My illegal steel tank

[archman]

I found this old steel tank in a UDT diver's attic, and had it serviced. The LDS says that the first stage (or the burst disk itself) is "illegal". However they also filled it up and VIP'ed it. They say that the first stage can be replaced since the threading is compatible with more recent steel tanks... still don't know why they filled the tank up if it's "illegal" however. Passed hydro just fine.
Here are some pics of the thing. Could someone tell me what's wrong with it and what has to be done (if anything) to fix it?

 

[Tiny Bubbles]

Looks like the tank might be just a little bit out of hydro.

 

[archman]

That's the original date. They stamped the new date on the other side.
And here I thought they'd chop the thing in half and I'd dump it in my flower bed... surprise surprise.

 

[COVCI]

Had someone at the shop who was properly trained done a complete visual cylinder inspection, they would have been able to tell you that you have a steel cylinder first hydrostatically tested in 1966, manufactured by Norris industries with a working pressure of 2470 if it is able to be hydrostatically retested to get a plus rating.

The problem with having it filled is that the valve is not equipped with a multi-vectored burst disk. The current burst disk looks a little like the head of a slotted screw. When this fails it blows out of the valve and creates projectiles about the size of the bullet part of a .22 caliber round.

Drain the cylinder, swap the valve with a new one, have a TRAINED visual cylinder inspector do an inspection after a new hydrostatic retest and dive the thing.

Chris
COVCI

 

[Scubakevdm]

They probably didn't even have the tank valve when they hydro'd the tank. We take ours off before we even send them out, so I know that at least in the case of the hydro Co. that we use the valve is completely unrelated to the testing. You may run into people who won't fill them, there are some folks around here that flat out refuse to. I probably would, based on the condition of the tank, and the fact that this is the first Non-factory Hydro. Hopefully you won't have to drive all the way out here to fill your tank, but if you do I'll show you that cyanobacteria bloom that goes along with the report by Ed Tischner you read a while back. I'd be interested to hear your opinion of the state of things. By the way, the report is almost done. - Kev

 

[quimby]

Had someone at the shop who was properly trained done a complete visual cylinder inspection, they would have been able to tell you that you have a steel cylinder first hydrostatically tested in 1966, manufactured by Norris industries with a working pressure of 2470 if it is able to be hydrostatically retested to get a plus rating.

Ok he said it is hydroed and the new stamp is on the other side. As far as the blow out plug is concerned I cannot be sure if its one with the "little lead worm" or one with the just the copper disk so till then its open season. And if it was hydroed the inspector did his visual as required by dot and from there on it overkill, also its dam rare that a old steel if tested for it doesnt get its plus and probably a question mark for the tester if it doesnt.
The subjectivity as far as filling goes after testing is another reason I pump my own.

 

[FredT]

The problem with having it filled is that the valve is not equipped with a multi-vectored burst disk. The current burst disk looks a little like the head of a slotted screw. When this fails it blows out of the valve and creates projectiles about the size of the bullet part of a .22 caliber round.

Drain the cylinder, swap the valve with a new one, have a TRAINED visual cylinder inspector do an inspection after a new hydrostatic retest and dive the thing.

Chris
COVCI

Chirs.

That isn't the melt disk plug, but a single outlet rupture disk. The rupture disk normally won't toss metal as the disk tends to fold over into the flow path at rupture, but can inject a lot of air under your skin if you happen to have a hand near it when it goes. Melt disk plugs are the ones that can really hurt you.

If that plug will come out the valve can be recovered for use simply by installing a modern burst dsk assembly. The threads are the same. Note: get a large cheap screw dirver and grind the end to exactly fit that slot. Bending the top end of those flush disks with the wrong driver is what kills a lot of older tank valves. Once bent they DO NOT come out.

Stubby valves are a handling comfort issue and the diver may want to replace it for that reason, but otherwise they'll work just fine. Generic or "old style" Sherwood parts will fit the older Healthways and Dacor valves.

It would also be good to check to see if the tank is galvanized under the paint by examining the more recent hydro markings. If not a paint strip and cold galv may be in order before putting the tank back in salt water service.


FT

 

[ScubaJewel]

As I understand it the main problem with this type of burst disc is that when they do blow it has a tendency to push the tank over potentially causing further problems such as a wildly spinning tank or a situation where the valve may be nocked off causing tank propulsion.

You should be able to replace this disc with it's modern couterpart or simply replace the valve. New valves can be purchased for under $50 almost anywhere.

Julie

 

[Hallmac]

As FRED T stated just replace the burst disk with the modern side vented multi discharge one and your back in business.

Hallmac

 

[archman]

Wow, all this technical expertise makes me feel stupid. How RARE.

Being mechanically deficient (I don't even change my own oil), it sounds like the most prudent course of action is to have the LDS replace the entire first stage. I'm not even sure where the burst disc IS (that's why I have two pics of the first stage).

Now should I have my LDS replace the first stage, or find someone more professional? I don't like to knock the head instructor at my local LDS, but he IS somewhat flaky and remarked about "having some spare steel tank parts that would probably work". In his defense he immediately identified the burst disc thing when I brought the tank in, and appeared to have at least some experience with steel tanks. The question is, is it enough?

Oh yeah, and will this tank need to be hydrostatically tested AGAIN after the first stage is replaced? Ick.

I'm pleased that the tank most probably is in fact usable. I have a soft spot for quality, working "antiques". And this tank belonged to my best friend's father, one of those amazing Navy UDT folks that predated SEALS. This dude did solo missions in Cuba during the 1960's. Wicked!