AncientGeek Posted February 6, 2014 Share Posted February 6, 2014 Getting a vacuum buildup in my tank on long trips to the point of worrying about collapsing the tank. I had a look and studied rave but cannot figure out how it compensates for vacuum. There's a breather pipe going to a box on the inside of the fender above the filler. This has another 2 pipes, one goes to the charcoal canister, the other going to atmosphere, presumably an emergency vent. These have pressure valves on them and seemed to be designed only to work with positive pressure. The fuel cap is sealed Unless one of these or the charcoal canister act as a one way valve I cannot see how vacuum is relieved. What am I missing? Quote Link to comment Share on other sites More sharing options...
Ash.Witty Posted February 6, 2014 Share Posted February 6, 2014 I think the point of the vacuum (negative tank pressure) is to reduce the amount of oxygen in the fuel tank, with only highly concentrated fuel vapours this will mean much less chance of ignition due to fuel pump problems etc. Don't know if that is a load of rubbish but sure I've heard it somewhere before, my efi v8 didn't have a charcoal canister so not entirely sure what its purpose is. Quote Link to comment Share on other sites More sharing options...
Nigelw Posted February 6, 2014 Share Posted February 6, 2014 Mine used to do this also, got annoyed and drilled a small hole in the cap, it as higher than the breather so it didn't matter, never had any problems with it with the vacuum but it just annoyed me, 1.5mm drill bit and 10 secs all sorted. Quote Link to comment Share on other sites More sharing options...
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