Venturi adjustment: real benefit?

[beanojones]

It seems then, that the Atomic's venturi titrates cracking effort to minimize work of breathing with depth.
I understand the above points in relation to work effort, but I guess that's my point: if work of breathing is to be minimized, is manual adjustment/titration really of particular benefit? Why not have it just as the Atomic or SP D400?
Sorry to belabor the point ; just curious....must be the turkey

Two things are being run together here. One is cracking effort, and the other is venturi effect breathing assitance. The external knob on an Atomic is a spring tensioner which effects cracking effort. The venturi thing (which in an Atomic is automaticaally adjusted with depth) is there so that once breathing is intitiated, air flows without additional effort. Many (most?) regs have two separate knobs to contol the two different things. The spring tensioner is usually in line with the air hose, but on the other side of the second stage from where the hose connects to the second stage. The venturi knob can be almost anywhere on the second stage depending on design.

If you had a magnehelic gauge you could see the difference between the two adjustments pretty easily.

As to why you might want to increase the cracking effort, it usually has to do with entry and exits, or othe situations when the reg is not necessarily your mouth. An octopus for instance is not usually being used so you might want to make the cracking effort higher to prevent little leaks of air. As far as the venturi effect goes, you might want to turn off the venturi assist on an octopus so that if for some reason the purge button is pushed the reg will not continuously deliver air.