What sort of one way / non return valve do you fit on the Fuel tank vent pipe. Is it anything special, or just any non return valve?

just how necessary is it, and is it a SVA requirement.

As its fuel related, I am just being a bit cautious.

I recommend a two way valve if you have a fuel return or fuel injection.
If you continually draw air in to replace used fuel, when some of the fuel is returned, it will have no space to occupy and so pressurise your tank.
I destroyed a fuel pump that way!
A valve is not necessary for sva, but some form of breather is required to make your tank safe.
I bought a 2 way valve from thinkautomotive. It would close if the fuel level rose or the car was inverted

[Edited on 31/3/06 by nitram38]

[Edited on 31/3/06 by nitram38]

I just use an open pipe, routed so that in the likely stances of the car post-roll, it won't leak.
Perfectly SVA ok and perfectly safe, if it catches fire with this setup it would catch fire anyway basically.

I use 3/16 kunifer wrapped around the tank 1 full turn and terminated low down under the car to vent to atmosphere.

You can use 1 way Aquarium breather valves - about £1.50 at your local pet shop.

All do the same thing. Or you can pay £10-£15 for one like nitram has. Fortunately, I've not experienced a problem like his - but if I do - it'll be a case of 'told ya so'