"Hot" First Stage

[chrismortell]

This almost turned into a serious problem:

I just had my Conshelf reg serviced and went to a nearby quarry for a test dive. I have had this setup since 1990. Yes, it's old, but I have it serviced regularly and it has performed beautifully...until now.

The dive was proceeding normally. I might even say it was going great as I was using much less air than usual. I might say great, but I won't. At about 52 min, I checked my air and was at approximately 950 psi breathing normally. Two minutes later, I suddenly went from normal, easy breathing to breathing like I was trying suck air through a straw. My SPG was still indicating about 900 psi...until I took a breath. Then, the needle would drop down to 100 and go back up when I exhaled. At 30', this was disconcerting but not panic inducing. I grabbed my buddy and we made a normal ascent. Fortunately, I wasn't deeper and didn't need a safety stop. That could have been a problem.

I went back to the shop where I had it serviced and the manager (who is not the tech) hooked it up to their test rig. That showed the pressure in the first stage was way above normal. His explanation was that the first stage wasn't adjusted properly.

Has anyone else had this happen before and how much of an issue is it?

 

[Packhorse]

Was your valve right open? Was there an obstruction in the dip tube, valve or reg filter?
I cant see how a mis adjusted IP could cause such a problem.
Did the problem go away/ get better as you ascended?

 

[beanojones]

Was your valve right open? Was there an obstruction in the dip tube, valve or reg filter?
I cant see how a mis adjusted IP could cause such a problem.
Did the problem go away/ get better as you ascended?

Seconding this.

Lesson learned from DIR, that they learned from cavers: When you turn on your valve, turn it all the way on, and leave it. Do not turn it all the way on and then back a half turn.

 

[=C=]

Seconding this.

Lesoon learned from DIR, that they learned from cavers: When you turn on your valve, turn it all the way on, and leave it. Do not turn it all the way on and then back a half turn.

I forget whay they taught us to back it off half a turn... It was something having to do with valve design wasn't it?

 

[captain]

I forget whay they taught us to back it off half a turn... It was something having to do with valve design wasn't it?

It is more of an solution to a problem that doesn't really exist. The idea was to prevent someone thinking it was closed and try to open it with too much force that could possibly damage the valve. If you open your own valve open it all the way, you will know its open. If someone volunteers to check it say no thanks it is already open.

 

[FrankPro1]

PADI teaches to turn the valve back 1/4-1/2 turn after fully opening it. What the pros and cons for doing such action? I remember my instructor telling us that modern valves don't need this, but it never hurts anything. Or does it?

 

[beanojones]

PADI teaches to turn the valve back 1/4-1/2 turn after fully opening it. What the pros and cons for doing such action? I remember my instructor telling us that modern valves don't need this, but it never hurts anything. Or does it?

Actually PADI instructors teach this, but IIRC PADI itself has nothing to say about this.

Here's the deal: The guy who started this thread likely went into the water with his valve closed all the way and then opened a quarter turn. No problem at the surface since the valve supplies air even open a little bit. But as you go deeper that "little bit open" won't supply enough air.

So yes turning your valve back a bit does have a major flaw. (And more importantly it serves no function other than to screw things up underwater.)

If you want to go diving, open the valve all the way, and then leave it the fsck alone. If you always open it (or close it) all the way, you can never start a dive with a mostly closed valve. If you breathe off your reg, and your SPG needle does not move then you are OK.

If you get in the habit of turning the valve back a bit, you might just be opening it a little bit after it was fully closed.

 

[chrismortell]

I won't say that it's impossible that I went into the water with the valve mostly closed. Mistakes happen. However, I've made almost 250 dives and never done that before. I was taught to open the valve all the way and then back it off 1/4 turn. In this case, I am 95% certain that it was open.

The needle didn't move until the pressure in the tank got low. As I understand it, if the valve were closed part way, the needle would move at any pressure. Or is that not correct? If it was a dumb@ss mistake on my part, I want to be reasonably certain. I can correct that, but I'd like to have faith in my gear.

 

[beanojones]

I won't say that it's impossible that I went into the water with the valve mostly closed. Mistakes happen. However, I've made almost 250 dives and never done that before. I was taught to open the valve all the way and then back it off 1/4 turn. In this case, I am 95% certain that it was open.

The needle didn't move until the pressure in the tank got low. As I understand it, if the valve were closed part way, the needle would move at any pressure. Or is that not correct? If it was a dumb@ss mistake on my part, I want to be reasonably certain. I can correct that, but I'd like to have faith in my gear.

Here's the deal. You can breathe off on almost closed tank on the surface, especially when the tank is full and the full force of the air pressure is pushing the tanks valve seat open. The needle won't 'necessarily' move. If you have a full tank and gear at home you can try it out. But as the tanks pressure falls the amount of force the air is pushing against the seat drops. Additionally, as you go deeper the amount of air you need per breath increases.

It's also not necessarily the case that you did it. DMs on the boat are generally running around doing that "all the way open and back a half turn" thing to everyone's gear. They even do that to divers about to jump into the water. If you get a DM who happens to be standing on the wrong side of the gear they may accidentally close it all the way and then back it open.

Plus you can always bump things under water and roll your valve open or closed. On a single tank generally if you bump it going forward it will tend to open. But that means that if you stick your head in somewhere to take a look, and back out you can roll it closed.

Open your valve all the way open and leave it alone is always the best plan. But that does not prevent an overzealous DM from checking your valve, thinking it is all the way closed (even though it is really all the way open), and closing it and then opening it a little. Which would leave you in exactly the sort of situation you found yourself in.

Bad instructor/captain trick: When a just starting out DM is getting too full of himself, walk behind him and close his valve just before he jumps in. He's supposed to look at the gauge while taking a breath but rookies sometimes forget the basics. This trick also works on newbie instructors.

The solution: If your gauge is moving, your valve is mostly closed (or completely closed). Reach back and turn the valve on. And turn it on all the way. And leave it.

Old habits die hard. The "turn it on and back it off a bit" trick maybe made sense when valve stems were packed with waxed thread (maybe). But now that many valves just have just teflon on the stem, and not even Orings, much less waxed thread, it makes no sense. But once you become an instructor (or DM), you are not required to ever learn anything else. If someone became an instructor 35 years ago, their knowledge can stay frozen at the state of the art, but 35 years ago. And since they have a lot of influence over younger instructors, the 35 year old 'state of the art' gets passed on. Most instructors learn how to teach by watching experienced instructors.

Household valves have largely moved to 90 valves for just this reason. There are meant to be two states for most valves: ON and OFF. The only household valves that are still using a free spinning valve are specifically pressure reduction valves, which are designed to restrict flow to reduce pressure.

 

[pescador775]

I always back off the valve by an eighth or a quarter. It's probably not necessary anymore but I think it reduces the shock to the valve stem if bumped. Also, it is easier to do a quick check on the valve position without misapprehending that it is stuck in the closed position. Chris, you should have that valve inspected. If the valve seat has popped out of the spindle it might cause some funny business. More likely than stoppage, the tank might slowly leak down but it would not be a bad idea to check all equipment in the air circuit. This stuff about the regulator IP is odd, a coincidence, maybe, but I am not so sure. Typical suspects would be the regulator filter screen, a piece of debris somewhere but I doubt it. I would investigate the length and position of the pin which lifts the HP seat, although that has probably been fixed if the wrong one was installed or if it was bent or installed at a cocked angle. Even working properly, those Conshelf seats only lift 1/32 inch. A partly opened valve would, of course, cause the problem exactly as observed but you say that you are a careful, reasonably experienced diver and I have no reason to doubt it.