Balanced Mixed With Unbalanced - Pros And Cons?

[OldPhotog]

Just wondering if one gets an advantage at all if one mixes an unbalanced 1st stage with a balanced 2nd stage? Or vice-versa?
Or does one need to have both first and second stages balanced to reap any benefit?

 

[gopbroek]

Here is a pretty good article Balanced vs Unbalanced - Regulator Basics for Beginners
I would want a balanced 1st to maintain a uniform IP but I do not think the second really matters. Until you go below the IP point there is no real benefit to a balanced second and perhaps it would be a good thing to notice you are just about out of air. That being said I run an Atomic balanced second because it breathes very nicely and it can run an extended time / cycles between servicing but I can also tell a slight difference in breathing when I run my bottle down below the IP point.

 

[tbone1004]

ok so first we have to understand what the balancing mechanisms do
in an unbalanced first stage, the IP is determined by the delta between the spring pressure and the tank pressure. This is less than ideal because IP determines how well the second stages function.
A balanced first stage will have a theoretically constant IP regardless of tank pressure which helps with predictability in second stage function

Second stages work exactly the same as the first stages, except instead of tank pressure, they function off of intermediate pressure. If the IP changes on an unbalanced second stage, the work of breathing will change accordingly.

I would not purchase an unbalanced first stage unless you are using it for suit inflation or other non-breathing activities. If you have unbalanced second stages, it is not significant, however the second stages have to be tuned against the first stage that they will be used with for optimal performance. For reference, all of my regulators, I believe 10 sets right now, are balanced first stages, with unbalanced second stages. I use Poseidon Jetstreams. Most all modern regulators are balanced first and balanced seconds with the exception of the low performance octo's

 

[OldPhotog]

Thank you for your responses. I get it now.

 

[Eric Sedletzky]

Unbalanced first stages will gradually begin to reduce available and quick reaction flow to the second stage, so an unbalanced first stage combined with an unbalanced second stage will give the diver plenty of heads up when air is running low, starting somewhere around 500 psi.
A balanced 1st stage will provide quick responsive flow to the second stage all the way up until the tank pressure begins to go lower than than the set IP, then the IP follows the actual tank pressure down. So a balanced 1st combined with an unbalanced second stage will breath fine until the tank gets below the set IP, then it will begin to breathe harder but there still will be some heads up.
If you use a balanced second stage with an unbalanced first then the second stage will cover for the gradual draw down and quick recovery of IP from the first. Balanced second stages will breathe well with almost no IP because the poppet is pressure assisted so they will still breathe with literally 10 psi of pressure.
When the tank runs out there is a little heads up but not much.
When both are balanced then both are optimized for max flow to the end so there is almost no warning when air runs out.
Of course all this is increased as depth increases due to ambient pressure placed on the system. All my tests have been in shallow water at 10' or less.
But regardless, no diver should ever find themselves in a position to find out how good a reg will breathe at depth at critically low tank pressures, this is careless and there is no excuse for running OOA at depth.
This why for some who have difficulty checking their gas supply regularly should consider using a basic unblanced first and second so they have a physical sensory warning of when their gas supply is beginning to get low.