Long range tank - breather line versus fill line

[dom14]

Hey Guys,

I'm just wondering about the reason that in my long range tank(LRA automotive tank), the breather line & fill line
is at the same level.
This means, if I fill the tank to slightly above the fill line, the breather line will also get filled with petrol!
How does that help as a "breather line"?!!!
Shouldn't the breather line come out from the highest point of the tank(like the charcoal canister line level in the picture below)??!!

Thanx

P.S. I think it's also pretty bad design to put the breather line right next to fill line that close. It creates a fitting nightmare when it comes to access the hoses and hose clamps to them.

[BigRAWesty]

So the one next to the filler is a fast fill line. That's what allows the fuel to fill the tank without going back up the filler neck..
The smaller one on top of the square is the low pressure breather.
This allows for expansion and contraction of the fuel

[dom14]

So the one next to the filler is a fast fill line. That's what allows the fuel to fill the tank without going back up the filler neck..
The smaller one on top of the square is the low pressure breather.
This allows for expansion and contraction of the fuel

Thanx mate.
I'm beginning to understand the fuel system mechanics/physics now.

[dom14]

I'm about to do a complete fuel system plumbing/breathing diagram of the RB30 fuel system with real pictures attached to it. It will come handy in future for everybody.

[dom14]

If I had time, I would've moved the "fast fill line" bit further away from the fill line(same level of course).
It's a pretty bad design to make it that close to the fill line, I think, 'cos there's no obvious reason for it to be that close
to the fill line, even though being at the same level as fill line makes sense.

[BigRAWesty]

If I had time, I would've moved the "fast fill line" bit further away from the fill line(same level of course).
It's a pretty bad design to make it that close to the fill line, I think, 'cos there's no obvious reason for it to be that close
to the fill line, even though being at the same level as fill line makes sense.

That fast fill only returns to the top of the filler neck, just past the flow of the nozel. .
So air can quickly get past the flow of the fuel..
Once the hole is covered then the fuel comes back up the line and clicks off the pump.

The slow breather I'm pretty sure is vented to atmosphere threw a tiny filter which is tucked up on top of the fillers..

[dom14]

That fast fill only returns to the top of the filler neck, just past the flow of the nozel. .
So air can quickly get past the flow of the fuel..
Once the hole is covered then the fuel comes back up the line and clicks off the pump.

The slow breather I'm pretty sure is vented to atmosphere threw a tiny filter which is tucked up on top of the fillers..

"Slow Breather" is the charcoal canister line by the looks of it, 'cos there's no other line that vents to the air, not even from the metal pipe near the fill point on the body. There a one way valve( and possible a filter inside as well) on the charcoal canister line(right above the tank, where the hose joins the metal charcoal canister fuel line)

Does that sound right?!!

I've attached few pictures below.

[dom14]

That fast fill only returns to the top of the filler neck, just past the flow of the nozel. .
So air can quickly get past the flow of the fuel..
.

Yeah, I was wrong. Obviously closer the "fast fill line" to the fill line is, quicker the overfilling fuel enters the "quick fill line" to cut off the pump at the filling nozzle. I wish it's an inch more away from the fill line on the tank, 'cos it was an absolute bastard when it came to access it and fit the pipes properly and tighten them properly.

[BigRAWesty]

Yes the breather is the charcoal canister line..

[dom14]

Yes the breather is the charcoal canister line..

I'm wondering whether LRA has done a half hearted job on mine(some twenty five years ago).
There's no "vent to atmosphere" hole/filter/valve from the tank or the fill line/quick fill line plumbing.
Only valve is the black cylindrical one in the picture, which is on the charcoal canister line which comes out of the top of the "expansion tank" on the top of the tank.