What's the role of the passage to atmosphere on that valve ? I don't think fuel vapors should be allowed to get out to the atmosphere even if pressure is too high. Is it a vent for the charcoal canister assuming it does not have its own ?

Also, what happens if the fuel tank is under vacuum, is there relief via the gas cap ?

Just wondering if someone on the know could enlighten me on this piece of hardware.

Thanks,
Hugues -

 

i think the check and cut valve is so the fuel is shutoff if you have the car upside down, but i might be talking about something else

 

The check-and-cut valve prevents the build-up of pressure or vacuum in the fuel tank. The open hose is where the air goes in or out when the valve opens.
They do.
The check-and-cut valve lets air in.

 

Thanks Jason for the reply ...

I do understand that if the pressure in the fuel tank is too high, then the flow goes from fuel tank to the canister, thanks to the 'pressure valve' within the check-and-cut valve.

I also understand that when the fuel tank is under vacuum, then the air is allowed from the outside to the fuel tank via the 'vacuum valve' of the check-and-cut valve.

After further review, the atmosphere port of the check-cut-valve also serves as a vent for the charcoal canister, otherwise I don't see how the fuel vapors can go back into the intake via the purge control valve (no flow). I don't know, maybe I am wrong on this, but it seems correct.

Where I disagree with you (no big deal really) is about the check-and-cut valve releasing fuel vapors into the atmosphere when pressure is too high by allowing a passage from fuel tank to atmosphere. Looking at how the check-and-cut valve is constructed (at least the one on s4 models) [picture in the Haynes manual], I don't see how it could happen but I could be wrong. The check-and-cut valve seems to vent only under vacuum from either the fuel tank side or the charcoal canister side, which makes sense in my opinion.

I have compiled all this into:
http://www.geocities.com/huguesdc1/evapcrank.html
and I hope it is correct.

hugues -

 

Y'know I think you might be right.

There are instructions for testing the C&C valve in the FSM, and I think I misinterpreted the last time I read them. Air definitely gets sucked into the valve to revieve vacuum, but it looks like pressure gets relieved out via the charcoal cannister as you say. This makes more sense from an emissions point of view.