Scubapro S555 To S600

[DA Aquamaster]

I've always adjusted Scubapro adjustable second stages so that it is just short of a free flow with the knob turned all the way out to the stop.

In other words, I leave the knob all the way "out" and then adjust the orifice inward until it just stops free flowing.

Then I confirm the lever height is correct (starts to purge with no more than 1/8" of movement on the purge button), and check the inhalation effort.

How low it can be sets depends on the specific second stage and the case design. Anything under about 1.0" of water will cause an S600 to start free flowing slightly in a normal swimming position, so setting the micro adjust so that it cracks at 1.0 to 1.1" of water gives optimum performance with the adjustment knob all the way out, and also gives the diver maximum adjustment range to detune the reg if he or she desires in surf, swimming into a current, riding a DPV, etc.

Over time, the second stage seat also takes a set, and I adjust the orifice inward an additional 1/16 of a turn in anticipation of this. If you don't do that the reg will start free flowing slightly with the knob all the way out, and with the diver in a normal swimming position.

As someone noted above, that freaks some divers out - mostly the ones who don't understand the "diver adjustable" feature of the second stage and they bring it back in because "the tech didn't do it right".

I've had a few "special" customers over the years who got freaked if the regulator free flows in any usual attitude, surf or current condition and they're generally only happy when the reg breathes like a rock, so they got theirs set around 2.0" of water so that they wouldn't darken the door for another year. Don't be one of those...

 

[redacted]

The benfit is knowing you can get the best performance your adjustable 2nd has to offer. Sure, few divers can tell the difference between 1.0 and 0.8. 1.2 may be in that same indistinguishable group. But 1.4 is pretty noticeable and 1.6 is readily noticeable. With this approach, you don't need to carry a magnehelic with you or even take it off the "shop" shelf unless you are just curious.

 

[halocline]

As DA aquamaster pointed out, the design of the case will have a limiting factor on how lightly the reg can be set without freeflowing in a face-down diving position; this has to do with the difference in depth between the diaphragm/lever point of contact and the exhaust valve. But there are other factors, one of which is that the seat is a soft material, and after a few dives the whole thing is out of tune by a small fraction of an inch anyway. Another is that even without a constant freeflow, 2nd stages set very close to the edge will free flow more easily. Another is that fluctuations in IP will affect the stability of even a balanced 2nd stage, although slightly. Add these factors up and its a good idea to err slightly on the side of conservatism when setting cracking effort. This is where adjustable 2nd are so convenient; if they stray over into slight freeflow or too touchy for a diver's taste, he can simply adjust the knob to compensate.

I set mine without a magnahelic gauge and my experience allows me to set them right where I want them. One nice thing about using feel instead of relying solely on a test gauge is that IME each 2nd stage is a little unique. I have several balanced/adjustables and several D300s, they all breathe just a little differently. I'm guessing that slight variances in the orifice, spring, lever, and poppet account for this. An experienced tech should be able to feel very slight differences in cracking effort and should be able to judge where the reg is most likely to be stable underwater while providing the best possible performance.