Balanced second stage regulators

[MoonWrasse]

I've seen that some of the more pricey regulators boast balanced second stages in addition to balanced first stages. I understand the importance of a balanced first stage, but how does a balanced second stage augment the configuration?

 

[DA Aquamaster]

Generally speaking a balanced second stage can use (but does not always use) a much larger orifice than a traditional downstream unbalanced second stage and can potentially have a much higher flow rate.

With the balanced second stage, air pressure on the other side of the balanced poppet can be used to offset most of the downstream air pressure from the first stage so a much smaller spring can be used in the second stage even with a much larger orifice and the whole system will generally be better responding and will potenitally (but not always) have a lower inhalation effort.

A balanced second stage will also always be better able to accomodate changes in first stage intermediate pressure. Some balanced piston first stages can still have a small change in intermediate pressure as they are not completely balanced and some balanced diaphragm designs resort to overbalancing where the IP increases slightly more than the increases in ambient pressure at depth to improve flow rate (something not needed on a high performance piston design which already has bags of excess flow rate.)

 

[rescuediver009]

I won't say anything more, except that balanced second stages often accept the increase in pressure delivered from oever-balanced first stages. (i.e.- apeks) see picture for a diagram of a balanced second stage.
#2 is the low pressure seat
Air passes through it (balanced seats have a hole in them) and through #3 where it stops at #4 and the air pressure expands the spring.