Potential last ditch fix for a free flow?

[wetman]

I supposed i could have worded this another way so here goes:

Has anyone ever bent a hose and been able to cut off the air or severely restrict the air flow by doing so. What this has to do with buddy diving i have no idea. I've had one answer that actually deals with the gist of the question (i.e. says it cant be done), a few that deal with air flow (which certainly stems from the issue) and many orations on why buddy diving or proper procedure is the cure. I don't care about proper procedure for the time being. Let me pose a scenario that might just put this in the right light: If i was down there and my buddy was being attacked by a great white and my backup hose was cut completely by my 20 inch diving sword as i happened to be attacking a school of sharks so my buddy can deal with the great white by itself and we're 150 feet down with aluminum 80s in an overhead environment and my feet get caught in a fishing net: do you think i could prolong this enjoyable dive by bending the hose of the 2nd stage that got sliced off?


steve

 

[Cave Diver]

wetman once bubbled...
Let me pose a scenario that might just put this in the right light: If i was down there and my buddy was being attacked by a great white and my backup hose was cut completely by my 20 inch diving sword as i happened to be attacking a school of sharks so my buddy can deal with the great white by itself and we're 150 feet down with aluminum 80s in an overhead environment and my feet get caught in a fishing net: do you think i could prolong this enjoyable dive by bending the hose of the 2nd stage that got sliced off?

The proper thing to to in this situation would be to tuck your head between your legs and kiss your posterior goodbye.

However, since that does not address the hose issue for you I decided to test it for myself. After hooking up my regs to my LP112's that were just filled to 2700 psi, I turned the air on and depressed the purge button on my octo. While holding the purge button, I kinked the hose and was able to substantially reduce the flow of air, but I was unable to completely shut it off. Perhaps if I was not having to hold the purge button with one hand I would have been able to kink the hose better.

And BTW, the hose returned to original shape with no problem and no damage done. Rubber is very pliable and hard to damage permanently unless subjected to extreme temperature.

Hope this helps.

 

[mddolson]

Cave Diver bubbled: "I kinked the hose and was able to substantially reduce the flow of air, but I was unable to completely shut it off. "

At room temperature the intermediate pressure pressure will be around 140 psi. In cold water, (about 38-40°F) which is where Wetman experienced his freeflow in the first place, ( without a silicone oil barrier) Ice crystals form the 1st stage of the regulator and can ramp up the IP to 175-200 psi.

It would be interesting to repeat the test under these conditions.

Mike

 

[Rick Murchison]

wetman once bubbled...
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.

Two points here.
(1) If you cannot make a controlled emergency swimming ascent from where you are, you've no business being there without real redundancy of your gas supply. That real redundancy may be as simple as getting together with your buddy and making sure you're within easy reach of each other, or it may be two first stages with a way to isolate either. (Doubles with isolation manifold, single with "H" or "Y" valve, or bailout bottle). The buddy option is the least desirable because it requires two of you actually plan and execute the dive with coordination and attention - something that often fades at the depths where most needed.
Bottom line - don't dive below your personal CESA limit without a redundant air supply.
(2) A safety stop is just that - for added safety. It is by no means a "required" stop. I'd been diving twenty years before I made my first "safety stop." Not because they (safety stops) aren't a great idea - they are, and they reduce the number of "silent bubbles" dramatically - just because they didn't exist as part of recreational diving when I started, and I didn't get back into the training loop for twenty years to find out about 'em. Bottom line - skipping a safety stop in an emergency is no big deal.
--------------------------------
As for making an ascent on a freeflowing regulator, you can, but ouch! Frozen teeth isn't my idea of fun. Use the octopus and let the other one go.
Rick

 

[Rick Murchison]

wetman once bubbled...
Has anyone ever bent a hose and been able to cut off the air or severely restrict the air flow by doing so.

I do not recommend this as an option. Most freeflows are first stage and not second stage problems. The freeflow is the preplanned response to elevated pressure in the IP hose. As has already been mentioned, the first stage can supply gas to the second stage at a much higher rate than the second stage can release it - when you have a freeflow, you already have a precarious IP hose pressure, and crimping it can (1) further exacerbate the problem by raising the pressure even more, and (2) weaken the IP hose. Either of these can easily procede to a ruptured IP hose and a vastly accelerated gas loss rate.
Cave Diver's experiment was conducted with a correctly operating first stage, so he's dealing with only about 150psi IP - with a real freeflow you can be dealing with substantially higher pressures, and crimping the hose could cause the pressure to build to as high as tank pressure - BANG!
Bottom line - crimping the IP hose in an attempt to reduce freeflow could very well take you from the frying pan to the fire. At the very least you'd start a freeflow on the octopus as well.
Rick

 

[Scubaroo]

Apeks make a freeflow control device - which is a little valve that goes on the end of your hose between the hose and second stage - it lets you "turn off" that hose if you experience a free flow.

It's something I'll never be installing personally.

 

[wetman]

I saw that device on the web a while ago. Why wouldn't you wan't to use it? It would seem like a simple enough device (no clue what would be inside though).

steve

 

[Scubaroo]

It's just something else to get sand in and ruin a dive. I do a lot of shore diving - the stuff gets everywhere. And if the one on your backup/octopus is turned off, most people I see diving don't bother to check their backup/octopus to see if you can actually breath off it during a dive - once they get underwater they just start diving without checking to see their "other" reg works. They're going to find out it's turned off when they most need it - either they're going to breath off a backup that's turned off, or hand off an octopus to a buddy in dire need of air, which doesn't give them any. Instead of being a freeflow control device, it becomes a panicked diver creation device. Solves one problem, creates another. It would be a perfectly acceptable solution to the problem except it's not without it's own new set of problems - it can cut off the air to a perfectly working regulator. And no-one can say with absolute conviction that they will remember to check it prior to each and every dive - I've had instructors jump in off the boat who have had to get me to turn on their tank valve because it was turned off. These people are diving "professionals" who do this every week. Most divers simply aren't attentive enough for such a device NOT to create problems. If I'm forgetful enough to try a beach entry without deflating my BC, even though I know that it's the wrong way, if I'm forgetful enough to not set my compass before submerging, because I was too eager to start diving, if I'm forgetful enough to not add extra weight while diving a rental LP 80 instead of my own LP 95, because I always use 10 pounds, I know I'm going to forget to check that freeflow control doohickey one day. And you can bet Mr Murphy will be there waiting to remind me.

(That's not to say I'm an absentminded forgetful diver! Some days things just don't go smooth).

As discussed in this thread there's already acceptable ways to deal with a freeflow - you abort the dive, either breathing off the freeflowing reg, your buddy's donated regulator, or a controlled emergency ascent. But regardless, you abort the dive. Adding another piece of equipment isn't always the best way to deal with the situation.

Anyway, that's my take on the situation.