Tank valves problems and failures

[Scuba]

What sort of problems can one encounter with regards to the complete tank valve assembly, and how can it fail?

I was reading the thread about burst discs and apparently they always rupture before the dive, and would most likely only rupture at the begining of the dive underwater, if this where to occur, do to diminishing air pressure.

On the Yoke assembly the O-ring can blow out, and I suppose if the tank is dropped and the O-ring retaining structure is damaged it could cause a bad seal and O-ring failure. The threads could likewise be damaged on a DIN assembly.

I haven't seen anything negative about carrying a tank by the valve knob.

Is anyone aware of any instances where the valve knob may have been turned completely or partially off in an entanglement situation or overhead environment? .... Or broken where you could'nt manipualte it if you had to.

Anyone hear of any instances where the airflow can be impeded or cut-off otherwise? Possibly due to loose rust flakes inside the tank.

Does this valve ever have to be serviced or overhauled? Does it accumulate rust or deposits that could cause problems?

If tank is dropped and valve strikes a hard object fairly hard, should it be inspected internally for possible damage even if everything looks ok from the outside?

Anything else.

I know, a lot of ifs, just trying to get some feedback on subject that doesn't get much discussion, maybe due to its reliability.

 

[metridium]

Scuba wrote...
I was reading the thread about burst discs and apparently they always rupture before the dive, and would most likely only rupture at the begining of the dive underwater, if this where to occur, do to diminishing air pressure.

I've read reports of UW ruptures, including one on a cave dive, though how early in the dive I don't know. That's why cave and technical divers will double-disc or plug their burst disc ports.

Scuba wrote...
I haven't seen anything negative about carrying a tank by the valve knob.

Just make sure it's not the isolator valve.

Scuba wrote...
Anyone hear of any instances where the airflow can be impeded or cut-off otherwise? Possibly due to loose rust flakes inside the tank.

I believe Aldora in Cozumel had this problem with their steel tanks a couple years ago.

 

[Wreck/Tec]

Guys, If you take a new tank and valve and are good to them they will be good to you. If you take a used tank and valve, get them inspected throughly, they should be good to you as well. I on the other hand use my stuff! I get my stuff inspected as we all should. I however, take the origional burst discs in the valves in my steel Fabers and replace them with a higher pressure one, every year! I routinely overfill them so by the time they cool I have 3200 or so. Some fill them higher, I'm happy here. I also take the valve every year and clean them in Simple Green, then change the Viton "o" rings with new ones. The only exception would be the tank with 100%. You will hear horror stories, some will be true. If you know your gear, how it's maintained, and how it functions, your chances of being one of the unfortunate are enormously reduced, as is the stress level your heaping upon your self now! There are many spirited discussions about types of valves, din or yoke, or which regulator to use. The thing they all have in common is they all have limits, purpose, and all require attention. Your attention to your gear, is just as important as your partners attention to you, or your attention to training. It's like a triangle, they are all entwined and follow each other. You remove one and you allow more potential for trouble! You may be lucky, or good, but the margin for error is greater. Moral of the story......................
Take care of your self, Train! Take care of your gear, inspect often, and invest in it! Take care of your partner and they will take care of you. If that isn't the case get a new partner!
Wreck/Tec

 

[BlueWaterDiving]

Man that was good I don't think anybody can top that. You covered that well.

 

[pescador775]

Scuba, rebuild a valve after five years, clean, grease lightly, replace parts. There is virtually nothing that can wrong with them. Some have an O ring in the valve stem packing and this will disintegrate over a long time. Some have a replacable copper washer. The valve seat can wear. On a yoke valve, replace the original black facia O ring with a white ring after one year, then five years or with the regular overhaul. Take care, use a brass pick to remove ring, NOT ice pick or similar. When in use, don't overtighten the valve knob and don't bang it against anything hard. It's Ok to carry by holding valve. That's why Sherwood designs their valves with a T shaped boss.

Years ago, I received a new 3300 psi tank with a 2250 service burst disk. I never noticed. After ten years, the LP disk blew out while in the back of my truck. I had made hundreds of dives with that tank. Don't worry about disks but replace with regular service. Double check the rating. Some are rated by service pressure, others by burst pressure.

 

[JamesK]

Scuba once bubbled...

Is anyone aware of any instances where the valve knob may have been turned completely or partially off in an entanglement situation or overhead environment? .... Or broken where you could'nt manipualte it if you had to.

Yes. I have rolled off my left post partially before, as I am sure lots of cave and wreck divers have at one time. I have also seen damaged knobs. Also, metal and plastic knobs are more prone to break if impacted, that is why you should ue a soft rubber knob.

 

[Scuba]

Thank you all for your reply's.

Funny thing, before a dive a few days ago my buddy notices one of his tanks is low when it was supposed to be full. Upon close inspection he had a leak from the burst disc. It turns out the burst disc bolt on his tank protrudes leaving it exposed to impact, as opposed to others which sit protected from impact by a surrounding case. He's not sure if it was bumped or something else caused it to leak. Anyways, if you have one of these something to keep an eye out for and take a close look if bumped on something.