Question re: Overturning tank valve back & Regulator

[bleeb]

Does anyone recall hearing talk about one of the agencies or something thinking of changing the recommendations and doing away with the 1/2 turn? As others have pointed out, there's not much value with modern valves.

The idea may have been that with full on or full off, it was easier to detect a shut-off valve on the surface, rather than it not being apparent until the tank had been partially breathed down or at depth. I think it was particularly a concern in areas with a lot of infrequent vacation divers who may be less skilled dealing with unexpected out-of-air situations.

At one time, I also heard a comment that tech divers (or maybe it was cave divers, or even just a particular agency) divers don't normally do the 1/2 turn back. Any of those here willing to comment?

 

[1_T_Submariner]

On U.S. Submarines they go through a process of verifying valves are in the correct position prior to diving. If the valve is open and tight against the stop and stuck might not be able to turn it indicating that it was shut when in fact it is open this could be bad. The 1/4 or 1/2 turn back allows for easy verification of an open valve.

Verify the valve like your life depended on it.

Once you get in the habit you'll never leave a valve turned hard against the open stop.

 

[battles2a5]

I had a situation occur a while back that I don't understand at all; maybe someone here can explain, as it is somewhat similar in nature to this thread. My brother and I were diving a local quarry, had been down for approximately 20 mins. and during one of the checks of our air press., I noticed a fairly good amount of needle deflection on my brother's gauge. We stopped and hovered, I did a check of his valve, and it was on full, his gauge was reading around 1850psi and everytime he took a breath, it dipped to about 1200psi. I rolled it back 1/2 to a full turn and then back to full and back a 1/4 turn and it stopped dipping. At the time this occured, he experienced no air delivery problems, water temp was 67F, @ 35ffw. This has not occured since. It makes no sense whatsoever to me and he had his gear checked out with no problems found.

It could also be some debris in the dip tube or the filter on the first stage. If it is your tank that you were using I would send it in for a visual and have them inspect the valve assembly. Also check the orifice on your first stage and make sure there isn't any junk in there.

 

[Noboundaries]

The way I check mine is as follows: This is with a single tank, valve knob on your right side. With gear strapped on, reach behind with right hand. palm forward. Now, just as with the throttle of a bike, need more gas, twist the same way.

Ooooooh, I like that. Even easier to remember.

Thanks!!!!

 

[irishsquid]

I would look at the plastic knob on that tank he was diving. What you described is the classic indication of a valve only partially open and then being unable to deliver the amount of air demanded at depth. The valve shaft is a male square shaft not unlike the drive end of a socket wrench. The knob is a square female hole that can be very easily rounded out if the knob isn't tightly screwed onto the shaft. I'd suspect that the knob was loose and you probably got the knob a tad crooked on the shaft and was able to turn the valve fully open when you fooled with it underwater. If you look in the end of a tank valve knob, you can see the threaded end of the valve shaft protruding through the screwdriver slot on the retaining nut. If the shaft doesn't protrude slightly above the top of the nut, the nut's loose and the knob will wobble on the shaft and eventually round itself out.

The tank he was using is mine and it was about 3 months old at the time of the incident. It has been used many times since then, trouble free. I just checked the knob as you suggest. I can see the shaft sticking through the nut and it is above the slot but below the very top of the nut. I did get maybe a 1/4 turn on the nut with a small screwdriver. I can't get a screwdriver in the slot because the shaft does stick out. Thanks for the idea, it was worth looking at. I guess I'm back to the bizarro/ nebulous wonderment of WTF? What really was weird it was a one time event that has never shown it's head again.

 

[tfsails]

As Battles2a5 states, it could also have been a partial blockage of the dip tube in the valve. That's a small tube that protrudes about 2" into the tank from the bottom of the valve whose sole function is to prevent any depris that is in the tank from clogging up the air passages inside the valve.
A visual inspection will determine if there's any debris in the tank. Normally there is none. At the same time the technician will check that the dip tube is screwed in tightly to the valve. Good luck!

TF

PS--there should be no wobbling of the knob on the shaft. Sounds like your shaft nut is tight.

 

[Charlie99]

A diver descended to 40 or 50 feet when his regulator stopped giving him more air other than about 2 gulps
........
Anyway,when he got back on the boat he realized that he had fully opened the tank valve but apparently "rolled" it back more than a half turn and as he descended his air supply to his regulator was vanishing

A much more common problem than having a partially open valve is somebody checking their air pressure, and then turning off the valve, leaving the SPG showing a full tank.

The diver looks at the SPG, thinks "OK. Full tank", and hops in with his air completely shut off. He'll get about 2 breaths of air off the hp air inside the reg before running out of air.

IMO, there's a pretty good possiblility that is what really happened, but the "rolling off the valve" story is less embarassing.

I minimize my chances of doing this dumb trick by purging down to about half pressure when shutting the valve for a long boat ride after checking the tank pressure.

If for some strange reason I didn't do my normal pre-dive "watch SPG needle while breathing main, breathe octo, and then listening for air going into BCD", just a glance at the SPG works as a reminder that the air isn't on. Always purging to roughly 1500psi also makes it easy for me to see whether or not the yoke valve to regulator seal is leaking by seeing what the SPG reads when I look at it later.

Charlie Allen