Fuel Tanks

[mud90mike]

Hi All

I have been asked a few times to make aluminum fuel tanks for people for modified vehicles, I have seen plenty being sold on ebay etc but I don't know where we stand with Regulations about them, HAs anybody had any experience with this type of thing and whether they need to be tested or certified before they are allowed to be used?

Many thanks

 

[hotrodder]

Unless something has been soooooo quietly introduced no one has heard about it then AFAIK there's nothing specific to the tanks themselves (for PLG vehicles at least) beyond common sense stuff as long as they're made from metal and for liquid fuels

EC Directive 70/221 is about laws regarding fuel tanks and underbody protection of automotive stuff but is more about vehicle type approval. Still worth reading but it's way more involved/complicated/expensive than expected* for replacement parts/modified vehicles. BIVAs take on the subject is more applicable for aftermarket & custom tanks... https://www.gov.uk/government/uploa...data/file/354071/M1_IVA_inspection_manual.pdf search the pdf for 03A but it's more about how & where the thing is fitted than whether it's well designed & made. Especially relevant with aluminium due to it's fatigue properties

*IIRC the EC 70/221 thing calls for hydraulic testing at twice the working excess/max pressure or 0.3bar/4.35psi (whichever is higher). The tank needs to survive without leaking or splitting and can become permantly deformed without failing the test. Easy enough to pass but inconvenient for a one off custom tank as many fuel tanks start to change shape elastically with as little as 1 or 2 psi in them and will be a very different shape with 4+ psi in 'em.

 

[Pete.]

From my experience welding and leak testing a couple of aluminium motorcycle tanks, I found that I could safely pressure-test to 5psi after that it would start to visually swell. At 8psi it'll take start to take a permanent set. The one I accidentally got to 30psi suffered only a couple of tiny seam leaks but was hugely over-sized by then and so far out of shape I had no option but to scrap it. This is an irregular-shaped tank welded from a pair of stamped halves, if you are making a flat-sided tank I expect the sides would permanently deform a lot sooner.

 

[hotrodder]

Good point about size & shape. I was tunnel visioned on car sized/shaped tanks, i don't generally do simple flat sided boxes but something like

which is probably 60 odd litres, has a fair bit of shape and lots of baffles (further stiffening it) would start to change shape before 4psi i reckon. Last tank i made was bigger and had less shape in it and above 2psi would've been a gamble if you wanted it to be the same shape afterwards. OEM pressed car steel tanks often start to change shape at even lower pressures and FWIW i usually try and talk the punter into a 'proper' rollover valve which typically have lower pressure/vaccum thresholds than OEM systems, opening at something like + 0.8psi / - 0.08psi, less likely to stick/go wrong and less likely to leak if the car ends up on it's side/roof after saying "watch this" to a mate

http://european-aluminium.eu/media/1579/aam-applications-power-train-5-fuel-system.pdf pic at the end of that pdf is relevant

 

[mud90mike]

Thanks Guys, I will have a read through all of this.