How dangerous is this ?

[Divingblueberry]

Here’s how I understand it :

With a full tank (3000 psi) the pressure on the valve prevent it from moving. Only a situation like a free flow or an equivalent can bring down the pressure low enough to be able to unscrew the valve like I did.

I guess, the two are related in a sense that without the tank bleeding out, there is no way I ( or anybody else) could have unscrew the valve.

Looking at the situation after the fact may have led to think that there was laziness involved, but that wasn’t the case. One led to another.

 

[CT-Rich]

No way is a tank with 3000 psi, or 400 psi going to have a valve that is going to be finger tight. Once the tank was completely empty, some manhandling of the the gear could probably get it loose (it may well have not had sufficient torque on it to meet recommended specs). The valve is designed to be periodically removed, so I guess it won't be particularly tight when the tank is empty. I have removed valves from tanks and never found it particularly difficult.

the tank will need to be reinspected to make sure no moisture got inside after it bled out.

 

[Russjstewart]

For what it is worth, I have seen instances of tanks leaking, even with the valve done up, I guess they were caused by a damaged valve o ring, in both cases they were hire tanks, and the leaks were only noticed when they were in the water. The contents gauges read close to 200 bar, so I am assuming that either
A. The tanks had just been filled
B. The rate of gas loss was quite slow or
C. Both the above

 

[DanielRJones]

For what it is worth, I have seen instances of tanks leaking, even with the valve done up, I guess they were caused by a damaged valve o ring, in both cases they were hire tanks, and the leaks were only noticed when they were in the water. The contents gauges read close to 200 bar, so I am assuming that either
A. The tanks had just been filled
B. The rate of gas loss was quite slow or
C. Both the above

I have had a tank that worked fine with air and nitrox but as soon as your started outting helium in it leaked like hell

 

[Divingblueberry]

the tank will need to be reinspected to make sure no moisture got inside after it bled out.

That is a very good point. I, however, doubt they'll do it : the guy in the shop just got the rubber mallet out and tightened the valve in place before I left.

 

[EireDiver606]

As @decompression said, another piece of evidence which highlights the importance of a pre dive check...on everything.

 

[Jack Hammer]

Though a common way to tighten and loosen the valve, wacking the valve with a rubber mallet can bend the stem. The parts are brass and I've seen enough bent stems that I just use a wrench these days.

 

[Stoo]

That being said, does the pressure in a full tank have any impact on how easy it'd be to unscrew the valve ?

Absolutely. It's virtually impossible to unscrew a properly mounted valve by hand with more than perhaps 2-300 PSI in the tank.

To answer your initial question, yes, a partially unscrewed valve is extremely dangerous. At some point, the neck o-ring could be forced out of it's proper position and this would result in a catastrophic (i.e. REALLY fast) loss of air. It's hard to imagine a shop filling a tank with a lose valve, but I suppose anything is possible.

I'd be sure to bring it to the shop owner's attention. He dodged a bullet, as did you.

And as others have said, a lose valve would have no bearing on a reg. (Other than perhaps if the same technician installed the valve and serviced the reg recently!)

 

[boulderjohn]

The parts are brass and I've seen enough bent stems that I just use a wrench these days.

I just put a wrench on the valve and turn it until it is snug. That works just fine.

A few weeks ago a dive instructor came to me house so we could tumble (if needed), inspect, and O2 clean his tanks. We struggled to get them open. I put my longest wrench on the valves and beat the end of the wrench with a mallet repeatedly. We eventually got them all open, although we almost gave up on one of them. He said that they had been put on last by some guy who had some kind of a jig he used to open tough valves, and he wondered if he had used the same device to tighten them. The whole time we struggled with this, I kept muttering about how unnecessary it was to make them that tight.

We finally got all the tanks serviced as needed, and I set about putting gear away (etc.) while he put all the valves back on. I came back into the room to see him do it. He was reversing the process we had used to take them off, putting on my longest wrench and beating the end of it for all he was worth with the mallet. "What are you doing??!!" I asked. He wanted to make sure they were tight. I hope I am not involved with getting them off the next time they need it.

 

[Rollin Bonz]

When replacing a valve after a VIS it is very common to tighten with a sharp tap with the hand or a plastic mallet. So, it is quite possible that it was knocked or bumped in transit to the dive site. Just another item to go over in your predive check.

Not sure I understand...
How do you pre dive check to be sure the tank valve is tight? If the tank is full, the pressure will hold the valve tight, right? Wouldn't it be that only when the tank is empty that the loose valve would be detectable? Making a valve tightness check on a full tank useless?