most welding supply shops can fill high pressure bulk tanks. the booster pump at our shop probablly came with a mannual but i have yet to see it
. i am a trained "filler", its not rocket science but one minnor mistake can be fatal. i have talked to several people that can tell horror stories, and have one or two close calls myself. heard about one guy hooking up the booster pump wrong, it exploded. it sent a chunk of metal into him. didnt kill him but close.