cheaper version fuel tank breather valve

[Rustam]

Hi Erich, how does one know it requires replacing?

The correct name is charcoal canister purge valve or EVAP purge valve.

I did a writeup on this back in the day with internals pictures, here:
http://web.archive.org/web/200612140.../e34a/id7.html

Apply battery voltage to terminals and listen for a click and blow through. It should allow blowing from engine end to charcoal canister end, and should block blowing the opposite way. If energising the controls shuts the flow (or de-energising, don't remember exactly), then the valve is fine. If a click is not heard then it's clogged. Spray carb/throttle body cleaner and repeat the blowing procedure. This is a pretty much a fool-proof item, and does not need to be replaced.
2) this valve is more of a gimmick rather than a functionally valuable piece. The ventillation of the gas tank occurs through the charcoal canister. The charcoal is used because it does not allow gasoline fumes through, however it does allow air through. Looking at the bottom of a charcoal canister we find holes through which air enters into the canister and through the ventilation line into the gas tank. (Gas tank gets three lines Gas Out, Gas In , Ventilation). This and only this canister, is essentially the gas tank breather valve allowing air into the tank while retaining the fumes. Looking into earlier engine management systems through ETK, one can find applications that do nor have the EVAP purge valve, yet simply and only have the charcoal container connected to the gas tank. And the charcoal canister does not get carried out to under the hood, but remains next to the gas tank in the rear end of the car. If I remember correctly, this was the case in for example BMW e9 2800, 3.0 CS, etc.