Hydro testing/visual expectations?

[an0br1]

TL;DR: burst discs in recently hydro'd tanks were leaking. Is this to be expected?, and something I should be checking myself when I get tanks serviced?

I'm returning to diving after a long absence.

I recently took four Al 80's in to the local shop for hydros. Two of the tanks hadn't been used since ~2002 and had ~1500psi before I dropped them off at the shop. When I picked the four tanks up, the tech/service guy checked the pressure on all and said they were full, though I didn't see what the psi was.

A few days after bringing the tanks home I checked the pressure and found 2 were at 3300psi, 1 at 3200psi, and one at 2700psi. It's been a long time since I had a tank filled, but recalled tanks could be overfilled 10%, but maybe vague memory that that was only for steel ... I assumed maybe the 2700psi had been filled separately and got a hot fill.

A couple weeks later, used the two 3300psi tanks and had them refilled in Monterey over the weekend. Checked pressure on all tanks this morning and those refilled in Monterey were 2950psi, but the two tanks that were still unused were now down to 3000psi (from 32) and 2200psi (from 27). :-\ I dunked all the tanks in the bathtub this morning and found the 2200psi burst valve was leaking very steadily and the 3000psi leaking steadily but very very tiny bubbles.

Is _ANY_ leaking from the burst disc (threads) acceptable? The two that are leaking are Sherwood valves with exposed discs (vs. the two others not leaking that are recessed). Given the leaking tanks were at 1500psi after being unused for 20+ years can I make any assumptions that they were loosened during the hydro/visual inspection?

And is there any expectation that when you get a tank back from a visual inspection that it's safe/ready to use? I didn't pay attention to the valve o-rings before I dropped the tanks off (I did tighten down the first stage regulator tight when I checked the pressure before dropping off and didn't listen for hissing), but when I got them back and looked at the o-rings saw they were not fit for service at all (hard/brittle). Googling at that point it sounded like o-ring changes come with a "valve service" and I replaced them myself, but I would have expected them to point out the need to change them and offer the service.

 

[rjack321]

Is _ANY_ leaking from the burst disc (threads) acceptable? and offer the service.

No leaking is acceptable

It's normal to replace the burst disks at hydro time, but valve service (neither parts nor cleaning... other than the new oring) is never really included by any shop in hydro - which are expensive enough as is.

Since you're going off lots of 20+yo memories in general I would recommend a refresher course

 

[BoltSnap]

The valves should be fully serviced, including replacing the burst discs with each hydrostatic test. Hydro stations don't normally perform this service; dive shops do.

 

[TravisD]

A typical hydro test does nothing with the valves other than remove and replace them - if that. Did you also receive a valve overhaul as part of the service? That's likely a separate, extra cost service. My understanding is that burst discs are a one-time-only thing -- you don't loosen them unless you intend to replace it, since installation slightly deforms the 'burstable' part.

They're a wear item, basically, and can corrode which weakens them. DGS has a good writeup on their page, at the bottom.

 

[Eric Sedletzky]

Put new burst discs in all your old valves. If the valve itself isn't leaking don't fix it. Don't tear the rest of the valve down (knob and guts) unless you have a kit ready to go in. Once you disassemble an old valve the old parts are unsavable in my experience and it will leak.

 

[macado]

No leaks are acceptable. Zero, zip, nada.

The question you want to ask them is did they service the valves or replace the burst discs? Burst discs should typically be replaced at the time of hydro (every 5 years in the US) however I can tell you most people and shops do not do this unless specifically requested.

It is possible if they did replace them that they didn't torque them down to spec. They should be torqued to 100-120 in-lb for installation. Over torquing or under tightening can cause leaks. Slightly tighten / torque them down to specifications and see if the leak goes away is the simplest fix.

I'm guessing they did what most typical amazing highly professional dive shops do. They sent your tanks out to hydro facility that mostly does fire extinguishers (the hydrostatic requalifier doesnt service the valves), the dive shop briefly looked inside the tank with a light or maybe they didn't look inside at all and declared it "good enough", they then smeared some huge globs of silicone grease on your valve and maybe replaced the neck o-ring if you're lucky. Finally, they stuck on their super official professional visual inspection sticker on the tank, smashed your unserviced valve handle with a rubber mallet probably damaging/bending the valve stem and then charged you $25 for this "service" and called it a day. Sorry.. I'm only partially joking here..

The reality is their visual cylinder inspection should have included a leak test as a final inspection and they should have caught the burst disc leaking. It's not a huge deal to fix, just annoying. '

If they didn't service the valves it might be worth asking them to do it or at least ask them to replace the burst disc assembly. I would tell you this is a very easy and straight forward request but dive shops continue to amaze me to no end.

TL;DR - Ask them to replace the burst disk assembly or torque to spec.

 

[an0br1]

Since you're going off lots of 20+yo memories in general I would recommend a refresher course

Advice taken to heart.

I sat in on my son's SSI OW class as he's under 18 and the shop required it, and also read all of the SSI e-learning so I'd be on the same page as he was and be able to make sure he really understood it. My OW and AOW classes were each 16 week college courses for grades, and the 4 night SSI course he took seemed to be a tad bit lighter (and my 1988 printing of the Jeppesen OW Sport Diver Manual only mentioned the "+" on steel tanks for 10% overfill -- SSI didn't have any information on tank markings ).

We've since done a lake dive where I could get reacquainted being in the water and leisurely get our weight requirements dialed.

The valves should be fully serviced, including replacing the burst discs with each hydrostatic test. Hydro stations don't normally perform this service; dive shops do.

No leaks are acceptable. Zero, zip, nada.
...
I'm guessing they did what most typical amazing highly professional dive shops do.
...
TL;DR - Ask them to replace the burst disk assembly or torque to spec.

Thank you all for your responses. I do expect it is the case of "what most typical ... dive shops do". The burst discs don't look new and I expect they're the same ones that came with the original tank. I did tighten them so they'd stop leaking, but annoyed I had to, and that I'll need to go back to have it topped up.

 

[Eric Sedletzky]

Advice taken to heart.

I sat in on my son's SSI OW class as he's under 18 and the shop required it, and also read all of the SSI e-learning so I'd be on the same page as he was and be able to make sure he really understood it. My OW and AOW classes were each 16 week college courses for grades, and the 4 night SSI course he took seemed to be a tad bit lighter (and my 1988 printing of the Jeppesen OW Sport Diver Manual only mentioned the "+" on steel tanks for 10% overfill -- SSI didn't have any information on tank markings ).

We've since done a lake dive where I could get reacquainted being in the water and leisurely get our weight requirements dialed.






Thank you all for your responses. I do expect it is the case of "what most typical ... dive shops do". The burst discs don't look new and I expect they're the same ones that came with the original tank. I did tighten them so they'd stop leaking, but annoyed I had to, and that I'll need to go back to have it topped up.

What I would do is drain the tank(s) and at least replace the burst discs before any new fills or top ups. You don't tighten existing burst discs, they are torqued to where the crush washer crushes and that's it.
I don't know if you've ever had a burst disk go off but it will scare the crap out of you and could cause some physical damage, including hearing damage. The cost of a fill is peanuts compared to other things.

 

[happy-diver]

Those terror stories written about them, then convolutedly shared, to keep people dumb

A cockamamy scuba diving system idea that don't do anything, that Europe doesn't have
There is nothing to them if you understand them, so don't be scared just punch a few out

We used to fill the plug with solder, not sodder, but SOLDER



It is the pressure of the first fill that deforms the centre of the disc into a dome shape

So if they can handle that pressure and me screwing and unscrewing them on a whim
reusing all the parts you can dislodge the disc with air you know then all the rest is BS

So if you understand them no need for concern

Those 290bar tanks in my car in the QLD sun, had air in them when I dived on Sunday

 

[happy-diver]

You want more, yes of course I've got some more

Crazy John has got it right, Crazy John knows too!

S/S Blanking Plug for Burst Discs

john@northeastscubasupply.com

northeastscubasupply.com

How about the disclription, I told you Crazy John knows
So I thought I would share, so youse all get to know too