First reg, need to buy two, rec diver

[MichaelMc]

For Akimbo's running out of air awareness, Poseidon's upstream unbalanced seconds seem to not help. As I read it, if IP drops, Poseidon seconds get easier to breath and ultimately free-flow. I think there was a recent up vs. down stream comment that I glossed over on this.

Thanks.

(Presumably above you meant the 70's for their last unbalanced *first* stage)

 

[Akimbo]

For Akimbo's running out of air awareness, Poseidon's upstream unbalanced seconds seem to not help. ...

True and good point. I was referring to the common downstream regulators that dominate the US market. My comments don't apply to upstream and servo valve seconds.

 

[tbone1004]

For Akimbo's running out of air awareness, Poseidon's upstream unbalanced seconds seem to not help. As I read it, if IP drops, Poseidon seconds get easier to breath and ultimately free-flow. I think there was a recent up vs. down stream comment that I glossed over on this.

Thanks.

(Presumably above you meant the 70's for their last unbalanced *first* stage)

correct on the jetstreams and xstreams. They actually have a really obvious "hey you dumba$$, start ascending" notification when the IP gets too low and in that case they will start to freeflow a little bit when you stop breathing as it takes a second for the IP to catch up. That's what I use on exit in a cave to tell me to switch to the next stage bottle.

The Cyklon behaves like a normal unbalanced second stage and will start to get stiff as the IP drops

correct on the first stage being from the 70's as the last time they had an unbalanced first stage. The quality of balance was somewhat questionable up to the current MK3, but they are balanced

 

[MichaelMc]

correct on the jetstreams and xstreams. They actually have a really obvious "hey you dumba$$, start ascending" notification when the IP gets too low and in that case they will start to freeflow a little bit when you stop breathing as it takes a second for the IP to catch up. That's what I use on exit in a cave to tell me to switch to the next stage bottle.

Are you using Poseidon's first stage, or something like the Apek's UST, to avoid over compensation for depth? Or I guess an unbalanced?

 

[tbone1004]

Are you using Poseidon's first stage, or something like the Apek's UST, to avoid over compensation for depth? Or I guess an unbalanced?

I use stock Poseidon 3790 first stages. I am hunting for a good turret, but haven't found one I'm in love with yet so haven't pulled the trigger as they're quite expensive

 

[Caveeagle]

For Akimbo's running out of air awareness, Poseidon's upstream unbalanced seconds seem to not help. As I read it, if IP drops, Poseidon seconds get easier to breath and ultimately free-flow. I think there was a recent up vs. down stream comment that I glossed over on this.

Thanks.

(Presumably above you meant the 70's for their last unbalanced *first* stage)

Which Poseidon 2nd stage is Upstream & Unbalanced? I am pretty sure both the Xstream and the Jetstream are Balanced and the Cyklon is Unbalanced/Downstream. Not really sure about the Triton, but those are rarely seen

 

[MichaelMc]

Which Poseidon 2nd stage is Upstream & Unbalanced? I am pretty sure both the Xstream and the Jetstream are Balanced and the Cyklon is Unbalanced/Downstream. Not really sure about the Triton, but those are rarely seen

From their website, Xstream and Jetstream are upstream, Cyklon downstream, as you say. I had missed the downstream part in reading their site. They are all pilot valve operated. They do not say that is unbalanced but high or low IP affect them. To the point that they are reportedly rather sensitive to IP, where over compensation for depth, as seen in sealed diaphragms messes up their nice breathing.
Poseidon Xstream Regulator

 

[tbone1004]

Which Poseidon 2nd stage is Upstream & Unbalanced? I am pretty sure both the Xstream and the Jetstream are Balanced and the Cyklon is Unbalanced/Downstream. Not really sure about the Triton, but those are rarely seen

the jetstream/xstreams are not balanced. I don't believe the servo design can be balanced. to balance a regulator they use IP on both sides of the spring. IP on the downstream side of the seat is used to artificially increase the spring rate of the spring holding the seat closed. In the jetstream/xstream design there is one spring on the servo with no way to put air on the opposite side. The "seat" is the silicone diaphragm that goes against the metal body and again, no way to put IP on that side

 

[Caveeagle]

That makes sense...

 

[halocline]

A design characteristic of balanced second stage regulators allows shifting some of the counterforce of the mechanical spring holding the seat closed to the counterbalancing pneumatic "spring". That translates to a less force required on the lever so the diaphragm area can be reduced. That doesn’t mean that a diaphragm must be smaller, but most are. It is literally a design balancing act... pun intended. Compare the size of an old metal-body Conshelf to a new Legend for example.

Edit: @Luis H is one of the regulator gurus on Scubaboard, he can probably explain it far better.

I understand how balanced 2nd stages work. I also understand how increasing the size of the diaphragm (and resulting lever length) present a mechanical advantage. But the two things are not related. A balanced 2nd stage still has to oppose IP, it just does so with a combination of IP and a small mechanical spring, instead of a large mechanical spring. Increasing or decreasing the size of the diaphragm has exactly the same effect on balanced and unbalanced poppets.

There are two performance advantages of balanced poppets; 1) Since IP is part of the opposing force keeping the valve closed, any changes in IP are mirrored and partially cancel each other out. This allows the 2nd stage to tolerate larger changes in IP without as noticeably changing cracking pressure. 2) Since IP drops during demand, so does part of the force closing the valve during inhalation. This 'should' result in lower effort to sustain inhalation, all other factors remaining equal.

I think the move to smaller diaphragms in more modern 2nd stages has to do with marketing and increased venturi assist, not balancing.