What does venting mean?

Can anyone simply explain what the difference is between a vented and unvented tank, what the importance is and how this is achieved?

I believe mine is unvented but haven't a clue why

Bootneck

[1sportyrich]

From my limited knowledge, a vented tank, is one that lets' the build of fumes from the petrol escape. The build up of fumes could be danderous in the instance of, you stopping, lighting up a tab & thinking "wonder how much petrol I have". Opening up the tank & whoooosh a fireball!


How it's done, I know not.

[S.T.Chapman]

put quite simpley
your tank has a limited capacity you fill it with fuel
its say black
you sit it in the sun
the fuel within gets hot
it expands
its got no where to go
you left your fuel tap open
it pisses out your carb
generally an un vented tank is dangerous
also as you draw fuel from your tank, the dimminishing liquid is not replaced and so a vacumn starts to develope resulting in fuel starvation

[girlyglide]

Also worth knowing left hand fatbob tanks use unvented caps, right hand Fatbob tanks use vented caps.

There were issues with some "metric" cruisers having thier tanks implode to some extent due to blocked vents and Very thin tank material.

Ta very much for the advice.

one final question, i'm told my tank is unvented, does that mean I can simply get a fuel cap that allows the air to vent? or are some tanks built to be used unvented?

Cheers Bootneck

[S.T.Chapman]

Originally Posted by bootneck

Ta very much for the advice.

one final question, i'm told my tank is unvented, does that mean I can simply get a fuel cap that allows the air to vent? or are some tanks built to be used unvented?

Cheers Bootneck

running an unvented tank can result tragedy, i know no examples of running one by design

a vented cap could work out,
points to remember
a vented cap also acts as the overflow and will result in a petrol sodden crotch (an incentive to stop smoking )
unvented, leads to a pressure build up, theres nowhere for expanding petrol to go, as fuel is removed a vacumn developes causing fuel starvation.

Im a little surprised this tank has no vent at all?
what make is it?
I had a zodiac tank once and the vent had been braized closed, however they invited you just stick a 1/8" bit up it to clear, something to do with pressure testing.

Many thanks ST, I have established the tank vents through the filler cap but I hoped to avoid the fumes heading out that direction as it has got under the lacquer and caused it to lift.

I understand now that the venting by that means is unavoidable so will have to try to figure a way of protecting the re-lacquering.

But thanks for the explanation I real insight.

Bootneck