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"The fuel tank must be fitted with a vent (to permit release of a pressure build up) which does not exit on to the exhaust or into the vehicle or be situated at such a height that fuel would be likely to leak when the vehicle is driven."
A breather valve is not mentioned at all and providing the vent hose is routed via a point exceeding the highest fuel level (ie fuel potentially in the filler hose when you have just topped up the tank) I cannot see the need for a valve. The valve supplied by Marlin is a one way valve which will either release pressure in the tank on a hot day or allow air in to replace the fuel as it is used, but it certaily won't do both. A simple piece of fuel hose, routed as I said will.
Am I missing something..........................??
I am pretty sure that's a new requirement as for the SVA I fitted a valve to let air in - but not out. Or more to the point not fuel out just in case of an accidental err "inversion". But being aware of the need to also let air out in the case of temperature change I modified the valve to allow a slow leak out. So I have slow out but fast in.
You need to be able to let air out, because of expansion in the tank, and air in as you use fuel (if you don't then the tank will collapse as a pertial vacuum is created).
On my cabrio I've a vent pipe with a valve that lets air out, and the filler cap itself lets air in.
I have never considered running without a valve but I suspect you'll get fuel fumes wafting around in your garage without a valve.
The Marlin valve is to let air in as the fuel is used up but doesn't let the air out when the fuel expands, which it does alot!
Previous discussion from a few years back here....
I think the Marlin arrangement (Fords really) included a charcoal filter in the valve to contol vapour, so the use of a simple tube could be a problem from a serious pong perspective.
Its the petrol vapour which is far more flammable than the petrol itself so I think a valve rather than just a vent hose is essential from a safety perspective (ex-petrol station manager ). I fitted the Merlin two-way valve and it has worked fine.
). I fitted the Merlin two-way valve and it has worked fine.