Yes, an air charger is a 1 way valve but the proper place to install the air charger is at the vacuum lead hose from intake manifold (where you usually connect your vacuum meter with a T-junction hose).
The reason being is that an air charger supplies extra external source of vacuum to your existing vacuum pressure rather than getting it all from your air filter.
Logically, it will supply you with the vacuum needed to your system when under full throttle (at idle, you won't see any difference). If you have a Vacuum Meter you can tell the difference as it can help in maintaining a stable vacuum pressure under load given that you
adjust the air charger valve appropriately.
For example, I installed my air charger in between the intake manifold and the FPR. Resulting in better fuel pressure stability at high revs and full load. (It is for my testing purposes only and does not apply to all engines.
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On another note, I'm not supporting the fact that an air charger is a good or a bad gadget. All of this is done in the name of testing and researching on whether it works or not. After all, we all want to save a few bucks on fuel here and there right?