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Misconceptions about pipe threads

scsmith

Well Known Member
I keep reading posts by some folks in threads that indicate a serious misconception about pipe threads.

Pipe threads are tapered. When a fitting with a pipe thread is tightened, it will tighten until the thread flanks contact and make a contact seal on the thread flanks of the mating part.

*****BUT****

The peak of each thread has a small radius, and the valley between the threads has a small radius. These are not the same radius, and when the thread flanks contact, the peak of the thread does not contact the valley in the threads of the mating part.

What does that mean?

If you assemble a pipe thread fitting without sealant, and tighten it until the threads contact, you will still have a spiral leak path, following the spiral path of the valley between the threads.

YOU MUST USE PIPE THREAD SEALANT

or the fitting will leak.
 
My favorite is Permetex Aviation #3, non hardening and impervious to oil and fuel, but not alcohol. I have been using it for 35yrs, but not on airfcraft, and it has never failed me. EZ Turn MSDS was no help for ingredients.

Bob, (you are up late/early, prepping for a race? ) what did the Lycoming engine school have on sealants for NPT fittings?
 
It makes sense - is EZ-Turn an acceptable seal material?

Bob Axsom

No, Fuel lube or EZ turn is not a thread sealer. I use "titeseal Light" and "Bakerseal" exclusively. Will try Loctite 567 one of these days as I hear it good also.
 
Steve - great visual description. Thanks!

My A&P gave me a list of "consumables" the first time we did my condition inspection. A can of TiteSeal was on that list. It's going to last me a couple life times (assuming I'm a good boy and don't get reincarnated as a scat beatle).
 
Race next week on the 29th in Marysville, Ohio...

We went over a lot of special lubes in the Lycoming school, some food grade but I would have to go to my notes to recall them. We mostly focused on lubricants used in the build up of the engines. There is a Lycoming document dedicated to lubricant usage - I'll dig out the number I gave all of my documents from the course to Red Hamilton. They are quite expensive but as I am getting more into this I can see I should buy a set for myself.

On 10-10-12 which was day 3 of the theory (CLASSROOM) part of the two course program we spent most of the day on the lubrication system. At one point I wrote the following in my notebook:

Oil Publications (SI = Service Instruction, SB = Service Bulletin, SL = Service Letter):

SI1014 Lubricating oils
SI1059 Pre-Lubrication of Parts Prior to Assembly
SB480 Oil Change Interval
SI1409 Oil Additive LW16702
SL180 Preservation for Active and Stored Aircraft
SB52* Oil Pump Impellers
SI1505 Cold Weather Starting
SI171 Spectrometric Oil Analysis
SI1462 Propeller Oil Control Leak Tests

Walt, what do you use on the sump drain plugs. I have used nothing and seen seepage, Teflon tape which seemed to work fine but I felt guilty and EZ-Turn which worked also but required a lot of force to remove at oil change time.

Bob Axsom
 
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Walt, what do you use on the sump drain plugs. I have used nothing and seen seepage, Teflon tape which seemed to work fine and EZ-Turn which worked also but required a lot of force to remove at oil change time.

Bob Axsom

I use the items listed in post #4 on all pipe threads, including sump plugs.
 
I have heard from many reputable sources that Teflon tape should never be used in any fuel or oil lines on an aircraft. I don't use it on anything. I use seal lube sometimes and tube of white loctite (dont remember the number). Every pipe thread in the airplane has one of these on it with very seldom any leaks. E sealer also libricates the threads allowing them to tighten further than they could dry with the same force.

Also, flared fittings should never have any sealer on them.
 
Thanks - I now have Titeseal LT on ordedr

I use the items listed in post #4 on all pipe threads, including sump plugs.

Searched ACS site and ordered gre titeseal LT. The search for Bakerseal was not successful.

Bob Axsom
 
I have had excellent results with Loctite 561 in a stick and Loctite 567 in a small tube. EZ turn seems to always leak under pressure i.e, oil system and brakes. FWIW!
 
Just out of curiosity... Then what application would you use EZ Turn or Fuel Lube for on an RV? I used it on most of my fluid pipe thread fittings. Six years and 770 hours later, I haven't had any issues with leaks. Please school me. I really want to learn. I used an aluminum based anti-sieze on other fittings and I use a copper based anti-seize for my spark plugs and the spark plug bushings on my electronic ignition.

Jerry
RV-8 N84JE
 
Just out of curiosity... Then what application would you use EZ Turn or Fuel Lube for on an RV? I used it on most of my fluid pipe thread fittings. Six years and 770 hours later, I haven't had any issues with leaks. Please school me. I really want to learn. I used an aluminum based anti-sieze on other fittings and I use a copper based anti-seize for my spark plugs and the spark plug bushings on my electronic ignition.

Jerry
RV-8 N84JE

Personally, I use EZ-Turn on the fuel caps, and fuel selector valve.
 
EZ Turn is for things like brass plug valves like vans old selectors and the Eastman valves that Piper used forever. The name says it all. Its not a sealer, its a lubricant.
 
NPTF threads

Just a slight addition to the op's comments concerning NPT threads with which I completely agree.

There is an alternate thread system that does not require sealant known as NPTF used in systems under high temp or pressure where a sealant might fail. NTPF threads look the same but are cut with different taps and dyes that produce threads that fill and crush to produce a metal to metal seal.

The pipe threads we encounter in our building are NPT and do require sealant for the reason Steve so nicely described. And for the umpteenth time, Fuel Lube is not a sealant but might, I suppose, be useful in assembly of NPTF systems.

CWM
 
EZ Turn is for things like brass plug valves like vans old selectors and the Eastman valves that Piper used forever. The name says it all. Its not a sealer, its a lubricant.

It meets the old Mil Spec MIL-G-6032D and is sold by many manufacturers as a sealant.

Another manufacturers description for the same Mil Spec product -

NYCO GREASE GN HC is based on a very viscous synthetic oil and can be used between - 20oC and + 100oC. It is intended for use in tapered plug valves, as a gasket lubricant or seal. It is also used for general plug valve service in systems where gasoline, oil, alcohol or water resistance is required.

And a second one -

ROYCO 32 is intended for use in tapered plug valves or as a gasket or seal lubricant and in high-pressure lubrication
equipment where solvents or oil resistance is needed. This product is recommended for applications
at temperatures up to 250oF


And from the Aviall catalog -

United Erie's EZ-Turn is a specialty lubricant/sealant for fuel and oil line valves and is resistant to high temperatures. It will not gum, crack, or dry out. Anti-seize, anti-corrosion lubricant Fuel, chemical, and salt water resistant. Meets Mil-spec MIL-G-6032D, AM 1, Type 1

Even the MIL Handbook on grease uses says it can be a seal as well as a lubricant (page 3) -

https://assist.daps.dla.mil/docimag...essionid=5c30eb5e94c976bf1292e74416519787257a

I for one am satisfied using it as a seal on pipe threads, and have many years of effective sealing in several locations.
 
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I initially used EZ Turn on everything. The two items where I had leaks were my oil cooler fittings and brake master cylinder fittings. I resealed those with Leak Lock...

http://www.highsidechem.com/leaklock.html

I should have used it on everything. My Dad also used it on refrigeration systems 30+ years ago. It can be purchased locally.
 
Fuel Lube okay on vent lines?

I haven't gotten to the high pressure lines yet, but used Fuel lube on my fittings for the fuel tank vent and the fuel pickup bulkhead fitting. Am I certain to get leaks or what? I haven't pressure tested yet, but once my tanks are closed these will be a bugger to get to...
 
Mike,

I think my brakes leaked due to more pressure (400+ psi)than EZ Turn can handle. I think oil cooler fittings leaked due to exposure to 180-205F/75 psi oil, along with larger threads. Everything else on the plane is EZ Turn and dry as a bone. Don't worry about it unless it is easy to access right now. Use one of the excellent sealants above from now on out. Keep building, it is a lot of fun.
 
Is the Fuel Lube people are referring to actually "Seal Lube"? I know I used to use the term fuel lube, but my can days Seal Lube, which, I assume, means it seals and lubes. I've had precious few leaks when using this. Spruce sells it in a small pint sized can which should last you a lifetime.
 
I haven't gotten to the high pressure lines yet, but used Fuel lube on my fittings for the fuel tank vent and the fuel pickup bulkhead fitting. Am I certain to get leaks or what? I haven't pressure tested yet, but once my tanks are closed these will be a bugger to get to...

Aren't those fittings flared? If so, they get no sealant.
 
After using Titeseal light on my RV9A build I decided to try it at work. I now seal all water lines in die cast molds that can reach several hundred degrees F. With Titeseal. I never get leaks now. Great stuff. I only use EZ turn on the o rings on the fuel caps.
 
Is the Fuel Lube people are referring to actually "Seal Lube"? I know I used to use the term fuel lube, but my can days Seal Lube, which, I assume, means it seals and lubes. I've had precious few leaks when using this. Spruce sells it in a small pint sized can which should last you a lifetime.

No, it's Fuel Lube, which has been replaced by EZ-Turn at Spruce.
Both made to the same Mil-Spec MIL-G-6032D.

Seal Lube http://www.aircraftspruce.com/catalog/cspages/siliconeglue.php?clickkey=17452

EZ Turn http://www.aircraftspruce.com/catalog/cspages/ezturnlube.php?clickkey=5414
 
customer assistance

Where do you buy Loctite 567? ACS doesn't list it. Amazon shows a couple. Just wondering if it could be bought locally?

Doug
RV-7 Finishing Kit
 
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