How cold is too cold for piston regs

[halocline]

halocline, those mk25's have all been sealed which changes things dramatically.

No they are not. Scubapro abandoned the SPEC (packed ambient chambers) long before the MK25. They now use teflon-coated springs and a few plastic bushings called the "TIS" to discourage ice build up, but they have never been sealed.

 

[Luis H]

My old 1967 Conshelf XI is small but I believe it's balanced.

All Conshelf are balanced. They are all the same inside.

You have to go to a US Divers Aqua-Div to find the unbalanced diaphragm first stage (similar to the non-balanced Aqua Master). But the Aqua-Div has a up-stream tilt valve demand second stage design.
The Poseidon Cyklon 300 was the last non-balanced diaphragm regulator, but that is such a good performer that it won't give you much of an advance warning of low air condition.
The unbalanced diaphragm second stages actually get better breathing performance as the air drops, so they are not really good indicators of low air.

For your purpose, from what you are describing, I would recommend the Mk-2 with a 109 second stage.

 

[Eric Sedletzky]

The big difference in cold weather performance from a flow through piston and other first stages (flow by piston or diaphragm) is that in the flow through piston the super cold air flows through the piston and cools it down. All the super cold air actually flows inside the piston, cooling it down.

On a flow by piston, very little air flow actually goes into the piston since it is a dead end. Only enough air to pressurize the piston head. That air goes in and out of the piston. Most of the super cold air flows just past the piston tip and out the hoses. The little air that actually flows into the piston has a chance to warm up. Therefore, the piston in a flow by regulator (like the Scubapro Mk-2) doesn’t get as cold as in a flow through piston (like a Mk-5 or Mk-25).

The diaphragm regulator has similar advantages to the flow by piston, plus (big plus) the fact that it doesn’t actually have a sliding piece of cold metal (the piston) submerged in water. The cold air doesn’t actually flow much past the diaphragm, it goes from the first stage valve to the hoses. Even on a wet diaphragm regulator, any possible ice crystals on the wet chamber are less likely to affect the motion of the diaphragm.

Note: for this discussion above, I was comparing wet environmental chambers in all three examples. With a seal environmental chamber (using grease, oil, or dry type chamber) the concern of water freezing in the chamber is not really an issue.

BTW, (just for information) flow through piston and flow-by piston does not always represent balanced and unbalanced first stage regulators respectively. I have clear examples of unbalanced flow through piston regulators (Deepstar II, etc) and balanced first stages with flow-by piston.


A metal second stage like a 109 is for all practical purposes freeze almost impossible to freeze. I have tried freezing a 109 and could not freeze it. Pushed the purge button on the surface (during an ice dive) to let it free flow. I could see ice forming, but the moment I put my finger on front of the mouthpiece it stopped.


If you really want a freeze resistant regulator, try a double hose. Both the first and second stage are dry. There is no water to freeze.

Yes I had a DA Aquamaster for a time. I ordered all the new silicone rebuild parts from Bryan and tricked it out. I enjoyed it for several years but then wasn't using it much anymore so I sold it figuring someone else might be able to use it more that me.
I'm more into futhering the cause of modern minimalist diving.

 

[Couv]

Great post from the usual suspects; however I think my friend made a slight fingerfelder here. For clarity:

.......The unbalanced diaphragm second stages actually get better breathing performance as the air drops, so they are not really good indicators of low air.......

Shouldn't that be "unbalanced diaphragm first stage"?

As IP drops, the cracking pressure increases more in an unbalanced second stage one that is balanced.

Which is why

.....For your purpose, from what you are describing, I would recommend the Mk-2 with a 109 second stage......

is an excellent idea.

The unbalanced piston first will reduce the IP as tank pressure decreases, and the unbalanced second will increase in breathing resistance-which is what the OP is looking for aside from avoiding freeze flow.

 

[Luis H]

Originally Posted by Luis H
.......The unbalanced diaphragm second stages actually get better breathing performance as the air drops, so they are not really good indicators of low air.......

Shouldn't that be "unbalanced diaphragm first stage"?

Yes, I should have proof read that.


It should have read:
The unbalanced diaphragm first stages actually get better breathing performance as the air pressure in the tank drops, so they are not really good indicators of low air. With an unbalanced diaphrgm first stage, the IP actually increases as the tank pressure drops.

 

[eelnoraa]

Great information by Luis.

As to Eric, I have dove Mk25/Atomic B2 down to 46F. Both are not as freeze resistant as Mk2/109. So I think Mk2-109 should have no problem at 45F either. Most OW class conduct in Monterey seems to use Mk2 type of 1st stage (unbalanced flow-by). I think they it should be safe choice.

 

[Eric Sedletzky]

Great info!
So now I need to find a kit for my Mk2. I pulled it apart a while ago and there was one black plastic washer on the cap side of the spring that was smashed out, so I removed it. The IP now sits at 120 since that washer is gone. I'm not sure if that washer is included in a service kit or not.
If I remember right it was a cupped shaped washer that probably also kept the spring centered?....I'm guessing.
Maybe somebody who knows can tell me what's included in a service kit and if it comes with all the plastic washers, or just the HP seat and a few O-rings?.
If I take it to my dive shop it's going to be at least $50 for the first stage. I suppose I could throw them a bone since the A hole that used to own it is gone and I like everyone there now.
But you know how DIY people are, like Halocline says, we're all cheap and cranky and don't like anyone to touch our stuff.

 

[NotSure]

I believe the MK2 PLUS is slightly more cold tolerant than the MK2. The only difference is the T.I.S. spring and a better shim bushing. If you can find an MK2 PLUS upgrade kit it would have the shims you need plus the coated spring.

 

[Couv]

Great info!
So now I need to find a kit for my Mk2. I pulled it apart a while ago and there was one black plastic washer on the cap side of the spring that was smashed out, so I removed it. The IP now sits at 120 since that washer is gone. I'm not sure if that washer is included in a service kit or not.
If I remember right it was a cupped shaped washer that probably also kept the spring centered?....I'm guessing.
Maybe somebody who knows can tell me what's included in a service kit and if it comes with all the plastic washers, or just the HP seat and a few O-rings?.
If I take it to my dive shop it's going to be at least $50 for the first stage. I suppose I could throw them a bone since the A hole that used to own it is gone and I like everyone there now.
But you know how DIY people are, like Halocline says, we're all cheap and cranky and don't like anyone to touch our stuff.

The fact that the POS broke tells me to leave it out. Just use a regular spring shim in it's place if you want to raise the IP. The service kit does not contain new shims-as you guessed just a seat and o-rings. They can be purchased from Bryan for $9 at VDH Shop Online Recently Bryan has added IP spring shims to his inventory too Shop Online you may as well get a pack ($6 for 6 shims) see my review here:
http://www.scubaboard.com/forums/do...ro-piston-spring-shims-now-available-vdh.html

Stay cranky (and cheap) my friend.

Couv