Half Turned Valve

[BarryNL]

The time it takes to go from full on to off vs. half or whatever to off is insignificant when compared to pulling a boner and thinking you turned it off when you just opened it up more.(I call it the lefty-loosey, righty-tighty 'issue') lol.

This is actually an issue; I did see some tests recently which suggested that a ruptured LP hose can empty a (single) tank in under 30 seconds (does anyone know if this is correct).

If that's the case then the amount of time to shutdown the isolator value is very important - tec courses seem to expect you to do it within 30 seconds - or just after your tanks have emptied.

 

[do it easy]

I recall it was more like 90 sec for a cut LP hose and 22 MINUTES for a cut HP hose.

 

[Walter]

This is actually an issue; I did see some tests recently which suggested that a ruptured LP hose can empty a (single) tank in under 30 seconds (does anyone know if this is correct).

If that's the case then the amount of time to shutdown the isolator value is very important - tec courses seem to expect you to do it within 30 seconds - or just after your tanks have emptied.

Why would you shut down an isolator in that instance? Shutting down the valve will save all your air, shutting down the isolator will only save half.

 

[Thalassamania]

Don't know if a Cobra would repond as described. Please try it out and let us know.

 

[ianr33]

Why would you shut down an isolator in that instance? Shutting down the valve will save all your air, shutting down the isolator will only save half.

If the ruptured hose is behind my head and I dont know which hose it is then I would shut the isolator first.

 

[Rick Inman]

Funny, we were just talking about this.

I just got back from today's dive. At the beginning of the dive, in very shallow water, I unclipped my SPG to have a look at it and make sure the clip was above the stage clip where I like it, and as I pulled the hose forward, air started bubbling loudly behind my head. I assumed the blow was the cause-and-effect result of my tugging on the SPG hose, so I reached back and shut off my left post, which stopped the leaking.

I surfaced to inspect the situation, and it turned out that when I pulled forward my SPG, I unscrewed the hose from the first stage. I grabbed a wrench from my truck, tightened the hose back on (and double checked the others while I was at it) and continued the dive uneventfully.

The whole thing only cost me about 200psi (from dbl 95s).

 

[rigdiver]

I recall it was more like 90 sec for a cut LP hose and 22 MINUTES for a cut HP hose.

It also depends on the type of regulator. Some 1st stages deliver more than others. Either Deep Tech or Advanced Diver Magazine ran this test and published results. There is a very tiny hole that goes into the HP hose. This is why it would take more time to deplete a cylinder.

 

[TheRedHead]

Don't know if a Cobra would repond as described. Please try it out and let us know.

I tried with my tank at home (with 652 psi) and didn't see the drop and jump as you predicted would happen with an SPG. After 3 or 4 breaths, it read 641 psi. I'll get my tank filled and try it again.

 

[Scuba_Steve]

The thing I think Barry and Ian are both missing as far as the point I may not have made quite clear enough, which is, that I have seen far more ACTUAL issues with folks that love to dink with their knobs than with hoses mysteriously exploding...not saying it can't happen, but bubble checks will catch this stuff so darn early in so many cases.... The point being I have seen many actual cases of one, and none of the other. I call that unwarranted and ungrounded fears actually causing poorly conceived ideas and protocols.

And of course with the buddy system that we ALL EMPLOY (everyone nodding here....) we're never without a pair of perfectly positioned eyes to see EXACTLY what is going wrong and of course how to fix it, not to mention yor buddy is carrying all your spare gas so the thought of going completely 'gasless', which isn't going to happen when all the bases are covered as above, becomes a rather moot point.

There's no doubt you can shut a valve down that is 3/4 shut vs. a fully opened one faster, with the problem being as mentioned that's the time you pull a boner and your mind goes AWOL and then the extra fiddling occurs which only serves to waste more time. The single 'problem' you're trying to fix is not the bigger problems you're now introducing. THAT happens fairly regularly as seen here even on scubaboard reports.

Keep ehm all the way open and you're golden with the mind-fudges, bad fills etc. You don't have a gas problem, period.

regards

P.S Barry, try it for yourself under controlled circumstances. See if you can shut down an offending post in time. You'll find you probably can. I agree with "Do it easy", I have seen numbers similar to his. The big issues are ruptured LP hoses, so let your reg F/F and see.

Question.....anybody ever see an LP hose rupture in the water without a pile of advanced noticed, spread over dozen of dives or just shear lack of looking for problems before hand (including bubble checks etc)?

thanks

 

[KMD]

If a valve is off and you go to take a breath you may get part of one and that's it. So you know the problem.

When you open your valve and then the DM closes it and backs it off a half turn the only way you'll know there's a problem is to take a breath while you look at your SPG (until you get air-starved at depth). There have been any number of accidents involving this problem.

Just as a side note, if one is diving doubles, checking the SPG is only of limited use. Breathing off the primary will not cause your SPG to move no matter what the state of your right post valve is.


Here a question for Redhead: After your buddy fixed the problem, did you do a flow check of all your valves?