First reg, need to buy two, rec diver

[halocline]

the jetstream/xstreams are not balanced. I don't believe the servo design can be balanced.

The SP pilot is a balanced, servo assisted 2nd stage. The pilot valve itself is a small downstream bias valve, and the main valve is a center-balanced 'spool' that eventually evolved into the D series.

 

[halocline]

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?

Why would balanced/unbalanced make any difference for depth compensation? The two are completely unrelated, despite the confusing sales literature about so-called "overbalanced" 1st stages.

 

[MichaelMc]

Why would balanced/unbalanced make any difference for depth compensation? The two are completely unrelated, despite the confusing sales literature about so-called "overbalanced" 1st stages.

Balanced/unbalanced and over depth compensation might be unrelated in principle. My question was a bit of a side comment asking about what feature combinations occur in the current marketplace. And what might serve a Poseidon second stages if you wanted a turret (which Poseidon does not offer). They are sensitive to being in a narrow IP range. I’ve read that environmental seals are a cause of the over depth compensation IP shift, hyped as overbalanced. I mostly recall them with respect to diaphragm first stages, and I do not know of any modern unbalanced diaphragms. A bit of conflating a few factors. Happy to hear of any sealed unbalanced non-depth overcompensating regs if you know of any though, as I am curious about unbalanced regs.

 

[buddhasummer]

Balanced/unbalanced and over depth compensation might be unrelated in principle. My question was a bit of a side comment asking about what feature combinations occur in the current marketplace. And what might serve a Poseidon second stages if you wanted a turret (which Poseidon does not offer). They are sensitive to being in a narrow IP range. I’ve read that environmental seals are a cause of the over depth compensation IP shift, hyped as overbalanced. I mostly recall them with respect to diaphragm first stages, and I do not know of any modern unbalanced diaphragms. A bit of conflating a few factors. Happy to hear of any sealed unbalanced non-depth overcompensating regs if you know of any though, as I am curious about unbalanced regs.

I don't think there are any.

 

[MichaelMc]

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.

Yet by allowing a weaker spring, a balanced system lets me get away with a smaller, more sexy, diaphragm. If the first stage's balancing is not so great, then adding balancing to the second stage completes the isolation from tank pressure changes, allowing use of a smaller mechanical advantage from the size of the diaphragm. It seems to do with marketing, and ergonomics, but balancing seems to enable it.

 

[tbone1004]

The SP pilot is a balanced, servo assisted 2nd stage. The pilot valve itself is a small downstream bias valve, and the main valve is a center-balanced 'spool' that eventually evolved into the D series.

forgot about that one. I think the Oceanic Omega series may actually be balanced as well before the servo, but I maintain that I don't believe the servo itself can be balanced. I'm not entirely sure balancing behind it would matter to the WoB though since all you are having to "crack" is the servo itself. If you can crack that, then the big whoosh of air should have no issue coming out. That may also be the design nature of the downstream servo vs an upstream servo like the Poseidon.

 

[halocline]

Yet by allowing a weaker spring, a balanced system lets me get away with a smaller, more sexy, diaphragm.

Sorry, this is not true. In balanced 2nds, the mechanical spring is weaker, but because it is aided by pneumatic force, those two forces are still equal to the force of a larger mechanical spring. They have to be; otherwise the valve would open and freeflow. That force (or combination of forces) pushes the lever up against the diaphragm. The diaphragm has no way of "knowing" that the lever is being pushed by a fully mechanical spring or a combination or mechanical and pneumatic spring.

All the diaphragm does is collapse under force from the water and push on the lever. The larger the diaphragm is (assuming a rigid plate in the middle) the more force there is for a given amount of pressure differential between the dry and wet side of the diaphragm.

The longer the lever, the more mechanical advantage it has in opening the valve. OTOH, it also has to travel further to get the same amount of opening. I'm not sure how that actually figures into total WOB, but certainly once air is flowing and there's a venturi assist, that has a major role.

As far as I can see it, the diaphragm and lever geometry simply have nothing to do with the use of diverted air pressure vs mechanical spring in the poppet. The poppet action is entirely IP based, and the diaphragm is entirely ambient based.

 

[Akimbo]

There are a number of factors you aren't taking into account. The assist only comes into play after the valve is open enough to reach the lower threshold for the venturi. That would not affect cracking pressure. Another issue is the different characteristics of mechanical compression springs and a counterbalancing pneumatic pistons. Compression spring force increases and has wider manufacturing tolerances as the valve opens while the pneumatic force drops as the IP drops when measured at the seat (not in the hose). Finally you have to consider the simple leverage ratio, which effectively increases by the square-root of 2 as that little flat-arm rotates to 45° pushing the poppet off the seat.

All these factors make a noticeable difference in diaphragm diameter when you consider that force relates to area so diameter reductions are by a factor of PI x radius squared. To be honest though, diaphragm diameters have reduced more because of affordable and usable 3D solids modeling software with kinematics and fluid dynamics analysis than any features listed on the regulator's specifications.

I saw a cool photo recently of a diaphragm from a double hose Aquamaster next to one from a Legend. That is dramatic and doesn’t take into account how much better the Legend's WOB is.

 

[tbone1004]

@Akimbo on that last comment, my understanding is that with a new HPR second stage, the double hoses can be tuned to a lower WoB and cracking effort than any "normal" style second stage on the market. Basically everything except the Xstream from Poseidon. I know the Kraken did it as I have seen the graphs, but I believe an upgraded Aquamaster can beat them as well

 

[Akimbo]

@Akimbo on that last comment, my understanding is that with a new HPR second stage, the double hoses can be tuned to a lower WoB and cracking effort than any "normal" style second stage on the market...

I don't doubt it, when you are in the right position (double hoses are more position sensitive in the water). Big diaphragms can overcome a lot of technical refinement by employing the Brute Strength engineering principal.

Recreational divers, which include the majority of technical divers, need to keep in mind that the most important thing is "what is good enough". You can spend way more money buying Kirby Morgan regulators that meet US Navy requirements for working divers at 1600' than <$400 for performance that is just as good for your application. Regulators don’t come with bragging rights, just endless "mine is better than yours" arguments.