SP D-Series Reg Question

[Timothy Moran]

I have 6 D-Series regs. There are 2 different configurations of PN 11-011-122 diaphragm covers on them. One is what I call the "tall" version, and the other is the "short" version. I have reviewed all the schematics, kit lists, etc. I have, and can find no reference to these 2 different configurations of diaphragm covers. Thinking about this, the only two effects I have come up with, are cover height difference (1) affects exhaust bubble dispersion; and (2) affects water flow over the exhaust flapper during sideways current flow into one side of the exhaust rubber cover.

Do any of you "SP reg heads" out there know the reason for the differences? - - performance enhancements? - - product improvement? - - undocumented production change? - - change at D350, or D400 production? - - or whatever?
I didn't bother posting this question in the SP mfg forum as they never seem to answer questions about vintage unsupported regs.

Thanks in advance,
TJ Moran

 

[axxel57]

I guess you are right about the bubble dispersion.

I remember that before abandoning the D-Series production, SP was fighting with the relatively high exhaling effort of this 2nd (D400) which gave a quite high WOB value on the ANSTI machines.

In the end they could not really solve this 'problem', which was one reason among others to quit the production.

Ever since they gave up designing 2nds with improved excellent inhaling qualities, but concentrated in bigger exhaust valves to get better ANSTI values.

For me is the evaluation of the ANSTI test anyway questionable since it values the inhaling and exhaling equal, which misses the point.

So if you have an average 2nd with average inhaling effort, but with a good exhaling qualities,you get better ANSTI values than a 2nd with brilliant inhaling qualities, but not so good exhaling values.

Anyway, maybe there is no other way to evaluate the overall performance of a 2nd.

 

[DA Aquamaster]

There were a few major changes in the D series design.

1. The case design was changed early in D350 production - thus the early D350s use the same case as the D300 and the later D350s use the same case as the D400. I have no idea why the change was made/required.

2. The diaphragm cover was shortened to improve the ability to purge the regulator. Then shorter cover enables you to press or squeeze the rubber purge cover over a much broader area to purge the regulator.

3. The aspirator was changed from a design with an integral metal orifice to a design using a plastic insert orifice late in D400 production. The latter design allows the orifice to be replaced, but performance suffered as the plastic orifice versions could not be tuned to the same level of performance. This was marketed as an improvement in terms of corrosion resistance, but I suspect it was just cheaper to make, and cheaper to replace if a crappy tech goobered up the orifice when installing the poppet.

4. The lever was changed to a longer lever between the D300 and D350 and that was a good change, however the lever was changed again late in the D400 production to a lever with two flats rather than one, in order to help the D400 meet those truly stupid CE free flow requirements. It turned a finely tuned and superb breathing regulator into something that breathes like hammered crap, particularly at higher flow rates.

----

In general, I agree that the pursuit of low WOB numbers really killed the D400 design. Subjectively the D350 and early D400 second stages were some of the finest breathing second stages ever made, regardless of the numbers.

A large of that was the reality that the coaxial exhaust valve allowed the reg to be tuned to very low cracking efforts and still be stable, producing a very natural breathing reg. You can design a reg with a negative inhalation effort by using excessive venture effects, and use a giant exhaust valve to get low exhalation efforts, but the large exhaust valve in a conventional case, requires a higher cracking effort to initiate gas flow, or else you get a free flow. The end result is that you can have great WOB numbers, but the reg will have a high cracking effort and feel harder to breathe to the diver- and unless you're hovering gas with rapid inhalations and effectively trying to over breathe the regulator, you'll find no advantage in the lower WOB numbers.

 

[Timothy Moran]

DA Aquamaster:
Once again thanks for taking the time to respond, and lending your vast expertise to answer my question. I hadn't even thought of the rubber cover purge effect the taller versus shorter diaphragm would have. Reading your response, it sounds like the best combination in a D-series reg is an all-metal orifice set up for a single cut 400 lever and a short diaphragm, if you want greater purge button (rubber cover) effect.

Any thoughts on the older (rebuildable) metal poppets versus the newer (one piece) plastic poppets.

Thanks again,
TJ Moran
PS. Finally logged my 1000th dive in Belize last November. (A personal goal for me as an average sport diver.)