Suddenly no air from 2nd stage or Octo; tank at 2800 psi

[mikeyjoe]

What you're describing is very typical of what happens when you fully CLOSE the tank valve and then turn it 1/4 turn open instead of fully OPENING the tank valve and turning it a 1/4 turn closed.

R..

If this happened to be the case, it is exactly why I never back it off a 1/4 turn. I like that sure feeling of knowing it is all the way open, fully seated against the stop. The breathing on the surface while watching the guage is an excellent suggestion - part of my pre-dive routine. I also take a look at my guage after my initial descent.

 

[willembad]

I'm with you. I've never had anyone explain why the 1/4 turn back. If anyone has a valid reason, let us hear. Or ignore if this is to much of a hi-jack

Willem

 

[ScubaSteve]

Not to echo what has already been said but this sure sounds a lot like your valve was not vully open on your tank. I dive an air integrated computer so it is easy to notice if the air goes down normally as I breathe during my pre-dive check. With a console, that has been explained here. Glad you came out OK but all the more reason to turn on your tank fully and check it a couple of times. An extra time checking it is better than what happened to you (except for the experience of what you have handled)

 

[Teamcasa]

I'm with you. I've never had anyone explain why the 1/4 turn back. If anyone has a valid reason, let us hear. Or ignore if this is to much of a hi-jack

Willem

Older valves would get stuck in the full open position and some would even damage the valve if cranked open to hard. Neither condition exists with he modern tank valve.

Today they just do it for that sense of OK, it's loose so it must be open feeling.

 

[herman]

Not to echo what has already been said but this sure sounds a lot like your valve was not vully open on your tank. I dive an air integrated computer so it is easy to notice if the air goes down normally as I breathe during my pre-dive check. With a console, that has been explained here. Glad you came out OK but all the more reason to turn on your tank fully and check it a couple of times. An extra time checking it is better than what happened to you (except for the experience of what you have handled)

Be careful trusting an AI computer. Some have a sample rate that is slow enough to mask the drop and rise in pressure, esp if you breath shallowly.

 

[death_by_bloop]

I'm with you. I've never had anyone explain why the 1/4 turn back. If anyone has a valid reason, let us hear. Or ignore if this is to much of a hi-jack

Willem

(Hoping this isn't too hijack-y) In my PADI OW course, it was explained that the 1/4 turn back made it quick and easy for one's buddy to confirm that his air was fully on during the pre-dive check. The idea is that the diver opens the valve most of the way and his buddy does the final fractional turn to finish the job and confirm it's fully open.

I, for one, would rather open the valve all the way myself and trust that I've done it right, but I suppose I can understand a conscientious buddy's desire to know that he's checked my setup thoroughly. One would think that his attempting to turn the valve and having it fail to budge would reassure him. Maybe the 1/4 turn is to reassure buddies with weak arm strength that the valve isn't stuck "off." (Then again, that's what the SPG check is for...)

 

[DevonDiver]

Look at your pressure gauge and take a few deep breaths before splashing and it never will.

Not true.

The needle can stick.

The air pressure drives the needle forwards, but the spring pressure is insufficient to drive the needle lower as the air pressure falls.

I had this one time...after the reg set had sat in storage for a while. Luckily the problem presented itself as I did some routine maintenance on the regs...and not on a dive.

This could have caused the problem mentioned by the OP.

Alternatives (as others have mentioned) are..

1. Valve not fully opened.
2. Blockage of the cylinder valve.

 

[Diver0001]

(Hoping this isn't too hijack-y) In my PADI OW course, it was explained that the 1/4 turn back made it quick and easy for one's buddy to confirm that his air was fully on during the pre-dive check. The idea is that the diver opens the valve most of the way and his buddy does the final fractional turn to finish the job and confirm it's fully open.

I think ... but I'm not sure ... that it was originally the way valves were opened because they could get stuck open if you opened them all the way. I have, in contrast to Dave, seen a modern K valve get stuck open but I'll go so far as to say that it was probably badly in need of maintenance. (as an aside it's not a major problem if the valve is stuck open. You need to bleed off the remaining air to to get the regulator off and then take the tank in for maintenance, which it probably needed anyway....)

The explaination that it's easier to confirm that it's all the way on probably came later, and if you ask me it's a bad idea for the very reason we're seeing in this thread. If it's either ALL of the way open or ALL of the way closed then you are SURE that it's one or the other and you can't get the situation where it's closed and 1/4 turn open.

Something for instructors to consider. This is one of the real nonsense things that are still being taught.

R..

 

[Crowley]

I don't think it's a nonesense at all - another good argument for the 1/4 turn back is that you don't put added pressure on the valve stem during the check(it takes less pressure to twist an open handle than turn a closed handle). In itself this is probably not a serious problem but winding a tank open or closed too tightly will eventually round off the valve stem - more annoying than anything but it's a sucky way to abort a dive! In my experience I still maintain that the 1/4 turn is a better check. You might also argue that mistakenly having a tank 1/4 open is better than having it completely closed; at least it will function in shallow water.

Note that the 1/4 turn back will make no difference to the dlivery of air from the tank. The valve will probably function fully even if the tank is only half open (certainly at recreational depths anyway).

Back to the possible cause of the OP's problem - it's possible for a tank to be opened incompletely but enough so that the needle on the SPG doesn't deflect at the surface during a buddy check but the problem of the swinging needle and associated breathing difficulty then becomes manifest at depth. That doesn't preclude a problem with the regulators, but certainly in my experience the partially opened tank is more common than the latter.

Safe diving,

C.

 

[Nemrod]

If you were descending and the flow stopped then it might be a missing dip tube and FOD in the tank.

As well, having left over parts when you reassemble an item can cause odd happenings. I don't let strange people workonmy stuff, I do it myself for exactly these reasons.

N