WE Airsoft P226 Part No. S-78 Exhaust Valve

The WE P226 Part No. S-78 Exhaust Valve is specifically developed for WE's G17 and refers to the GBB (Gas BlowBack) magazine.

The exhaust valve allows the gas to escape from the magazine, thus firing the bb. If necessary, you can also release all the gas from the magazine by pressing the button.
However, we do not recommend this after a day of shooting and always recommend leaving gas in the magazine. This is so that the silicone addition in the gas keeps the rubbers of these valves wet.