LDS vs The Burst Disk

[viperwsu]

I bought a new valve/reg from Piranha, and it has a burst disk in it with the simple marking of "4250".

The LDS has it right now because I brought in my pony for hydro last week - last night while I was there for something else, the owner pulled me in the back because of an "issue" with the valve. He pulled out a tupperware box filled with the parts of my brand new, USPS-delivered-20-min-before-I-dropped-it-off, valve - which I specifically said was brand new and not be screwed with. I even gave them the receipt from Piranha to prove it was new.

The issue, LDS says, is that the burst disk is for 4250PSI rated tanks and isn't safe on a 3000PSI tank.
Randy from Piranha assured me that that number is the burst pressure, not the service pressure. Since I've never heard of a dive tank rated to that high of a pressure I'm inclined to believe Randy. LDS is emphatic that the disk is dangerous, and says it needs to be replaced before the valve can be used despite the shop owner having spoken with Randy personally.

Has anybody else seen burst discs marked with nothing but the burst pressure, and not the tank service pressure? My research shows me a variety of markings, but nothing that's just the burst pressure. I'd love to be able to show some evidence to the LDS even though I'm going to go rescue my valve before they start taking off more parts or otherwise screwing with it.

 

[runsongas]

my guess is whoever piranha is having oem their valves is using an industrial pressure rupture assembly instead of one specifically for cylinders. those are not marked for service pressure but only the rupture pressure.

4250 psi burst disc is low for a 3000 psi tank though. 3000 psi tanks like al80s usually use a 5000 psi burst disc. 4250 would be closer to the 4000 psi you usually see on 2400 psi low pressure steels.

and fyi, europe has 300 bar steel tanks that would nominally be 4350 psi service pressure.

 

[Matt Vandercook]

burst discs are marked with the burst pressure. the pressure of the disc should be 4 thirds of the working pressure.
3000psi (AL80) 4000psi burst disc
3442psi (HP100) 5250psi disc

 

[ScubaBunga]

I had some older burst disks for my steel tanks - just the copper disk, not a packaged set and they were marked 2250 - and as I've been reading more (as I need two more to put in thermo valves I got on CL) many come listed with burst pressure but some come with service pressure so ya gotta check. I think a normal 3000psi tank is a 5000psi burst disk. If that 4250 is service pressure then that's a over 7k burst pressure - you don't want that for sure. Unless you can find the manufacturer of the burst disk - it's probably just easier to get a $10 3000/5000psi replacement. If that is burst pressure, I'm not sure what size tank that would be (2550psi service using 5/3 guide) as a 2400psi service is 4000burst and even if you calculated that with the + (2640) the burst would be 4400psi. So in any case it's an odd burst disk and probably best just to replace it.

As for the actions of the LDS - I understand they need to protect themselves by knowing what they have before putting 3000psi into the tank, but taking apart the valve without consulting you first is unacceptable! The burst disks aren't really made to be reused - if you take it out, it "should" get replaced (I say should as I've reused many, but I'm not an LDS working on OTHER people's gear). So even if it was correct, it should now be changed. It's hard to find a good shop that also has a good tech (these are sometimes independent items). All I can say is good luck, hopefully the LDS is being overly cautious and doesn't ding you for extra costs.

 

[lv2dive]

A burst disc that supports an extra 250 psi of pressure is fine - mine are all greater than that standard of 5/3s of rated pressure. I’d find a new LDS

Edit - mine meaning for my steel tanks... my aluminum tanks may be closer to the standard but 250 psi should not make a difference.

 

[runsongas]

burst discs are marked with the burst pressure. the pressure of the disc should be 4 thirds of the working pressure.
3000psi (AL80) 4000psi burst disc
3442psi (HP100) 5250psi disc

5/3 for DOT 3AL/3AA, 3/2 for exemption

 

[rjack321]

Well both the valve and your LDS are wrong. Burst disks are NOT marked with the service pressure, they are labelled with the burst pressure which should be the hydrostatic test pressure.
There's is no common scuba cylinder which gets a 4250 psi burst disk. Its more than safe, in fact its 750psi lower than your (aluminum right?) pony actually should get.

burst discs are marked with the burst pressure. the pressure of the disc should be 4 thirds of the working pressure.
3000psi (AL80) 4000psi burst disc
3442psi (HP100) 5250psi disc

nopes
3000psi tanks get a 5000psi burst disk
2400psi tanks get a 4000psi disk
3442/3500psi tanks get a 5250 disk
Steel cylinders for cave diving get a stainless steel plug lol
European valves have no burst disks at all...

 

[viperwsu]

and fyi, europe has 300 bar steel tanks that would nominally be 4350 psi service pressure.

And now I've heard of one

I’d find a new LDS

Yeah, I'm starting to lean that way. They've been around for a long time and are really popular, but I'm starting to uncover some issues with their technical knowledge that make me lean away for anything but mundane stuff.

The burst disks aren't really made to be reused - if you take it out, it "should" get replaced

The problem here is that it's some wacky part that "isn't available yet" - which raises concerns for another thread. If it was that simple I'd have just told them to swap it out. A $10 part is better than the headache. Fortunately, when I was there last night they hadn't taken it out. Hopefully they still haven't.

 

[viperwsu]

There's is no common scuba cylinder which gets a 4250 psi burst disk.

To be fair, I think it said 4250. It might be 4500, or 4200. Most definitely more than 4000 and less than 5000. I'd only had the thing for 20 minutes before the LDS got it, so I'm probably off. Either way, it seems general consensus is that it's the burst pressure, it's safe, and LDS is making a problem where none exists.

And yes, it's an AL13.

Thanks all for the info.

 

[rjack321]

To be fair, I think it said 4250. It might be 4500, or 4200. Most definitely more than 4000 and less than 5000. I'd only had the thing for 20 minutes before the LDS got it, so I'm probably off. Either way, it seems general consensus is that it's the burst pressure, it's safe, and LDS is making a problem where none exists.

And yes, it's an AL13.

Thanks all for the info.

Lately, DIN valves seem to almost always seem to come with 5250 psi burst disks by default. Which are technically "too high" for 3000psi tanks. If your shop wants to put in a 5000psi disk then they are correct and the easiest thing is to just let them do it. Practically speaking, the 250psi difference is irrelevant.