confused about reg types

[fnfalman]

Buy a high quality reg; either piston or diaphram, and keep on truckin'. The good ones are balanced for ease of breathing anyway, so the issue is moot.

 

[Puffer Fish]

Lead, thanks for taking the tme to put all that down. Nice job.

Emoreira, you will find a mix of technical answers and a bunch of "just get a good reg and don't worry about it" answers.

Both have value, by the way.

Most (I think all, but don't know every one) high end regulators are balanced.. and you are dealing more with the diaphram versus piston, and the which company do you want to own questions.

I own...ah... well more than I should, but if I could only have one, and I went anywhere near a beach that had sand, it would be a sealed diaphram design. But I have several piston.

All have been really reliable...I know of no major company today that has any reliability concerns.

But the search for gear can be as much fun as using it (ok, almost as much).

The "usual suspects" here in the regulator board can answer this better than I can, but I'll take a stab:

Modern balanced 1st stages will keep the IP very stable, regardless of tank pressure (until the pressure gets very low, I believe).

Balanced 2nd stages are really semi-balanced (if they were completely balanced, they would lose the ability to act as a downstream overpressure "relief" valve in the event of a high pressure seat failure in the 1st stage). Balanced 2nd stages are by and large "air balanced", and this allows them to use a lighter spring to keep the demand valve closed, compared to an unbalanced 2nds stage which relies 100% on spring pressure to close the valve. My understanding (which may be flawed) is that using a lighter spring offers some advantages, one being possibly lower breathing effort after the demand valve is "cracked" open (I may have this wrong).... however, well-designed unbalanced 2nd stages with a efficient venturi effect (Mares 2nd's with the VAD bypass tube springs to mind) can breath as well as balanced 2nd's.

So to answer your question, if you have a balanced 1st stage, there should not be much difference between balanced and unbalanced 2nd stages, as long as they are high quality and tuned properly.

Best wishes.

 

[halocline]

The reason that the flow-by unbalanced piston design (scubapro MK2, aqualung calypso, etc) cannot have the absurd flow characteristics of the the MK25 is because the orifice size is limited by the design. The larger the orifice, the more air can flow through it, but this also means that a proportionally larger downstream force is acting on the HP seat. This causes more IP drop throughout the tank range.

The bit about needing higher flow at greater depth is yet another mis-use of quasi technical explanation to sell more expensive products. Yes, we do breathe higher volumes of gas at greater depth, but since the tank valve and 2nd stages are both much lower flow than ANY first stage on the market, in use a MK25 will flow exactly the same as the MK2, specifically whatever the 2nd stage and/or tank valve can produce. Plus, the difference between "shallow" recreational diving and "deep" is almost inconsequential to the performance of any properly tuned and adjusted regulator. Technical and very deep diving is another issue, but at that point there are so many other equipment considerations that regulator choice is relatively minor. Until fairly recently (a few decades at most) professional divers were routinely doing very extreme dives on regulators that a typical modern sales brochure would decry as unworthy of a pool dive.

If I had to choose one regulator to take on an extended dive trip in which I had no access to parts or tools or a spare, I'd take a MK2 with a 109 metal 2nd stage, left unbalanced. This set up is the model of simplicity, reliability, and surprisingly good performance; good enough so that 90% of recreational divers would not be able to tell the difference between it and many much more expensive, higher end regs. The unbalanced piston 1st stage in conjunction with the unbalanced 2nd will start to breathe a little more stiffly once the tank goes under 500 PSI, but in this hypothetical "desert island' scenario that's an advantage, as I'd get a warning when the tank was low. This would allow me to keep diving even if my SPG failed.

New divers are routinely bombarded with hype about regulators. Among the most insidious is the "buy the best (read: most expensive) reg you can, your life depends on it." It was that sentiment from a LDS that helped send me down the path of DIY reg service and general curiosity about regulator design and function. If the lower end models were somehow not as "safe' as the higher end models, why was the dive shop even selling them? Total BS.

 

[Greg Barlow]

The reason that the flow-by unbalanced piston design (scubapro MK2, aqualung calypso, etc) cannot have the absurd flow characteristics of the the MK25 is because the orifice size is limited by the design. The larger the orifice, the more air can flow through it, but this also means that a proportionally larger downstream force is acting on the HP seat. This causes more IP drop throughout the tank range.

The bit about needing higher flow at greater depth is yet another mis-use of quasi technical explanation to sell more expensive products. Yes, we do breathe higher volumes of gas at greater depth, but since the tank valve and 2nd stages are both much lower flow than ANY first stage on the market, in use a MK25 will flow exactly the same as the MK2, specifically whatever the 2nd stage and/or tank valve can produce. Plus, the difference between "shallow" recreational diving and "deep" is almost inconsequential to the performance of any properly tuned and adjusted regulator. Technical and very deep diving is another issue, but at that point there are so many other equipment considerations that regulator choice is relatively minor. Until fairly recently (a few decades at most) professional divers were routinely doing very extreme dives on regulators that a typical modern sales brochure would decry as unworthy of a pool dive.

If I had to choose one regulator to take on an extended dive trip in which I had no access to parts or tools or a spare, I'd take a MK2 with a 109 metal 2nd stage, left unbalanced. This set up is the model of simplicity, reliability, and surprisingly good performance; good enough so that 90% of recreational divers would not be able to tell the difference between it and many much more expensive, higher end regs. The unbalanced piston 1st stage in conjunction with the unbalanced 2nd will start to breathe a little more stiffly once the tank goes under 500 PSI, but in this hypothetical "desert island' scenario that's an advantage, as I'd get a warning when the tank was low. This would allow me to keep diving even if my SPG failed.

New divers are routinely bombarded with hype about regulators. Among the most insidious is the "buy the best (read: most expensive) reg you can, your life depends on it." It was that sentiment from a LDS that helped send me down the path of DIY reg service and general curiosity about regulator design and function. If the lower end models were somehow not as "safe' as the higher end models, why was the dive shop even selling them? Total BS.

Very well said, Mattboy...Truth be told most recreational divers would be well equiped with an unbalanced piston first stage. I often use Mares R2 first stages on my deco and stage bottles due to their absolute reliability.

Greg Barlow