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Tip: Fuel drain warning

jlfernan

jlfernan

Well Known Member
There I was this morning just doing some detail things to kill time while I wait for some parts. I decided to install the fuel drain on my left wing. I put some fuel lube on the threads and started screwing it in. It went about four turns and stopped. Fearing I had it crossed threaded, I pulled it out and verified the the threads in the valve and the fitting were fine. I put a little oil on the valve but still no luck. The drawing shows the fuel drain flush with the fitting. I couldn't find anything in the directions. I measured the valve and saw it was a tapered fitting. Before I grabbed a bigger wrecnh, I called Vans. They said, "Oh yea, the drain only goes in three to four turns, that's an error on the drawings". Good thing I didn't grab that bigger wrench. I can't imagine the havoc I would've created if I had followed the drawing. For those of you coming up to this part, the drain sticks out, about 5/8th's of an inch of threads showing. Torque to about 70 in lbs and you should be all set.
 
I tapped mine out a little bit to get it to screw in farther. It isn't flush but much better than the 3 turns you get.
 
I managed to get mine all the way in. However, after seeing a few RVs, it's different on just about every one of them.. some have it close to all the way, others are not quite as much in.. etc.. Bottom line is.. it needs to go in as far as it can and it doesn't leak.
 
me too...

Perfect timing for me too. I have to replace one that is 17 years old. Keep that in mind when you reach for that bigger wrench :)....

John
 
Not too far now!

It's best to do at least a test fit with the tank baffle still off. Remember, you want this drain to be at the low point. If the threaded portion sticks up inside your fuel tank, it's no longer a sump and you continue to accumulate a good bit of unwanted material and water in the tank. With the baffle off, you can do a test fit and visually ensure that the end of the drain is still below the level of the skin.

These are low-wing planes. This is not a readily visible item and I doubt the drain valve sticks out far enough to significantly slow anyone down. Fuel lube it, and put it in to the proper torque and forget about it. Form follows function here.
 
Proseal ?

Also good timing as I had noticed the same problem when I screwed my drains into my QB Tanks.....but not for the final time so my Q relates to proseal...have people used this for the final fitting of their drains ? (Obviously whilst making sure that they don't block the drains :eek: )
 
Don't use proseal on your fuel drains. The fittings are tapered and will seal themselves. You might put a little fuel lube on them so you don't get galling between the drain and the fitting in the wing.

Putting proseal on them will make them harder to remove (and you will need to remove them at some time, if only to replace the little "O" ring inside). In addition, if you use proseal, then remove and reattach the drains, you're running a real risk of knocking some proseal loose and having trash in your fuel.
 
Info noted

Kyle Boatright said:
Don't use proseal on your fuel drains. The fittings are tapered and will seal themselves. You might put a little fuel lube on them so you don't get galling between the drain and the fitting in the wing.

Putting proseal on them will make them harder to remove (and you will need to remove them at some time, if only to replace the little "O" ring inside). In addition, if you use proseal, then remove and reattach the drains, you're running a real risk of knocking some proseal loose and having trash in your fuel.
Click to expand...

Kyle that is all noted, thanks for the info

Best regards

David
 
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.
 
briand said:
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.
Click to expand...
EZ Turn (formerly known as Fuelube)
http://www.aircraftspruce.com/catalog/cspages/ezturnlube.php (get the tube, not the can, unless you're lubing for say 100)
 
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.
 
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.
 
moving water

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.
 
General pipe thread info

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
 
IowaRV9Dreamer said:
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.
Click to expand...


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.
 
Heating ?

briand said:
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.
Click to expand...

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
 
AN Fitting Sealant??

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?
 
Gsuit said:
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?
Click to expand...

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