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  #11  
Old 10-19-2017, 01:55 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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Quote:
Originally Posted by Piper J3 View Post
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.
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  #12  
Old 10-19-2017, 02:59 PM
redbaron redbaron is offline
 
Join Date: Aug 2013
Location: Lucerne,Ca
Posts: 187
Smile 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
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  #13  
Old 10-19-2017, 10:20 PM
Harvey rv12 Harvey rv12 is offline
 
Join Date: Apr 2015
Location: Seattle
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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 ?.
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  #14  
Old 10-19-2017, 10:23 PM
RFSchaller RFSchaller is offline
 
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Location: Phoenix, AZ
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Iíve been flying mine since March 2012 and have about 650 Hours on it. I still use the vented cap exclusively. Simple works great!
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  #15  
Old 10-20-2017, 02:36 AM
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Piper J3 Piper J3 is offline
 
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Location: Hinckley, Ohio
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Quote:
Originally Posted by Harvey rv12 View Post
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/communit...2&postcount=28 and http://www.vansairforce.com/communit...1&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.
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80 hrs Flying Aeronca Chief 11AC
1130 hrs Flying 46 Piper J-3 Cub
RV-12 E-LSA #120058 AWC 7/12 Bought Flying 10/2015 with 48TT - Hobbs now 315
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  #16  
Old 10-20-2017, 05:46 AM
Pat Stewart Pat Stewart is offline
 
Join Date: Jan 2005
Location: Granbury Texas
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Quote:
Originally Posted by Harvey rv12 View Post
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.
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  #17  
Old 10-20-2017, 07:30 AM
Harvey rv12 Harvey rv12 is offline
 
Join Date: Apr 2015
Location: Seattle
Posts: 138
Default 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!
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Tom O.
RV-12, bought flying
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  #18  
Old 10-20-2017, 07:49 AM
Mich48041 Mich48041 is offline
 
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Location: Riley TWP MI
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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.
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  #19  
Old 10-20-2017, 10:23 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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Quote:
Originally Posted by Piper J3 View Post

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.
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  #20  
Old 10-20-2017, 03:22 PM
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Piper J3 Piper J3 is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
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?
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Jim Stricker
Hinckley, Ohio
PPL - 1970
80 hrs Flying Aeronca Chief 11AC
1130 hrs Flying 46 Piper J-3 Cub
RV-12 E-LSA #120058 AWC 7/12 Bought Flying 10/2015 with 48TT - Hobbs now 315
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