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What do you use to seal the redcube

Lan Vinh Do

Lan Vinh Do

Well Known Member
I am about to install a redcube fuel flow transducer.
What do you use to seal the fitting In the redcube? I didn't find it today but i remember that i read that it need sealant and if not it will leak
 
Tite-Seal Medium...many other choices as well. With NPT fittings, you must use a sealant. Just a dab on the threads in the middle will get the job done and keep it away from the end of the fitting.
 
And it should be mentioned if no one has heard about the RV 10 crash, NO RTV with any fuel system.
 
I am happy with LOCTITE 567. It also handles fuels with ethanol (UGGH!) content.
 
No Teflon Tape

Do NOT use Teflon tape. Little shards can come off and get lodged in your carburetor (or fuel injection).
 
The sealants (except RTV) above will work but most people I have seen use too much and not in the correct way. Read the instructions. A little goes a long way.
Same with Teflon tape. Only reason people say not to use it is because they heard not to use it based on incorrect application. I once saw an IA taping a fitting in the wrong direction. Sheesh!
 
bullojm1 said:
Fuel Lube / EZ-Turn is what I've always used for NPT fittings in the fuel system. Never a leak. Works well also to coat the O-Rings in the fuel filter and tank drains.

http://www.aircraftspruce.com/catalog/cspages/ezturnlube.php
Click to expand...

Unfortunately, Fuel Lube will leak. It's just a question of how long before it does. Over the last three years, I've had to address just about every location that I used fuel lube and replace it with a thread sealant.
 
rleffler said:
Unfortunately, Fuel Lube will leak. It's just a question of how long before it does. Over the last three years, I've had to address just about every location that I used fuel lube and replace it with a thread sealant.
Click to expand...

Interesting. In the 6 years and nearly 500 hours I've had my RV, I haven't had any leaks while using Fuel Lube. I will keep a close eye on this. Thanks for the heads-up, Bob.
 
Red Cube Issue/sealant

Some time ago a batch of red cubes were sold with thread cuts
of insufficient depth. As a result, the in and out fittings would bottom out before they could completely seal.
I was the lucky winner of one of those cubes and reading rleffler's post you might have the same issue. We finished our planes at about the same time.
The resulting leak was just enough to infuse the cockpit with a whiff of fuel smell but not enough to cause wetting anywhere.
I found the blue stain around the fittings some 6 month into flying and in this case only Pro Seal would do the job.
No issues since.
 
dlloyd3 said:
Only reason people say not to use [Teflon tape] is because they heard not to use it based on incorrect application.
Click to expand...
Yes, it's OK to use if done correctly - holding the first two threads clean and wrapping the right way. I think the real problem comes if you ever have to change a fitting, the female threads have lots of little Teflon debris pieces in them that are difficult to remove. (Ask me how I know) If you don't remove them completely, they'll contaminate the system. Oh, and JPI cautions against using Teflon tape on their fuel flow sensors. Why risk it?
 
I understand that Permatex 56750 is essentially the same as Loctite 567 and is what I have been using on brake fittings etc.

I find the Permatex equivalents easier to source locally at Auto parts stores.
 
Fuel Lube is normally a good choice for most pipe thread fittings. However, as mentioned, it can migrate. Floscan specifically warns against this for that reason. It can foul the impeller. It won't bring an airplane down, but it can ruin an expensive part. Perhaps the Red Cube is designed differently.
I no longer use Fuel Lube except as a gasket conditioner. Permatex thread sealant seems to do a better job for most pipe thread applications and doesn't migrate. It also seems to be a decent lubricant for stubborn to line up fittings just remember, once tight, don't back off the fitting or it can leak.
Follow the instructions for whatever product you decide on.
I wouldn't use Proseal. I am sure it seals very well but if you ever have to change a fitting, cleaning the threads might be a challenge. Also, if overdone, it can flake off in chunks like RTV and lead to the same problems.
 
I am a fan of permatex #2 for NPT thread sealing in gasoline and oil applications. It's non-hardening and cleans with laquer thinner or alcohol. It's cheap and can be found at any auto store. I have used threadlockers in some applications, but as mentioned before they leave bits and chunks upon disassembly. This also a reason I never recommend them to newbies that tend to put on too much. You don't want something that can break off when it is applied too close to the last thread.

Larry
 
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rv8ch said:
What Dan said is the right answer - doing this wrong has killed people.
Click to expand...

Yep. I've been using Teflon tape on critical applications for more than 20 years - but it's very specific and has to be done correctly. It's a whole lot easier to just use the blanket rule "Never on fuel!!" than to try to teach the masses how to do it correctly and trust that they will keep on doing it correctly.

And RTV in the fuel system is definitely a hard "Never on fuel!!"
 
I ran across this today at work and thought I would throw it out here for educational purposes. This is an NPT fitting threaded into a bung on a boat exhaust pipe with teflon tape. Not only is it blocking flow, but it eventually would break away and clog something downstream. This situation is why a non hardening paste is recommended for NPT fitings. Even if some is squeezed forward, it will not form firm chunks leading to blockages.
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snopercod said:
Yes, it's OK to use if done correctly - holding the first two threads clean and wrapping the right way. I think the real problem comes if you ever have to change a fitting, the female threads have lots of little Teflon debris pieces in them that are difficult to remove. (Ask me how I know) If you don't remove them completely, they'll contaminate the system. Oh, and JPI cautions against using Teflon tape on their fuel flow sensors. Why risk it?
Click to expand...
 
Permatex #2 data point

Here's another data point for Permatex #2.
Six months ago I rebuild a Macnaught rotary drum pump used exclusively for Avgas, and I used Permatex #2 to seal the two halves when it went back together. Before joining the halves I called Macnaught tech support, and they confirmed that #2 should be adequate. I had just read Eliot Seguin's article on fuel leaks with #2 so I was a little skeptical, however it was all I had on hand at the time. Sure enough, six months and a few thousand liters of avgas later, and the seal has dissolved and the pump is leaking. Time to try some locktite 567 instead.
Tom.
 
bullojm1 said:
Fuel Lube / EZ-Turn is what I've always used for NPT fittings in the fuel system. Never a leak. Works well also to coat the O-Rings in the fuel filter and tank drains.

http://www.aircraftspruce.com/catalog/cspages/ezturnlube.php
Click to expand...

Both of these dissolve in avgas relatively quickly. I once put a blob of EZ-Turn into a jar of avgas and while it looked OK a day or two later, it came completely apart when slightly disturbed.
 
#2 +1 =#3

lr172 said:
I am a fan of permatex #2 for NPT thread sealing in gasoline and oil applications. It's non-hardening and cleans with laquer thinner or alcohol. It's cheap and can be found at any auto store. I have used threadlockers in some applications, but as mentioned before they leave bits and chunks upon disassembly. This also a reason I never recommend them to newbies that tend to put on too much. You don't want something that can break off when it is applied too close to the last thread.

Larry
Click to expand...

I use #3 but just a more liquid version of #2. It will dissolve in alcohol, so not for mogas with alcohol. I have used it on 1000's of engine, fuel, oil, fittings/gaskets over 40 yrs. It may not be the best out there, but I stopped looking after finding it and have yet to be disappointed. How many speciality goos can you maintain in a tool box anyway?

Do a pre-check of the NPT penetration with a touch of clay at the bottom. That will ensure the treads are in spec. We have read, that the cube can be sealed with good AN fittings with only a lubricant, but do some experiments first. I just was not taking that chance, I am into eliminating as many issue probabilities as possible.
 
fire hose on REdCube

In addition to thread sealant you might consider what you will put around it. I bought a large diameter fire sleeve and slipped it onto the redcube. Made a hole for the wires to come out. Also on my production plane an A&P IA did the same sometime ago. If it does leak the fire sleeve will turn a potential spray into a drip.
 
Loctite 577?

Has anybody tried Loctite 577 to seal pipe threads in fuel lines? It seems to be compatible with fuel and gets even stronger over time in the presence of oil. I've had good luck using a similar product to seal the pipe fittings in my landing gear hydraulics.
 
I would not advise this procedure.

sglynn said:
In addition to thread sealant you might consider what you will put around it. I bought a large diameter fire sleeve and slipped it onto the redcube. Made a hole for the wires to come out. Also on my production plane an A&P IA did the same sometime ago. If it does leak the fire sleeve will turn a potential spray into a drip.
Click to expand...

OTOH the fire-sleeve can "mask" a minor leak.
 
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