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  #21  
Old 10-22-2015, 08:30 AM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by DanH View Post
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...
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.
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  #22  
Old 10-22-2015, 08:43 AM
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Default 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)
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  #23  
Old 10-22-2015, 08:43 AM
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Quote:
Originally Posted by mburch View Post
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.
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.
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  #24  
Old 10-22-2015, 09:20 AM
ccrawford ccrawford is offline
 
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Quote:
Originally Posted by mburch View Post
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.
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.
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  #25  
Old 10-22-2015, 09:39 AM
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Quote:
Originally Posted by 1001001 View Post
Flare fittings are not designed to have additional lubrication applied to the nut threads, especially when the fittings are tightened to a torque specification...
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.
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  #26  
Old 10-22-2015, 10:44 AM
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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.
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  #27  
Old 10-22-2015, 11:02 AM
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RV7A Flyer RV7A Flyer is offline
 
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Quote:
Originally Posted by ccrawford View Post
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.
Add me to the list of people who did this to prevent galling the fittings.
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  #28  
Old 10-22-2015, 11:13 AM
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BTW:

http://static1.squarespace.com/stati...60_install.pdf
(from this website: http://www.fdatasystems.com/fc-10/)

Quote:
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?
Hmmmm....

And just to add

Quote:
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.
http://www.skygeek.com/united-ez-turn-fuelube.html

Last edited by RV7A Flyer : 10-22-2015 at 11:24 AM.
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  #29  
Old 10-22-2015, 01:55 PM
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az_gila az_gila is offline
 
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Quote:
Originally Posted by RV7A Flyer View Post

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.
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  #30  
Old 10-22-2015, 02:18 PM
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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!
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