I had my Rochester valve out this weekend while doing some other work in
its area. Due to some earlier postings here I thought it stopped flow
in either direction until the tank pressure exceeded ca 2.5 psi or the
engine manifold vacuum opened it.
I found that it allows free flow of fumes out of the tank into the
charcoal canister. It blocked flow if the tank is under vacuum less
than ca 2.5 psi. At vacuum above that point it began to allow flow to
allow air into the tank, but with restriction. (All tests done with
lung power, no gauges.)
With even a small amount of suction on the manifold vacuum line the
valve popped fully open to allow unrestricted flow in either direction.
I was happy to find the three connections clearly labeled (canister,
tank, engine) to avoid error in installation.
1991 XJ-S V12 Conv about to come out of hibernation
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