well this bites...

[captain]

You know, if I ever film a movie where there is a diving scene, I'm going to have one of them run out of air. He'll ask for the octopus, but the other guy won't know what he's talking about. Then the OOA diver will pull out his slate and write a note. The other diver then suggest rock paper scissors. OOA guy loses all three tries. Then the diver with air signals that they ascend, and you see they are in 4 and a half feet of water. The shot jumps back a few feet and you see that only the OOA diver even has a tank, the other divers reg hose leads to his snorkel.


Just a thought.


I know what it feels like to be out of air, I want to know at what psi my reg starts breathing harder. Can't practice everything though.....what'd be best is to do it at 60 feet and do a real practice emergency ascent (almost always swam up way too fast in class, but most of our emergency stuff was done pretty shallow (25 feet? deepest dive was around 50 feet) and the shops depth gauge didn't work well. ) and all that, but i don't want to get the bends while practicing stuff!

Dive a tank with a J valve and you will get a good idea what running out of air feels like. Then pull the J lever down.

 

[JahJahwarrior]

The tank I'm getting hydroed has a J valve. I think I might replace it with a K valve though, a lady I know but have never met has told me that I shouldn't use such an old valve, and offered to give me a free K valve. She's a friend of a friend that helps me out with some dive stuff from time to time

 

[captain]

Nothing wrong with a J valve, all my tanks have them.

 

[Ed Palma]

...But if you could get a free valve, why not?

 

[JahJahwarrior]

That's what I said, but if she give me a free K valve, I might accept and sell the J valve online or something. I don't need a J valve, and this one in particular is awkward to carry: kind of wide, spreads the fingers far apart when carrying in one hand, and the edges aren't sharp, but aren't flat....there are wrench flats on it, and the points dig into the hands. I can manage ok if I carry it by the J valve part of the J valve

I'm quite amused by how long this thread has gotten. I post to find out about tank hydrostatic testing laws and stuff and suddenly it's 7 pages long. I would love to know more about the alloys and how DOT does all of its things on how long tanks can stay in service. It's interesting.

 

[Ed Palma]

yeah, but let us know what happens after your tank's hydro. I just brought mine in yesterday - y'know, the LP100 with the J-valve. Anyway, I wanted it tumbled because of flash rust, but the inspector said it was quite normal and wasn't "powdering" off. I insisted on a tumble anyway (just to avoid having my reg re-serviced). Anyway, I'm gonna get it next week. Hope it passes.

 

[JahJahwarrior]

So do I!!

Just got my reg back today, about $90 with parts and all. $6 on a new mouthpiece (MUCH smaller than the old one, doesn't force my jaws into a wierd position), $3 on a brass clip to clip my SPG to my BC, and $7.50 on an adaptor to get the SPG hose to fit on my ridiculously old reg. Borrowing some tanks from a friend and cannot wait to dive something with this stuff! I think it'll be a week before I get some real diving in, but I'm gonna jump in the pool sometime, maybe tonight.

 

[rjk75]

I'm quite amused by how long this thread has gotten. I post to find out about tank hydrostatic testing laws and stuff and suddenly it's 7 pages long. I would love to know more about the alloys and how DOT does all of its things on how long tanks can stay in service. It's interesting.

JahJahwarrior,

I'm new to this board so here's my first contribution.

I, too, bought a tank on the thrifty side for the same reason of convenience--to keep a filled tank ready to go at a moment's notice.

However, I bought a good used steel 72cf USD tank from an LDS for $99 Cdn. It comes with a J-Valve and a four-month old VIP and hydro test. The tank was manufactured May 1971 and rated for 2250 psi with a "plus" rating from the factory.

Except for a bit of spot rust on the bottom under the boot, this was a good buy. I fix rusty cars (I use a product called Rust Mort) and so that's no problem.

Now the point of my posting here: I would never buy a used Al tank unless either it is a very new or I know of its provenance. Here are the reasons why:

http://www.airsource-one.com/beaver.html

http://www.scubabomb.freeservers.com/Scubadag.htm

http://www.scubabomb.freeservers.com/index.htm

http://www.scubabomb.freeservers.com/Cscuba.htm

http://www.scubaboard.com/showthread.php?t=4400&page=3

The ff. diveoz URL is especially useful for your tank--read it completely.

http://www.diveoz.com.au/discussion_forums/topic.asp?ARCHIVE=true&TOPIC_ID=4168

http://www.scubaengineer.com/tank_servicingx.htm

I just finished looking at each URL and cut-and-paste then in. The last one is perhaps the one of most interest to you and anybody else considering buying a used Al tank. Read esp. the red text under "Special Notes for Fill Station operators." This ought to answer your questions.

You can also enter your tank's DOT number you gave us into a Yahoo! search and see what you get. You'll find lots of other good info there. Google fails here IMHO.

And as a last resort, if you get the tank tested successfully all around and a dive shop still refuses to fill it up, ask them nicely if they'll fill it up to say just 2300 or 2400 psi. If they do, then you've got your own tank and source of air.

Hope this helps; it's really important to be informed of the dangers of these first few Al tanks put on the market. I wouldn't fill them up for anything!

Regards,

RJK75

 

[JahJahwarrior]

I'd read some of those links. I cannot deny the fact that this is an old tank and it's made out of a "bad" batch of aluminum. However, as long as it passes hydro and passes well, then it should be safe to fill it. For hydrostatic testing, they overfil the tank (I believe to 5k psi for a 3k tank), which would be more than enough to burst it, if it were going to burst at 3k, it will burst at 5k. Secondly, they measure how much it expands. If it were going to expand much at 3k, it will expand all the more at 5k. Then they measure howmuch it shrinks when pressure is removed. If it passes a test at 5k, then I have no problem trusting it at 3k.

If I get it back and they tell me that it passed butjust barely (there are ranges for passage of the shrinking/expanding test) then I won't use it. I'll ask them if they can overstamp the numbers on it, condemning it, but not drill through it. My dad might use it as a 150 psi storage tank or something. If he doesn't want to use it, then I'll dril a hole in it.

 

[MikeFerrara]

I'd read some of those links. I cannot deny the fact that this is an old tank and it's made out of a "bad" batch of aluminum. However, as long as it passes hydro and passes well, then it should be safe to fill it. For hydrostatic testing, they overfil the tank (I believe to 5k psi for a 3k tank), which would be more than enough to burst it, if it were going to burst at 3k, it will burst at 5k. Secondly, they measure how much it expands. If it were going to expand much at 3k, it will expand all the more at 5k. Then they measure howmuch it shrinks when pressure is removed. If it passes a test at 5k, then I have no problem trusting it at 3k.

If I get it back and they tell me that it passed butjust barely (there are ranges for passage of the shrinking/expanding test) then I won't use it. I'll ask them if they can overstamp the numbers on it, condemning it, but not drill through it. My dad might use it as a 150 psi storage tank or something. If he doesn't want to use it, then I'll dril a hole in it.

A tank only gets hydro tested every 5 years. How many pressure cycles does it see inbetween? How long does it typically take for SLC to develope to the point it's going to burst? I've heard plenty of experts running their mouth on the subject but I haven't seen any test data...like life test data on the tanks or any testing that characterizes the failure mode beyond a few pictures. Statistics can be a real fooler here bucause I think there are lots of very old tanks that haven't been filled very often.

I think every one of these tanks that we had, eventually showed cracks and have since been retired. None exploded but if you want I'll send them to you and you can fill them a bunch of times and see if they will. We saw the cracks during visual inspection but would the guy down the street have seen them?

Personally I'm glad that I don't have to fill tanks in a shop any more...especially these tanks. You spent $20 on the tank, 22 on the hydro and you still need to get it visualled. What are you really saving?

The proabability of an explosion is probably very low but so are the chances of surviving it if you're standing very close. When they go, they pretty much take out the whole shop. I don't see where they are worth messing with. Well, it might be worth it to you but it doesn't sound like you're going to be the guy who gets himself and his property blown up if it goes.