Looking at ScubaPro...

[rescuediver009]

If the IP is stable in the first stage then, no - a balanced reg will not perform significantly better than a non-balanced reg as the forces required to open the valve will still be equal as the IP, and consequently the downstream force, does not change.

Depth makes no difference either as the IP will increase by the same amount as the ambient pressure and the relative difference between IP and ambient pressure will still be the same whether you are at the surface or at 250 ft.

First, is your comment based on the original overbalanced second stage?
If so I hesitate to disagree. If balanced regs do not perform any better, why would they be in use? Also what of the reciprocating pressure of the air in the balancing chamber pressed back on the poppet? would this not reduce cracking resistance? For example, I would say that (for sake of argument) an Apeks ATX40 would breathe easier than a Scubpro R190 at a depth of 150ft. if they were both connected to a DS4 first stage.
I do not intend to argue, just curious.

 

[uberspeed]

I'd like to see standardized tests and then apply the methods to a scenario of a balanced first stage and mate it to a balanced second stage and then an unbalanced second stage. I wonder what the results would be. Perhaps DA has some info on this.

 

[redacted]

First, is your comment based on the original overbalanced second stage?

I believe SP claims to have overbalanced the Mk20/25 1st stages. I believe the seating end of the piston is flared a bit. An overbalanced 2nd stage might not allow the poppet to pull away from the orifice.

Edit:
I got to thinking more about what you could have meant by an overbalanced 2nd and I realized you must be talking about the S600/G250HP design. It uses 2 balance chambers. One is a conventional chamber which applies upstream force on the seat against the orifice. The other is contained in the adjustment knob and has a stop which prevents the force in that chamber from being transmitted to the seating surface. But it does allow all pressure between the seat and the orifice to be relieved reducing seat engraving when the system is not under pressure.

Sorry

 

[rescuediver009]

I believe SP claims to have overbalanced the Mk20/25 1st stages. I believe the seating end of the piston is flared a bit. An overbalanced 2nd stage might not allow the poppet to pull away from the orifice.

Yes all theflowthough piston designs are overbalanced thanks to the holes that allow water pressure to increase the IP

Edit:
I got to thinking more about what you could have meant by an overbalanced 2nd and I realized you must be talking about the S600/G250HP design. It uses 2 balance chambers. One is a conventional chamber which applies upstream force on the seat against the orifice. The other is contained in the adjustment knob and has a stop which prevents the force in that chamber from being transmitted to the seating surface. But it does allow all pressure between the seat and the orifice to be relieved reducing seat engraving when the system is not under pressure.

Sorry

There is no such thing as an overbalanced second stage. Just balanced. The ones you mentioned are balanced similarly to the entire Apeks line.

As far as what uberspeed is asking. That is where I think you would find the difference between balanced and non balanced second stages.

 

[WarmWaterDiver]

Scubapro now claims its Mk16 & MK18 first stages are overbalanced - see this thread . . .

http://scubaboard.com/t61089.html

 

[DA Aquamaster]

Overbalanced is a hard word to define as the marketing types from different companies use it differently.

Scubapro uses the word to refer to the use of a piston with a slightly smaller piston stem relative to the hard sealing edge of the piston. This is used in the current Mk 20/25 first stage and compensates for the area of the sealing edge itself and allows the piston to be completely balanced and results in a very stable and unchanging IP.

But not all "balancing" is created equal. The older MK 5,7,9,10 piston first stages had constant diameter stems and a 4-6 lb change in IP as tank pressure fell from 3000 to 300 psi was common. The area of the seating edge, although small, does add up and is affected by the downstream force from the tank. So unless this area is accounted for and accomodated with a smaller diameter where the piston stem meets the HP o-ring, a change in IP will result as tank pressure falls.

Regulators have had holes in ambient pressure chambers to compensate for ambient pressure since God was a private, even unbalanced regulators so that certainly is not what is referred to as "overbalancing".

In a diapragm reg, the same basic idea applies - the area of the hard seat has to be accounted for in the design of the balance chamber and seat carrier.

 

[uberspeed]

OK, so...the second stage doesn't need to be balanced as long as the first is, right? I thought I had that nailed down but perhaps not? Is it worth the premium to go say, from a MK16/R190 to a MK16/S550? I thought you had said no, but maybe it's worth it in the long run to go balanced second?

 

[rescuediver009]

OK, so...the second stage doesn't need to be balanced as long as the first is, right? I thought I had that nailed down but perhaps not? Is it worth the premium to go say, from a MK16/R190 to a MK16/S550? I thought you had said no, but maybe it's worth it in the long run to go balanced second?

I said that it would be, and from what I understand DA said it wouldn't.

Any reg that takes adavantage of increasing hydrostatic pressure is overbalanced. Scubapro does this withe holes in the side of the MK25 first stage, and any diaphragm that is open to the elements or has a load transmitter is also.

 

[DA Aquamaster]

Any reg that takes adavantage of increasing hydrostatic pressure is overbalanced. Scubapro does this with the holes in the side of the MK25 first stage, and any diaphragm that is open to the elements or has a load transmitter is also.

By your definition, any scuba reg ever made would be overbalanced. I cannot think of any scuba reg ever made that did not incorporate a mechanisim for compensating for increased ambient pressure. This is in fact a defining trait of all scuba regulators and is what sets them aprart from other types of pneumatic regulators.

That would strongly suggest that your definition of overbalancing is not what is commonly meant by "overbalancing".

 

[moxie]

Regarding a BC, you might look at the Zeagle 911.


See here:

http://www.zeagle.com/index.php?submenu=SpecializedBC&src=gendocs&link=911