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10-21-2015, 08:44 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by ccrawford
For the AN fittings, is it normal practice to skip the thread sealant because the flare is there to create a "mechanical" seal and there is a concern that any sealant could cause those two flared/beveled surfaces from completely sealing?
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The flare forms an entirely mechanical, metal-to-metal seal. Not only is sealant unnecessary, it is almost guaranteed that some of it will be extruded out of the flare contact, into the flow passage...a bad thing.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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10-21-2015, 08:52 PM
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Join Date: Sep 2005
Location: Maple Grove, MN
Posts: 2,333
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Quote:
Originally Posted by FasGlas
I do use teflon tape on most fittings but I make sure there is no tape on the first few threads. After I wrap the threads I go over the tape with my fingers and tighten the wrap. I only wrap the tape in the opposite direction the fitting screws in so it stays tight while threading it in.
It's hard to believe someone would use RTV to seal and use so much as to fill the inside threads like this.
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Teflon tape is considered a no-no in aircraft plumbing, for the same reasons that the rtv is. Can both be applied without any problems? Of course, but it reduces margins for errors, sometimes with catastrophic results. Suppose the next person to do maintenance does not see that teflon tape was used, and therefore does not know to clean out the shards from the threads. That tape becomes almost invisible upon dis-assembly.
Using non-aircraft methods is all risk for no gain. Use one of the sealants and the method that Dan recommended in his OP.
__________________
Alex Peterson
RV6A N66AP 1700+ hours
KADC, Wadena, MN
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10-21-2015, 08:56 PM
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Join Date: Nov 2006
Location: Oklahoma
Posts: 672
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Quote:
Originally Posted by FasGlas
I do use teflon tape on most fittings but I make sure there is no tape on the first few threads. After I wrap the threads I go over the tape with my fingers and tighten the wrap. I only wrap the tape in the opposite direction the fitting screws in so it stays tight while threading it in.
It's hard to believe someone would use RTV to seal and use so much as to fill the inside threads like this.
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I understand you are being very careful, but copied directly from section 5.27 of Van's instructions:
Because we cannot always fully tighten tapered thread fittings, and because even after fully tightening the fitting a small spiral leak path remains along the full length of threads, a thread sealant must be used during assembly. Two sealants popular for use on aircraft are Tite-seal and Permatex #2. Teflon based pipe dopes and sealants, and some of the anaerobic thread sealants are also used by some builders with success. Do not use Fuel Lube. It is not a sealant. It is meant for lubricating moving parts in fuel valves, etc. Teflon tape is also not recommended. Small pieces of this tape may be cut by the threads, become loose, and cause all kinds of problems in aircraft systems. Teflon tape has even been the cause of engine stoppages.
Why take the risk when there are better choices? I had many years of using Teflon tape in industrial applications. I'd challenge those who believe it is a good idea on aircraft to disassemble some of the fittings you used it on and use a magnifying glass to examine the female threads. Unless you get every speck and thread string of that cut up tape cleaned out of there before you re assemble the fitting you risk introducing trash during future maintenance. Follow best practices, please guys... for all our sake.
Oops Alex beat me to it!
__________________
Joe Schneider
RV-7, IO-360, BA Hartzell, N847CR
Flying since 2008
Last edited by Caveman : 10-21-2015 at 09:06 PM.
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10-22-2015, 06:55 AM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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Teflon tape can and is used on aircraft - if used correctly. I've certainly seen it in our company's aircraft (and we're the OEM), and Mr. Dye explains this in last months issue of Kitplanes (October, page 3).
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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10-22-2015, 07:00 AM
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Join Date: Jun 2012
Location: Frederick, MD
Posts: 821
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Quote:
Originally Posted by FasGlas
I do use teflon tape on most fittings but I make sure there is no tape on the first few threads. After I wrap the threads I go over the tape with my fingers and tighten the wrap. I only wrap the tape in the opposite direction the fitting screws in so it stays tight while threading it in.
It's hard to believe someone would use RTV to seal and use so much as to fill the inside threads like this.
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From a previous doubter that thread tape was bad if used properly. Even if you hold it back several threads from the end, it can extrude through the threads into the inside of the fittings when you tighten the fitting. If you don't beleive me get 2 pipe thread fittings a male and female threaded fitting and try it. As you tighten the fitting, the inner threads tend to extrude parts of the teflon tape inside the fitting. Not every time but some times. Particularly if you are heavy handed with the tape at all. It works in my house, but not in my airplane.
__________________
Dan Morris
Frederick, MD
PA28-140
Hph 304CZ
RV6 built and sold
N199EC RV6A flying
Learn the facts. "Democracy dies in darkness"
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10-22-2015, 07:04 AM
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Join Date: Feb 2011
Location: USA
Posts: 3,179
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Quote:
Originally Posted by Mel
Thread sealant is used on the pipe threads only; not the flare fitting. Note where DanH shows "no sealant" on the flare side.
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The A&P I worked with for my first condition inspection was very instructive during the process. He was very specific when he described and demonstrated what DanH has diagrammed.
Thanks DanH for pulling this information out into it's own thread.
Walt: could you provide the name of a recommended "sealant" ?
Last edited by humptybump : 10-22-2015 at 07:08 AM.
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10-22-2015, 07:23 AM
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Join Date: Feb 2013
Location: Switzerland, Europe
Posts: 199
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Loctite 577
Does anybody have experience with Loctite 577 ?
http://www.grosvenor-group.com/image...te/tds-577.pdf
According to the specs. it's chemical/solvent resistant and can be applied on all metal type threads. To me it looks like a product to go for sealing the NPT threads of my fuel and brake lines, even though it's quite pricey here.
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10-22-2015, 07:52 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by Toobuilder
Teflon tape can and is used on aircraft - if used correctly. I've certainly seen it in our company's aircraft (and we're the OEM), and Mr. Dye explains this in last months issue of Kitplanes (October, page 3).
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Re teflon tape, RTV, fuel lube, etc.....fact is, you CAN seal successfully with almost anything, if you start with new, clean fittings, and apply the sealant carefully.
The problem starts when the fitting is disassembled and reassembled, and yes, we do that sometimes, for a variety of reasons. (A) Solid sealants tend to form chunks or shards, and the debris gets into everything during dis-assembly. (B) If you reassemble without cleaning out the female threads, the old sealant gets cut, pushed, and/or extruded into the fluid area. Take a good look at the NTSB photo in the first post. That's exactly what happened, and it killed someone.
You want a sealant that remains more paste than solid, and can be easily and thoroughly cleaned from the female threads, while working upside down, in a hot hangar, toward the end of a long day. Anything else, and human nature will have fittings going back together like the one in the photo.
Chunks and shards can hang around in a system for a long time. This one almost got James Clark, when it momentarily blocked the inlet to the Facet pump on the RV-1. I'm rather sure the unknown mechanic who used RTV many years ago applied it carefully, and it probably gave no trouble in the initial assembly. However, over the years, as it passed from owner to owner, and from mechanic to mechanic, someone R&R'ed the fitting, and the silicone flap got loose in the system.

__________________
Dan Horton
RV-8 SS
Barrett IO-390
Last edited by DanH : 10-22-2015 at 07:54 AM.
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10-22-2015, 08:03 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by magiccarpet
Does anybody have experience with Loctite 577 ?
According to the specs. it's chemical/solvent resistant and can be applied on all metal type threads. To me it looks like a product to go for sealing the NPT threads of my fuel and brake lines, even though it's quite pricey here.
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Cures hard, crumbles into chunks upon dis-assembly, and not so easy to clean from female threads. From the datasheet:
Cured product can be removed with a combination of
soaking in a Loctite solvent and mechanical abrasion
such as a wire brush.
Besides, why chase some unknown exotic, when a bottle of Permatex #3 costs less than 10 bucks and lasts the rest of your life?
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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10-22-2015, 08:26 AM
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Join Date: Feb 2005
Location: Northwestern USA
Posts: 1,209
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I will admit that I use a tiny amount of EZ-Turn (fuel lube) on the threaded portion of aluminum flare fittings, just to prevent galling. Never anything on the sealing surfaces of course. I forget who showed me this practice, years ago, but this thread has got me thinking critically about what I've been doing. Hmm.
__________________
Matt Burch
RV-7 (last 90%)
http://www.rv7blog.com
VAF #836
Any opinions expressed in this message are my own and not those of my employer.
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