Question Are most people confused about unbalanced first stages?

[BoltSnap]

Yep, from the responses above, they are indeed confused

 

[johndiver999]

deleted

 

[ams511]

I've been told many times by very experienced divers that unbalanced first stages are not good at depth.

From what I understand, all first stages are "balanced" with respect to ambient pressure. At a given tank pressure, all first stages will deliver constant IP no matter the depth.

If a first stage is "balanced", it will also deliver constant IP no matter the tank pressure.

Is this correct so far?

I dove unbalanced first and second stages in the past. Sure enough, they became harder to breathe below 60 ft. I always assumed this was due to depth, but overlooked that of course tank pressure would also be lower at that point in my dive. I was shore diving and it took a bit of time to reach 60 ft from shore, which means tank pressure would have been lower.

First, welcome to Scuba Board.

Second, all open circuit scuba regulators should deliver gas at ambient pressure or very close to it. In theory a "balanced" first stage should maintain a constant IP regardless of than pressure, in practice there is a shift in tank pressure, but not as much as an unbalanced first stage. There are several threads on SB discussing this. @rsingler or @buddhasummer could probably tell you which first stages are the most solid.

Where things get confusing is that some manufacturers promote "overbalancing" where the deeper you go the IP increases. From what I remember, this is a byproduct of the way the environmental sealing is done. The manufacturers say this is a good thing but if your second stages are tuned to the edge then you could experience a freeflow at depth.

 

[buddhasummer]

@herman (where are you sir) ran the numbers a while back and he noted ip increased by around 1.5 PSI for every 10 feet using "over balanced" first stages.

Regulator Performance With Increasing Depth

I read a post in another thread that contradicted my understanding of the effects of depth on regulator performance, specifically regarding balanced and unbalanced regulators (balanced, unbalanced, and "over-balanced??" 2nd stages in particular). I think this topic comes up often enough...

scubaboard.com

 

[herman]

I's still around sir but not as much as the old days.

To answer this question, first you have to understand what balancing is, what it does and the difference between balancing and depth compensation. You also need to understand the difference between psig and psia. Basically, psig (pounds per square inch gauge) is what we mostly use, it's the pressure of something MINUS the air (ambient) pressure around it as opposed to psia (pounds per square inch absolute ....measured against a vacuum) . We live under the atmosphere which exerts a pressure of around 14.7 psiA at sea level but since we live in it we tend to ignore the pressure and use psiG for our measurements. I have capitalized the G and A to make the difference clear.

First off, ALL scuba regs are depth compensated (maybe some rebreather ones are not but that is out of this scope). Which means the IP (intermediate pressure) remains constant as measured against ambient pressure.....the pressure around it, which increases as depth increases. At the surface the IP (just to pick a numbers close to what is used) is 140 psiG over the 15 psiA air around it for a total of 155psiA. As you go under water, every 33ft increases the ambient pressure another 15psi for a total of 30 psiA at 33 ft, the regs IP is still at 140psiG over ambient but now ambient is 30 psiA so it's total pressure 170 psiA. Not only is the reg surrounded by the increased pressure so is the diver, consequently he and his lungs are at 30psia just as his reg is so he can't tell any difference in the air he is breathing. The ambient pressure continues to increase as the diver descends and the absolute pressure of the regs IP continues to increse to match it but keeps a constant 140 psiG regardless of depth as long as the tank has enough pressure in it.

So that leads to balancing, which has nothing to do with depth compensation (that is handled above) but rather is the regulator keeping the breathing resistance/work of breathing (and cracking pressure- how easily the reg starts to supply air) of the first and/or second stage constant AS THE TANK PRESSURE CHANCES. This is where we get deep into subject. What a lot of folks don't realize is either the first , the second or both can be balanced and it really doesn't matter which is balanced and it's not necessary to balance both to accomplish the goal. Without getting into the mechanical ways it's done, the first stage accomplishes this by keeping the IP at a constant pressure (psiG) as tank pressure changes, whether the tank pressure is 3000 psi or 1000 psi, the IP remains a constant (or at least close to it) pressure which in turn allows the second stage to keep delivering air the same. Since the IP is constant, the second stage does not have to be balanced since it sees a constant IP. In contrast, the second stage can be designed to be balanced which means it compensates for a changing IP and keeps it's delivery of air constant regardless of IP (within reason of course) . Balancing both is not necessary because as long as one stage is balanced, the other doesn't need to be to accomplish the goal. With that said, balancing the second stage does have some benefits but not really relevant to the balancing discussion.

Hope that makes it clear as mud.

 

[buddhasummer]

Good to see you again