Tip: Fuel drain warning

[dan]

Originally Posted by briand

OK it appears I'm having trouble getting my drain threads to seal. Can I use teflon tape? Is there a suitable product that I can pick up locally? I pressurized my tank and the only place I see bubbles is around these threads. I torqued the fitting to 70"-lbs which helped but I still have a small leak.

EZ Turn (formerly known as Fuelube)
http://www.aircraftspruce.com/catalo...ezturnlube.php (get the tube, not the can, unless you're lubing for say 100)

[Kyle Boatright]

Teflon tape is not recommended in any fuel, brake, or oil system. Even if no tape fragments get loose (and inside your fuel, oil, or brake system) during installation, there is virtually no way to prevent bits of it from getting into the system when you replace the fitting after pulling it for whatever reason.

You don't want bits of teflon tape stopping up your fuel, oil, or hydraulic lines.

[briand]

I put in an order for a tube of the fuelube from Spruce this morning, I needed some blind rivets for my LE ribs to spar connection anyway. I decided to use some teflon tape on the threads last night so I could move foward on leak testing the tank. I was careful not to get any of the tape past the threads so the tape shouldn't even see the inside of the tank. I'll make sure I clean all the tape off when I'm done. I think it worked but the level of the water is moving up and down, the temp inside my house is stable so I'm not real sure why its doing this. I expected an initial drop in pressure once the air inside the tank cooled to room temp. but I don't understand why there is a fluctuation. Maybe I'll use some dyed mogas for extra insurance.

[IowaRV9Dreamer]

Brian - the water may be moving up & down because the outside air pressure is going up and down. We built a surprisingly senstive barometer just this way for my daughter's school project. If you hunt around on the internet, you can find hourly archived METAR data, extract the air pressures, and see if they match the water level in your tube.

[mlw450802]

A good thumb rule for sizes 1/8 through 1 inch iron pipe size (ips) is that the male pipe should turn in by hand ~3-1/3 turns to 3-2/3 turns for properly made threads. You should wrench tighten another 1 to 2 turns. Tightening to a torque spec doesn't make much sense due to the variability in tolerances and due to the fact that the threads are tapered ~3/4 in per foot.

The NPT thread form will always have a spiral leak path that must be closed using a sealant.
NPTF threads (NPT Fuel spec) are designed such that the roots and crests of the threads have interference and should seal dry (NPTF is often referred to as Dryseal threads. Dryseal, I believe, is a trade-named threadform that complies with the NPTF specification).
Mixing and matching male NPT with female NPTF and vice versa will result in a spiral leak path that will require sealant.

The safe bet is to always use sealant unless you know for absolute certain that the mating threads are in-spec NPTF threads.

-mike

[smithhb]

Originally Posted by dan

EZ Turn (formerly known as Fuelube)
http://www.aircraftspruce.com/catalo...ezturnlube.php (get the tube, not the can, unless you're lubing for say 100)

ACS sells a 5oz tube for $11.00...What a deal!

[briand]

Originally Posted by IowaRV9Dreamer

Brian - the water may be moving up & down because the outside air pressure is going up and down. We built a surprisingly senstive barometer just this way for my daughter's school project. If you hunt around on the internet, you can find hourly archived METAR data, extract the air pressures, and see if they match the water level in your tube.

I don't think the data quite shows evidence of the outside pressure being the cause my water level fluctuating. This is the data I found (muskegon is about 20 nm NW of my house):

http://www.glerl.noaa.gov/metdata/mkg/

8:00 PM on 9/5/06 I was at 7" of water on my scale, 5:00 AM 9/6/06 I was at about 6.6", 4:00 PM 9/6/06 I was reading 7.5ish, 9:45 PM (right now) I'm getting 6". I will leave it set up 1 more day and see what I have when I get home from work tomorrow. It almost seems like the day light is affecting it, making the water go up, but I can't imagine how.

[flydjd]

Originally Posted by briand

I don't think the data quite shows evidence of the outside pressure being the cause my water level fluctuating. This is the data I found (muskegon is about 20 nm NW of my house):

http://www.glerl.noaa.gov/metdata/mkg/

8:00 PM on 9/5/06 I was at 7" of water on my scale, 5:00 AM 9/6/06 I was at about 6.6", 4:00 PM 9/6/06 I was reading 7.5ish, 9:45 PM (right now) I'm getting 6". I will leave it set up 1 more day and see what I have when I get home from work tomorrow. It almost seems like the day light is affecting it, making the water go up, but I can't imagine how.

Airlines load fuel according to it's specific gravity ie temperature - maybe this is the cause as it seems you are getting higher readings during the day than at night

[Gsuit]

Thanks Jorge - great timing. Man, from all the posts says that - it looks like we'll turn out a fleet of RV's at the same time!!

But, to my question: I understand not using ProSeal to seal the AN fittings that exit the fuselage (vent lines, brake lines). So, what should you use as a sealant? Is FuelLube alone ok?

[kevinh]

Originally Posted by Gsuit

But, to my question: I understand not using ProSeal to seal the AN fittings that exit the fuselage (vent lines, brake lines). So, what should you use as a sealant? Is FuelLube alone ok?

Yep - a little fuel lube on threads (not the mating face) helps prevent galling.