Practical limits for unbalanced reg sets?

[Eric Sedletzky]

Just wondering what the consensus is on the practical limits of unbalanced first and second stage reg sets. For example, a Scubapro MK2/R195 combo, about the most basic set there is, what would be the practical depth limit for that setup? Notice I didn’t say “safe” because I’m sure it would be plenty safe mechanically.
I’ve heard people say those regs shouldn’t be taken below 60’, and I heard Dan Volker say once he took one to 300’ no problem. I’ve also heard people say that an unbalanced set would be fine for any recreational diving kept within recreational limits because theoretically a rec diver should never be in a position that they are caught OOA by surprise from negligence especially at depth, therefore an unbalanced reg used with recreational protocol should be fine. The gradual increase in breathing resistance as a tank goes lower seems like it would be a good warning device for those who tend to be on the complacent side about checking their gas supply. The only downside I could see would be in an air share situation down deep when two divers are depleting one tank with an unbalanced setup, that could get a little “sporty”.
I’m just wondering for conversation sake. I hear a lot of people bag on unbalanced regs whenever the topic comes up, and recommend to always buy balanced everything, but I think it’s a little unfair sometimes. Unbalanced designs are dirt simple and amongst the most durable and bulletproof designs ever produced.
What do you think are some of the advantages or disadvantages to owning and using an unbalanced reg set?

 

[northernone]

I like and dive them on air below recreational depths and do not find their design to be limiting. Can't tell breathing resistance changing much until 5 breaths from empty. I've tried to blind test taking down five 1st stages with identical second stages (conshelfs) and my sucker isn't sensitive enough to pick up a marked difference.

That said, some regs breathe horribly at way shallower so I'm not completely tone deaf as a tester.

 

[MichaelMc]

There is an old Navy study showing work of breathing for some of the common older unbalanced second stages (108, 109) does not compare well with that of the G200/G250 (?) series as work load increases, all on mk10s I believe. But I can not seem to find it. And it seemed to be about the case not necessarily the unbalanced.

 

[Bob DBF]

I read that 60' comment and was having a good chuckle, and before I could come up with something I saw Dan's reply and moved on. Sounded like a sales pitch to me, life support and such.

I haven't gone as deep as Dan on one, but was well past rec limits without any problem. To be fair, at the time most were unbalanced and I'm not all that picky as long as I'm getting air. I think it would be an exceptional diver that could breathe a well tuned reg blindfolded and tell whether or not it is balanced.

As far as two divers on a reg deep, i would think it would depend on the flow rate of the reg rather than it being balanced or not.


Bob

 

[JackD342]

In general, I suspect that modern designs from the major brands are now pretty good, and the cons of unbalanced are less significant than in the past. If you are able to find WOB specs, with the ANSTI test parameters documented, that would be ideal. Maybe check some Scuba Lab reviews?

I do know for sure the Aqualung Calypso unbalanced piston with an unbalanced 2nd stage is pretty darn good. You will see the average WOB listed is 1.0 joules/liter. They don't describe the test, but it was using the specs for the CE test and is stamped EN250A. I don't have the specifics handy, but that test is deeper than recreational limit, on a lower tank pressure than I would want at that depth, and at a decent breathing rate. Color me impressed. It even qualified for cold water use. But I'll keep on diving my Legend. The "A" also indicates okay for octo use, but just to 30 meters. They want anything deeper to be a redundant source. If you find anything current marked EN250 but without the A, it is not approved for supplying more than one 2nd stage in the EU.

Any model sold in the EU has that evaluation done. Unfortunately manufacturers don't publicize it well here, if at all, and in some cases only put the CE stamp on the EU product and skip it on US production.

 

[Eric Sedletzky]

There is an old Navy study showing work of breathing for some of the common older unbalanced second stages (108, 109) does not compare well with that of the G200/G250 (?) series as work load increases, all on mk10s I believe. But I can not seem to find it. And it seemed to be about the case not necessarily the unbalanced.

Well, a MK 10 is balanced so not really part of the discussion. But the 108 and 109 certainly are unbalanced and are OK breathers, certainly adequate for average recreational diving. The G200 was also unbalanced but the G200B and G250 were balanced (someone please correct me if I’m wrong). The newer plastic 2nd stage bodies with the VIVA venturi vane supposedly increases flow and keeps it running once it’s started improving performance. But I’ve also heard some people say this is hogwash since the adjustable vein only decreases performance in the detuned mode to keep it from freeflowing and not necessarily to make it a better breather than the 109’s when it’s wide open. The 109 afjustables are designed to be wide open all the time at the mouthpiece but they have a tuner knob instead to tighten them up to avoid freeflows. It would be hard to try and place an adjustable venturi vane in an all metal case.
I have to agree, my 109’s breathe pretty damn good.
Knowing what I know now, when I started diving I would have just bought a simple MK2/R-whatever? and been happy. I could have saved a lot of money and spent it on diving instead. Later when I got into tech diving I could have moved the MK2 to a stage bottle. I needed to buy two new sets anyway for my primary backgas on a set of doubles which would have been MK20/G250’s at the time.

 

[TrimixToo]

I've had inexpensive regs as deep as 200' with bottom gas in them. Maybe the He helped, but they seemed to breathe OK. However, both back gas regs were good balanced regs, and I never had to work hard on the slung extra bottle using an inexpensive unbalanced reg at depth. Today, everything I use deep is balanced and the unbalanced regs serve as deco regs.

 

[reefrat]

I know the OP is particularly referring to unbalanced first and second stage regs but further to that I am tempted to try a combination of a good high flow unbalanced first stage with a balanced second. My rationale is that something like a MK2 EVO should flow plenty of gas at any reasonable tank pressure while being fail-safe reliable and very simple to DIY service annually. The balanced second stage should smooth any IP drops and most of these are also downstream reliable and easy to DIY service.
Where I live there is no service/repair available in the country so I need to be able to look after stuff myself and the KISS principle seems appropriate.
I have an Apex TX50 (ex-military) that I have serviced and breathes really nicely that I would like to pair with a MK2 for a simple bullet proof beater and travel set.

 

[tr3a]

Unbalanced diaphragm, IP increases as cylinder pressure drops.
My Mistrals breath better at 140ft than they do at 10ft.

 

[John Dickerson]

This thread makes an old guy smile. My uncle bought 2 new style Voit single hose regulators to teach my cousin and I to dive because he thought it would be easier for us to learn with than a double hose. My cousin and I weren't "allowed" to dive deeper than 150'. We just thought being able to breathe underwater was cool - never noticed if it got harder or easier to breath. If your wondering, I also walked 1.2 miles to school rain, snow, or shine, but it was only uphill one direction.