in-line shut off valves

[HeatCker]

do many/any of you cold water divers have in-line shut off valves installed on their primary reg to help deal with free flows.
what are the pros / cons of having an inline shut off valve installed.
thanks

 

[rhwestfall]

cons: increase in failure points, extra maintenance item, should then have an OPV on the first stage (repeat of points prior are expanded to this item).

pros: another mitigation method.

I'm on the fence as to the usefulness of these. Curious as to what others will say. I dive cold water exclusively, and incorporate strategies including h-valves on singles, independent reserves, & doubles with isolation.

Perhaps another tool in the toolbox.....

 

[tbone1004]

most freeflow issues stem from the first stages not the second stages in my experience, in that case an inline shutoff would only cause the other second stage to start freeflowing or require an OPV to keep it from blowing a hose if both had them. Best to just have a good cold water setup if you're going to be doing those types of dives regularly and make sure you aren't breathing them at the surface especially while in the water.

 

[Subcooled]

It is safer and easier to switch to the alternate breathing apparatus and shut down the leaking one by turning the cylinder valve shut. Using two cylinders (even small ones) and two first stages and two second stages is recommended.

If you have an inline shutoff valve then it could be triggered inadvertently and possibly cause you some extra excitement at depth. Especially if you have big gloves and clumsy hands. An overpressure relief valve would also be needed as stated in the previous post. You do not want a burst hose in case the free flow comes from the first stage.

Feathering the valves is also a lovely method if your kit and your flexibility allow for that.

If the free flow is caused by an ice crystal in the second stage (which is possible due to the moisture in exhaled air - especially if water is near freezing or the surface temperature is extremely cold), then it might even melt after a while and become usable (this has actually happened to me).

My experience is different from that of Tbones, but perhaps we dive in different environtments, with dissimilar gear/gas stations, different type of diving, different type of luck, don't know. Anyway he made a very good point. But in my experience: Almost all the free flows I have seen have been caused by second stage freezing due to moisture build up from exhalations. Very rarely have I seen a first stage free flow, but then again we keep our own cylinders very very dry and take great care in maintaining our compressors. When there is no moisture in the cylinder, then there is nothing that can freeze inside a diaphragm first stage. With rental gear and someone elses compressor (etc etc etc) you don't have this control and risks increase. So sometimes it is out of your control. Could me many more reasons.

 

[tbone1004]

subcooled, my cold water diving has always been with second stages with lots of metal in them if we are diving below say 35F, or with Poseidons if possible so it is pretty much a nonissue, but most of the freeflows I've seen happen with a diver is at the surface and the first stages are wet from being in the water and they either do a cold water treatment, test breathe regulators prior to descending, or use power inflation for either drysuit or wing and that causes the moisture on the first stages to freeze solid and it's bad news bears. Nothing to do with the air inside of them having moisture, literally just them being wet by divers sitting at the surface and using some sort of LP device. Have yet to see anything freeze under water, but that is just my experience.

 

[HeatCker]

thanks guys
i believe both my free flows were caused by second stage issues, one at 20'/39 F, one at 70'/43 F
one flow was major (20') and when i got to the surface the 1st stage froze while shutting off the valve
scubapro regs s555 / mk17

 

[kwinter]

I also think there are plenty of free flows caused by second stage problems, not just first stage. So if you want to have access to anything else coming off that first stage (wing or drysuit inflateion, etc) then using a flow stop is a good idea. Just make sure you stick an OPV in the first stage. Otherwise just shut down that post. rhwestfall did a good job of listing the pros and cons.

 

[rhwestfall]

thanks guys
i believe both my free flows were caused by second stage issues, one at 20'/39 F, one at 70'/43 F
one flow was major (20') and when i got to the surface the 1st stage froze while shutting off the valve
scubapro regs s555 / mk17

S555 is plastic air-barreled. Its a good reg, but not ideal for the cold water..... Upgrade it to a S600 and life is "much better" in cold water. Beaver Divers did mine. Worth every penny.....


(I'm still on the fence of the plastic orifice is "better" (so they claim) than the stainless ones of days past....)

 

[lowviz]

...//... when i got to the surface the 1st stage froze while shutting off the valve
scubapro regs s555 / mk17

Froze as in a casing of ice formed around it or froze and in a first stage free-flow?

That reg will work just fine encased in ice, but loses its heat transfer capabilities with the water. You can get away with it if your air is dry and you were diligent about keeping water out of the primary while it was off the tank.

I don't like inline shutoffs, unnecessary complication. I find myself "reacting as I've practiced" more than "contemplative thinking" when things get rough.

 

[HeatCker]

rhwestfall
what is involved to upgrade the s555 to an s600
my reg isn't due for service until the fall but next time i'm in the shop i'll ask if its something that they can do
thanks for the tip


lowvis
sorry, i'll clarify .. Frozen as in a casing of ice formed around it


thanks guys