Thoughts...mk25 sealed

[lexvil]

Not to get into the necessity of sealing or not but I’ve noticed the mk20 SPEC actually fits onto a 25, not ideally and not sure if adequately but with James79 attempting a silicone version of the old cap I’m finding myself contemplating the viability of the idea.

 

[James79]

I'm not a modern reg kind of guy, so I can't speak to the advisability/amount of benefit this would provide. But if smart guys like Lex and @rsingler say it would help, then I'm sure I'll end up taking a crack at it!

Respectfully,

James

 

[rsingler]

Viability is completely a function of the volume under the boot. It that's sufficient, it might work better with silicone rather than Christolube
if the seal at the top edge (turret edge) of the boot isn't real tight.

Two ways to approach - by calculation and by trial.
Area of piston head x travel on pressurization. Travel during breathing will be insignificant compared with the extrusion of grease from the hole when you pressurize. Maybe 1.5mm valve open to valve closed?? Don't know what that comes out to. Does boot have that much room? Can also do that by calcs.

Alternatively, carefully wrap saran wrap around the body and secure with rubber bands above and below the ambient holes. It will want to leak out the bottom, so I'd wrap it and fill with a syringe and needle, alternately adding water and aspirating air until the chamber is full and there's not too much bellying out at the bottom.
Once filled, and with a little slack in the saran wrap (but a piece of tape over the needle hole), turn on the pressure and see how much water puffs up the wrap. Guesstimate whether boot has that much room.

My 2psi.

Seem's like a lot of work to make an inferior design work like a T3.

But yeah. Anything to keep the grit out of the inside.

 

[lexvil]

I’ll send James a MK 25 this week, I think having external reinforcement at the top, maybe cast in or a groove for an oring?? If I were a calm sea or boat diver I wouldn’t be as concerned but diving these active shores out west IV seen to much scoring inside these 25’s, of course just getting an Atomic is easier but the one real good thing about the 25 is the external IP adjustment, I remember how much I loved having to reset/shim a sealed system that took a little long to hit its final mark.

 

[rsingler]

You've got me there, @lexvil !! Can't beat tuning the IP on a Mk 25.

As for securing the top edge of the boot, if this ends up being done as a project, I'd recommend adding a small ledge at the top end - room for a thin zip-tie. That's what I did on my Mk10 to hold the bicycle tube seal in place. Room is tight, though, under the turret.

 

[tmassey]

Dead serious question: remind me why you would rather dive a piston reg in a situation where being completely sealed is warranted?

As an actual cold water/under the ice diver, environmental sealing is important to me, so I dive diaphragm regulators. I’m just wondering what would be so compelling that you would be willing to deal with packing a regulator full of silicone grease, rather than switch to a diaphragm regulator.

Truly curious: no mocking here. My understanding is that flow-through balanced piston regulators are a little simpler, and can deliver a larger volume of air, though any modern regulator can supply enough air for any three divers to at least several hundred feet. If environmental sealing weren’t a need for you, then sure, take the advantages. But when it is, those don’t seem to be compelling enough to deal with silicone grease.

Please inform my ignorance.

 

[lexvil]

Dead serious question: remind me why you would rather dive a piston reg in a situation where being completely sealed is warranted?

As an actual cold water/under the ice diver, environmental sealing is important to me, so I dive diaphragm regulators. I’m just wondering what would be so compelling that you would be willing to deal with packing a regulator full of silicone grease, rather than switch to a diaphragm regulator.

Truly curious: no mocking here. My understanding is that flow-through balanced piston regulators are a little simpler, and can deliver a larger volume of air, though any modern regulator can supply enough air for any three divers to at least several hundred feet. If environmental sealing weren’t a need for you, then sure, take the advantages. But when it is, those don’t seem to be compelling enough to deal with silicone grease.

Please inform my ignorance.

No real compelling reason, for my diving the 17 pretty much does all I need but it is hard to escape the simplicity of the piston. I dive mostly from the shore in California, for the most part it’s a very active shore with a lot of grit, it’s not a one time thing but this stuff can score the sealing surface pretty badly (my reason for the 17) over time. Unlike the boot the packed ambient chamber alone was a little more messy and didn’t offer a great barrier from the grit that could work its way back in. And the biggest reason is to see if it can be done, I can get mk25, non EVO pretty cheap usually, often cheaper than an Atomic Z so, why not. The MK 20 and first MK 25 were set up for the boot

 

[rsingler]

Dead serious question: remind me why you would rather dive a piston reg in a situation where being completely sealed is warranted?

...I’m just wondering what would be so compelling that you would be willing to deal with packing a regulator full of silicone grease, rather than switch to a diaphragm...

You are years ahead of us piston guys.
From a simplicity standpoint, despite the extra parts count, it's far easier to prepare a diaphragm for true cold water diving than a sealed piston without an IP adjustment screw. But if you're talking true ice diving, the reg you might want to consider is a double hose. That's a diaphragm whose second stage is right next to the first, where icing is much less of a concern. But that's a minority opinion. For some real data, consider the attached file below.
Now, back to the regularly scheduled program. If you look at the original NEDU study from the 80's, (and this is what started me down the diaphragm route) the old Poseidon 300 delivered unbelievable flow at great depth and low temperature, compared with stars like the MkV. That was an unbalanced diaphragm with a tiny little hole for gas flow from the tank. WTH?! And the Cyklon Maxima and Odin were even better. See the NEDU study below. (G250NavyTest.pdf)
You can't argue with the data.
So I figured if a diaphragm can handle that, maybe I ought to rethink my piston obsession.
Now you still need to consider freezing and overbalancing, which is why environmentally sealed diaphragms may not be as preferable as unsealed diaphragms. But at least the ambient chamber is dry.
Doing the same with a piston probably requires a low temp grease like Tribolube 71 rather than silicone, and retuning for lower IP and higher cracking effort. Viscosity really begins to play a role here.

I'll let the true ice divers weigh in here, but you can't argue with Poseidon's XStream photo of icing over and still functioning.

There may be more to be said about the second stage in extreme cold water, but that's another discussion.

 

[tmassey]

I want to like Poseidons... I’ve owned several complete sets of Odin/Jetstream and XStream... but they put bubbles in my face too much, and fill my hood with freezing-cold air. On top of the unusual breathing feel, and the YOU’RE GONNA DIE!!! upstream demand valve... (Sarcasm in case the all-caps weren’t enough.)

I’m still fascinated by the engineering. But I find my Apeks-like regs much more operationally friendly.

And double hose... in a wreck... 150’ or deeper... with isolated manifold doubles... I think that might be optimizing for one aspect (cold water) just a *little* too much... (Yeah, I *know* you guys were doing just that 50 years ago... But we use pressure gauges now... )

Seriously, double hoses (and Cyclons) are on my must-try list. But given practical concerns, both of them would be segregated into the novelty category.

Thanks for the answers. I appreciate the information.

 

[rhwestfall]