Lessons My sidemount cylinder valve spun itself completely shut during a dive

[rick00001967]

But the point is they were (maybe) NOT trying to shut off your tanks, but rather to make sure they were open. Turn it the wrong way, then back a "quarter turn." Which turns it off, then back on just a quarter turn. Note it was your right tank with the "backwards valve;" easy to make that mistake.

i hate to have to agree with tursiops but if you are 100% sure you opened both valves before the start of the dive, then my money is on this.

 

[NW Dive Dawg]

The simplest explanation is that the tank was barely open, so a small nudge closed it.
Your theory is plasuble, but not as simple or likely.

I agree that this is the most likely explanation.....and one reason why I personally think the "old school" rule of "turning your tank valve all the way on and then back a 1/4 turn was a stupidly "bad rule"....and glad that for the most part is no longer taught. I want to know that my tank is either all the way on or all the way off.

 

[jstotz]

For reasons unknown to me, some people don't think in terms of "CCW = open". They think "top of the valve away = open": this works great for a standard valve in a tank rack, which becomes ingrained over thousands of repetitions. Unfortunately, it also closes a non-standard valve.

Right! I was confused by the initial suggestion because I am apparently am a CW/CCW thinker, and therefore never consciously noticed a difference in closing the left-hand vs right hand valve. But this is a totally plausible theory.

 

[BRT]

I agree that this is the most likely explanation.....and one reason why I personally think the "old school" rule of "turning your tank valve all the way on and then back a 1/4 turn was a stupidly "bad rule"....and glad that for the most part is no longer taught. I want to know that my tank is either all the way on or all the way off.

I've been diving 40 years and was taught the 1/4 turn rule. I did not believe it and have always turned my tanks on all the way. For some reason several times in Mexico we have ended up with tank valves stuck in the open position after a dive. I am trying to remember to turn them back a quarter now.

 

[USdiver1]

The old addage, "lefty loosey / righty tighty" adds to the CCW/CW thinker mindset. Agree with starting off your interrogaton with the soft approach with your friends, "Did you, by chance, check if my valve was open?" - just keep open the enhanced interrogation [waterboarding] option.

 

[USdiver1]

I've been diving 40 years and was taught the 1/4 turn rule. I did not believe it and have always turned my tanks on all the way. For some reason several times in Mexico we have ended up with tank valves stuck in the open position after a dive. I am trying to remember to turn them back a quarter now.

I was taught the same 1/4 turn rule back in the 1970s. It was explained to me that the purpose was to prevent stripping of the plastic knob [this leading to a valve stuck open] if the user would accidentally strike an overhead object. Old divers knew a lot more than we sometimes give them credit for.

 

[JoeTPhilly]

Old Habits Die Hard

Make it your standard practice to gently and completely turn on your air. If you’re an instructor, consider not teaching students the quarter-turn back.

dan.org

 

[BRT]

I was taught the same 1/4 turn rule back in the 1970s. It was explained to me that the purpose was to prevent stripping of the plastic knob [this leading to a valve stuck open] if the user would accidentally strike an overhead object. Old divers knew a lot more than we sometimes give them credit for.

It was explained to me that the cooling of the mechanism with the air going through it would shrink the stem and bind it. I suspect that this sometimes happens.

 

[davehicks]

I was taught the same 1/4 turn rule back in the 1970s. It was explained to me that the purpose was to prevent stripping of the plastic knob [this leading to a valve stuck open] if the user would accidentally strike an overhead object. Old divers knew a lot more than we sometimes give them credit for.

If the plastic knob is stripped, service the valve. Is the valve is so hard to turn that you think it might strip, service the valve.

 

[BRT]

If the plastic knob is stripped, service the valve. Is the valve is so hard to turn that you think it might strip, service the valve.

Trouble is that the valves were not hard to open and were not hard to shut, after I got them to turn in the off direction.