How does the Poseidon Xstream first stage work?

[tbone1004]

@shurite7 the 25 has always had ambient holes, it has to in order to be depth compensating. They just keep getting bigger with every revision in an attempt to make it more cold resistant.
Servicing the Xstream is infinitely easier than the MK25 *have done both several times*. The Poseidon first stages have always been incredibly easy to work on.

@lexvil what do you mean by that? There is still a "soft" seat in there that is part of the parts kit. What seals against that soft seat is analogous to the knife edge of a piston or the hard crown in normal first stages. Poseidon has historically used a "bullet" looking seat which was nice because you can polish them during service if they are being annoying with IP creep and they're cheap to replace if you mess one up vs. the crowns inside of most regulators that are non-repairable as @The Chairman annoying found out with one of his regulators a few weeks ago. A few have replaceable crowns *Apeks FSR being the only one to my knowledge that is still using one but the Deep6 Signature and HOG d3 originally had them*, but Poseidon decided to one up themselves and go straight to the sphere which can rotate around and is super hard so it won't get scratched and leak like the steel ones did.

 

[lexvil]

@shurite7 the 25 has always had ambient holes, it has to in order to be depth compensating. They just keep getting bigger with every revision in an attempt to make it more cold resistant.
Servicing the Xstream is infinitely easier than the MK25 *have done both several times*. The Poseidon first stages have always been incredibly easy to work on.

@lexvil what do you mean by that? There is still a "soft" seat in there that is part of the parts kit. What seals against that soft seat is analogous to the knife edge of a piston or the hard crown in normal first stages. Poseidon has historically used a "bullet" looking seat which was nice because you can polish them during service if they are being annoying with IP creep and they're cheap to replace if you mess one up vs. the crowns inside of most regulators that are non-repairable as @The Chairman annoying found out with one of his regulators a few weeks ago. A few have replaceable crowns *Apeks FSR being the only one to my knowledge that is still using one but the Deep6 Signature and HOG d3 originally had them*, but Poseidon decided to one up themselves and go straight to the sphere which can rotate around and is super hard so it won't get scratched and leak like the steel ones did.

It was a simple question, the “ball” seals against a “seat” as does the “knife” edge of a piston seal against a seat, I was just trying to clarify the terminology and the actual function of the ball. There is usually a soft part that is replaceable and I wasn’t clear on that.

 

[tbone1004]

@lexvil ahh, I was confused by what you meant by valve.

 

[rhwestfall]

"Typical" piston:

 

[rhwestfall]

To my knowledge the Mk25 has always had the ambient holes

Yes, and would need them to function.... however, it seems that they have significantly increased them in size in the EVO....

 

[rsingler]

To answer the OP's question, the Poseidon has two features, the combination of which make it unique in the diaphragm world:
1) the ball valve discussed above, and
2) having a floating seat which is the component that responds to changing tank pressure, rather than the HP poppet, like most diaphragm regs.
That seat is absolutely magical, and when combined with the ball valve makes for incredibly reliable performance.

Having a diaphragm which sheds ice is an engineering call that is beyond my qualifications to criticize. While having a dry chamber with a secondary diaphragm that transmits ambient is a great choice, the soft, malleable diaphragm of the Poseidon is a third, unique feature.

 

[shurite7]

Yes, and would need them to function.... however, it seems that they have significantly increased them in size in the EVO....

Not really. My older Mk25s had larger port holes than my current Mk25EVO. Now, I haven't counted the number of holes, but the EVO probably has a couple more holes than the older 25 which makes sense, bigger holes less space, smaller holes more space to add a hole.

 

[rhwestfall]

The "typical" HP seat in the pic above is not used in the Mk25.

Here:

same general purpose.... The one I showed was for a "knife edge" piston, and used in numerous piston stages. The MK-10+. MK-20/25 went to a flat edge, so the cone was replaced with a simple "indent" shown above...

The principal s basically the same, and fairly different from the Poseidon....

 

[Luis H]

In the geometry of most (if not all) diaphragm regulators, the cold gas flow doesn’t get anywhere near the adjustment heavy spring. Therefore, if the spring is in a wet chamber, the water is not as likely to cooling from the gas expansion.

Even an old Conshelf without any environmental seal has a decent fighting chance of not freezing. And their wet chamber had very poor water circulation. The dry environmental chamber adds a nice clean contaminant free solution.

A flow through piston on the other hand is a heat transfer nightmare if you don’t want the water around the piston to cool down and freeze.

The Poseidon diaphragm design is very clever. The open water chamber with good heat transfer is a simple alternative solution.

I like the Poseidon floating (piston) balancing HP seat. It actually reminds me of the balancing design used by Sherwood in some of their piston regulators, the volcano orifice was also mounted on its own floating piston. The pneumatic concept in both is the same.

A while back I once serviced a Mares regulator that also used a ruby curved poppet that also sealed in a soft orifice.

I haven’t serviced a Poseidon first stage in decades, but I am very familiar with their old Cyklon 300 conical poppet into their old soft square edge orifice.

 

[js47]

Thanks everyone for the informative replies. I understand the TDA system much more clearly now and that spherical ruby ball is very intelligent design.

@rhwestfall The schematics you posted were extremely helpful, thanks for those. One question that arose from looking at them (and I know this has been beaten to death), but do you know why it is that Poseidon insists on warning everyone not to use anything but the Xstream Duration with enriched air? No other equipment manufacturer that I’ve come across warns against using anything below 40%. Honestly for me it is a little disheartening that a top-tier brand like Poseidon would sell a "defective" product like this at all; If it truly is as they say and the Deep can only be dived with air then they should cut it from the lineup and only sell the Duration. It just leaves a bit of a bad taste in my mouth that they would cheap out on the o-rings and oxygen-safe lubricant on a particular model, especially considering how thoughtfully engineered all of their products are. It seems to me they are intentionally handicapping the Deep, which certainly violates the principles of good engineering. Unless nitrile o-rings and silicone grease have some other redeeming qualities that make them superior to viton and christolube under certain conditions?

@rsingler Great CAD rendering and very interesting to see the actual ruby sphere! Would you mind explaining a little more about the magic of the floating seat? Very interested in learning more about that.

@tbone1004 Any idea what it is about the water swirling around in the spring chamber that keeps the reg from freezing? @Luis H pointed out that it is all about the heat transfer, which is all I could think of as well. Is it just that the ambient water temperature is necessarily above the freezing temperature whereas a first stage in cold water might have been adiabatically cooled to below the freezing point, in which case the cold but not freezing through-flowing water will warm it up a little? Also I’ve got to give you a special shout out — I’ve read a countless number of your posts on dozens of threads regarding Poseidons…. I owe a significant portion of what I know about them directly to you, and I’ll be picking up a double set based on your recommendations in the very near future!