Long range tank - breather line versus fill line

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.

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

Quote:

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Originally Posted by bigguwesty

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

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

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.

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.

Quote:

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Originally Posted by 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.

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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..

Quote:

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Originally Posted by bigguwesty

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..

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"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.

Quote:

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Originally Posted by bigguwesty

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..
.

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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.

Yes the breather is the charcoal canister line..

Quote:

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Originally Posted by bigguwesty

Yes the breather is the charcoal canister line..

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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.

Quote:

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Originally Posted by dom14

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.

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I'll take a photo of mine when home mate

Mine doesn't have it either, it's identical to yours, never been an issue.

Quote:

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Originally Posted by Throbbinhood

Mine doesn't have it either, it's identical to yours, never been an issue.

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Ok cool, thanx mate. That makes me feel better.
I was contemplating whether I need to drill a hole on the metal pipe at the fill point and fit a venting valve+filter there.
Sounds like I don't need to worry about it.
Cheers.

P.S. I think, as Kallen advised above, charcoal canister line does the job of venting the tank to atmosphere, though I may have to find out whether the charcoal canister is blocked or not. I've overfilled the tank couple of times(to check fuel economy).
I might have flooded the charcoal canister by doing that and caused some damage to it.

Fuel fill point photos.

To be honest, if I remember correctly my breather line (the right angle one) was blocked off. I plumbed everything else up as per the LRA diagrams and it all works perfectly, even on hot days. So far has not been an issue and touch wood it doesn't become one in future.

Fuel cap photos

Quote:

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Originally Posted by Throbbinhood

To be honest, if I remember correctly my breather line (the right angle one) was blocked off. I plumbed everything else up as per the LRA diagrams and it all works perfectly, even on hot days. So far has not been an issue and touch wood it doesn't become one in future.

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If we're talking about the one that allows the "breathing" when filling up the tank to cut out the petrol at nozzle when petrol if filled up to the fill hole on the tank, then only downside of that is you just have to manually control the fuel filling to ensure you don't overfill the tank. Since yours is straight petrol, even if you overfill it once or twice, you end up using few litres after that and end up not creating extra pressure inside the tank on hot days. Besides, any expanding petrol might get through the charcoal canister line and flood out of the charcoal canister eventually(assuming the canister is not blocked). So, I reckon chances of it can turn dangerous is pretty slim.
Besides, you have two tanks, don't you? That pretty much eliminates most chances of pressure build up accidents(assuming tanks are connected to equalize the pressure between them?)

Quote:

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Originally Posted by dom14

If we're talking about the one that allows the "breathing" when filling up the tank to cut out the petrol at nozzle when petrol if filled up to the fill hole on the tank, then only downside of that is you just have to manually control the fuel filling to ensure you don't overfill the tank. Since yours is straight petrol, even if you overfill it once or twice, you end up using few litres after that and end up not creating extra pressure inside the tank on hot days. Besides, any expanding petrol might get through the charcoal canister line and flood out of the charcoal canister eventually(assuming the canister is not blocked). So, I reckon chances of it can turn dangerous is pretty slim.
Besides, you have two tanks, don't you? That pretty much eliminates most chances of pressure build up accidents(assuming tanks are connected to equalize the pressure between them?)

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The line I'm talking about is the 'charcoal canister line' in your first pic in this thread.

But yeah everything goes to the dual tank filler thing, from memory they are all interconnected etc. Honestly cant remember 100%, but it's sat in the sun in 40+c weather with full tanks and no issues.

Petty tanks aren't supposed to have a 'breather' direct to atmosphere
That is the job of the Charcoal Canister.

You should have the fill line breather that goes from your tank to the top of the filler so you don't get blowback when filling.
Both the filler and fill breather should be sealed from atmosphere with the cap on.
The tank 'evaporates' to atmosphere via the Charcoal Canister and not a separate line

Quote:

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Originally Posted by Throbbinhood

To be honest, if I remember correctly my breather line (the right angle one) was blocked off. I plumbed everything else up as per the LRA diagrams and it all works perfectly, even on hot days. So far has not been an issue and touch wood it doesn't become one in future.

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Or did you mean the "charcoal canister line"(as it's connected in mine) from the top of the expansion tank?
If that's the case, that means "slow breathing/venting" isn't happening in your tank, and fumes just stay inside the tank.
But, having two tanks still minimizes your chances of any pressure build up accidents. Besides, some pressurized fumes might escape from weak points like fuel cap.
I've been wondering whether the fuel cap is designed to allow that to happen, 'cos if you look at the pictures of the fuel cap above, it doesn't look like a simple fuel cap, but some mechanism appears to be there at the bottom of it.

Quote:

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Originally Posted by the evil twin

Petty tanks aren't supposed to have a 'breather' direct to atmosphere
That is the job of the Charcoal Canister.

You should have the fill line breather that goes from your tank to the top of the filler so you don't get blowback when filling.
Both the filler and fill breather should be sealed from atmosphere with the cap on.
The tank 'evaporates' to atmosphere via the Charcoal Canister and not a separate line

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Ok cool, thanx mate. I'm pretty confident now, that I can leave the fuel tank system as it is. :)
Kallen was telling me the same thing, but I was still bit paranoid. :D ('cos I dismantled every part of the fuel tank system, including the fill point, to clean them).
Cheers.

Quote:

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Originally Posted by Throbbinhood

The line I'm talking about is the 'charcoal canister line' in your first pic in this thread.

But yeah everything goes to the dual tank filler thing, from memory they are all interconnected etc. Honestly cant remember 100%, but it's sat in the sun in 40+c weather with full tanks and no issues.

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Yeah, I think it's ok, 'cos you divide any possible issues between two tanks(namely the pressure buildup inside). Charcoal canister is also an emission control thing I reckon,(other than saving some petrol fumes and redirecting it to the intake & venting the tank positive or negative pressure to the atmosphere), so it's a modest saving of fuel.
I bet some of the extra pressure is escaping from the petrol cap as petrol fumes, 'cos that's the only way I can think of, since your charcoal canister vent is blocked off.

Apparently in olden days, petrol fumes just escaped to atmosphere from a petrol cap vent valve(or a simple small hole on it).

Quote:

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Originally Posted by dom14

Or did you mean the "charcoal canister line"(as it's connected in mine) from the top of the expansion tank?
If that's the case, that means "slow breathing/venting" isn't happening in your tank, and fumes just stay inside the tank.
But, having two tanks still minimizes your chances of any pressure build up accidents. Besides, some pressurized fumes might escape from weak points like fuel cap.
I've been wondering whether the fuel cap is designed to allow that to happen, 'cos if you look at the pictures of the fuel cap above, it doesn't look like a simple fuel cap, but some mechanism appears to be there at the bottom of it.

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The fuel cap will in the case of vacuum for whatever reason will allow air through so your tanks don't get sucked in. They should never vent as that's the job of your charcoal canister

Quote:

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Originally Posted by lucus30

The fuel cap will in the case of vacuum for whatever reason will allow air through so your tanks don't get sucked in. They should never vent as that's the job of your charcoal canister

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Thanx mate.
Yes, now it's obvious charcoal canister performs few important functions and a vital part of the fuel system.
Apparently, it's an emission control requirement as well.
But, old charcoal canisters aren't likely to function well, and I'm pretty sure there are many out there with charcoal canisters not functioning properly.
I'm not sure mine's working properly either, but I'm gonna let it be. :)