NC Fatality?

[rjack321]

I have tried a couple of my tank valves, and at 1/4 turn open they will pass any but the most aggressive tank check. My training was to make the tank check to insure you had air, not to check if the tank was open, which can only be done by checking the valve itself. If you have a problem getting air as you decend, surface and check the valve first.


Bob

I agree at 1/4 turn open the lumen between the HP seat and the orifice is basically as big or bigger than the seat orifice itself so it's fully open. That and compared to an O2 compatible valve, scuba valves are most definitely fast opening.

 

[rjack321]

The threads on the valve seat in a scuba valve are uniform. Which means that the longitudinal movement of the valve seat opening, is directly proportional to the degrees of rotation of the handle and this relationship is fixed. I'm not sure if gas flow is directly proportional to the opening area, but the whole discussion of how a valve opens on a scuba tank doesn't seem that meaningful for the practical utilization of the device,

I prefer to have the vale opened and then backed off a little bit, when you crank the valve open hard, you squish the hell out of a little o-ring on the stem. That seems like something we can avoid by gently opening to the stop point and then closing a little.

Just squish the oring and service the valve periodically.

"Saving" the stem oring is not worth the potential confusion about whether the valve is open or not.

 

[johndiver999]

I agree at 1/4 turn open the lumen between the HP seat and the orifice is basically as big or bigger than the seat orifice itself so it's fully open. That and compared to an O2 compatible valve, scuba valves are most definitely fast opening.

In my experience opening a scuba valve 90 degrees is not going to get you unrestricted access to your air supply, especially at depth and as pressure drops.

 

[pedo]

If they didn't report a problem with the gear, then I would suspect a medical issue.

As for the tank valve opening question - it surprises me that some divers don't have the curiosity to see EXACTLY what will happen when the valve is only slightly cracked open.

Rather than listen to people on the internet, why not take 3 minutes and a 100 psi of air and try it yourself after a dive. Just leave the reg attached after a dive, shut the valve down, suck the air out and then open the valve 5 degrees and see how the regulator performs. If you get nothing open it a tiny bit more. It seems obvious to me that a diver should gain the experience of exactly what it feels like to have the valve partially open (while sitting safely on a bench on a boat).

Similarly, it amazes me that people don't experiment and see how the regulator performs (with the valve fully open) and as the pressure drops to 100 psi or even "zero" on the gauge. So many people seem to think the air will just stop, but it doesn't -at least on the regulators I have used - it just gives you an extremely reduced flow rate for probably longer than most people suspect.

We did this in the pool as part of open water class. The instructor would close the valve down just till you could feel the difference in effort to breathe then open it back up.

 

[dmaziuk]

So if the cylinder "required 2-4 turns to close", it was fully open, no flow restriction there.

 

[Bob DBF]

I agree at 1/4 turn open the lumen between the HP seat and the orifice is basically as big or bigger than the seat orifice itself so it's fully open.

I am not saying the valve is anywhere near open, just that breathing the reg and checking the SPG may very well not show a deflection. At 1 ATM you don't need much flow for proper breathing and the SPG does not deflect, as you get deeper more flow is needed and a 1/4 turn open won't give it to you, and if you were looking at the SPG it would be deflecting.


Bob

 

[johndiver999]

Just squish the oring and service the valve periodically.

"Saving" the stem oring is not worth the potential confusion about whether the valve is open or not.

I have to wonder about this idea of avoiding confusion. This is my thought process.. perhaps it is faulty?

I like to check the valves on tanks before people splash. What I do is grab the valve and GENTLY try to turn it back and forth maybe a quarter turn. Once I have determined that it is not in a locked position, I will open the valve all the way - GENTLY so as not to squish the O-ring, and then back it off 30 degrees or something.

Now if I grab a tank valve of a diver who is ready to splash, and it does NOT move back and forth, then it presents a question. Is the valve completely shut or is it cranked open? You really can't tell without applying considerable force.

If it is actually off, and you try to crank it closed, then you are squishing a seat. If it is actually all the way open and you decide to try to open the valve, now you are really squishing the o-ring. So there seems to be no sure fire way to turn the valve to check for position if you don't already know for sure it is either cranked open or cranked closed.. And obviously, if you actually know that information, then there is no need to verify it.

So to check someone's valve you need to turn it either clockwise or counter clockwise and depending on if it is entirely open or entirely closed, then you have the potential to actually damage the valve components as you attempt to "help". You either hammer the o-ring or the seat because you must determine the valve position by moving the valve.

On the other hand, if the person has opened the valve fully open and backed off a quarter turn - then the handle will turn back and forth easily and "testing the valve" has really zero potential to damage either component of the valve (seat and stem o-ring).

So from my perspective, cranking the valve open hard and squishing the O-ring is really NOT helpful in avoiding confusion. Keeping the valve just a little loose does help to avoid confusion.

I personally have no problem with a buddy checking my valve. If I am going to trust them to dive with, then I am pretty sure I trust them to VERIFY my tank valve position.

 

[Jcp2]

What ever happened to lefty loosey righty tighty?

 

[Steelyeyes]

What ever happened to lefty loosey righty tighty?

It got replaced with righty tighty lefty loosey.

 

[chillyinCanada]

Whatever happened to no longer needing to do the quarter turn to save damaging the tank?