250 psi really make a difference?

[TSandM]

I bought a 6 cu ft tank for argon. It came with a 5250 psi burst disc. My LDS has told me I have to replace the burst disc with a 5000 psi one. I've asked what the difference is, and they've said it's for safety in case somebody doesn't shut off the compressor. But their compressor only goes to 4000 psi. They've said they've seen burst discs go off at much less than rated pressure (as have I) but I can't see any reason why one would expect that of one psi rating and not another.

I can't come up with ANY rational reason for replacing a burst disc with one rated 250 psi less. I'm going to do it, because they're my LDS and they fill my tanks and they say I have to, but I'd feel better if there really is a good reason for doing it and somebody can tell me what it is.

 

[Cheekymonkey]

I don't understand the argument about seeing them go off at lower pressures commonly having anything to do with having you lower the pressure of your burst disc. Is it Aly or steel, just find out what its hydro pressure is and make sure that hte burst disc is rated to below there.

 

[Jim Lapenta]

They get to charge you for a new burst disc for a tank you presumably did not buy from them. Also how long does it take to fill a 6 cuft bottle from a comercial compressor? About a minute and a half with a 4.5 cuft per minute delivery system. Are they that busy that they would leave a bottle of that size on long enough unattended for it to blow the disc? also if you are getting argon fills are they actually using the compressor or just filling it from a banked bottle. Our compressor has an auto shut off when the desired pressure is reached. In short- There is no reason to replace a perfectly good disc. BTW I've got 5000psi discs on all my lp tanks.

 

[pickens_46929]

I can't imagine that 250 psi would make a difference in this case since you will likely only get 2400 psi from an argon fill if they don't boost it, however, you didn't mention which 6 cu.ft. tank you purchased... AL 6 or Steel 6... rated pressure, etc. I am assuming AL since they want a 5000 psi burst disk (5/3 of 3000 psi = 5000).

It sounds like you have a burst disk for an HP tank in the valve. (3180+ or 3446 psi)

I would swap it out to make them happy if it comes down to it, otherwise I'd wait a year and swap it out the next time the tank is viz'd.

dave

 

[Dive-aholic]

First, I hope they're not filling your argon bottle from the compressor. Their reasoning fails in logic. It's a small tank. Even off a compressor, as JimLap has pointed out, it wouldn't take very long. It takes even less time off a bank, which is where the argon should be coming from. Second, what does the burst disc going off at much lower pressure have to do with putting a lower rated disc on?!? The burst disc is there to prevent the tank from going boom. If the disc fails at a lower pressure, then that's good, right?!? I would present this information to them and tell them, if they want to replace it, fine, but you shouldn't have to pay for the new disc because their reasoning lacks any logic at all.

 

[TSandM]

It's the Catalina Al 6 sold by Scubatoys, working pressure 3000 psi.

The whole argument doesn't make sense to me, either.

 

[DA Aquamaster]

DOT regs require a burst disc to fail within a range of 10% below the tank's hydro test pressure to the hydro test pressure.

So for a 3000 psi 3AL Aluminum tank that is tested to 5/3rds of the service pressure, the burst disc should fail between 4500 and 5000 psi. 5250 psi is, legally speaking, in excess of the allowable 4500-5000 psi range.

Practically speaking, burst discs get weaker with every fill cycle and if they have been in service for any lenght of time, they will fail before they reach their rated pressure anyway. If they get old enough, they will eventually fail at or even below the service pressure of the tank.

The concern with having a burst disc is not so much to protect the tank monkey who overfills a tank (very unlikely to happen as few compressors or storage banks hold air over 4500 psi.) but rather to prevent the tank from bursting in a fire where the heat of the fire could cause the pressure to increase beyond the test pressure of the tank.

Even that logic however is a little flawed with regard to aluminum tanks. In a fire the temperature of the tank itself may exceed 350 degerees, soften and fail before the pressure is high enough to cause the burst disc to fail. So unless you store your aluminum tank at a nearly full pressure, it could burst before the burst disc fails to vent the excess pressure.

 

[dsteding]

The whole argument doesn't make sense to me, either.

The only thing I could think of is that the 5000 psi disk is to protect the booster (this LDS boosts argon), but even then I'm having a tough time wrapping my mind around it.

 

[SparticleBrane]

While I can understand their reasoning behind it--common sense lost this battle.

 

[in_cavediver]

I am guessing the tank rating and burst disk rating just don't line up. Burst disks are cheap. I think I gave $5 bucks for the last 4 5000psi disks I got. For that, make it legal. It won't matter for a 2400psi argon fill anyway.