Yes, a coffee bag with a valve can maintain coffee flavor.

After the coffee is ground it releases gas (mainly carbon dioxide). With a completely sealed coffee bag, there’s a risk that the amount of gas in there will inflate the coffee bag which could in extreme circumstances probably through one of the seams popping open. So we need to valve to come out the gas in order to grind it as needed it is the best way to preserve coffee’s flavor.

The function of a one-way valve – it lets the gases out so the bag doesn’t start to inflate, but it also doesn’t let the outside air in, meaning that there’s less chance of the oxygen in the air making the coffee stale.