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tank removal

Harvey rv12

Well Known Member
Hello fellow RV-12 flyers;
I am faced with removing my RV-12 fuel tank, as I have developed a leak. It appears to be from proseal on the underside of the tank, but until I get up on a bench, and clean it up, I wont be able to pinpoint the source of the leak. One disadvantage I have is, I did not build my airplane. I looked through the KAI and don't see a specific procedure for removing & reinstalling a tank on a completed airplane. I thought I read on an earlier post where the filler neck needs to come out, but I have loosened the rubber sleeve and moved it up the filler neck. It would appear that when I remove the three bolts supporting the tank, the tank will slide/move toward the center of the fuselage, and then I will be able to bring it forward.
How do you get the tank up and around the cross bar behind the seats?


Any help appreciated.
Thanks in advance
 
You may find that the fuel return line sticks up from the tank into the filler tube and interferes with the sideways movement of the tank -- that is why the filler tube has to be removed. Believe it or not, with a bit of wrangling the tank will fit between the rollover bar and the cross brace.
 
What I do - -

Drain tank. Use crows foot wrenches to loosen and remove both lines on bottom after removing both rear inspection plates. Take screws from filler neck out. Twist as needed to remove filler neck. Remove fuel sender wire. Remove 3 bolts that hold tank in. CAUTION if you have the frangible bolts on front, do not over tighten them when reinstalling. Use the balloon method to pressurize the tank and spray soapy mixture on areas to find leak. If not too bad, you can clean, sand, and put new tank sealant on outside in most cases. I had a leak on mine very recently after 8 years. It happens.
 
Before you remove the tank you may want to double check the fittings below the tank. I found them to be problematic.
 
John nailed it, unfortunately I am also doing this on a friends airplane. Take the fuel vent line off the bottom of the tank first and when you reinstall put it on last, it will be much easier to remove the fuel line if you do this. The back panel will prevent you from moving sideways and you must also lift the front of the tank high enough to allow the fittings to clear, you need to remove the filler neck and then you can get the tank high enough to move sideways.
 
fuel tank

After pumping as much fuel out as possible prop the front of the plane up so the remaining fuel flows to the rear of the tank so when you undo the fuel tank fittings the remaining fuel wont run down your arm!
 
Pat;
You mention removing the "vent line from bottom of tank first". The only vent I have is the fuel cap, and the only lines to the tank are the return line, and the fuel outlet to the pump, both on the bottom of the tank. Am I missing something ?.
I am going to install the newer design tank vent that I believe has vent line out the top of the tank and runs aft through the bulkhead.
 
Pat;
You mention removing the "vent line from bottom of tank first". The only vent I have is the fuel cap, and the only lines to the tank are the return line, and the fuel outlet to the pump, both on the bottom of the tank. Am I missing something ?.
I am going to install the newer design tank vent that I believe has vent line out the top of the tank and runs aft through the bulkhead.

You've got it right. Just as an aside... When I did SB for my tank I elected to not install the new tank vent and instead to keep the vented cap. My reasoning is that I run 93E10 fuel and don't want a lot of air exchange in the tank which introduces moisture and reduces fuel octane. Best to keep tank sealed accept of small vent hole in the cap. 300TT and no problems with fuel flow.
 
You've got it right. Just as an aside... When I did SB for my tank I elected to not install the new tank vent and instead to keep the vented cap. My reasoning is that I run 93E10 fuel and don't want a lot of air exchange in the tank which introduces moisture and reduces fuel octane. Best to keep tank sealed accept of small vent hole in the cap. 300TT and no problems with fuel flow.

I'm pretty sure I have mentioned this before......

The fuel tank vent system wasn't redesigned to solve a fuel flow issue (the original design did work just fine).

It was redesigned because a few owners overfilled their tanks with cold fuel, which then warmed and expanded, and leaked out the cap vent hole and ran down the side of the fuselage for an extended period of time which damaged the paint.
 
New tank support and aft bulkhead

Check that the updated tank support and the split aft baggage bulkhead has been done. I must due items
 
I double checked the fittings on the bottom of the tank, I don't believe that is the source of the leak. I now understand that the return line runs all the way up into the filler neck. What is the logic behind that ?, to prevent bubbles from forming ?. I am not sure if I will put the extra tank vent in, have to think about that. What is wrong with drilling 2 vent holes in the fuel cap ?, for a little redundancy ?.
 
I?ve been flying mine since March 2012 and have about 650 Hours on it. I still use the vented cap exclusively. Simple works great!
 
I double checked the fittings on the bottom of the tank, I don't believe that is the source of the leak. I now understand that the return line runs all the way up into the filler neck. What is the logic behind that ?, to prevent bubbles from forming ?. I am not sure if I will put the extra tank vent in, have to think about that. What is wrong with drilling 2 vent holes in the fuel cap ?, for a little redundancy ?.

Look here for easy method to find source of tank leak...http://www.vansairforce.com/community/showpost.php?p=1167652&postcount=28 and http://www.vansairforce.com/community/showpost.php?p=1167801&postcount=30.

The fuel return line ends in the filler neck so that head pressure is consistent. The flow is unimpeded by the level of fuel in the tank. Return fuel flow is always the same as seen on the EMS.
 
Pat;
You mention removing the "vent line from bottom of tank first". The only vent I have is the fuel cap, and the only lines to the tank are the return line, and the fuel outlet to the pump, both on the bottom of the tank. Am I missing something ?.
I am going to install the newer design tank vent that I believe has vent line out the top of the tank and runs aft through the bulkhead.


Your correct, remove the return first.
 
Why does return line run up into filler neck?

Ahh, constant head pressure. Why didn't I think of that.
Thanks to all for the guidance. These guys at Van's are pretty sharp!:D
 
With the return line outlet being high in the tank, fuel can not siphon backwards. If a pilot elects to pull the red knob to shut off the fuel, he can be confident that fuel will stop flowing from both the supply and return lines.
An advantage to the fuel vent being located on the bottom of the fuselage is that if the airplane ever flips upside down, then fuel will not leak out of the vent.
 
The fuel return line ends in the filler neck so that head pressure is consistent. The flow is unimpeded by the level of fuel in the tank. Return fuel flow is always the same as seen on the EMS.

This is the reason.

Since the RV-12 doesn't use a flow sensor for the return flow, positioning the return outlet so it is always above the fuel level makes the actual return flow constant which allows for a relatively accurate fuel flow calibration even without a second flow sensor.
 
This is the reason.

Since the RV-12 doesn't use a flow sensor for the return flow, positioning the return outlet so it is always above the fuel level makes the actual return flow constant which allows for a relatively accurate fuel flow calibration even without a second flow sensor.

Do I win prize for having the right answer? Maybe RV-12iS? :D
 
I certainly owe ya a small prize!
I learned there is a lot more to a fuel system than just a filler cap and an outlet to the engine.

Design of vent line to run down below the tank to prevent fuel running out if upside down.

Return line raised above the high fuel level for constant head to keep accurate fuel consumption readings.

What I am still confused about is the dwgs for the newer vent line attachment show a plastic "t" line at the top of the vent tube, with 2 lines running to the bottom of the fuselage. Is that some kind of anti siphon system ?.
 
What I am still confused about is the dwgs for the newer vent line attachment show a plastic "t" line at the top of the vent tube, with 2 lines running to the bottom of the fuselage. Is that some kind of anti siphon system ?.

That is exactly what it is for

BTW, avoiding fuel draining if the airplane ended up upside down was not even a consideration as a reason for the change......
 
Guess I didn't win the RV-12iS... :(

Scott - have a nice weekend. I think I speak for all... Thanks for all you do on this forum.

Oh, and it was a pleasure meeting you at KOSH this summer.
 
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