Alternatives, for use with unregulated CO2 Make your own, as Rex did for Cassius, from the front fork of a motor bike. You'll need one of these connected to the front port of the cylinder. Seems to be more of an adjustable speed limiter. Decanting system To fill the tank, you'll need some way of connecting to a large supply bottle. This system needs to be carefully manufactured and tested to withstand the pressures involved.
Hydraulic hose is a popular choice.
You can get CO2 bottles as either gas draw or liquid draw - we would want liquid draw. Quick release connector is at right-hand end of hose. Hose is 6mm i.d. and can take 210bar. Outer sheath is pinpricked to avoid ballooning if any air seeps out. Quick release, self-sealing connectors should make filling nice and easy.