhead fitting.
With over 40 years in the HVAC business, I just haven't found sever cases of dissimilar corrosion between aluminum & steel. We'll always protect the copper from steel, but not aluminum.

What's interesting, is your typical air conditioner coil. It will be copper tubing pressed into aluminum plates...........and with a lot of moisture present. So what's the secret? It's the fact that the copper is expanded, and pressed so tightly against the aluminum.

So............let's get a few more opinions, perhaps.

L.Adamson --- RV6A
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  #5  
Old 03-13-2011, 06:07 PM
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9GT 9GT is offline
 
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IMHO, all fuel and oil fittings FWF should be steel. You did the right thing swapping out the aluminum bulkhead fitting with steel so don't use the Vans hose with an aluminum fitting,,,,send it back for credit or sell it to someone who doesn't care and replace the hose(s) with some nice aeroquip hoses with fire sleeve and steel fittings. If you want to use that hose though,,, just use some EZ Turn (fuel lube) http://www.aircraftspruce.com/catalo...ezturnlube.php on the fitting when you assemble,,,,,it will be fine. DO NOT USE PIPE DOPE or TEFLON SEALANT!
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  #6  
Old 03-19-2011, 10:20 AM
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Default fittings

Thanks for the feedback, Gents.
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  #7  
Old 03-19-2011, 12:52 PM
prkaye prkaye is offline
 
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Default Titeseal

After a leaky oil cooler fitting, I was recently taught that Fuel Lube is not the best sealant to use for the oil system because of the high pressure it is under. A better choice is Titeseal, available from aircraft spruce. This stuff has a much different consitency than fuel lube.

A question I posted years ago about putting steel nuts onto aluminum fittings was that of what torque value to use. I believe the concencus was to use the smaller (aluminum) torque value, but I've never seen authoritative data on this. I guess the authoritative sources would say you shouldn't be mixing the two.
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Old 03-19-2011, 03:00 PM
Flying Scotsman Flying Scotsman is offline
 
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Isn't the oil cooler itself aluminum?

Seems to me that at *some* point in most of the systems we're talking about here (oil, fuel), you'll have steel-to-aluminum in some fashion or another. E.g., fuel...There's a mix of steel and aluminum parts and fittings. The fuel servo is aluminum, the fittings are what, brass, I think? (Not in the shop at the moment). Steel fittings on steel-braided hose to the pump, which has steel fittings, but what's the pump made of? From there, steel fittings-steel-braid-steel fitting at the firewall, but then Al fittings and AL tube from there, right?

So what's the *general* principle of when it's okay to mate a steel fitting to an Al fitting?
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  #9  
Old 03-19-2011, 03:43 PM
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Default no lube on AN fittings?

Quote:
Originally Posted by prkaye View Post
After a leaky oil cooler fitting, I was recently taught that Fuel Lube is not the best sealant to use for the oil system because of the high pressure it is under. A better choice is Titeseal, available from aircraft spruce. This stuff has a much different consitency than fuel lube.
Hi Phil - I thought that you weren't supposed to use sealant on AN fittings... that the seal came from the fitting tightly holding the flare in the tube against the matching shape on the mating fitting.

Are you putting the Titeseal on the threads, or on the flare? Or am I way off base here?
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Last edited by IowaRV9Dreamer : 03-19-2011 at 03:44 PM. Reason: learning to use English
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  #10  
Old 03-19-2011, 04:05 PM
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I believe he was referring to the pipe threads requiring sealant, not the flared end. No sealant on the flared end (but a dab of engine oil does not hurt).
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