Well assuming you have a Milwaukee regulator, that has 2 gauges...one for the internal
CO2 cylinder tank pressure, and the other that shows pressure leaving the tank.
A full
CO2 cylinder at room temperature should be between 900 - 1000psi. The gauge for psi exiting the regulator should be set at about 20psi, and then your needle valve is used to decrease the bubble rate until you get it dialed in for your tank. I'd start at 30 bubbles per minute, and work up from there.
Also, to hook up your regulator, make sure the knob on it is all the way closed (un-screwed, no tension on it) when you connect it to the cylinder. Tighten it down. Then open the valve on the
CO2 cylinder first, pretty much all the way open.
Then open the regulator valve.
If you have the valve on the regulator open when you open the
CO2 cylinder, you can damage the regulator with the sudden pressure (900psi is a tremendous amount of pressure...the 'hiss' is so loud it hurts my ears...the one time I vented the last bit of a tank so I could refill it...)
If you got a Milwaukee, lemmie know. I know where to find the instructions on the Internet....in fact, here they are!
http://www.automatedaquariums.com/mw_957_info.htm
It'll work for a JBJ too, just the JBJ has only one gauge, for the cylinder pressure, because it's a fixed output.