Van's Air Force
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Fuel vent check procedure
- Thread starter mbuto
- Start date
You can put a hose on the vent, remove the cap, and one person blows in the tube, while the other person listens though the filler hole.. or go the other way and blow in the fill opening while someone listens at the vent.
if you are getting spillage though the cap (blue stains) I would recommend rebuilding the fuel caps, lubing with Kryox grease, and adjusting them properly.
D-Dubya
Well Known Member
As a start, see if the fuel cap will twist after it's locked down. If it moves, it's too loose and needs adjustment. That should address the main O-ring on the standard Van's fuel caps--but it's possible the smaller O-ring on the center shaft could still leak.
As far as the vent system goes, slip a piece of 3/8" vinyl tube over the vent fitting on the bottom of the aircraft and blow on the tube with the fuel cap off. With a helper positioned at the open fuel cap, listen for air coming out. If they can hear air, then you've confirmed the vent system is venting. Blow again with the fuel cap on and locked down and there should be no air escaping. If it is leaking and the big O-ring was tight, it could be leaking past the O-ring on the center shaft. You could spray a TINY amount of soapy water on the cap and see if bubbles form, but there's less risk of water intrusion if you just listen.
If you don't want anyone to see you blowing on your fuel tanks or if a helper isn't readily available, you can use a longer piece of vinyl tubing and listen at the cap yourself. Not sure if that addresses your concern, but hopefully it will.
As far as the vent system goes, slip a piece of 3/8" vinyl tube over the vent fitting on the bottom of the aircraft and blow on the tube with the fuel cap off. With a helper positioned at the open fuel cap, listen for air coming out. If they can hear air, then you've confirmed the vent system is venting. Blow again with the fuel cap on and locked down and there should be no air escaping. If it is leaking and the big O-ring was tight, it could be leaking past the O-ring on the center shaft. You could spray a TINY amount of soapy water on the cap and see if bubbles form, but there's less risk of water intrusion if you just listen.
If you don't want anyone to see you blowing on your fuel tanks or if a helper isn't readily available, you can use a longer piece of vinyl tubing and listen at the cap yourself. Not sure if that addresses your concern, but hopefully it will.
Roadjunkie1
Well Known Member
Which Kryox grease is best for this type of application. There are several available....
RV7 To Go
Well Known Member
I use the 205. Do the caps at the annual. Just needs a light film on both o-rings. Use it to lube the standard Vans fuel valve if you have one as well.
RV8JD
Well Known Member
It's Krytox GPL 205 grease:
Usher Fuel Caps:
Adjustment instructions and parts shown below. Instead of fuel lube/EZ Turn for lubrication many folks use Krytox GPL 205 grease with good results. Expensive, but the small 0.5 ounce tube will last a long time.
Don't forget the small O-ring around the stem. Lubricate both O-rings and properly adjust the cap.
Parts are available from Van's:
Usher Fuel Caps:
Adjustment instructions and parts shown below. Instead of fuel lube/EZ Turn for lubrication many folks use Krytox GPL 205 grease with good results. Expensive, but the small 0.5 ounce tube will last a long time.
Don't forget the small O-ring around the stem. Lubricate both O-rings and properly adjust the cap.
Parts are available from Van's:
Last edited:
The easiest way, and it can be done without help from another person, is to remove the cap and then put air into the vent fitting on the belly using an air hose.
If air is flowing into the tank, you can see fuel vapor coming out of the top of the filler opening as long as you’re not in a super dark hanger.
If air is flowing into the tank, you can see fuel vapor coming out of the top of the filler opening as long as you’re not in a super dark hanger.
If the caps haven’t been rebuilt, order the Orings from Spruce for the “Usher” fuel caps, there is a big one and a little one. Remove the caps, close the tab, loosen the 9/16 nut, then unscrew the lower casting. The little -12 Oring is in there. If the caps don’t snap closed or they spring open, you can use a file and re-profile the latch to be a few degrees less than 90, and they should snap closed..
