Potential last ditch fix for a free flow?

[wetman]

Hey all. I was discussing this tonight with someone and wondered if its ever been tried or thought through:

In the event of a freeflow that you know will run you out of air before you get to somewhere safe, would bending the low pressure hose 180 degree do anything for you? even slow down the exhausing air or complete cutoff? i would think it would reck the hose for sure but i hardly want to try it as an experiment.

any thoughts?

steve

 

[mddolson]

You cannot bend and pinch the LP hose as you might a garden hose. The hose wall sections are just too thick, and prevent it.

The only technique I have found that works is,
1) shut the tank valve off and switch to your buddy's octopus, after a few 30 seconds turn the air back on see if it's ok.

or IF HE'S NOT WHERE HE'S SUPPOST TO BE( right there)

2) Throttle the valve to give you enough air to breath, but not a massive free-flow, start your ascent.

Mike D

 

[redacted]

How much of a problem is this for recreational divers? I dug out the technical specs for my Mk20/G500. It tells me the first stage delivers more than 8500 liters per minute at 200 bar and the second delivers 1800 liters per minute. (OOPS - guess where I bought them.) A trip to the old physics book lets me convert that to something more understandable to some of us: About 30 cu. ft / min. from the 1st and 6 from the second. The first isn't the issue with an uncontrolled freeflow so the problem is gas is disappearing at about 6 cu. ft. / minute which, assuming an Al80 equates to about 225 psi drop per minute. Unless you have some other problem also, this should get you to the surface at least as well as a spare air. Just had to add that!

Working that tank valve is a tech diver solution to such a problem but may well be unnecessarily complicated for a recreational diver. Unless you are double jointed, I would think you want that valve in front of you. Then you need to throttle pretty carefully to get gas when you need it and turn the flow down when you don't. Also making sure you don't blow the 2nd out of your mouth as you hold your tank and work the valve. Sounds like something you should practice if you plan to exercise such an option.

I think I'll give it a try next trip to the pool. I'll have to figure out a rig to force the freeflow. Maybe the old "seat saver" device.

 

[devilfish]

Why all the fanfare. It's simple, make an ascent breathing from a freefow regulator. Doesn't anyone teach this technique anymore? With 1000 psi in an al80 which is approximately 26 cuft of air/gas there is plenty of time to make a safe ascent and even a safety stop. The tank will not go empty that fast. Chances for a reg to start freeflowing on a low tank is very low, usually it happens on a full tank, or very cold water the first stage freezes up, or two divers sharing air sucking air fast through the same first stage.

 

[wetman]

But i'm talking specifically in a case where your air will run out before you can get to the surface or do a safety stop correctly.

This happened recently to someone i know. It started fairly deep in very cold water and was at about half a tank when it started. The freeflow stopped at the thermocline and had it not stopped there wouldnt have been enough air for a safety stop.

The title of this thing is "last ditch effort" so lets just pretend things haven't gone right to the point of being alone and thats your last option - i just want to know if thats feasible. I'm not interested in the merits of the buddy system or anything else that should have been done if everything was perfect.

steve

 

[MikeFerrara]

Don't do deep dives in cold water without...
Good cold water regs
redundant regulators on dual output valves
the training to use them.
An alert competant buddy

This is the only solution that I know of that is reliable. The situation you mention should never happen. You can only make so many mistakes on the same dive.

 

[ajarvis]

Surely air flow from a second stage also depends on your depth. Is that 6 cu ft/min rate at the surface?

A free flow at 33 ft should empty your tank twice as fast...

awap once bubbled...
About 30 cu. ft / min. from the 1st and 6 from the second. The first isn't the issue with an uncontrolled freeflow so the problem is gas is disappearing at about 6 cu. ft. / minute which, assuming an Al80 equates to about 225 psi drop per minute. Unless you have some other problem also, this should get you to the surface at least as well as a spare air. Just had to add that!

 

[Spectre]

ajarvis once bubbled...
Surely air flow from a second stage also depends on your depth. Is that 6 cu ft/min rate at the surface?

A free flow at 33 ft should empty your tank twice as fast...

I could be wrong... but I don't believe that is the case... When you fill your BC at depth it takes _way_ longer than on the surface.... [due to the fact that the air is pressurized to a point above the ambient pressure].

 

[redacted]

I believe ajarvis is correct.

A good regulator should continue to deliver about the same volume of gas at depth. So the 6 cu. ft. delivered by the 2nd at 30 ft. (2 atm) would expand to be 12 cu. ft. at the surface (1 atm).

But I see this as another reason to abort and head for the surface as soon as you realize the freeflow is not coming under control. The sooner you head up, the longer the gas will last at the rest stop.

 

[divernva]

Find your buddy, get air and THEN deal with the situation. Call the dive and start the ascent, or try to resolve the situation. Shut down the valve to conserve air. If the reg is malfunctioning, not frozen, try unscrewing the cover slightly to relieve pressure on the lever and allow the poppet to seat. If sand may be the suspect, press the purge and shake to dislodge particles (only press purge if reg is pressurized; valve on). Best idea is still to call the dive and live to dive another day.

The rule to dive with a buddy is not enough. Buddy and situational awareness is key to every dive no matter what level. It's definitely not stressed enough in OW classes... or any curriculum for that matter.