Originally Posted by FatherLandDescendant
Some diffusers need a minimum pressure to operate, so yes working pressure (right hand gauge) can matter in certain applications. If you close the needle valve just until it stops (DO NOT tighten it after it stops), turn on the tank, then turn the center knob until the right hand gauge gets to the operating pressure you want, then open the needle valve to the bubble count you want, you'll be set.
If you follow their directions you'll be forever trying to get the regulator set to a stable pressure and bubble count. Following their directions, when the solenoid closes the pressure in the regulator will go up, when it opens it'll dump a CO2 charge then taper off. This can be a problem for those who run controllers, we (I do at lest) who run controllers often run them right on the verge of gassing our fish, that sudden dump can succeed in doing just that.
Oh, so having the needle valve closed first instead will help prevent that sudden dump when the tank nears the end? I hate when the tank does that.