Of quarter turns of tank valve knobs and diving physics in Scuba Diving

The following is a conversation that occured on FaceBook about that quarter turn of a tank valve knob, Charles Law as well as a host of diving physics. We welcome you to agree, disagree and above all learn. Please join the conversation by adding to the comments thread at the end of the article.

We pick it up in mid conversation. . .

. . . . K you are right! S, you hit the nail on the head, it is because of old J valves.

The remainder is something all should think about. In ice diving with old valves in the 80s freeze up would occur, and so those divers got into the habit of quarter turning their valves, which is stoopid because it if it froze, wouldn't you rather it freeze open?

Now a days it is a stoopid substandard teaching agency thing. Technical divers do valve drills on a regular and consistent basis in the event of a manifold failure. You would have to pile drive a valve into a bulkhead to have it fail. So short answer is when is an open water diver going to slam their valve into a wreck? Furthermore it has nothing to do with the valve knob.

What makes it dangerous is on boats where you have people (divemasters, buddies, fans, deckhands, idiots. . .) playing with your valve knob. Get in the habit of being the only person who touches your valve. If anyone else touches it, immediately do a valve check (and you should be able to accomplish this standing up with your gear on. . .before you leave the boat/enter the water on the beach. Watch me and make me demonstrate it for you. If you cannot, your tank is too low.

A, I touched your valve when we entered the water, how did you know I didn't turn off your air, if you reached back to check if it was on/off. . . and it was quarter turned. . . how do you perform a valve check? Y, therein lies the problem. . . if the valve is at full on, you can quickly ascertain if it is all on. . . it is a quick pop, and remember you are doing this behind your back . . .



Note, I have had a DM turn my tank off and then a quarter turn back on at Casino Point. . . breathed fine until I descended to 100 fsw. then the pain came. . .

This is a GREAT discussion, as learning can occur here. What is most important all is that you all have a responsibility to ask WHY and discover what is the truth. . .

to this I say. . . bring it!

I am so going to make this a blog article Y would you mind?

A grateful thank you to Y, for bringing the learning

I am learning something new every time I talk to you guys, I have learn we can sometimes be wrong and there will some one out there to bring it!!!
Peace and Love to you all ~ P

My dear Tevis, I think you missed my point. The valve is not freezing, this is the first stage that does due to sometimes divers inflating their BC and breathing at the same time, thus increasing the air flow in the 1st stage leading to a decreased temperature in the mechanism. If there was some kind of humidity in the first stage, then you have icing conditions. In that case, even with the most recent regulators, the spring may get stuck open and you end up with a LOT of bubbles. You need then to ascend and the best way is buddy breathing. Some organizations used to advise that once the buddy breathing is established, to avoid excessive bubbles during the emergency ascent, you would shut down the continuous flow of air (remember in the old days, you needed to ascent by looking at the bubbles, not your computer).
And for those who wonder how to check if your valve is open correctly and won't feel funny at 100ft, you can look at you manometer while breathing hard on the reg. If the needle moves up and down your air is not on correctly. I think also you got that with a J valve with the reserve not engaged but I hope nobody dives with these anymore... And if you don't have a manometer but these fully integrated single-point-of-failure computers that give you everything, then you'd better learn how to twist your body like Tevis to reach for that damn valve...

YC

Tevis Verrett

December 13 at 11:30am

Point well taken mon ami, and I too am learning here. Yes, you are exactly right in a first stage freeze up, as this is a direct application of Charles Law (b'member that from the substandard physics taught in the padi manual?) Volume is directly proportional to Temperature.

and while I am padi bashing, let me add naui to that also. It isnt necessarily the agency, it is directly attributable to the instructor.

Can you imagine the world of physics that would open up if Daniel was our instructor?

And all please note that I have 10 solid years of junior college edumication, and am well versed on manifold valve checks. . . (I say this not to brag but to share my faulting) even with all of my training, when reaching back behind my head, if my valves weren't completely on (but in the quarter turn position), I would inadvertently turn off my air as I would have no perceptive "stop on."

I have shut my valves down inadvertently, and it has scared the crap out of me when I go to my reg. . . .and nuthin'! (but narc'd, I have been able to turn them back on. . . . practice) When we are sitting around eating chips and drinking beer, ask me about this dumbass situation, it is a good story. . . .

In an emergency when you need to reach back and power that valve off and on (in the case of the o ring not seating properly) which way to you turn the valve, if both ways seem viable?

So Yves, my humble apology and grateful thanks. And also, you might consider becoming an instructor my friend! We need intelligentsia in the education of the diving public.

Y brings up a good point. . . . when was the last time y'all practiced buddy breathing/out of air drills?

Booyah!

Love to all,

Tevis

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December 13 at 8:18pm

Reply

Bernoulli's principle=low pressure, high velocity, low temp=icing (regulator valves, wings, venturies, etc. Icing can and does occur and is most common at temps below 70 deg and humid conditions for flight and should also apply at depth for a reg (i knew my flight training would be useful for something at some point). anyway, thank you all for this input and training! you all are helping us "younger" divers learn proper technique and to be safer to all involved. My gratitude to all!

MH

Tevis Verrett

December 13 at 8:26pm

D, you can weigh in with this at annnnny time!

Master of physiology and the stuff o life because of medicine, only a plebe in physics. . .

. . . I bemember Bernoulli's has something to do with turbulence and vortexes over a wing. . .

. . . doesn't can you generate that type of turbulence in a reg?

Let the learning continue!

Tevis

December 13 at 8:29pm

That is ONE of his principles. He also has one that deals with velocity, pressure and temperatures and that is what we deal with in venturis (wing curved surfaces, hose nozzles, and restricted orifices (regulators).

See you tomorrow at the pool Tevis. Cant wait to learn to be buoyant and trim.

MH

December 13 at 9:30pm

Reply

Bernoulli wrote the conservation of energy of fluids. By setting a few parameters in the equation, you end up with many different equations (or principles). The venturi effect is found by setting the parameter "altitude" to a constant. You found that the flow of a fluid is constant. Funny enough that means that the bigger the pipe the higher the pressure (one would think of the contrary).

An interesting effect is found in history: pirate ships created a venturi pipe when approaching a ship they wanted to capture (the pipe is the water between both ships), at high velocity this creates a drop in pressure between the two ships, thus attracting them to one another, making the capture easier.

As far as turbulence are concerned, you're in the boundary layer so Bernoulli does not work, Navier-Stokes & Kutta-Jukowski is what you want to look for. If you ever wondered why golf balls have little holes, then your answer is there too... In a reg, I don't think there is a lot of turbulence, because the viscosity of air as well as the velocity at which it got transferred in the hose are not high enough.

Back to diving, I have seen icing at around 6°C (=43F). So I think I'm safe in Fiji... Gee, even in Shaw's!

Tevis, you can blog our thread if you want.

YC