Burst disc

I'm trying to find an answer about a burst disc. I have a steel 72 lp 2250 tank. I purchased a new Sherwood 5000 valve. On the box it says it's for a 2250 tank. It came with a 3000 burst disc. I talked to the person that did the hydro on the tank, he said that he hydro'd the tank to 3750 and that the 3000 burst disc would work on the tank. Where I have my tanks filled, they refuse to fill the tank unless it has a 2250 burst disc. I have had several people tell me that a 2250, 3000, and a 3750 burst disc is the correct disc for the tank valve. Could you please tell me which is correct?

Dear Skipper,

You want a disc that has an operating pressure of 2250 and a bursting pressure of 3750. The standard for all compressed gases is that the bursting disc is 5/3 of the operating pressure. This means the bursting pressure is 5/3 more than the operating pressure. For example, 5 /3 = 1.666, (1.666 X 2250 = 3749.85). Thus the 3750 bursting pressure.

The 3,000 psi disc is incorrect. Again, you want the disc that has an operating pressure of 2250 and bursting pressure of 3750.

Make sense?

Hope this helps.

Thanks for the responce. Is the # on the burst disc operating pressure or burst pressure. If it's the operating pressure then I'm correct to assume the the steel 72"s with an operating pressure of 2250 at a LDS all have the wrong burst disc in them. (About 8 of them). On the disc itself it shows 3000, and on one tank it shows 5000. Also on my "new" aluminum tanks 3000 psi that came with Sherwood 5000 valves, the burst disc shows 4000 120 3000, if they are for 3000 psi tanks, then why doe's it have the # 4000 on it?

You will have to look closely on the disc. Some manufactures use engrave the bursting pressure, some engrave the operating or service pressure (operating and service pressure are the same thing).

Sherwood engraves the 4000 120 3000 is the part number. That item is a 3000 psi operating pressure. A 4000 120 2250 would be what a 2250 plug would read.

Thanks,

Thanks, This has been bothering me for a while now I know how to read a burst disc and I can tell the LDS that their tanks have the wrong burst discs in them. They always seem to belittle me because I'm new to diving but willing to learn anything I can. I can't wait to hear their explanation on their tanks. 2250's with 3000 burst discs