Balanced 2nd Stage with Unbalanced Alternate

[maniago]

Balancing deals with tank pressure not depth. All regulators are depth compensating. If you dive an unbalanced combination say a MK-2/190 or a Calypso you will notice that at the end of the dive when the tank is near empty it is harder to breath than when the tank is full. Where if you are using a balanced combination say a S600/MK-25 or a Legend you will not notice a difference in breathing regardless tank pressure.

All regulators will breath worse at depth because the gas is denser. This is more pronounced in unbalanced regulators because they are cheaper and lower-performing.

---------- Post added April 27th, 2014 at 10:29 PM ----------

Say what? You got your nomenclature assbackwards.

All firsts compensate for dropping tank pressure to provide a constant IP. A balanced first stage also takes the depth pressure into account so that the reg breathes the same at 10' as it does at 100'. An unbalanced will breath harder at depth than in the shallows.

 

[LeadTurn_SD]

Say what? You got your nomenclature assbackwards.

All firsts compensate for dropping tank pressure to provide a constant IP. A balanced first stage also takes the depth pressure into account so that the reg breathes the same at 10' as it does at 100'. An unbalanced will breath harder at depth than in the shallows.

Nope. ams511 was actually correct.

Balanced versus Unbalanced 1st stage: Balancing refers to maintaining a constant intermediate pressure (IP) as tank pressure changes. Unbalanced first stages will show a change in IP as the tank empties. This change in IP can effect breathing performance if it is large enough. Whether the IP rises or drops depends on the design of the 1st stage. Again, it has nothing to do with depth, other than the fact that you empty your tank faster at depth.

All first stages are depth compensating. That has nothing to do with balancing !!!! (Did I emphasize that enough? )

It has to do with the effect of water pressure.... increasing water pressure with depth acts on the first stage and raises the IP proportionately.

Balancing in 2nd stages is a different animal. But the main effect is to enable a lighter demand valve spring to be used, thus making breathing just a tad smoother and easier... but the best unbalanced 2nd stages will breath almost (or in some cases as) well.

Mares' upper end unbalanced, non-adjustable classic downstream 2nd stages are a good example of this, they are fine breathers at depth, and have been used on world record deep dives.... but those had lots of Helium in the mix so density was not the concern... but I digress.

If an unbalanced 2nd breathes badly, that is just the result of tuning or overall design, not simply because it is unbalanced.

And I've taken what would now be considered "vintage" unbalanced 1st and 2nd stages to 200', and they breathed as well (or poorly) as they did in 20' of water. But I was a bit narc'ed....

We really need the "usual suspects" to do a "Balanced" vs "Unbalanced" sticky thread.

Best wishes.

 

[axxel57]

@maniago

You got it pretty wrong.

Stay on the board and learn.

 

[maniago]

Hmmm. Well I'm sure that I'm plenty unbalanced; but the below is how I remember it, eventhough I might not be able to use my first language to write it proper... Balanced vs Unbalanced Regs: Does it Make a Difference? | Scuba Diving

"Balanced First Stage
It’s all about the springs when discussing the difference between balanced and unbalanced first stages. With both piston and diaphragm regs, there’s a high-pressure valve and seat assembly and a spring. An unbalanced reg basically has a different pressure on each end of this valve-spring assembly that causes varying effort to overcome the force of the spring as conditions change — such as change in depth or tank pressure. This translates as variations in the medium pressure traveling through the hose to the second stage, resulting in harder breathing effort at depth or low tank pressure. A balanced first stage routes medium pressure air to both sides of the valve-spring assembly, so that the effort to move the spring is consistent and unaffected by variations in external conditions, giving the diver unvarying pressure to the second stage and consistent breathing effort."

 

[redacted]

Hmmm. Well I'm sure that I'm plenty unbalanced; but the below is how I remember it, eventhough I might not be able to use my first language to write it proper... Balanced vs Unbalanced Regs: Does it Make a Difference? | Scuba Diving

"Balanced First Stage
It’s all about the springs when discussing the difference between balanced and unbalanced first stages. With both piston and diaphragm regs, there’s a high-pressure valve and seat assembly and a spring. An unbalanced reg basically has a different pressure on each end of this valve-spring assembly that causes varying effort to overcome the force of the spring as conditions change — such as change in depth or tank pressure. This translates as variations in the medium pressure traveling through the hose to the second stage, resulting in harder breathing effort at depth or low tank pressure. A balanced first stage routes medium pressure air to both sides of the valve-spring assembly, so that the effort to move the spring is consistent and unaffected by variations in external conditions, giving the diver unvarying pressure to the second stage and consistent breathing effort."

Try this explanation: Balanced vs Unbalanced Scuba Diving Regulators - Reg Basics for Beginners Then we can probably discuss it more if you would like.

I suspect Floyd is a better salesman than an engineer or technician.

 

[axxel57]

@maniago

Okay, you are for now excused.

If you find websites who publish such a nonsense and you don't know it better, what can you do?

Better you orientate on the explanations of LeadTurn and the other 'usual suspects', there you are on the safe side.

2nds are breathing worse at depth when supplied by an unbalanced 1st? At full tank? BS.....

 

[LeadTurn_SD]

Try this explanation: Balanced vs Unbalanced Scuba Diving Regulators - Reg Basics for Beginners Then we can probably discuss it more if you would like.

I suspect Floyd is a better salesman than an engineer or technician.

Thanks for posting that link! A far better explanation than I could ever muster, and his grammar is far better than mine!

Best wishes.

 

[Luis H]

Hmmm. Well I'm sure that I'm plenty unbalanced; but the below is how I remember it, eventhough I might not be able to use my first language to write it proper... Balanced vs Unbalanced Regs: Does it Make a Difference? | Scuba Diving

"Balanced First Stage
It’s all about the springs when discussing the difference between balanced and unbalanced first stages. With both piston and diaphragm regs, there’s a high-pressure valve and seat assembly and a spring. An unbalanced reg basically has a different pressure on each end of this valve-spring assembly that causes varying effort to overcome the force of the spring as conditions change — such as change in depth or tank pressure. This translates as variations in the medium pressure traveling through the hose to the second stage, resulting in harder breathing effort at depth or low tank pressure. A balanced first stage routes medium pressure air to both sides of the valve-spring assembly, so that the effort to move the spring is consistent and unaffected by variations in external conditions, giving the diver unvarying pressure to the second stage and consistent breathing effort."

Wow, that is such a mixture of some incorrect statement, with some correct statements, that it is hard to follow.

A balanced valve by definition is one that is not affected by the pressure that it is controlling.

In the Scuba world, this applies to the first stage (the tank pressure does not affect the first stage operation, and therefore the IP is constant) and to a balanced second stage (if the IP changes it does not affect the suction effort).

In reality the second stages are not 100% balanced, they are by designed meant free flow if the IP raises due to a first stage leak.
Also many first stages are not 100% balanced or should I say, many are not perfectly balanced.


All first stages used in open circuit Scuba are by designed ambient pressure compensation.


Unbalanced first stages are affected by tank pressure, but they do have pressure compensation. The only modern unbalanced first stages still in production are piston first stages.

All unbalanced pistons will have a lower IP with lower tank pressure. The high tank pressure pushes the piston to open and requires higher IP to close it.

What makes it a bit confusing is that unbalanced first stages are designed with a smaller volcano orifice (the orifice where the piston seat seals). The smaller orifice reduces the effect of tank pressure on the IP. But, the side effect is that the smaller orifice also restricts gas flow, which can be notice on very deep dives (deeper than most recreational depths).



Note about pressure compensation:
A friend of mine was diving a Sherwood with the dry bleed, but it had a malfunction, a clogged dry bleed. This malfunction defeated the pressure compensation. She could notice a difference in performance starting a 30 feet deep. By about 60 feet she could not handle the poor performance.

---------- Post added April 28th, 2014 at 07:46 PM ----------

Try this explanation: Balanced vs Unbalanced Scuba Diving Regulators - Reg Basics for Beginners Then we can probably discuss it more if you would like.

I suspect Floyd is a better salesman than an engineer or technician.

That is a very good explanation. He is saying the same thing that I said, but his explanations are probably better (and a bit longer).
OK, I will use language as an excuse... English is not my first language.


The only thing he didn't mention is the side of effect of the smaller orifice that is used in all unbalanced first stages. This side effect is the reason why (marketing types) have given a bad reputation to unbalanced first stages in very deep dives. The problem is that the effect has been in most cases exaggerated and not explained well.

---------- Post added April 28th, 2014 at 07:52 PM ----------

Wow, I just realized who wrote that. That is very good!

I should have known.

 

[ams511]

Say what? You got your nomenclature assbackwards.

As others pointed out you are mistaken.

I find your comment sad because you are a divemaster, a dive professional. So one would think you should know more than mere amateurs like me.

I have a divemaster manual and was surprised how little information it contained. It had cute stories, a rehashing of basic scuba information from the OW, AOW, and rescue training, and a sales pitch to be an instructor. I became somewhat interested in vintage diving and purchased some older books. I was surprised at how much more information they give than the modern books. Maybe you should pick up a few. They are cheaper than the modern ones also.

 

[5hundo]

it is one of the few octos I tried that I thought breathed worse than the Aqua Lung ABS.

That said, the ABS is a poor excuse for a reg....it will work but its poor quality.

Yeah, the ABS I own is admittedly a piece of garbage. Out of the water, it is really uncomfortable to breathe from. In the water, it's better but still not "good", and there are no adjustment features at all. When I was putting my Octo together, cash was a little tight but I got a good deal on the Legend, so I needed an alternate. Maybe its time to ditch the ABS...