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-   -   RV-12 Fuel Cap Vent (http://www.vansairforce.com/community/showthread.php?t=153980)

JPalese 10-06-2017 07:07 AM

RV-12 Fuel Cap Vent
 
Does anyone have the drawings of how to vent the fuel cap?

My recollection is it used to be in KAI 37 but I can't find it there any longer.

rgmwa 10-06-2017 07:23 AM

The cap itself is no longer vented. There is a separate vent line from the tank as per KAI 37.

scottmillhouse 10-06-2017 06:49 PM

Drill the vent hole anyway in the cap. You need it with a full tank on takeoff. Obviously fuel blocks the new vent and fuel pressure goes down which is kind of scary on a take off. It will stabilize when you level out and burn fuel. There is no problem with the cap vented too.

tomkk 10-06-2017 08:07 PM

Quote:

Originally Posted by scottmillhouse (Post 1209128)
Drill the vent hole anyway in the cap. You need it with a full tank on takeoff. Obviously fuel blocks the new vent and fuel pressure goes down which is kind of scary on a take off. It will stabilize when you level out and burn fuel. There is no problem with the cap vented too.

First time I've heard of this - I've never seen ithappen in my -12 ...

MMiller 10-06-2017 08:30 PM

John, you remember correctly, but the step was removed with the 12/27/2013 revision that added a fuel tank vent line.

Here is screenshot of the relevant instructions from a 2011 version of section 37.

Mich48041 10-06-2017 08:39 PM

Even if the fuel tank is so full that gasoline fills the vent line, the fuel pressure at the bottom of the tank will be higher than when the tank is not quite so full. That statement can be proven with a manometer.

DBRuth 10-06-2017 08:51 PM

Cap vent
 
I drilled the vent hole slightly smaller than the plans called for, tap drill size for a 4-40 tap. Then I tapped both holes. If you don't like the results of the new vented cap, you can put a 4-40 screw in one of the holes. YMMV

JPalese 10-06-2017 10:38 PM

Thank you - Exactly what I was trying to find!
 
Quote:

Originally Posted by MMiller (Post 1209142)
John, you remember correctly, but the step was removed with the 12/27/2013 revision that added a fuel tank vent line.

Here is screenshot of the relevant instructions from a 2011 version of section 37.

Thanks to all for your replies.

scottmillhouse 10-07-2017 09:33 AM

On drilling the vent anyway. Based upon my experience, ever time I filled my tank to the filler neck and fuel came out the vent, the next flight I would have low fuel pressure (1-3 psi) on climb out. A year and a half and about 170 hours since I drilled the hole in the cap, I have not had a low fuel pressure problem. I see no down side on having the cap also vented unless your plane is out in the rain without a canopy cover. Also it is a back up in case the dirt dabblers like your fuselage vent.

RFSchaller 10-07-2017 09:25 PM

The only time Iíve had insect problems was on another home built I had. Something took up residence in my pitot tube. Became pretty obvious on takeoff roll when the airspeed never cam alive. It was a pain to disassemble the hose fitting and blow out he tube because I had a hard time getting to fitting tomreseal.


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