The purpose of one-way-valve feature in coffee packaging is to allow the exit of carbon dioxide being produced by recently roasted coffee, but preventing the entrance of oxygen which can cause early spoilage.
This is how it looks on the outside. It looks like a dry seal with a small hole on center. The carbon dioxide which causes bloated coffee packaging passes through here. Whenever a coffee package is bloated, a gentle press will release the extra gas through this hole. The valve seals itself again after.
This is how it looks from the inside. The small piece of cloth is covering the three valve holes and preventing the entry of any coffee particles. The mechanism is ruined whenever a single particle makes entry. Surrounding the cloth is the name of item manufacturer.
Removing the cloth reveals the three holes. What blocking the holes is actually a thin piece of rubber. It is snugly fitted to prevent the entry of outside air. Forcing an air through from the outside will make the fit more tight making air entry more impossible.
Slicing out the leftover film gives a nicer view of black rubber covering the three holes. It is loosely supported by three protrusions. When the closed package is pressed, the black rubber bends slightly allowing air to pass through.
Is it applicable to other products other than coffee? Definitely not for liquid products, the likelihood of natural leak is very high. It is not as air tight as you might think. For other powders. The only powder I know that bent off carbon dioxide after processing is coffee. It is applicable but the one-way-valve feature will be of no use. It is just a waste of money.