Kim:
Hmmm... that was a typo...I meant TX20! Yes...venturi all the way +. When it wouldn't freeflow I adjusted the screw about 1/8th of a turn out and on reconnection had a leak so I had to tighten it back the small fraction. Like I said....it breathes fine and the purge works in the correct place (depressed around 2mm). The IP from the first stage is 138 (I didn't do anything to that) Although the specs say it should be 135 I can't really see that it's a big enough difference to effect anything. If anything I'd have thought that the slightly high IP would make it freeflow sooner.
Kim,
Having read all the posts here, now I can understand your question more fully.
First let me say that I have not had experience with Apex regulators beyond 2000, when Zeagle parted ways with them. But a quick check of their website shows that the AT20 is our old Zeagle Z-US4, and the ATX50 is still our old Tech 50D. Only the XTX20 regulator second stage looks at all different, but I would venture to guess that the principle of performance is not any different there either.
For that matter our new Zeagle 2nd stage regulators are also not different in principle.
Second it's now clear to me that you and Jonnythan have a pretty good grasp of how these regulators work. Usually the confusion involves the word "freeflow", which to some means a minor hissing leak and to others means a sustained venturi blast. To keep it straight I won't use the word at all.
When your TX20 does not venturi with a purge depression, the way your ATX 50 does, even though you have already adjusted the adjustable orifice out to the point where the 2nd stage begins to leak, it means that there are other contributing factors. As you suspected, 138 psi interstage pressure is not one of them. (BTW adjusting the second stage orifice while under spring pressure can cause damage to the seal.)
IMHO the most likely reason your regulator won't venturi or breathe as easily as your ATX50, on the surface, is that the seal is not as fresh, regardless of when it was last serviced. It is likely indented or grooved to where it is no longer allowing the same high flow of air. Other possible contributing factors are lever friction, breathing tube misalignment, poppet friction, lack of lubrication on the balancing chamber oring, or misalignment of the balancing stem and chamber. Techs, did I miss anything?
Not every regulator of the same make and model breathes (or venturi flows) the same. Usually this is more due to it's status since last being serviced, but many times also due to many of the above mitigating factors.
Since it's your back up regulator and you believe it breathes adequately, I would not stress over it. Since the second stage does not have an external cracking resistance adjustment you need to keep the orifice/seal setting somewhat detuned anyway, to avoid accidental air loss.
I hope this helps with understanding what's involved in regulator performance. It also brings up how important it is to have your regulators serviced by a good tech. One that is factory trained and authorized, experienced and has ample parts at hand.
Chad
FL Zeagle Rep.
