Fuel fill system design

[Deane Henderson]

How do you build a fuel fill system that does not burp or overflow from thermal expansion? We use a long skiny tank between the stringers. Is there any good reference material to go by?

[Corpus Skipper]

If you find out how, let us know. :D

[Sean Herron]

Hello...

Big vents (on tank) - fuel is denser than air - but still - you are displacing a lot of air - make a big vent and don't loop it downwards as so many do - it fills with wash water and air locks - take it up and then down to the the thru hull - NO LOOPS...

You can also Y the fill tube to its own vent such that fuel flow will not back up same vent - but air will be allowed into fill tube if you are plugging up the deck fill - just remember - fuel in air out - fuel heavy air light...

Burp...

You can also plumb in fuel resistant expansion tanks any where in the system...

Cheers...

SH

[FAST FRED]

Mostbuilders just install the fill pipe into the tank an inch or two.

This leaves a cushon of air that will take the warm fuel expansion from the engines tank return.

Fast fred

[Dutch Peter]

So to prevent the ...Burp, while filling you use a large vent pipe on the tank and to overcome the expension...is it an idea to have a day-tank with an overflow to the main tanks, that would take care of the expansion, wouldn't it?
But now somebody is designing this, what sizes are we talking about, rule of thumb?

[Sean Herron]

Hello...

All tanks that are displacing air with their volume MUST have venting...

I named my my dog 'stay' - bad bit - come here Stay - dog is going apolectic...

All tanks can vent to one vent above volume line...

Dutch - big as you can - air is less viscous than fuel - but the bigger the better - plumb the big hole...

Bigger then inlet driven by pumps is great - sounds simple but it is true - think about your car having a fill pump at near one inch but only having a vent of 3/8"...

Sorry...

SH

[Thunderhead19]

Vent out of the highest point in the tank. I'm not kidding, vent out of the highest point on the tank. If your keel runs downhill fwd and your tank does too, vent the aft end of the tank. If the other way, vent fwd. If running trim is bow up and static trim is bow down putting two vents in might not be a bad idea. Also, tank baffles are your friends too. When vapour in the tank is expanding, sloshing fuel can cover a vent opening and be forced up the tube.