Scubapro s600 free-flow details

[davebe]

I’m a new OW diver and am considering the mk17/s600 for my first reg. I’ve seen numerous posts which view the s600 favorably, but comment on its tendency to free-flow in very cold temps. Before purchasing it, I just want to better understand what this means. My questions are:

1) Below what temp. is this an issue? (below 40 deg.?)
2) When it does free-flow, is it only at the surface, or also at depth? (If at the surface, I assume it’s filled with water and not simply due to having the mouthpiece facing up.)
3) Is it full blown free-flow, or low-level leakage?
4) Does it occur when in your mouth (if that’s possible), or when out-of-mouth?
5) How do you stop the free-flow when it occurs? (Cover the mouthpiece with your finger?)
6) If you use the knob to increase cracking pressure, will it reduce the tendency to free-flow?
7) Is it less likely to occur if I pair the s600 with the mk17 first stage, rather than with the mk25?

I know the g250hp is nearly identical, and less likely to have this problem, but happen to prefer the look and feel of the s600.

Thanks,
Dave

 

[OE2X]

I’m a new OW diver and am considering the mk17/s600 for my first reg. I’ve seen numerous posts which view the s600 favorably, but comment on its tendency to free-flow in very cold temps. Before purchasing it, I just want to better understand what this means. My questions are:

1) Below what temp. is this an issue? (below 40 deg.?)
2) When it does free-flow, is it only at the surface, or also at depth? (If at the surface, I assume it’s filled with water and not simply due to having the mouthpiece facing up.)
3) Is it full blown free-flow, or low-level leakage?
4) Does it occur when in your mouth (if that’s possible), or when out-of-mouth?
5) How do you stop the free-flow when it occurs? (Cover the mouthpiece with your finger?)
6) If you use the knob to increase cracking pressure, will it reduce the tendency to free-flow?
7) Is it less likely to occur if I pair the s600 with the mk17 first stage, rather than with the mk25?

I know the g250hp is nearly identical, and less likely to have this problem, but happen to prefer the look and feel of the s600.

Thanks,
Dave

Dave - I use a bunch of MK25/S600's and live and dive in the sound. I haven't had any problems with the six that I own. I've also used them when air temps have been in the teens and water temps in the low 40's without issue. If you are going to be ice diving - then this might be a consideration. For any diving you will do in WA or BC in the ocean - then you'll be fine...

 

[ocrmaster]

go with the Mk25/S600 it is the very best.

 

[strider]

The S600 has no issues that other regs don't already have, it is an excellent 2nd stage.

What I believe the "freeflow" is that you have heard about is probably the viva, vacuum initiated venturi assist, which means that when the airflow starts it assists in opening the reg up and literally feeding you air until you stop breathing. In class I'm sure you noticed that when students dropped regs in the water or first got in their 2nds would hiss and freeflow, but a quick finger in the mouthpiece would stop it. The S600 has a great venturi assist, really eases breathing and until you get used to it it may surprise someone. I've actually had people bring the reg back in to me and ask me to detune it because it breathes so easily that they're not used to it and this is definately an advantage.

As far as the MK17 vs. MK25, depends on what you want, they'll both deliver more air than you should ever need until you hit 200+ feet, my personal preference is the MK25, the MK17 is supposed to deliver more than enough air and if you are worried about freeze ups it is sealed and less prone to freezing, but that should only be a worry in ice diving. I've had my MK25 in 39 deg. water a lot with no problems.

 

[akscubainst]

I'm using my MK25/S600 in Alaska 32-36 degrees in the winter.and I've never had a problem. Ask your shop to pull the technical bulletins on the Mk25 S600 in cold water and tune it accordingly. You might also get rid of the black cover on the regulator end of the hose. It's been known to insulate the hose and cause problems.

Dave

 

[DA Aquamaster]

In my experience (diving below 100 ft in 35 degree water) the S600 is prone to forming ice crystals inside the air barrel that can cause a very slight freeflow that frankly many divers probably would not even notice if they are not anal about their breathing patterns and regulator performance.

When paired with the Mk 25 in very cold water (mid 40's or lower) this extra demand on the TIS system from the extra adibatic cooling can push the Mk 25 over the edge and cause a full blown freeflow. The problem is worse with higher pressure tanks and is often a non problem with low pressure tanks due to the reduced adibatic cooling that occurs.

Reducing the IP of the first stage helps as it reduces the potential gas flow and reduces the cooling that occurs between the first and second stage.

Pulling back hose protectors and trim boots to expose the nmetal portions of the first stage hose fittings and the second stage inlet fitting helps to transfer heat and reduces the potential for a problem as well.

If you are doing cold water diving, go with the Mk 17 as it is a superb fully sealed cold water reg and is currently the most freeze resistant first stage available from anyone at any price.

If you are not planning on cold water diving, get the Mk 17 anyway as it is in fact a better reg than the Mk 25 for most diving situations as it is easier to rinse, offers good hose routing options for doubles and singles, is lighter and more compact and delivers more than enough gas for any rec or tech situation. Plus it costs less.

 

[Hoosier]

1) Below what temp. is this an issue? (below 40 deg.?) Mostly....

2) When it does free-flow, is it only at the surface, or also at depth? (If at the surface, I assume it’s filled with water and not simply due to having the mouthpiece facing up.) Both

3) Is it full blown free-flow, or low-level leakage?
Full free flow

4) Does it occur when in your mouth (if that’s possible), or when out-of-mouth?
Both

5) How do you stop the free-flow when it occurs? (Cover the mouthpiece with your finger?) Shut off the valve and ascend

6) If you use the knob to increase cracking pressure, will it reduce the tendency to free-flow?

Slightly... 1st stage should be tuned also.

7) Is it less likely to occur if I pair the s600 with the mk17 first stage, rather than with the mk25?

MK17 is the new on the market, so we would like to get some reviews, too.

 

[alo100]

7) Is it less likely to occur if I pair the s600 with the mk17 first stage, rather than with the mk25?

Question number 7 is very interesting, I also want to know.
Both in Scubapro web-page and the US Navy gear list mentioned that Mk25 S600 is a combination for regular water temp. Although many good divers have used the setup for colder water.

The 1st stage can freeze and the 2nd can freeze, but few of us have asked this question about the Mk17 S600 combination....

 

[DA Aquamaster]

I have used the Mk 17 X650 ice diving this winter and it does extremely well.

I initially had issues with the occassional ice chip being spit at me, but removing the trim boot over the 2nd stage inlet fitting resolved the problem. Not that it was really a problem as the second stage never froze up.

I noted the X650 had the same tendency as the S600 to freeflow slightly in between breaths in very cold water unless the inhalation effort were increased a bit. But again with the Mk 17 even if you tolerate the slight dribble of air, you would not nee to worry about a first stage freeze up.

In fact I found I was able to get away with all sorts of cold water bad habits with the Mk 17 like using the reg above the surface (supercooling it) before diving, filling the wing and dry suit while inhaling, filling lift bags, etc - all actions that can potentially cause a Mk 25 to freeflow in very cold water.

I then got to see some SP test results where the Mk 17 tolerated high flow rates in 35 degree water at 165 ft until the end of the 200 minute test without freezing up.

 

[WarmWaterDiver]

Why was 165 feet chosen? The differential pressure between the first stage and the IP + ambient pressure would be greatest the closest to the surface, providing more adiabatic cooling at shallow depths from a differential pressure standpoint. The greater depth would result in a greater mass flow for equal actual volume. Was 165 feet found to be the 'worst case combination' by the testers?