Maybe strange question, but I would like to use an Argon/Oxygen 20 L bottle to load with water, NaOH and Al to make hydrogen for a fuel cell project. So, to load this bottle I'm thinking of screwing off the cap, then put it back again. I can imagine this is very hard tighten. I would like to have around 150 bars of pressure. Of course I put safety first, and before I try anything, I'll get to know all the knowledge about this. Another option would be to generate hydrogen without pressure and then pump it in a bottle. I'm not sure what's safest yet.