Hi Guys:
Through my other hobby as a scuba instructor I am a certified high pressure cylinder inspector. I'd like to offer some safety tips as you are treading into Department of Transport (DOT USA) and Canadian Transport Commission (CTC) international regulations and standards.
1. get your cylinders professionally cleaned, inspected and hydrostatically tested (it is the law to have them hydro'd every five years). The cost is minimal (we pay about $50 (Cdn) for a 80 cubic foot scuba tank that holds 3000 psi). The tests and inspections include a visual inspection of the interior and exterior of the cylinder, an examination of the neck and threads using ultrasonic equipment and hydrostatically overpressurising the tank to see if the metal has retained its elasticity over the years; and
2. get them filled by a certified 'gas' company, again cheap and safe.
Its worth remembering that the cylinders are 3000 psi 'bombs' that when suffering a neck or thread failure act like a rocket motor and when suffering a hull failure look like an artillery shell that has gone off... I've seen both!
Mike