Cold Water 2nd Stages

[TN-Steve]

tbone, thanks. For you it was early, and I posted that late last night, so I may not have been as clear as I thought I was. Your explanation makes 100% sense and I'm tracking on it now.

I know that at the local quarry it's 44* around 65 foot even in the middle of summer, and we've had problems with students in particular going into freeflow with one one particular regulator model. That makes sense, student diver, first time hitting cold water, plus it's getting a bit dark down there, add in the fact that they are deeper than they have been before.... Resp. rate goes WAY up.... All the conditions are met.

Thanks for your time, I have an engineering bend to me, and like to understand the "WHY" and "HOW" on things.

Have a great week,

Steve

Steve, it's still early and I've had a long couple of weeks with work so I didn't follow you completely, but hopefully this helps

The 1st and 2nd stages are both capable of delivering much more air than any 2 people could need. Lowering the IP does have some merit for lowering the temperature drop, but the lower flowrates and slightly higher cracking pressure help to prevent freeflows which from what I've heard is the big push for that change. The cracking pressure can then be adjusted back with adjustable second stages. Poseidon solved this on the Jetstream with the Dive/Pre-Dive switch and when it is in predive it is all but impossible to freeflow.

Regarding the flowrates, the flowrate is determined by your breathing rate essentially because the demand valve is never open all the way. Take big huge fast deep breaths and it will open farther and flow more, this is a double edged sword though because you need it to be fast enough to the point that there is enough time for it to stay closed and warm back up to ambient.


FWIW this is pretty much only an issue in true ice diving scenarios, people blow "cold water" way out of proportion and unless you are diving in sub 40F water or diving in sub50F water with below freezing air temperatures, this is mostly a nonissue.

 

[ams511]

If I can find the article on cold water regulators I will try to post it or link it. One thing that I thought was interesting was that the Sherwood Maximus could be used as a cold water regulator by adding the brass (copper?) fins from the Blizzard that transfer the heat from the diver's exhalation to the valve. The Maximus is a downstream design (not a barrel poppet) and has a plastic case. I watched a special on Antarctic diving and that is what they used.

 

[rhwestfall]

When 6 of 10 divers on the boat in Tobermory have FF issues in 42 degree water, it is not "blown out of proportion".....

There is gear I would never dive in waters below 60 degrees......

FWIW - I'll take a SP MK-5/MK-10 and a 109/156 over a MK-20/25 coupled with most modern seconds. I dove those for years My regs are MK-17 w/ 156/g250v/s600 or, a recently acquired HOG D1 (cold) and classic/zenith seconds....

 

[halocline]

I'm not quite sure I'm tracking on the lower flow part of your answer, help me out. Regardless of the IP I'm going to be breathing the same volume of gas in a given time frame.
Steve

You're absolutely correct, but if you were to purge or in any way stop controlling the flow for a few seconds, the higher IP would speed up the flow, and as such, the adiabatic cooling effect. I believe that is where the lowered IP can be helpful in very cold water. It's mostly an old-school practice.

 

[TN-Steve]

Ah, so it's to some degree a supplementary measure, in conjunction with all the other items that we've discussed here or were in the article. Makes perfect sense to me.

I may have to take a spare tank to the quarry and experiment with that a bit with some different reg sets.... I best let the rest of the folks know first however, before that stream of bubbles comes up from 90 foot.

Steve

You're absolutely correct, but if you were to purge or in any way stop controlling the flow for a few seconds, the higher IP would speed up the flow, and as such, the adiabatic cooling effect. I believe that is where the lowered IP can be helpful in very cold water. It's mostly an old-school practice.

 

[USdiver1]

This is an important thread, using the wrong regulator in cold water conditions is just asking for Murphy's intervention. IMO an environmentally sealed first stage is the most important line of defense against FF, more than any particular second. That said, I tend to go with old metal standbys such as Conshelf XII and XIV models, Mares' Abyss Navy, and (as a vintage equipment diver) a good double hose to eliminate all possibility of FF.

 

[ams511]

This is an important thread, using the wrong regulator in cold water conditions is just asking for Murphy's intervention. IMO an environmentally sealed first stage is the most important line of defense against FF, more than any particular second. That said, I tend to go with old metal standbys such as Conshelf XII and XIV models, Mares' Abyss Navy, and (as a vintage equipment diver) a good double hose to eliminate all possibility of FF.

Here is a link on an old (1991) conference on polar diving. Actually their results suggest that double hoses are more prone to free flow than a good single hose. They liked Poseidons. They did qualify their findings by saying that result could be because the double hoses were 20 years old while the single hoses were brand new.

---------- Post added May 5th, 2015 at 02:58 PM ----------

If I can find the article on cold water regulators I will try to post it or link it. One thing that I thought was interesting was that the Sherwood Maximus could be used as a cold water regulator by adding the brass (copper?) fins from the Blizzard that transfer the heat from the diver's exhalation to the valve. The Maximus is a downstream design (not a barrel poppet) and has a plastic case. I watched a special on Antarctic diving and that is what they used.

Link: http://www.si.edu/dive/pdfs/proceedings_ipdw.pdf