How cold is too cold for piston regs

[Eric Sedletzky]

I've always heard to rule never dive a piston reg in cold water because they might freeze up and freeflow. I used my SP MK20 in 42 degree water once and it worked fine. So my question is, what is too cold for pistons, assuming all piston regs are not created equal.
Just out of curiosity, how cold of water can a simple unbalanced unsealed reg like a Scubapro MK2 be used without it freaking out?
What exactly happens when a reg freezes up - what is the technical reason piston regs are susceptible to freeze up more than diaphrams?

 

[tbone1004]

no temp is too cold for them, they will function down to freezing. The issue is how much you are using them. As regulators work, they get cold due to the drastic pressure reduction. It instantly goes from working pressure to IP, which is not a lot, so it gets super super cold. If you breathe on them too much/fast, they don't have time to equalize back to the water temperature so ice starts to build because the regulator is now well below freezing. This actually regularly happens at the surface if your valves get wet and you have them above water. In my experience this is more common than at depth at least on the first stage. If you're not using them at the surface, and you're a slow breather and not going crazy inflating your bc and what not, they will function quite well down into the 30's.

The balancing mechanism of all first stages requires ambient pressure to be put on the back side to allow it to compensate for depth. This is important because your 2nd stage need a certain amount of IP to breathe well and IP has to be depth compensating. With a piston design, this very difficult to seal water out *can't have ice inside the reg if there is no water inside the reg*. The way they are sealed is by packing the piston chamber with grease and that way the water pushes on the grease. It is nasty and expensive at service time but it works just fine. On your mK2 this is the end cap where the holes are. On a MK25 it is the holes that go around in a circle between the HP and LP ports.

With a diaphragm regulator, they can have a piece that looks like a bar table without legs that reaches through the IP spring and presses on the diaphragm itself. This is pressed on by a piece of silicone on the environmental seal and is depth compensating that way. This is on the "top" of the regulators and is called the environmental seal. On Apeks regs its the black bit with the Apeks logo on it, on the Hog d3 its the black bit with the red hog logo.The other nice feature this does is keep all water outside of the regulators so during rinsing you don't have to be as thorough as with an unsealed piston due for salt buildup, or any particulate in the water.

 

[Eric Sedletzky]

So would standard MK2/R190 be fine in 45 degree water?

 

[tbone1004]

underwater, the R190 might have more issues than the mk2, but at 45 it shouldn't be an issue. The 2nd stage at that temp would be my bigger concern. Be slow and deliberate with your breathing and it shouldn't be an issue

 

[Eric Sedletzky]

underwater, the R190 might have more issues than the mk2, but at 45 it shouldn't be an issue. The 2nd stage at that temp would be my bigger concern. Be slow and deliberate with your breathing and it shouldn't be an issue

I have a few metal 109's and a metal balanced adjustable (156), would those be better than the R190?
I wanted both units unbalanced for certain reasons, that's why I'm asking about MK2/R190 and or replacing the R190 with a standard poppet 109, since that being all metal maybe it would somehow be better in cold water?

 

[tbone1004]

all metal is certainly better than plastic.... Why all unbalanced?

 

[halocline]

Just out of curiosity, how cold of water can a simple unbalanced unsealed reg like a Scubapro MK2 be used without it freaking out?
What exactly happens when a reg freezes up - what is the technical reason piston regs are susceptible to freeze up more than diaphrams?

What makes 1st stages freeze is the cooling of the metal parts that come into contact with water. This cooling is adiabatic cooling, caused by the rapid expansion of compressed air. It's the same principle that makes A/C work.

The reason some piston regs are more susceptible to freezing than diaphragm regs is that the metal parts that get cooled the most by contact with expanding air (primarily the piston) are in closer contact with water than those parts in diaphragm regs.

The MK2 is a different animal than the MK20 et al in terms of freezing. With the MK20, the piston edge is the site of the air expansion as depressurizing air rushes around the piston edge and into the shaft, and there is very little mass to the metal, or any other metal in contact to act as a heat sink. So the piston cools very quickly, and the shaft is in contact with water in the ambient chamber.

In the MK2, cooling air rushes past the orifice and around the teflon seat before coming into contact with the piston shaft, then travels through a small hole in the side of the piston before traveling up through the shaft into the IP chamber. The entire piston is in either ambient or IP, whereas in the balanced piston design the piston edge is in supply pressure. This means that the MK2 piston itself is not subjected to rapid changing (lowering) air pressure as efficiently as the MK20, and in the MK2, there's a big orifice machined into the reg body that acts as a heat sink, while the teflon seat essentially insulates the piston from direct contact with the expanding air.

I don't know at what temp various piston regs will freeze, but it definitely depends partially on the cold water technique of the diver. Thousands of very cold water dives have been successfully made with MK25s, considered to be among the most freeze-prone regulators.

---------- Post added July 12th, 2015 at 05:56 AM ----------

I have a few metal 109's and a metal balanced adjustable (156), would those be better than the R190?
I wanted both units unbalanced for certain reasons, that's why I'm asking about MK2/R190 and or replacing the R190 with a standard poppet 109, since that being all metal maybe it would somehow be better in cold water?

The 109 is a better cold water 2nd stage because it is all metal, and metal is much more efficient at transferring heat from the water, and from your exhaled warm air, essentially keeping ice from forming on the valve parts. A MK2/109 would be a good choice for cold water diving.

 

[tbone1004]

halocline, those mk25's have all been sealed which changes things dramatically. Once they're sealed they're all in the same boat.... They also can't touch the Poseidon MK3 for freeze-resistance, but that's irrelevant.

 

[Eric Sedletzky]

all metal is certainly better than plastic.... Why all unbalanced?

I want the slow draw down and gradual increase in resistance for some minimalist stuff I'm doing. For some of my less aggressive diving (excercises in discipline) I'm leaving the SPG behind and using depth and time combined with starting pressure and SAC rate to calculate the dive and gas supply. I have a J valve on a couple tanks so with an unbalanced reg set it's another heads up system when air is getting low.
The problem is I dive in cold water so all my diaphragm regs are balanced like my conshelfs, Hog, other Aqualungs. And my SP MK20 and MK5 are balanced and big so they wouldn't be ideal. My MK2 seems perfect because it's small, light weight and unbalanced, and bullet proof. If there was a small button unbalanced diaphragm that would be great but there isn't. My old 1967 Conshelf XI is small but I believe it's balanced. Halocline may know.

 

[Luis H]

The big difference in cold weather (cold water) 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 sealed environmental chamber (using grease, oil, antifreeze, vodka, 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.