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View Full Version : hydro, and 10% overfills



Iceguy4
07-11-2008, 14:55
Hi,
Its my understanding that the hydro inspector is the person who gives the tank the designation for a 10% over fill. I have new lp 121 cf steel tanks (big SOB's) and with out the over fill.2640 lbs instead of 2400lbs, these tanks will only be 109 cf. I like having 121 cf and that size works out well for me when diving with other guys with 80's. I was told when it gets its next hydro , I will loose the 10% over fill designation unless my hydro guys gives it . is this true, and if so what can I do , or who can I send it to ? Thanks in advance for your time...
Ice

gregor
07-11-2008, 15:30
It's true, if it's not tested to the + rating, it won't automatically get it. Most dive shops don't do hydro's in house, the majority of them are done at places that service fire extinguishers. If you look in the yellow pages you can probably find one near you. Call them up and ask if 1) they deal with individuals (many of these places only deal with other businesses) and 2) if they can do the + rating for scuba cylinders. You might have to try a few places before you get a yes to both of these. Or ask your local shop if the place they deal with does the + rating.

Personally i like to get it straight from the horses mouth (fire extinguisher place) so that if i go pick up the tank and it doesn't have the + rating i can complain to them.

The tank will still probably need to get a VIP sticker from your dive shop because most of these fire places don't do VIPs (some do, it's worth it to ask).

cummings66
07-11-2008, 15:42
You just make sure the hydro shop can do the + rating, not all will do it.

in_cavediver
07-11-2008, 17:08
A little clarification. All the hydro places *can* do the plus rating as its a test pressure below that of an AL80. The question is whether they *will* or even check to see if they need to. This is more a case of operator education than anything else.

As for a VIP - as part of the hydro, the tank will recieve a DOT sanctioned visual inspection. This is to CGI section 6.X standards. (C6 is steel, C6.1 is Al). Whether a dive shop takes is as a VIP is another matter. VIP is a dive industry Visual Inspection Program thing and is NOT affiliated with the DOT Visual process. The DOT process is a standard in regualtions, the Scuba VIP is a 'norm' without published or enforced uniform standards. (though PSI would like to claim otherwise)

Personally, I like to do a quick VIP whenever the valve is off a tank. It only takes a few minutes more. This is especially true of the older 'bad' alloy AL tanks. I personally won't touch the 6351's though. Only 3AA and 6061's for me. (I might add an exemption steel at some point as well)

ScaredSilly
07-11-2008, 17:51
A little clarification. All the hydro places *can* do the plus rating as its a test pressure below that of an AL80. The question is whether they *will* or even check to see if they need to. This is more a case of operator education than anything else.

This is not completely correct. I have a set of MP Fabers that are 3000psi with a plus rating of 3300plus. Also Faber makes a 3180psi that has plus rating of 3498psi. When steel or AL the test is 5/3 of the working pressure.


As for the can and will this is correct. Especially if they have to look up the REE standards.

in_cavediver
07-11-2008, 21:05
A little clarification. All the hydro places *can* do the plus rating as its a test pressure below that of an AL80. The question is whether they *will* or even check to see if they need to. This is more a case of operator education than anything else.

This is not completely correct. I have a set of MP Fabers that are 3000psi with a plus rating of 3300plus. Also Faber makes a 3180psi that has plus rating of 3498psi. When steel or AL the test is 5/3 of the working pressure.


As for the can and will this is correct. Especially if they have to look up the REE standards.

I stand corrected. I didn't realize many of the 'medium' pressure tanks were 3AA with the '+' rather than an exemption - live and learn. Thanks for the tidbit!.

Now, just for fun, we could add the 4500psi and 6000 psi storage bottles for hydro test pressures. Now, not every hydro shop can do those tanks....(10,000 psi test on the 6K tank)

captain
07-12-2008, 09:55
The + rating has nothing to do with how the hydro test is preformed. The + rating is a simple mathmatical calculation using the elastic expansion rejection limit and the 10% expansion requirement.
In order for it to be calculated the tester must either know or be able to calculate the elastic expansion rejection limit. Some newer tanks come from the manufacture with the EER stamped on it. Many older tanks do not have it stamped on them and the only way to know what it is is to have documentation from the manufacture or calculate it using the specifications under which the tank was made, which most if not all hydro testers either can't do or will not do.
Only specification 3AA steel tanks can be + rated. If it didn't have a + rating from the manufacture it cannot be + rated at a later time.
All tanks of the same size made under the 3AA specs will have the same EER. It is knowing what it is is the problem. Myself and several others have been trying to determine the EER for the old steel 72 tanks. We have calculated it somewhere between 55 and 60 cc's but unless you can present a hydro facility with offical documentation from the manufacter it does no good.

example

Tank 1 has an EER of 55 cc's. Results of the hydro test are
maximum expansion at test pressure 60 cc's, residual expansion after pressure is released 3.5 cc's. Tank passes less than 10% expansion requirement (10% of 60=6 cc's) Passes with no + rating. EER exceeded, 60 cc's -3.5 cc's= 56.5 cc's, 1.5 cc's above EER


Tank 2 has an EER of 55 cc's. Result of the hydro test are 56 cc's maximum expansion at test pressure, residual expansion after pressure is released 3.5 cc's Tank passes less than 10% expansion requirement (10% of 56=5.6 cc's) and also passes EER of 55 cc's and can be +rated. 56 cc's - 3.5 cc's= 52.5 cc's, 2.5 cc's below EER

cummings66
07-12-2008, 17:46
the Scuba VIP is a 'norm' without published or enforced uniform standards. (though PSI would like to claim otherwise)


I might have drifted off to sleep during that part of my PSI course, but I do have material from them that specifically says the DOT has no authority what so ever on our cylinders used for personal use and that we don't even need to hydro them. However, that means a commercial op can't fill it, but as an individual you don't need to hydro or VIP them.

What PSI is attempting to do is to make the inspection process uniform and in enough detail to catch cylinder problems before they go boom. They have IMO a very good program for doing just that and it's based in part on the CGA standards. I just didn't get the impression that they tried to make it seem like there is a mandatory standard for scuba diving, only that they have a standard that they think is best. Of course, every agency thinks theirs is best.

in_cavediver
07-12-2008, 19:34
the Scuba VIP is a 'norm' without published or enforced uniform standards. (though PSI would like to claim otherwise)


I might have drifted off to sleep during that part of my PSI course, but I do have material from them that specifically says the DOT has no authority what so ever on our cylinders used for personal use and that we don't even need to hydro them. However, that means a commercial op can't fill it, but as an individual you don't need to hydro or VIP them.

What PSI is attempting to do is to make the inspection process uniform and in enough detail to catch cylinder problems before they go boom. They have IMO a very good program for doing just that and it's based in part on the CGA standards. I just didn't get the impression that they tried to make it seem like there is a mandatory standard for scuba diving, only that they have a standard that they think is best. Of course, every agency thinks theirs is best.

That is correct in the letter of the law. That said, and Vance Harlow states in the oxyhacker guide - its best to believe we are under the DOT rules. Pretty much for all of us, some comercial op will eventually have to deal with our tanks. When they do - the hydro matters.

As for the 2nd part - you summed it up pretty well. There is a supposed industry 'norm' for VIP and PSI has positioned itself as the big player. Kinda like dive instruction and PADI/RSTC. The big one sets their standards and most others meet that standard but not all. That said, there still isn't an enforceable standard out there. Its 'self policing' by dive shops so quality varies based on who does it and what, if any, training they have. This is different than the DOT visual which goes with the hydrostatic test. That does have specific criteria used and is enforced with law.

I wasn't trained by PSI for tank VIP's and I use the DOT/CGA 6.0 and 6.1 guides for the Visuals I do on tanks. (private - non-commercial only). Scuba Cylinder Inspectors International did my training and it was all DOT standards.