Regulator Geeks 2: Scubapro's Balanced Regs

[Geo7]

Can't wait for the next session btw. Both center-balanced regs and Poseidons will be fascinating to learn more about... Please PM me if I miss the thread!

A session on piston 1st stages would be great as well: performance, corrosion, sealing...

 

[Geo7]

Somewhat unrelated but still on topic of these regs:

One thing I have been wondering about whether the balance chamber in a end-barrel-balanced reg can act as a "servo valve" when combined with balanced piston regs. I mean when the IP drops before the piston moves and opens, does the pressure in the balance chamber react quickly enough to reduce pressure on the poppet and allow further poppet separation?

I mean, sure, the whole point of balancing is that opening force is constant through IP range. But can a quick drop of IP followed by quick recovery and huge flow achieve a quick drop in IP of the balance chamber, and then allow the recovery wave of high IP air to flow past the poppet before re-establishing IP in the balance chamber (and is this more pronounced in the G500)?

If so, then then the initial IP drop we seem to be observing just before a balanced piston 1st stage fully opens, might work to achieve an extra boost of air.

 

[rsingler]

Whoa! Look what I just found!
There's a company in the UK that markets an ANSTI machine AND a surface test machine.
They use the surface test to certify regs for rescue divers and the like. I've attached the manual for their surface test machine, but here is the nugget:
"The high flow demanded by the CSTF approaches the peak flow requirements equivalent to a depth of 50 metres and 62.5 litres/min ventilation."

And the flow they're talking about is 1000 lpm, or 35.3 SCFM.

That means there IS a correlation between surface tests and a WOB loop performed at 170 feet.
So our tests last night at 16 SCFM were equivalent to a diver breathing 2.3 CFM (62.5 lpm) at what, 25m?
Maybe the differences in those curves IS significant at recreational depth...

 

[Geo7]

Very interesting, cool we have some support of the theory!

I thought the flow rates of regs that some manufacturers publish (ie. Scubapro and Poseidon but not many others) are implying that sort of correlation. A 300 cuft/min flow of a MK25 has often been criticised as overkill, but I understood that number implies a large bore that will shine with moderate supply pressure at great depth.

I once compared an Aqualung Titan at 500 PSI on a stage tank against an Atomic T2X at almost 3000 PSI at 130 feet, and the difference was astonishing (don't remember the IPs though). The Legend 2nd on the old Titan 1st was very nice, but the Atomic was effortless, smooth and natural. All other comparisons among all sorts of regs I have done shallower than 60 feet depth and at similar supply pressure have never revealed dramatic differences (I am talking about breathing as a diver).

So expected that correlation to be there, but we might find a few exceptions where differences emerge with ANSTI testing at depth. I also think 3000 PSI supply pressure might mask shortcomings of some regs that might be apparent at lower tank pressure while at depth. We are probably on our way up at 1500 PSI, but for deep mix stage tank this might be of interest. And for us reg geeks!

 

[jakehbk]

I always thought that the Scubapro flow rates were more theoretical than practical. I mean what's the flow rate of your standard tank valve?

Back to the seminar, I was kinda hoping that evidence would come to light that I could replace my G250 with a nice compact S620, but apparently standard 2nd stage design peaked a few decades back. Guess I'm stuck with it.

Lots of good info over those 3 hours, can't wait for the next one.

 

[rsingler]

Well, I've been having an interesting conversation with some folks at Scubapro. I wish I were a gas flow engineer, instead of a geeky reg tech.

I'm coming to some conclusions that don't quite align with all of what I said at the seminar.
So when I post the video of the evening, I'm also going to record a brief amendment to some of the conclusions that I hope all the participants will take the time to watch.

Those endless flow graphs that we reviewed together didn't account for one factor that the D420 has brought to light, and one that I think wasn't completely appreciated by Pete Wolfinger when he wrote his book, either. While I'll never be a Scubapro fanboi, I am increasingly appreciative of the subtlety of their engineering. I think you'll enjoy the new development. I'm learning all the time...

 

[rhwestfall]

I am increasingly appreciative of the subtlety of their engineering.

This is the real take home about their regulators...

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A ScubaBoard Staff Message...

A selection of posts that follow has been split off to a new thread here: Mk11 Split-off from Regulator Geeks, Part II
Thanks for the suggestion, @Couv !

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[Open Ocean Diver]

Missed all the fun, that’ll teach me to set my alarm next time. Can’t wait for the next one.

 

[rsingler]

René Dupré from Scubapro responded to an e-mail regarding that G500 barrel that @Geo7 asked about.

He notes that the extra small hole was indeed added for Venturi flow control in that reg case. Specifically: to improve the Venturi effects during a transition from shallow to deep water.
Subtle stuff...

 

[Geo7]

To steer the discussion back to the end-barrel balanced seconds , I'll just share these pics. I love this because to me this is the closest thing to a "mini-G250"...