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Another red cube leak

I thought I smelled a faint fuel smell a couple times recently on takeoff and landing. I'm paranoid about fuel leaks, so thought I was crazy, but decided to open up the tunnel, and sure enough, I have a very small leak at the NPT threads on the "red cube" fuel flow sender, as has been reported by others previously. I know this is a recent occurrence, at 147 hours. I'm curious how often this is happening to others. I'd used fuel lube on it before tightening. What have others used?

Incidentally, I think every tapered thread fitting in a high-pressure application on the airplane has leaked: oil cooler, brakes, and now this. Haven't had any other leaks on the airplane.

Just another reminder to be vigilant. I don't get to fly for a month anyway, as I just dropped it off for paint at 52F this morning!

-Rob

fuel lube is not a sealant

Use Permatex aviation form a gasket. You won't have leaks.

Gary Specketer

I had the same problem ...

The inlet side of my red cube would not seal tight with fuel lube, even at ugly hi torques. I finally pulled it out, cleaned the threads completely, and reinstalled with #2 Perrmatex. That fixed it.

Maybe I'm wayyyy out of line--

but is seems that the red cubes could have AN threads with oring boss sealing.
Tom

Mine has never leaked a drop.

Used fuel lube on the threads.

The max torque listed in the directions of 25ft lbs won't do it.

While I did not design the thing, I think that torque listed is a hold over from the older Flowscan directions. Exceed at your own risk.

Quote from the factory man:

Quote:

Originally Posted by Mathew Sharp (Post 366024)

You do NOT want to rigid mount the transducer to the motor (any part) using just a fitting. It is a huge safety issue. The fitting could theoretically fatigue and break. You absolutely need to have flexible line on both sides of the Floscan 201B or the EI FT-60 (that Dynon now utilizes).

After manufacturing/supporting flow instruments for a good number of years we have seen that flow transducers accuracy is typically better when mounted after both fuel pumps. They simply seem to prefer to have fuel pushed through them, not pulled through. The truth of it though is that many installation drawings still read as though we were still using the older Floscan 201 transducers. I have seen installs that mount the transducer between the pumps with claimed success. The Floscan units were much more sensitive in regards to mounting location, angles of fittings in and out, and attitude. Our new design will tolerate a lot more. Frankly we don't care if the thing flows straight up, or if you put 90-degree fittings in and out (FT-60 only) of the transducer. Just don't mount it upside down or flowing sharply downhill.

Hope this helps,

Matt Sharp

http://www.vansairforce.com/communit...l+smell&page=6

I think those threads are not cut deep enough that's the only reason a NPT
does not seal.
Mine was certainly torqued enough and the last place I expected a fuel leak.
Proseal will do the job.
You'll never have to remove those nipples again and if you did, pro seal has no shear strength and in fact protects the threads very nicely.

I've had good luck with "Tite Seal".

ok I'm going to scream. :)

FUEL LUBE IS A LUBRICANT. IT'S NOT A SEALANT.

I can't count the number of times people have wasted their time with fuel lube on threads, but its one of those things that just wont go away.

Thanks, guys...

Regarding the fuel lube/sealant issue: aren't tapered pipe threads supposed to seal themselves?

-Rob

think water pipe...

Quote:

Originally Posted by RV10Rob (Post 693838)

Thanks, guys...

Regarding the fuel lube/sealant issue: aren't tapered pipe threads supposed to seal themselves?

-Rob

Most all plumbing applications will use some form of teflon tape... don't want tape strings in the fuel system in aviation but there are lots of sealant products with PTFE that are acceptable in fuel systems.