The Dangerous 1/4 Turn... - Sea Hunt Jerry got a discussion going in our Vintage email group concerning the practice of opening your scuba tank valve all the way and turning it back 1/4 turn. Apparently there have been people who get this mixed up and accidently go diving with the valve only opened 1/4 turn. That's enough to breathe okay in shallow water so people can start a dive not knowing the valve isn't open enough for deeper water breathing. And so, some divers have gotten themselves into a dangerous situation (like cave diving) before the lack of air was seriously apparent. - On the other hand, a valve turned all the way on or all the way off can't fool you... You'll notice you've got no air right away if your valve is all the way off. - I was taught "All the way open and a 1/4 turn back" and have continued to do it that way for years. - What do YOU think...
Last Edit: Dec 17, 2014 8:05:15 GMT -8 by surflung
I turn it all the way and leave it. My valves are either on or off - I hope.
I was also taught valve turn back in my open water class. I don't recall the exact reason, but I think it had to do with the valve freezing up. If you left the valve slightly closed, you could turn it back and forth to free it... Not sure that's true.
Once I got into diving surface supplied air with a bailout, the methods all changed. The bailout was charged and tested and then that valve was closed until needed. Those bottles were also slung upside down so the valve handle was within reach of your right hand.
Today, I'm no longer diving surface supplijed air very often, but I am a member of the public safety dive team. While doing Public Safety diving, we also wear a pony bottle, but it is worn upright and the air is turned on all the time and routed throw a breathing block. If you need to swithc to your bailout, you turn a selector knob from up to down and you are now breathing off the pony and by-passing your big bottle.
My public safety team is likely to switch away from this system in the future since there have been several training dives where the diver has entered the water on the pony, but then run our of air too soon. No one has been injured, but we did have a diver in the pool remove his FFM and switch to his Air II since he believed he had an equipment malfunction. Not really a difficult conclusion to reach since his SPG was still showing a full tank.
This is an interesting topic and I'm looking forward to hearing from some of the people who were instructed in the 60's or early 70's. Maybe they can remind me of why I was taught that way.
I do not believe in taking unnecessary risks, but a life without risk is not worth living. - Charles Lindbergh
Post by regulator68bj on Dec 17, 2014 12:43:58 GMT -8
Having made a few phone calls in the past hour with UK divers of the 1960/70 who were taught the method all the way on 1/4 turn back came about from the early "Non Balanced " pillar valves had a tendency to jam in the open position after the dive if the 1/4 turn back was not applied.( early cylinder WP 120Bar) However when eventually the "Balanced Pillar cylinder valve was adopted the turning back process fell by the wayside. Note:- From the early days circa1954 UK Scuba systems were fitted with a SPG so pre dive checks and air management would show up if the pillar valve was not in diving mode.
I still use the 1/4 turn back upon opening my valves. This was taught in the early days, and has a basis not only in what regulator68bj says above, but also in the way that the valve is manufactured and the type of diver that started diving in the 1960s. Here's what The Complete Manual of Skin Diving, by A.P. Balder (The Macmillan Company, Collier-Macmillan Ltd., London) stated on page 48:
Assembling Breathing Apparatus for Dives... ...Open the tank valve all the way counterclockwise, but gently. When it is open, give it a half-turn clockwise..."
Fred Roberts, in Basic Scuba, makes no such reference. The Jeppesen Sport Diver Manual, third edition, 1975 also makes no such mention. But that is the way I was told, and here is the rationale. These valves have a rather delicate nylon bushing or washer that seals the unit when open against the stem. The stem has a rather sharp ring on it that seats into the washer/bushing (some models, such as Dacor used a different sealing method using O-rings). If a young male opened this valve forcefully with the hand valve, and left it there, this washer/bushing could be damaged. So the 1/4 turn took the torque off this bushing/washer (which also had air pressure behind it for sealing), and allowed it to seat easily using only the air pressure without the torque of turning the valve stem into the bushing/washer.
The problem with a valve only 1/4 turn on is that with a full tank, a surface breathing test cannot tell that this has happened, as the pressure behind the air will force a lot of air through the small opening (about 1/32 inch). The opening is only about 1/8 inch when fully open (about turn turns of the valve handle). Because of the gas laws, we need about 1 cubic foot/minute on the surface at rest, and about 3 cubic feet/minute when working on the surface. But because of pressure changes with depth, we need at rest 4 cubic feet at 99 feet (3 atmospheres depth), but 12 cubic feet/minute at that depth under work. So having the air on only 1/4 turn is potentially dangerous.
A maintenance technician I know states "Lefty--loosey, righty--tighty" (counter-clockwise is opening; clockwise is tightening) as a way of remembering how to turn a valve. I'll put together some more info on this late.
Now, I have just gone out to my dive area (garage) and tried out four different regulators at 1/4 turn of the valve, and discovered something. It used to be, in the 1960s that we had a regulator on a valve. This was either a single stage or two stage double hose regulator, or a single hose regulator. This was in the time when there was only one hose on the single hose regulator. I have two double hose regulators set up (my Mossback Mk3 and my Trieste II), and each has a LP inflator hose, a HP gauge, and an octopus on it. I could not tell if the valve was only 1/4 turn (or even a bit less) when I test-breathed it. I tried it on my Dacor Olympic, with again a LP inflator, octopus and pressure gauge--couldn't tell if it was only 1/4 turn open. But I also have a Sherwood Magnum Blizzard, without any peripherals--I tested it, and could tell immediately that the valve was not open enough, as it pulled very hard on inhalation. Then I put this regulator on another tank, and could feel no difference with the 1/4 turn--the tank I tried it on was very low. I tried several other single hose regulators with similar results--couldn't tell. Then I tried the Scubair 300 with its sonic reserve, and it was immediately apparent that the valve was not fully on--it buzzed the sonic reserve. So that was an interesting little experiment.
When I first put a regulator on a tank I always just barely crack it open, to see if it's going to do anything stupid, like start free flowing--grumble, grumble, grumble... this way I can quickly shut the air off. But yes, I always do the quarter turn back thing too.
Sitka Dave said:
"I was also taught valve turn back in my open water class. I don't recall the exact reason, but I think it had to do with the valve freezing up. If you left the valve slightly closed, you could turn it back and forth to free it... Not sure that's true."
I believe this is SOP with ALL valves, especially with hydraulics! Hmmm, I can't help but wonder now if it has anything to do with wearing out the threads in the valve?!?!?!? I know that most people wear out valves because they have a need to over compensate and makes sure the valve is totally-absolutely-completely-honestly-without-a-doubt, either on or off Brass is kinda susceptible to metal-fatigue and I can imagine some guy with ape-knuckles who likes to make sure the air is on, then one day the valve stem sheers off in his hand, "Oh $#!+..."
But yes, I do do recall it has to do with valves sticking open..
Just a thought, Jaybird
Last Edit: Dec 17, 2014 17:05:23 GMT -8 by nikeajax
I still use this method today as it was taught in 1971 when I got certified, one thing we were told is in the use of J-valves if it was not open all the way that when the pressure got low in the tank or at depth it would have a tendency to shut off or restrict air flow. The USD Calypso J regulator would do this as well.
- I always thought the 1/4 turn back was so that you could check it with light finger pressure. You could feel the movement up to the stopping point and not have to torque the heck out of it. On the other hand, if a valve was turned all the way off hard, it might stick there a bit and feel like it was all the way open because it was so hard to turn.
I wanted to discuss this 1/4 turn in a different manner, talking about the air routing of different double tank manifold valves. Here is the U.S. Divers Company double manifold valve, disassembled:
Note the slotted brass piece, which USD titled a "nipple & disc." It has threads, and if you turn it only 1/[4 turn, it does not lift the disc off the seat very far (less than 1/32 inch, most probably. However, this is enough to give air to the regulator, and pass a breathing test on a full tank (with 2250 or more psig behind it). If you look at the valve stem above it, you can see the upper part of the step that seats into a "stem washer" that is housed in the bonnet nut (to the left of the "nipple and disc," above it. This is what can be scored to cause the valve to stick. Here's a closer look:
If you look down into the air routing, you can see that the seat is machined into the valve, and that lifting the "nipple and disc" by unscrewing it allows the air from either side to enter directly into the valve's machined hole to the regulator, making only a 90 degree turn. This routing allows the valve to have minimal turbulence within the valve that could affect air flow at low pressure (below 500 psig).
The Sherwood double manifold is differently routed internally. Here is the valve center piece: Note that the valve is elongated compared to the USD valve. The routing is very different, in that the air from the two cylinders goes to a drilled tube that is vertical, going up to the seat. This is a 90 degree turn, where it meets the valve seat/disc that is opened by the knob. When then opened, the air is routed up, hits the disc in the nipple (using the same USD designation, as these are almost identical), then makes a 180 degree turn to go down the tube to the regulator. This is about an 1 3/4 inch tube that the air goes through, before making its 90 degree turn into the regulator.
Looking at this, I have a better appreciation for the engineering that went into the USD valve. Apparently, because of patents Sherwood needed a different routing, and that is routing that can cause some turbulence and perhaps some restriction of air at very low tank pressures. I think this is the reason my experiment using a Sherwood center manifold for two LP hoses from single hose regulators failed--this manifold acted like a restrictor orifice at 135 psig.
John C. Ratliff Diving since 1959, at age 13. Haven't stopped, and still enjoy getting wet.
Post by Seahuntjerry on Dec 26, 2014 20:51:37 GMT -8
Here is a list of books that say 1/2 turn back,New Science of Skin and Scuba diving 1985,Skin and Scuba divers Digest 1975 including on divers check list. On the 1/4 turn back Nasds books 1976 including diver check off plastic sheet,SSI says in their book all the way open.
Post by scubadiverbob on Feb 18, 2015 21:43:30 GMT -8
First course I took was NASDS. Was taught on Scubapro equipment and always told the 1/4th turn back I don't think no one knew why. I was also taught Scubapro was the only equipment I should buy; so, I thought it might be scubapro valves required it. hummm .... ok ?? Still do it, I think out of habit.
The "dangerous" 1/4 turn. The 1/4 turn back was supposed to be a safety thing.
I think I remember being told the reason we did this was so that if you needed a buddy to do a last minute check to see if your valve was open, he could tell right away if it was open if he could move it either way. The idea was that there are a lot of people out there who just can't get the hang of which way is on, and which way is off. If you open it fully until it stops, some people wouldn't be able to tell if they are opening it or closing it when they find out which way it starts to move. They might end up shutting your valve when it was already open to begin with. Of course, any good diver takes a few breaths through his regulator to verify air availablity before entering the water any way, so I have often wondered if the 1/4 turn back is all that important afterall.
There may be another, more valid reason for the 1/4 back turn, but whatever it was I do remember the reason had to do with avoiding confusion as to whether the valve was open or closed when checking it.
Silly humans, fins are for fish. Mammals use flippers.
" Apparently there have been people who get this mixed up and accidently go diving with the valve only opened 1/4 turn." I had a buddy get into trouble that way some years ago. Apparently, their entire PADI/YMCA class had actually be TOLD to do it that way, three people from the same class all said the same thing. Which I suppose it part of why we were all told (and promptly forgot) that we're supposed to cross-check each other's gear.
Anyway...it is one of the things that says to me "This person was not really taught how or why their gear works, they should not be certified." And I'm still waiting for PADI to impress me with anything besides the fact that they'll guarantee everyone in the class gets certified. (Which not all agencies or instructors used to do!)
Okay, another stab at this question. I've looked at some of my older valves, and they have a very soft seal washer on the top. If you really crank the valve open hard, and leave it there, you can scar that seal washer. Take a look at the diagram of an older K-valve:
Note that #6 in the diagram above, the "1508-06 Washer" is the soft material that I was talking about. I think that has been changed now.
In one of the other threads, there was a link to the U.S. Navy's current dive training video. Guess what? They still train the 1/4 turn back after a full opening.
PS, the diagram is from Fred Roberts book, Basic Scuba.
John- Part of the "1/4" philosophy is probably a tradition from gate valves, which has no purpose with these. Gate valves in particular tend to corrode and fail, physically getting stuck. But any rotary valve has a "human interface" failure mode, where someone is hot, or cold, or tired, or seasick, and they crank the valve the wrong way. Now, if the valve was already all the way open and they crank the wrong way, they're really going to jam it, and now it is stuck open until you find a bigger gorilla. But if you back the valve off 1/4 turn, then it doesn't matter. They get to turn it 1/4 turn and it stops--which usually gives them the message "D'oh! Turn it the other way!" and there's no damage done.
At least, that's how we were taught the 1/4 rule was supposed to prevent problems. Washers? O-rings? Valve seats? That's what maintenance is for.(G)
Post by sitkadiver on Feb 25, 2016 10:02:50 GMT -8
I have a short story to tell: I was diving last summer using my standard single hose set-up: a back pack, tank and 3 hoses; reg, dry suit inflator and SPG. I'm a very minimalistic diver, even when using modern gear. Anyway, my reg was breathing difficult at depth. I noticed in about 80 feet of water that I was over breathing the regulator, which BTW was a brand new Conshelf 14. Impossible! Well, my good natured buddy of the day had turned on the air after our hike down to the beach and then turned the valve back a 1/2 turn(or maybe 3/4), just like he was taught. I was actually able to look at my SPG while breathing on the reg and watch the needle go from 1800 psi down to about 800 psi during inhalation, and then of course go back to normal when I exhaled.
OK. I'll get off my soap box now and let a smarter guy teach us something: