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Hi guys (and gals),

Is my understanding correct that the check valve that connects the charcoal canister to that port on the throttle body should only flow into the throttle body and NOT back towards charcoal canister?
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Yes, it allows the port on the throttle body to pull vacuum on the canister when the throttle is partially cracked open (why it's called "ported" vacuum as it does not have vacuum at idle), but won't allow pressure into the canister flowing the other way in case of boost etc.. (check valve for mechanical operation of evap system).
This is something you definitely need to leave if you are turbo and have the canister in place, as you do not want to pressurize the canister.

I want to say the top port on the canister also has a built in check valve in addition, as you can see in the diagram there is another path to the canister via a vacuum switching valve (vsv) for evap which can also let vacuum pass to the canister, except this is not mechanical and is controlled by ecu.

The ecu wouldn't generally try and actuate the VSV while you are on boost (with the turbo ecu's, n/a ecu who knows when it would try to do it), so it's the mechanical side that has the extra check valve but technically the top port of the canister is also a check valve (they can fail over time though so not a bad idea to check). If you have the evap system working then you will want at least one of these in place doing its job if not both.
 
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