Yes, SP experimented with an "air off" balance chamber for awhile on some models that was designed to reduce the engraving that occurs in the LP seat during storage by preventing any spring pressure from pressing the seat against the orifice. It was generally a really bad idea that caused far more problems that it solved.
Adjustment is less precise (both on the bench and by the diver and performance suffers, plus it is much more mechanically complex and also leaves the system open during storage allowing dust etc to potentially enter between orifice and seat. It also solves a non problem as if the knob is backed off during storage and the reg is serviced annually, engraving is never a problem that effects performance.
In the distant past SP used a small key that fit in the purge button on it's second stages (Air 1, Adjustable, Balanced Adjustable, High Performance, etc) that kept the lever depressed during storage. This served the same function in a much simpler manner and gave the user the option of using it or not.
The simpler adjustment knobs on the older metal barrelled G250's also had a much better feel and the balance chamber is both very effective and dirt simple - good qualities in a regulator. It's an area where SP moved backwards in terms of reg performance.
Dan Gibson:
But if they went back to the metal air barrel, you wouldn't save that 1 or 2 ounces and eveyone would have jaw fatigue
I hear you....I am so sick of the "reduced jaw fatigue" excuse used by so many manufacturers. That marketing gimmic has allowed them to compromise quality and perfomance in the name of light weight when the reality is that plastic components are so much cheaper to produce. The older metal air barrels were much more expensive to compared to their plastic counterparts that probably cost less than a dollar to produce.
Same with plastic cases. They were introduced with the promise of great perfomance increases due to the more complex shapes that could be used, but with the exception of the D400, I have not seen unique designs that offerred improved performance over older brass cased models and the D400 was ironically enough eventually discontinued as it's unique design put excessive demands on poorly trained techs.
Reduced production cost was certainly a factor but the savings were never passed on to the consumer or even the dealer as the "new" plastic models sold for as much or more than their metal cased stable mates.
So in the end we have lighter plastic second stage cases that are more expensive, crack and produce terrible cases of dry mouth. And despite over hyped marketing claims convincing largely ignorant divers they need small lightweight second stages, jaw fatigue is still much more impacted by mouthpiece design and hose lenght than the weight of the second stage - and when is the last time you saw a reg manufacturer offer you any choice in hose lenght?
