Let’s purge! Going to install some version of this stuff for tank-to-can venting. New canister (not in pic) is generic ACDelco. Can confirm the new/generic Rochester valves are one-way on the 2 psi opening, so gotta use 2 in opposite directions. Vent valve on left is for a 1994 Passat. No need to connect Rochester valves to vacuum (maybe as insurance in case Passat valve fails) – using just for 2-PSI function.
Fascinating.
So I installed the 12v solenoid (from a Mercedes) AND I kept a newer Rochester valve plugged in.
It have a much smaller whoosh when opening, which lessens as the tank empties out…but perhaps using a second Rochester valve would help indeed? I did cap off the vacuum hose as well, since when the car is on, the path is open. I pulled the 12v from a white wire going to the headlight relay.
What is the function of the Passat valve?
Pressure in the tank is of no concern, excessive vacuum is.
Actually, ignore the vacuum valve on the right of my original pic. I’d forgotten why I bought that. It’s for a different project. Planning to keep the original purge valve and two delay valves at the engine, connected to port vacuum. Eliminating original thermo vacuum switch as I have a temp gauge sensor in that location.
The “Passat” valve is a simple solenoid that opens the vent line to the tank when the ignition is on (credit to Kirby). Does the same job as the Rochester valve(s) under vacuum, but is supposedly more reliable.
Ended up simplifying the fixit plan, as the original Rochester valve tests OK. Beware: the “1994 Buick Roadmaster” Rochester valves are different. At rest (no vacuum), the Jag Rochester has a 2 PSI resistance tank-to-canister, but is open canister-to-tank. The Buick valve has the same 2 PSI resistance tank-to-canister, but is BLOCKED canister-to tank. This could cause a vacuum in the tank. I figure the OPEN direction of the original Jag valve is unlikely to fail, so I simply added the Buick valve as a Tank-to-canister backup. Note: with vacuum, both valves are open in both directions. In pic: original Jag valve is on the right.
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