Good day lads. Norwegian homebrewer here. I've come across this forum many times through google and I finally decided to sign up today as I've got some questions to ask regarding hand pumps... But that's not why I reply in this thread.
I work with gas and if that cylinder you've got there is anything like what we have over here, the little silver bit you pushed inside the valve(?) - sorry I don't know the technical terms in English
is a little gadget that's placed there to retain a tiny bit of pressure in the cylinder when it's empty so that if it's left open, moisture or water etc. can't get into the gas cylinder. This is so it won't rust or get filthy in the inside.
It can probably be removed with a tiny socket wrench, but there's no need to as you'll be able to use it as is.
co2 is filled by weight in liquid form so you can check how much you have left in the cylinder by weighing it as someone else suggested earlier. The weight of the cylinder empty and full should be stamped in somewhere on the cylinder. TARE weight is empty and GROSS is of course full. It often also says how many KGs of co2 it should contain full.
It was probably that missing o-ring you found that made it leak. Sometimes you wont even hear it and it'll be empty the next day. What you could do is to take a spray bottle with star san in it, shake it up, and spray it all over the places you think it could be leaking. If there's a leak there will be bubbles forming around that area.
Hope this helps
