SP Freezing

[redacted]

I expressed the same concern when it was described to me but the distance is extremely small, one mm or less. Just enough to keep it from touching the top of the cylinder if you will. I will try to find a schematic....

--Matt

I don't think it is so much that it is preventing metal to metal contact as much as that it limits the maximum airflow and thus the cooling effect. Actually I think it is a bit of a shade tree mechanic 5 cent solution to a rather costly problem if it works. It's just too bad they couldn't figure out how to make the duct tape work. I would guess that the total possible movement there is maybe a little more than 1/4 inch. So a 1/16 inch o-ring which will compress a bit should still leave plenty of air flow.

 

[Scuba_Steve]

HuH???

Reading along.......I get to the part where we're "adding" and O-ring tothe piston (or area).

So I'm thinking, it's either the "face" or the "stem" area.

I guess it's the "face" area. So it's being added to the LP side of the piston, in the bottom of the bore.....meaning the far end, by the LP ports?

And it just "stays" there all by itself?

I'm sure it would actually, but I'd personally like to see (If this infact is where it is) some sort of "positive" locating force from somewhere (Groove or otherwise). I just don't like the band-aid fix that this sounds like.

I must say, as much as I agree with the cold-water ability of the diaphram regs over the piston ones, I've never had a problem with my S/P MK25/G250HP's in mid-30's water, ever.

I don't wind mine up to "the notch before they F/Flow" either. That's just dumb, but I can't tell you how many regs I see set up this way. It's just asking for a problem.

 

[Compressor]

HuH???

Reading along.......I get to the part where we're "adding" and O-ring tothe piston (or area).

So I'm thinking, it's either the "face" or the "stem" area.

I guess it's the "face" area. So it's being added to the LP side of the piston, in the bottom of the bore.....meaning the far end, by the LP ports?

And it just "stays" there all by itself?

I'm sure it would actually, but I'd personally like to see (If this infact is where it is) some sort of "positive" locating force from somewhere (Groove or otherwise). I just don't like the band-aid fix that this sounds like.

I must say, as much as I agree with the cold-water ability of the diaphram regs over the piston ones, I've never had a problem with my S/P MK25/G250HP's in mid-30's water, ever.

I don't wind mine up to "the notch before they F/Flow" either. That's just dumb, but I can't tell you how many regs I see set up this way. It's just asking for a problem.

Well I am glad we got this thread back on track.
When I teach my advance courses, I take the students down to 100-130 feet. The water is very cold as the lake is spring fed.

I rather use a different regulator now that I have found both piston and diaghram regulators will free flow rather than detune my own SPs. Any of our European friends here who dive in the cold fjords of Norway orin the very chilly North Sea? I wonder if the SP regs there have the same problem? and I also wonder what our friends use there for regulators.


Also I think I am going to call SP and see what they might say about this? One can't dive like this? what would happen if you had to do a deco and you did not have enough gas?

 

[Scuba_Steve]

I know of a few folks around here that seem to be constantly crying about their S600 F/Flowing on thier deco bottles. I will resist the urge to think that they're just trying to sell the new Atomics over the S/P's they sold last year ;-).......That being said, since all the other variables are the same (Same nice dry breathing gas, good SAC rates etc) the only thing left is the set-up of the regs.

I ask again, why would anyone set them up so touchy? I think it's the root of the cause. Detuning a bit won't matter one bit. Shoot, these regs could give enough gas at depth for 3-4 people! C'mon!

As for this question..... "what would happen if you had to do a deco and you did not have enough gas?"

This problem would originate with the diver, and not the regs.

 

[DA Aquamaster]

I dove MK 25 D400's all last season and never had a freeflow. Bottom temps ranged from the upper 30's to mid 40's with a few ice dives in the 32-34 degree range.

Using low pressure tanks reduces the adibatic cooling load on the reg and in my opinion is, along with proper cold water technique, adequate to prevent a freeflow - at least with D400 or G250 second stage. In my experience the S600 is prone to developing a slight freeflow in the second stage in very cold water.

But despite 130 dives with no concerns, I have to admit that based on the Mk 25's less than perfect cold water reputation, the freeflow the gas you need for deco issue was always in the back of my mind given that I do a lot of deco diving, much of it solo. However that eventuality is easily addressed with independent doubles, isolator manifolded doubles or a adequately sized deco bottle with a suitable nitrox mix. Properly done, any of the three can insure adequate gas to finish the dive. Deco diving is not something that you should be doing unless you are diving doubles with redundant regs anyway.

For this year, however I went back to using a pair of Mk 20's with the larger late production spec boot. You can pack the ambient chamber with O2 compatible lubes if required but for backgas it usually is not as you are normally not going to use anything hotter than nitrox 36. And properly packed and maintained it is virtually impossible to freeze a SPEC equipped piston reg.

I like the idea of adding a piston head o-ring, or perhaps an even thinner o-ring of the same diameter, on top of the piston head in the compression chamber. The o-ring would be the same diameter as the walls of the compression chamber so it would be a snug fit and really has no where to go. It would reduce the working range and consequently the flow rate and adibatic cooling load on the TIS system so it should make the reg much more reliable in cold water.

But the questions are:

1) How much does it reduce the working range and flow rate.

2) How much does the reduced flow rate affect the stability of the IP during breathing, particularly at depth.

3) How well does the added o-ring wear over time acting as a stop for the piston.

I'd want to known the answers to all three questions before I took a Mk 20 or 25 modified in that manner on a deep dive.

 

[Scuba_Steve]

What's more, does the piston EVER bottom out in the bore in the first place? (While pressurized of course).

I'll almost bet that it NEVER does, as it doesn't take "Full open" to F/Flow a 1st stage, so odds a VERY GOOD that the piston "freezes" mid-travel, so the O-ring at the bottom is irrelevant.

As for 1, 2 and 3...........Minimal, Minimal, Irrelevant (As the way I see it, it's a useless fix).

 

[Compressor]

The last 2 posts have been most informative. Thank you.
I am still wondering what to do.

 

[Compressor]

I also called SP today directly. They stated that the regulatgor 1st and 2nd stage have to be detuned; ie: be made harder to breath!!

Now I am real disappointed. Perhaps time to get another cold water regulator or maybe there is no regulator that will perform well but will not freeze in deep cold water.

I would appreciate more insights please.

 

[DA Aquamaster]

What's more, does the piston EVER bottom out in the bore in the first place? (While pressurized of course).

I'll almost bet that it NEVER does, as it doesn't take "Full open" to F/Flow a 1st stage, so odds a VERY GOOD that the piston "freezes" mid-travel, so the O-ring at the bottom is irrelevant.

I'll take your bet (and your money). Just curious, but have you ever had a Mk 20 or Mk 25 first stage apart or tested one on the bench?

You are correct to a point in that with small air flows and small demands, the piston will not have to travel far before the valve is open enough to pass sufficient air to maintain the IP so total piston travel in that cycle will be slight. \

However under high demand situations where a large volume of air is required the piston will fully open in an effort to maintain the IP. The piston is at its full extent anytime there is a measurable and sustained drop in IP in an effort to try to balance the system. This can be demonstrated on the bench by fully depressing the purge button on the second stage. I have yet to see any first stage that will maintain a rock solid IP under those circumstances. The IP drop is relatively small on the Mk 20/25, but it there none the less indicating the piston is fully open.

If you install an extra o-ring on top of the piston you are limiting the maximum working range and flow rate that can be achieved and are also limiting the cooling that will occur over a given period of time. This will reduce the odds of exceeding the heat transfer capability of the first stage TIS kit just the same as you achieve by detuning the reg. But the potential advantage that I see is that you could possibly do so without compromising the cracking effort of the second stage.

Wear on the extra o-ring isn't irrellevant either even if the piston never bottomed out in operation. You have to consider that the mainpsring will be pressing the piston head against the o-ring/top of the compression chamber anytime there is no air pressure present in the first stage (the other 160 or so hours per week when most people are not diving.) I would expect after a year that that o-ring would be looking a little squished. With the extra o-ring installed, the mainspring will also be carrying a load at "rest" that is in excess of what it normally carries, so you probably also need to consider the long term effects this may have on longevity for the spring.

 

[scuba_volker]

@ compressor

that a realy old scubapro problem. i've had a scubapro mk25 /g250 regulator, but for diving in cold water it was dangerous. i am from germany and there you've got realy cold water about 37 degree. some guys are using scubapro, but no one is happy with it. most of the divers i know are using mares or apeks regluators, like the apeks atx 100 and they've never got any problems.