HOW TO PURGE AIR FROM A GREASE GUN
Luckily, fixing one is straightforward, and with just a couple of adjustments, you’ll have your grease gun back working in under a minute.
If you’ve just installed a new cartridge and your gun is not dispensing any liquid, simply turn the cartridge anticlockwise 2-3 times. This will help to get rid of the trapped air from the top of the tube.
With the tube still loosened, pump the handle in and out until grease is released.
With the handle compressed and held in, tighten the tube back up and your grease gun should be good to go, with the airlock gone.
Check out the video demonstration here: