Question re: Overturning tank valve back & Regulator

[dave4868]

I appreciate all the feedback on my inquiry, but here's another question:

In one of my basic scuba books (I think it was in "The Certified Diver's Handbook" by Dennis Graver) he advocates "rolling" open the tank valve all the way and leaving it there with no 1/2 turn back.

My understanding is that the custom of rolling back the valve a 1/2 turn has to do with reducing wear and tear on the valve seat (or something like that) but if that's the case why should I care whether the dive shop has to replace more valve seats if it could compromise my safety?

I think there are at least a couple good reasons not to peg the valve to the stop.

1. Some valves will stick a little when up against either stop. If the handwheel (knob) is moved a half turn away from the stop, there's less chance of overtorqueing from mistakenly going the wrong way. I want to avoid increasing the wear on my equipment.​

2. More importantly, when I check to see if the valve is open just prior to entry and find the wheel turns freely, at least I know it's open and will supply air, even if it's been mistakenly set closest to fully closed rather than fully open.​

Using the other method of leaving it up against a stop, a mistake could result in no air being delivered. Compounding that problem, an attempt to open the valve in the wrong direction might jam the valve quite a bit, further confusing the issue.

If the diver entered the water negative and sinking, confusion is the last thing he needs.... Personally, I don't do well when confused and sinking....

I saw it happen once and the diver was able to fin up to the surface, but he still wasn't able to sort out the right valve direction until he was back on the boat....

Of course, checking air delivery and gauge movement prior to entry can avoid the problem also, as many people wisely do.

I suppose for added safety one could do both: leave the valve a half-turn off the stop and check air delivery and gauge response, but just the first will suffice, IMHO.

Dave C

 

[PhilEllis]

Oh Phil
Yes, I have noticed that most modern valves (at least the ones available in the US) seem to have the same seats, but that was not always the case and there are plenty of good vintage valves around.

About the seat indentation, I have serviced valves (that the seat was still sealing) with a very deep groove. I don’t know the thread pitch on the seats, but my guess is that in the case of a heavily grooved seat it could even take a full revolution to fully open the valve

That is certainly a possibility. I am going to take a look as some of the "well-used" air valves we have and see if I can find a suitably worn one for flow bench testing.

Phil Ellis
Discount Scuba Gear at DiveSports.com - Buy Scuba Diving Equipment & Snorkeling Equipment

 

[Teamcasa]

I've been trying to find a reason why people do this. The only thing I can find is that people did this w/ the older style pillar valves to prevent damage in case the valve was knocked. I've never seen the inards of an older valve, so I'm not sure if this is accurate or not. Maybe one of the old guys...er.. veterans on the board can chime in on this one

I did find the following clip on youtube which is pretty cool for anyone who hasn't seen the insides of their valves.

Anatomy of a valve:

YouTube - Anatomia de una griferia - Scuba tank valve anatomy

Old guy here..
Opening a valve all the way and back a 1/4 -1/2 turn is not unique to scuba tank valves. As with many high pressure tank valves the need to close them is sometimes more important. If a valve (scuba or otherwise) is opened fully it can seize, break or bind in the full open position making closure difficult or impossible. This could be disastrous in a oxygen and acetylene setup should a hose or regulator fail.

Modern valves rarely suffer from this condition but some traditions are hard to shake.

 

[TSandM]

I had a potentially very unpleasant experience on a dive boat in Australia. I went to check my valve, and I couldn't move it. I asked the DM if he had opened it, and he said yes; I subsided for a bit, but then I was just too anxious, and tried to move the valve again. I couldn't, and asked the DM to help -- It took him some force to move it, and it turned out to have been closed. I don't think I would have gotten in the water with it in that state (although I was a VERY new diver at the time) but someone might have.

For this reason, I always turn my valves back just a tiny bit (not even 1/4 turn -- just enough to make sure they're not jammed open) to ensure they move freely. I also agree with the person who said that really ingraining the knowledge of which way valves are open or closed is critical information for a diver. This is more important when diving doubles, where you might expect to need to manipulate valves underwater, but my experience in Australia tells me it's important for single tank divers, too.

 

[Teamcasa]

HI Sy. I have heard (and I think read) the same thing about "saving the valve seat". This makes no sense, because once the valve is opened, there is no pressure on the valve seat. It is pulled away from the crown and tweaking it back does nothing.

This is also a common misconception that has history in fact. In the old days (mainly due to water valves BTW), low quality valves that were opened only a “crack” would allow water (or what ever fluid/gas) to squeeze through the narrow opening would indeed cut or abrade the seat where a fully opened valve this would not occur easily.

 

[Noboundaries]

Leftie loosee (open) Rightie tightee (closed) just doesn't work for me because I tend to use both hands (ambidexterous). I'm always stopping to think which way is left and which way is right. If I suddenly can't breathe and need to check the tank, that's not the time to go "leftie loosee...." I need something simpler.

On a single tank, my bubble blowin' wife said "just roll it away from your head to open it." Works no matter which hand I'm using or if it is before or during a dive. Ahhhh.....no more confusion! Might be common knowledge for everyone here, but just became so for me.

And I'll still back it off a quarter turn just because it is habit regardless whether it makes a difference or not. I learned long ago that habit patterns keep you alive, broken habit patterns invite trouble.

 

[sytech]

Thanks a lot for this video. It really helps me to understand these "mysterious" devices.

Anyone know if there are other such videos? I would love to take an online course which explains the mechanics of scuba equipment.

Thanks,

Sy

I've been trying to find a reason why people do this. The only thing I can find is that people did this w/ the older style pillar valves to prevent damage in case the valve was knocked. I've never seen the inards of an older valve, so I'm not sure if this is accurate or not. Maybe one of the old guys...er.. veterans on the board can chime in on this one

I did find the following clip on youtube which is pretty cool for anyone who hasn't seen the insides of their valves.

Anatomy of a valve:

YouTube - Anatomia de una griferia - Scuba tank valve anatomy

 

[irishsquid]

Leftie loosee (open) Rightie tightee (closed) just doesn't work for me because I tend to use both hands (ambidexterous). I'm always stopping to think which way is left and which way is right. If I suddenly can't breathe and need to check the tank, that's not the time to go "leftie loosee...." I need something simpler.

On a single tank, my bubble blowin' wife said "just roll it away from your head to open it." Works no matter which hand I'm using or if it is before or during a dive. Ahhhh.....no more confusion! Might be common knowledge for everyone here, but just became so for me.

And I'll still back it off a quarter turn just because it is habit regardless whether it makes a difference or not. I learned long ago that habit patterns keep you alive, broken habit patterns invite trouble.

The way I check mine is as follows: (Noboundries, this may work for you really well being a biker cause it fits well with muscle memory, habit, etc. I'm a bike rider as well)

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. If you have a problem doing it with the palm forward (lack of flexibility or whatever) and the palm faces back, use the the old bike phrase: If in doubt, turn out. This would be reverse of 1st description.
It may sound confusing or complicated but works as a natural way for me.

 

[irishsquid]

A small orifice can pass a reasonable amount of air on the surface at 1 ATM, but restrict air as it becomes compressed and more dense at depth (3ATM). This might happen if the diver or someone else got mixed up and turned his valve off, then on 1/2 turn thinking it was turning it on, then backing off 1/2 turn.

Edit for clarity: This also accounts for the diver reporting the valve was off when he returned to the boat. I am just stating that the valve did not roll off in open water, it was turned off (almost off anyway) by someone.

A check I do is to breath through my primary while watching the pressure gauge right before I decend. If the needle dips, it is indicating something like this has happened. It could have even been a helpful deckhand on the boat. Its not a replacement for knowing which way to turn a valve on, but a backup for me.

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.

 

[tfsails]

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.

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.

I am a retired aircraft electronics technician. Many were the times that I had to turn a screw or nut without being able to see it or even being able to put my fingers on it from the top end. As such, I had to learn to mentally place eyes on the end of the screw and figure out which way to turn it to tighten it. When you're doing this from the wrong end, it seems backwards. Why am I saying this? Read on:

My buddy and I were in Bonaire a few years ago (he's an airplane mechanic too) and we were swimming out from Buddy Dive's pier to do a dive on the house reef when I asked him to check my air even though I knew damn well the valve was fully open. He was on my left when he did this, so he reached his right hand across my tank and checked the valve. Yep, you guessed it: he closed it and opened it 1/2 turn. Everything was fine on the surface, but at 40 ft when I checked my SPG, sure enough it behaved exactly as you described. We surfaced and I turned around the right way to him and said "now will you please open my valve?" The only reason I checked my air when I did was because I had a nagging feeling that he'd gotten confused by being on the back side of my valve when he turned it. I felt no sensations of breathing difficulty, but we were headed to 90+ feet so I checked early. I'm glad I did; we had an uneventful dive after that. He was as apologetic as he could be and bought me a few Amstel Brights later that day. But that's another story...