Fuel tank air vents

[SeaStu1]

At the risk of asking what maybe an obvious question to some l have a question regarding the air vent on my tenders outboard tank and also the 12l remote tank kept onboard for the bigger outboard.

On the small outboard and the remote tank when l'm not using them l close off the air vent. I have always noticed the hiss when l open them back up but what is the correct procedure for the position of these air vents when l'm not using them. I sail about fortnightly.

My reason for asking is that l have just come from the garage where l noticed a plastic 5 litre fuel can l use for topping up the remote tank is balloning, which l put down to the warm weather and the fact the tank can't breathe.

Cheers.

 

[theoldsalt]

Petrol evaporates in a sealed container until the "vapour pressure" is reached. This is the pressure at which no further evaporation can occur. Vapour pressure increases with temperature so the container will "balloon" more on hot days. This is not just due to the expansion of the liquid petrol.

The correct container is designed to withstand this pressure. Keep the air vent losed until the tank is needed and then open the air vent - but not inside the boat or near a naked flame.

When finished with, close the air vent until the tank is needed again.

If you leave the air vent open the petrol will continue to evaporate until, given enough time, it will all be gone.

 

[VicS]

At the risk of asking what maybe an obvious question to some l have a question regarding the air vent on my tenders outboard tank and also the 12l remote tank kept onboard for the bigger outboard.

On the small outboard and the remote tank when l'm not using them l close off the air vent. I have always noticed the hiss when l open them back up but what is the correct procedure for the position of these air vents when l'm not using them. I sail about fortnightly.

My reason for asking is that l have just come from the garage where l noticed a plastic 5 litre fuel can l use for topping up the remote tank is balloning, which l put down to the warm weather and the fact the tank can't breathe.

Cheers.

Closed when you are not using them , but I must admit the way in which a plastic can or tank balloons is rather worrying. It illustrates, however, why you should not store petrol in plastic containers not designed for the purpose.

It would be unwise IMO to leave the vent on tank stored in a locker open.

All my petrol, other than what is in the car fuel tank and the small quantity in the Seagull outboard is stored in a shed at the bottom of the garden. I have a couple of metal cans for most of it ( outboard fuel kept over the winter) but there is at the moment also a gallon in a plastic can for the mower.