Burst Disk Pressure

[pearldiver]

That would be great. I am really at a loss on regulators and what the upstream and what not all means. You all are great.....

[Greg Barlow]

The gas industry standard for a burst disk is that it should rupture at approximately 140% of the tank's rated working pressure. The permissible range due to metalurgical tolerances is around +-15%. So, it could fail at 125% or as high as 155% and still pass the standards. Ideally then, a disk should fail at 3,150 psi in a 2,250 variety tank.

Each time that the tank is filled, the disk undergoes a bit more metal fatigue. Personally, I change the disk whenever I rebuild the valve.

Greg Barlow

[treasureman]

local dive store will not sell burst discs by themselves. They insist in supplying new discs and the bolts at the same time, at a ridiculously hi price. Any other places where I can get both bolts and burst disc without the hassle

[1969ivan1]

For what a burst disk is they are NOT cheap. I would love to buy a pile of them and re-disk all my valves at once but they are super expensive. Let me know if you get a cheap source. I have over 10 tanks currently.

[luis]

You do need to replace the bolt with the disc. The bolt provides the cutting edge for the disc and it should be a match pair. In the old days we only replaced the disc. But, by replacing them as a match set the relive pressure is controlled a lot better. A lot less chance of letting go at lower or higher pressures than predicted.

[time2dive]

We chage the burst disks when ever we hydro a tank. One reason to change them every five years is to get it out of the valve. You get salt and corrosion around the assembly. If it does not come out electrolisis may occure and thread damage may occure, we had an older valve that had damged threads and had to be replaced. We buy the kits or assemblys that are for the various tank pressures, they come either 3/8 or 1/2". Older steel tanks have a wide range of working pressures, I have seen 1800, 2000, 2250, 2400 and 2730, aluminums 2000, 3000 and 3300, then you have the HPs at 3500.

I have seen some of the "old" burst disk that were a leas slug the size of a 22 bullet that were pressed into the assembly. The problem with those is that they occasional worked thier way out.....violently.

Retail on a burst disk assemly or kit is gennerally less than $7.

Tim

[treasureman]

& bux is a steal. Up here to supply and install a kit, is ..are you sitting down... 35. 00 bux

Hence my looking for kits avaliable from more reasonably prices sources.

At 7 bux a kit, I would buy a few sets to have around

[Greg Barlow]

One nice thing about the new Thermo burst disk assemblies is that they are one complete unit. You simply replace, and torque to 100-125 inch pounds of torque.

Over tightening is not good, as it can overly crush the copper and thereby weaken it. I used to tighten them by feel, but now use a torque wrench. When one considers that 125 inch pounds of torque isn't a very large amount, then overtightening becomes more of an important issue.

Greg Barlow

[YankDownUnder]

I had a burst disc blow on my triple USD Broxton 44s. The tanks flipped over.....and they are heavy tanks. My car windows were open so I didn't loose a windshield from the over-pressure. The disc was a pre-bullet tube type.

The disc needs to be mated with the cap, as it is the size of the hole that rates the burst, not the disc itself in the kinds we use. Air expands at a rate greater than detonated TNT. One report of a blown valve (not just a disc) sent a tank six blocks and into a brick garage. Compressed air is not something to take lightly.

There is controversy, as Chuck points out. European valves often do not have burst discs and have to be drilled for one when imported. Some dive shops will not fill tanks with old type discs, so unless you don't plan on traveling, it might be worthwhile installing the new kind.