Fuel Tank Vent Lines / Are they Necessary?

His boat hasn't been launched yet. So it will be a 2015

 

Whew. This one opened a can of worms.

Ike is definitely the authority. Thanks for posting.

It's done now.

I skipped the carbon canister for now. Runnin non compliant.

The tank vents and the integrated fill/vents are 5/8" which makes a lot of sense for them to be the same size.

So... I have 1 1/2" fill hose, 5/8" vent hose (both terminating at the integrated fill) and the 3/8" vacuum fuel lines going to a Racor and fuel tank selector manifold, from there, on to the outboards.

And that is correct. It is a 2015.

 

Well then, on a new boat the system has to be designed to meet the standard. You can use a system with a canister, or one without if it meets the standard. I suggest you get a copy of the ABYC Fuel system standard H-24. They have it covered. The Perko web site has it covered better than most I have seen http://www.perkofuelsystems.com/system_design/

 

On a personal note, I prefer a vented system. The whole concept was (and still is) that you do not want pressurized fuel lines in a boat. Get a leak and the whole fuel contents empty into the boat. If the system is under negative pressure (fuel is being sucked to the engine rather than pushed) and you get a leak, the engine just starves for fuel. Under that system it takes a really big leak to dump fuel into the boat. Unfortunately you do get vapor. (boom)

Anyway. I had a lot of reservations about these new fuel systems, especially carbon canisters. You get any fuel or water into these things and they are done! Right now! and they aren't cheap. Sorry, just ranting now.

 

Yes, that's my thinking as well.

I have a negative pressure system.

The fuel pumps are in the outboards and outdoor generator. They pull fuel to them.

I'm not exactly sure how anyone can make me drill new holes in my fuel tanks to install a secondary vent system, as in the perko page though... I'll just run standard, canister free system for now, anyway.

 

You'll have to get a fuel tank that already has holes and fittings. That's my other complaint. Fuel system leaks are almost always at fittings. Reduce the number of fittings and you reduce the probability of a leak. The new systems double and triple the number of fittings.

 

Um, just guessing, but if you need a flowback tube to the tank, then the fuel filler hose becomes the vent, and with the cap on tight, vented gasses flow OUT the small nipple to the canister, where a return tube runs back to the tank at the "vent" fitting. Provided that all the other junk is hung correctly, this saves an extra fitting in the tank. Just a thought.

 

This is exactly my thinking as well.

This is gasoline here... below decks.

The less fittings, the better.

I already have my fuel tanks. 3 (qty) 50 gallon tanks. They are brand new, Moller tanks.

They have 3 fittings: Fill (1 1/2"), Vent (5/8") and Fuel Pick Up (3/8" hose barb).

Well, a fuel gauge sender too, but that's not a plumbing fitting.

The deck fills have matching sizes.
Again... who is going to make me comply with the environmental regulations? Nobody.

It's done. Already installed. I skipped the canister and used the integrated fill/vent deck fittings as pictured in the OP.

 

Phil, the deck fill is a combination fill/vent. It allows pressurized air out even if it's on tight.

Guess im the first guy here to play with these new deck fills.

 

Probably. If this is a privately owned boat, maybe never. But if you get it surveyed for insurance or for sale (should you decide to sell it later) then it won't pass a survey. This of course assumes the surveyor understands the new fuel systems.

 

Agreed.

I'll probably make several changes/additions if it goes up for sale.

 

Thinking about it (your fuel system) you have what is called a Managed purge system or pressure relief system. That cap you put on the fill allows the system to vent if and only if the system pressure exceeds 1 psi. That basically meets the EPA standard for diurnal emissions. With a Managed purge system you don't need a canister, or you can put one in the same vent line if the line has a inverted loop or a P trap to keep water out. see here http://www.attwoodmarine.com/internal-fuel-system-designs

 

Brilliant find, Ike.

Yes, the cap has a spring loaded air release valve that allows pressure out, but no water in.

That's exactly what I just installed.

 

You may have to install an inlet valve in the fill line but other than that what you have may meet the standard

 

Thank you.

I did notice that valve in the diagram and may add that at some point soon.

Seems convenient, but at least I have a couple of decades of listening to the fuel fill hose to know when to stop. That should work for a bit.