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Tip: NPT Thread Sealant

humptybump said:
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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Which sealant is like asking which primer...
I generally use titeseal light on fuel/oil pipe threads or Permatex aviation form-a-gasket #2 or #3, lately I've been using Loctite 567 on brake systems pipe threads with good results.
 
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Captain Avgas said:
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.[/quote[

Which would be the point, right? If it dissolved in avgas, it would no longer be sealing anything at all!

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.
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Agreed...incorrect application of ANY sealant is bad.

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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I have no experience with Loctite 567...that wasn't my question.
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I've got 2x 3oz tubes of this stuff left over from my SS brake line work. Used it only on the pipe thread ends exactly as DanH sketched. Can I use this on the fuel system pipe threads as well or am I better off going specifically with the Permatex #2?
 
cattflight said:
I've got 2x 3oz tubes of this stuff left over from my SS brake line work. Used it only on the pipe thread ends exactly as DanH sketched. Can I use this on the fuel system pipe threads as well or am I better off going specifically with the Permatex #2?
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It could be used, but says fast cure time on the package.

I am not sure to what degree they mean "cure" but non curing sealants are a better choice for reasons previously mentioned.
 
Im installing the NPT fitting on my fuel pickup in my RV10 fuel tank. I ordered Permatex from aircraft spruce. I noticed after installing the first one that it is Permatex #3 and not #2. Vans recommends Permatex #2. I certainly do not want to have any clogged fuel ports. Is Permatex #3 permissible, or should I pull it out and order some #2? What is the difference between Permatex #2 and #3?

Thanks,

Dave
 
Wyzepilot said:
Im installing the NPT fitting on my fuel pickup in my RV10 fuel tank. I ordered Permatex from aircraft spruce. I noticed after installing the first one that it is Permatex #3 and not #2. Vans recommends Permatex #2. I certainly do not want to have any clogged fuel ports. Is Permatex #3 permissible, or should I pull it out and order some #2? What is the difference between Permatex #2 and #3?

Thanks,

Dave
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Just my opinion here, but #3 is fine. It is a little more fluid as #3 goes on with a brush and #2 comes in the tube. I only use the #3. Both are impervious to fuel and oil. Neither get hard, and the only thing what will dissolve them is alcohol. Otherwise, it will be on your fingers until it wears off.

VW air-cooled case halves are installed with #3. No other sealant.
 
What about Sealube? I have heard from a couple A&P's in my area that build motors that Sealube works great on pipe threads.
 
Dan, can you upload your no-longer-viewable pics from the 1st post?

DanH said:
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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