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Tip: NPT Thread Sealant

DanH

DanH

Legacy Member
Mentor
This is how thread sealant is used:



The listed sealants are suggestions with long service histories. You'll also find the brands suggested in the Vans builders manual. The actual choice is the builder's responsibility.

They are non-hardening sealants, meaning they don't tend to form solid chunks. A good sealant is easy to clean from female threads, which must be sealant-free each time a male fitting is inserted. Failure to clean the female threads can allow the male to push cured or uncured sealant further into the fitting, which may form a blockage.

The point is to avoid something like you see below, in which a poor sealant choice was sheared loose into the fitting, resulted in loss of fuel flow.

 
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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.
 
Thanks for continuing this discussion.

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?
 
ccrawford said:
Thanks for continuing this discussion.
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?
Click to expand...

Thread sealant is used on the pipe threads only; not the flare fitting.

Look at Dan's drawing. Note where he shows "no sealant" on the flare side.
 
As a new owner (not a builder) are there any specific tips for checking these critical fuel fittings to ensure they were done in accordance with best practices?

My plane was completed in 2007 and has 570 TT. This upcoming annual I was considering replacing all my under the cowl fuel lines, but not before ensuring it's advised at this juncture.

This tutorial by DH is awesome.

Sorry for drifting.
 
ccrawford said:
Thanks for continuing this discussion.

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?
Click to expand...

Cory - it is indeed standard practice to not apply any form of sealant to AN flared fittings. The mechanical design of the flared fitting ensures tight metal-to-metal contact between the female flare of the pipe and the mating beveled surface of the male fitting.

The only "sealant" which may be used on flared fittings is a thin, soft aluminum flared fitting washer, referred to in the Spruce catalog as "DEL 37 degree fitting seal". This thin aluminum material is essentially compressed between the flared tube and the AN fitting. In doing so, it allows a good seal to be made in the event the male or female portion of the flare is marred by some minor imperfection such as a scratch.

Again, just to be clear, thread sealant of any sort (liquid, paste, tape) is not applied to AN 37 degree flared fittings.
 
ccrawford said:
Thanks for continuing this discussion.

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?
Click to expand...

Correct, it is normal practice. There is no sealant required or recommended for the flared fittings. The tubing used most often by Vans, AL 3003, is relatively soft and deforms slightly to seal properly.

You might take a look at Chapter 7 on this link. I have not studied it, but it may help.
 
ccrawford said:
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?
Click to expand...

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.
 
FasGlas said:
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.
Click to expand...

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.
 
FasGlas said:
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.
Click to expand...

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!
 
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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).
 
FasGlas said:
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.
Click to expand...

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.
 
Mel said:
Thread sealant is used on the pipe threads only; not the flare fitting. Note where DanH shows "no sealant" on the flare side.
Click to expand...

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" ?
 
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Toobuilder said:
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).
Click to expand...

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.

 
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magiccarpet said:
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.
Click to expand...

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?
 
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.
 
DanH said:
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...
Click to expand...

We are in agreement. You can easily plug up a fluid system with the correct sealant if the application is incorrect.

The point to be made here is that there is more to aircraft maintenance than just knowing what materials to use or the torque values of a fastener, etc. Just like flying skills, learning maintenance by rote vs. a real comprehension is only a partial solution.
 
best practices - in real life

What jumps out for me is the 'clean thoroughly before reassembly'.

If there's one thing I've noticed working on mechanical things, and especially aircraft, is the fitting you'd like to inspect most closely, and clean, and thread, and torque, are the ones that are almost impossible to access and accomplish any or all of the preceding tasks!
Could cleaning include vacuuming out the old sealant? sounds like the time-honoured blowing out with compressed air would be a very bad idea, for obvious reasons!....(and yet another shop process that might not be so obvious for inexperienced builders)
 
mburch said:
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.
Click to expand...

Flare fittings are not designed to have additional lubrication applied to the nut threads, especially when the fittings are tightened to a torque specification. The mechanical properties of the joint, including the metal to metal seal in the flare, depend on a certain load being developed in the threads. Some flare fittings come prelubricated with a dry compound (often silver based) but generally they should not be lubricated. The should be tightened either to a torque specification or to a clearance between the nut and the fitting, as specified by the fitting manufacturer. Often the manufacturer will provide a special wrench that allows the installer to meet and check the clearance specification easily.
 
mburch said:
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.
Click to expand...

I've been doing this as well, just a bit on the threads and ensuring that no Fuel Lube is on the sealing surfaces. (Which is why I asked the question about the AN fittings earlier). The fact that this would impact the torque brings up an excellent point.
 
1001001 said:
Flare fittings are not designed to have additional lubrication applied to the nut threads, especially when the fittings are tightened to a torque specification...
Click to expand...

This also is not an absolute. It is very common to apply lubricant to the threads and friction surfaces of the ferrule of AN fittings in military aviation. That's why there are multiple columns in the torque charts for "dry" or "lubricated" threads. This is very similar to the multiple columns used for torque values of threaded fasteners. A 10-32 fastener can have many different torque values depending on material, lubricated or dry, tension or shear, or whether you are turning the bolt or nut. Once again, it's a matter of knowing when and why you should be using a particular process.
 
I don't believe it's the sealant as much as it's the practice. ANY sealant used wrong could potentially cause problems. Yes... you must clean an check the threads on both fittings. It's always best to use a smaller amount of sealant as opposed to "More is better". Never put any sealant close to the last threads, this is where it can leak into the stream. These practices go for fuel, vacuum, pressure, pitot, static... Any connection.

Looking at the picture Dan posted it's obvious none of these listed practices were observed. It's a very tragic lesson for everyone to learn. This goes with all installation practices. I see this way too often; nicked tubing, over bent tubing, strained connections, misuse of RTV, way too many Adel's, duct tape, auto wires... This list is too long. Common sense.
 
ccrawford said:
I've been doing this as well, just a bit on the threads and ensuring that no Fuel Lube is on the sealing surfaces. (Which is why I asked the question about the AN fittings earlier). The fact that this would impact the torque brings up an excellent point.
Click to expand...

Add me to the list of people who did this to prevent galling the fittings.
 
BTW:

http://static1.squarespace.com/stat...0f66e779d18ff/1396858688880/FT_60_install.pdf
(from this website: http://www.fdatasystems.com/fc-10/)

When assembling fittings into the 1/4? NPT inlet and outlet ports do not exceed a torque value of 25 ft.-lbs.
Do not use Teflon tape in an aircraft fuel system. Use ?Fuel Lube/Ez Turn Lubricant?
Click to expand...

Hmmmm....

And just to add

EZ Turn is a revolutionary sealant and lubricant for oil and fuel line valves. Resistant to high temperatures, it is especially effective where high octane fuels and aromatics are present.
Click to expand...

http://www.skygeek.com/united-ez-turn-fuelube.html
 
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RV7A Flyer said:
BTW:

http://static1.squarespace.com/stat...0f66e779d18ff/1396858688880/FT_60_install.pdf
(from this website: http://www.fdatasystems.com/fc-10/)



Hmmmm....

And just to add



http://www.skygeek.com/united-ez-turn-fuelube.html
Click to expand...


And from the same source, but covering the FloScan sensor, which appears to be a cast aluminum rather than the machined block that is the red cube -

? When assembling fittings into the 1/4? NPT inlet and outlet ports do not exceed a torque value of 15 ft.-lbs. (180 in.-lbs.) or two
full turns past hand tight, which occurs first.

? Do not use Teflon tape in an aircraft fuel system. Use ?Fuel Lube?

? The transducer should be mounted down stream of a fuel filter.


10 ft.-lbs. less torque for the FloScan over the red cube.
 
If it is anything like the JPI Fuel Flow Transducer, which I thought was FloScan, don't use Fuel Lube. It can migrate into the fuel stream and gunk up the impellor. Not inherently dangerous, but not cheap to replace. I am surprised to see it recommended.

In most applications, Fuel Lube is a great lubricant for Pipe Threads that you do not need to clock, as a gasket dressing (awesome for that), and for sticking the odd stack of washers and nut together in those tight spots!
 
Dryseal NPTF thread form - AN Fittings?

Well, well, well. I saw the post about using fuel lube on the red cube and nothing else. I was curious, so after the days work (converting the W-715-0 to a -1) out came the machinery hand book. Low and behold, there is a tapered thread specification called NPTF a dryseal thread with a different thread tip that results in a mechanical seal requiring no sealant. My handbook is 40 yrs old, but the modern standards are NPT (also known as ANSI/ASME B1.20.1 Pipe Threads, General Purpose), and NPTF - Dryseal American National Standard Taper Pipe Thread (ANSI B1.20.3). The "F" stands for fuel. (Surprise!)

So - an answer and a question. If the red cube, AND the AN fitting thread are NPTF specifications, then "Fuel Lube" would be an appropriate material to lightly apply to ensure that no galling took place.

The Question: Does anyone know where to find the thread specifications for the AN fittings so we can determine if they are being made to the ANSI/ASME B1.20.3 standard?

Is is shameful that I have been totally ignorant of this fact for all my engineering career, but there are excuses if you want to hear them :D
 
The part number is also the specification number. Look up that specification and most likely it'll refer to the thread specification, which you can look up, too.

Reading these specifications is generally a wonderful way to understand more about our hardware.

Dave
 
BillL said:
If the red cube, AND the AN fitting thread are NPTF specifications, then "Fuel Lube" would be an appropriate material to lightly apply to ensure that no galling took place.
Click to expand...

Or just use ordinary moly anti-seize. Or wipe the threads with a greasy chicken leg ;)

Seriously, given a dry seal thread form, there is no need for a fuel proof property, and petro-base lubes are easily flushed/cleaned/removed.
 
David Paule said:
The part number is also the specification number. Look up that specification and most likely it'll refer to the thread specification, which you can look up, too.

Reading these specifications is generally a wonderful way to understand more about our hardware.

Dave
Click to expand...

OK - down the rabbit hole - AN816 states the thread is "ANPT" - Aeronautical National Pipe Taper - which leads to Mil-P-7105. Wading through poorly scanned copies, of copies, of microfiched prints, of carbon copies, of hand typed originals (with a worn out ribbon) is making me sleepy now and still haven't found out if they are dryseal. Still waiting for an expert.

DanH said:
Or just use ordinary moly anti-seize. Or wipe the threads with a greasy chicken leg ;)

Seriously, given a dry seal thread form, there is no need for a fuel proof property, and petro-base lubes are easily flushed/cleaned/removed.
Click to expand...

Greasy chicken leg it is! yeah, Dan, a petroleum base lube would be more appropriate, I was just surprised that (finally) a (possibly) true functional use for the product on a fuel system fitting existed. Put it on, wipe it all off, and then assemble. ( the residual would be the appropriate amount)
 
Tite seal

I bought a can of tite seal from spruce a long time ago and it has lasted forever. Kind of old fashion paint can top where you have to pry it up to get to the goouy stuff but it really goes a long way.
Cj
 
BillL said:
Greasy chicken leg it is! yeah, Dan, a petroleum base lube would be more appropriate, I was just surprised that (finally) a (possibly) true functional use for the product on a fuel system fitting existed. Put it on, wipe it all off, and then assemble. ( the residual would be the appropriate amount)
Click to expand...

The NPT plugs in my IO-390 are installed with nothing but anti-seize. No galling going in, any excess dissolves in oil, no leaks in service, they come out without grief at overhaul, and the residual is easily cleaned for re-assembly.
 
ANPT not technically drywall thread profile. I found some information on a gage makers website that indicates, but not definitively, that the ANPT is an NPT with smaller tolerance allowances. They have to be made with more specialized tooling, but not technically the dryseal thread profile.

Like many things, it is state of the art, facts and data that show we may use these as dryseal within the torque limits.

Disclaimer - builders should prove to themselves that this is acceptable for your installations. While other builders show that has worked with their specific parts in their specific conditions, does not prove it works with all parts in all conditions.

I will test it, if it does not leak, (FMEA complete) then it will get used. I have learned something. today.
 
BillL said:
ANPT not technically drywall thread profile. I found some information on a gage makers website that indicates, but not definitively, that the ANPT is an NPT with smaller tolerance allowances. They have to be made with more specialized tooling, but not technically the dryseal thread profile.

Like many things, it is state of the art, facts and data that show we may use these as dryseal within the torque limits.

Disclaimer - builders should prove to themselves that this is acceptable for your installations. While other builders show that has worked with their specific parts in their specific conditions, does not prove it works with all parts in all conditions.

I will test it, if it does not leak, (FMEA complete) then it will get used. I have learned something. today.
Click to expand...

You're always a wealth of info Bill. My fittings into the transducer are not sealed with anything. No leaks, 700 hours. Not sure what the profile of the threads are. They are steel fittings.
 
aerhed said:
Dan, don't you worry about them just spinning out of there? Did you safety them? Hah.
Click to expand...

Note to new guys; Dave is kidding here.

Off topic...I recently built up an AeroVee for a friend. The Brazilian-sourced engine case was delivered with push-fit aluminum plugs in the ends of all the oil galleries. I pulled them all, and tapped for NPT plugs. Some of them came out real easy.
 
DanH said:
Off topic...I recently built up an AeroVee for a friend. The Brazilian-sourced engine case was delivered with push-fit aluminum plugs in the ends of all the oil galleries. I pulled them all, and tapped for NPT plugs. Some of them came out real easy.
Click to expand...

Note to self...add that to my list during the Aerovee build...... ;)
 
DanH said:
Off topic...I recently built up an AeroVee for a friend. The Brazilian-sourced engine case was delivered with push-fit aluminum plugs in the ends of all the oil galleries. I pulled them all, and tapped for NPT plugs. Some of them came out real easy.
Click to expand...

Ironflight said:
Note to self...add that to my list during the Aerovee build...... ;)
Click to expand...

Now that we are off topic - why were they removed, have there been failures? I hand built more than 200 of these type 1,2,3 engines and as a service manager seen 200+ more. I have never seen and oil gallery plug popped out.

Time changes, manufacturing changes, quality changes, but the design is solid. Early in my learning, I watched case savers for cylinder studs result in cracked cases beginning at the threads of the tap used to rethread the case. Thereafter, I reshaped the tap so the bottom threads and drill bit shoulder had a rounded profile. Although I cautioned the owners that this might not work, from following the modification, I never had another cracked case. Granted, a case stud is a different application than a oil gallery plug.

You two guys have always said - "what is broken" and/or "what are you fixing" when builders apply preemptive "improvements" to nonexistent problems. Are there problems?

I am not saying there will be a problem by threading, or that no plugs will release, but you get the picture. Any change is risk, I am just trying to see if these plugs have become an issue.
 
BillL said:
I am not saying there will be a problem by threading, or that no plugs will release, but you get the picture. Any change is risk, I am just trying to see if these plugs have become an issue.
Click to expand...

Fair question. I don't know if pressed plugs ever come out on their own, nor did I have any idea how tight they would be before I started pulling them. They turned out be be highly variable. No other data.
 
I really like to know why NPT type fitting? I don't really see any advantage in them and only trouble. I don't know if there is any real standard for how tight to go. Would how this value (number of turns) changes if you reuse the fitting and how many times can it be re-used.

None of my fitting have leaked and I have not used sealant on any of them other than oil but my hand shake each time as I put the fitting in, thinking am I over torqueing this sucker or under torqueing it.
 
Loctite 567

For NPT fittings I use Loctite 567 PTFE thread sealant paste exclusively. It's impervious to fuel and has excellent anti galling properties for dissimilar metals.

It was recommended to me by a maintenance engineer with decades of experience. I'm a great believer in precedence and field experience when it comes to aviation products. It's also recommended by Matco for the fittings on their brake systems so I use it there as well.

This product has been discussed at length on previous VansAirforce threads and I have never heard of anyone having any problems with it. On the contrary, all reports that I have read have been very positive in that it provides an excellent seal for NPT threads.

Does anyone here have any further comments on this product.
 
Captain Avgas said:
[Product is] also recommended by Matco for the fittings on their brake systems so I use it there as well.

This product has been discussed at length on previous VansAirforce threads and I have never heard of anyone having any problems with it. On the contrary, all reports that I have read have been very positive in that it provides an excellent seal for NPT threads.
Click to expand...

Just a general question, not one specific to any product or sealing method, but...

Isn't there a significant difference in operation between a fuel system and a brake system? That is, in the fuel system, fuel is *flowing through* the system, so piece of RTV/whatever that comes off can actually block the *flow* of fluid, whereas in a brake system, we're dealing with basically a system under pressure all the time? That is, let's say a piece of Teflon tape came loose from a fitting on a master cylinder on the brake pedal...it's not really going anywhere, maybe a fraction of an inch within the chamber, forward and back, as the brake pedal is actuated and released. There's nothing for it to *block*, really, is there?

Or am I suffering from a severe misunderstanding of the brake system itself?

Point being...failure of a sealant on a brake system (or system like that) may be much less severe, or even unnoticeable, than a similar failure in a system with fluid flowing continuously through it...

Right?
 
FMEA - is different for each system

RV7A Flyer said:
Just a general question, not one specific to any product or sealing method, but...Right?
Click to expand...

The FMEA process evaluates each failure mode and the effect if it occurs. A probability and severity factor would be considered for each failure mode and used to rank all the potential failure modes. The preventative actions and/or tests would be considered for the highest ranking failure modes.

If you list the modes, probability for failure, and severity of result for the two mentioned systems the answer will become clear. Your thinking will be validated.
 
BillL said:
The FMEA process evaluates each failure mode and the effect if it occurs. A probability and severity factor would be considered for each failure mode and used to rank all the potential failure modes. The preventative actions and/or tests would be considered for the highest ranking failure modes.

If you list the modes, probability for failure, and severity of result for the two mentioned systems the answer will become clear. Your thinking will be validated.
Click to expand...

LOL! Yeah, I'm intimately familiar with FMEAs, FMECAs, FTAs, PRAs, risk management processes, risk mitigations, etc. I was hoping to NOT bring work home tonight ha ha!
 
RV7A Flyer said:
Isn't there a significant difference in operation between a fuel system and a brake system?
Click to expand...

Undoubtedly yes. However both require some sort of sealant for their pipe thread fittings. You seem to be advocating Fuel Lube for the fuel system. But Fuel Lube, like Ezyturn is highly resistant to aromatic hydrocarbons and therefore will not dissolve in avgas. It is therefore possible that these products used too liberally on NPT threads could migrate downstream in the fuel system. In other words there may be some element of risk in ANY sealant product used in the fuel system.

There is also some conjecture as to how effective Fuel Lube is as an NPT thread sealant.

Do you have any evidence to suggest that using Loctite 567 is any more dangerous than using Fuel Lube for NPT fittings in an aircraft fuel system.
 
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Captain Avgas said:
But Fuel Lube, like Ezyturn is highly resistant to aromatic hydrocarbons and therefore will not dissolve in avgas.
Click to expand...

Although I think there are better choices, at least fuel lubes don't harden into a solid. Personally, I restrict fuel lube usage to a light film on the fuel cap o-rings at annual, and valve rebuilds. As you say, when introduced into the system, it's not going away.

.Do you have any evidence to suggest that using Loctite 567 is any more dangerous than using Fuel Lube for NPT fittings in an aircraft fuel system.
Click to expand...

From the Loctite.au webpage:

Loctite anaerobic sealants cure to insoluble tough plastic thread fillers..

"Insoluble" means it's hard to clean from female fittings, and "tough plastic" spells potential blockage if a chunk gets pushed into the fluid passage on a second-time-around assembly.
 
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