Why is my fire extinguisher emptied after one use?
Fire extinguishers (here in the US anyway) are REQUIRED to not be usable after being discharged, partial or not, because you can never know HOW MUCH extinguishing material was discharged by just looking at the pressure gauge. So the valves are designed with breakaway seals that, once broken, will not hold the charge for very long, forcing you to replace it or have it recharged and re-certified by the manufacturer. These are devices used in saving lives, it's all very serious from their perspective.