Can't find a burst disk

[tc_rain]

Does anyone have or can direct me to where I can find two 1/2" 5250 lbs bust disks? I can only find the 3000 lbs 1/2" disks or the 3/8" 5250 lbs but not the 1/2" 5250.

 

[tursiops]

You want this for 3300 psi service pressure?

Burst Disk 3300 PSI.. Burst pressure 5300.. 1/2-20 Thread Size , Piranha Dive Shop |??

 

[tbone1004]

Does anyone have or can direct me to where I can find two 1/2" 5250 lbs bust disks? I can only find the 3000 lbs 1/2" disks or the 3/8" 5250 lbs but not the 1/2" 5250.

Couple bits of information
Burst discs are supposed to be no more than 90% of test pressure.
Common test pressures
2400psi *3aa steel*-4000
3000psi *al80's*-5000
3300 *AL100's*-5500
3442 *modern HP steels*-5163
3500 *older HP steels*-5250

Notice that with the exception of the LP steels, most of those test pressures are all "close enough" to each other, and well over the 4500psi that you'll ever see from a scuba compressor.
Now, burst discs can be called out based on their working pressure *not my favorite*, or their rated burst pressure *what they should be called out as because of the different working vs. test pressures of the bottles they are attached to*. Below is a link to the some of the burst discs that NESS carries and they're called out based on the tank working pressure to make it easier for most people to buy. If you reference above though, the test pressure is all about the same with the exception of AL100's and 3aa steels. Putting a higher pressure plug is against the law, but putting a lower rated plug is not. As such, when looking at their 3500psi burst discs and 3000psi burst discs, they are actually the exactly same part and are rated at 5000psi burst. One of them is actually rated for 5250, but that is too high for the modern 3442 tanks.
All of that to say, just buy the ones for AL80's with a 5000psi burst and you'll be more than fine.


Tanks - Valves - Valves - Valve Repair Parts - Burst Discs - Scuba Valve Burst Discs - Page 1 - Northeast Scuba Supply Store

 

[tc_rain]

I have two HP (3500) Genesis 120 tanks. I have not had any problems getting full fills in the past but when I took them to a different shop for a vis, they only put 3000 in them. I was told the burst disk should be stamped 5250 for a 3500 fill. He then pointed out mine were stamped 3500. Since he did the vis on the tanks I assumed he knew what he was talking about. Or maybe not.

So if i understand correctly, the 3500 stamped on a burst disk is actually the (working) pressure of the disk and not the rating that it is expected to burst. The busting pressure would be somewhere around 5000?

 

[tbone1004]

@tc_rain if it was stamped 3500, that was the working pressure, not the burst pressure. 3500 burst pressure would be for something like a 3aa low pressure tank, either 2250 or 2400psi working pressure

 

[rjack321]

Couple bits of information
Burst discs are supposed to be no more than 90% of test pressure.
Common test pressures
2400psi *3aa steel*-4000
3000psi *al80's*-5000
3300 *AL100's*-5500
3442 *modern HP steels*-5163
3500 *older HP steels*-5250

Notice that with the exception of the LP steels, most of those test pressures are all "close enough" to each other, and well over the 4500psi that you'll ever see from a scuba compressor.
Now, burst discs can be called out based on their working pressure *not my favorite*, or their rated burst pressure *what they should be called out as because of the different working vs. test pressures of the bottles they are attached to*. Below is a link to the some of the burst discs that NESS carries and they're called out based on the tank working pressure to make it easier for most people to buy. If you reference above though, the test pressure is all about the same with the exception of AL100's and 3aa steels. Putting a higher pressure plug is against the law, but putting a lower rated plug is not. As such, when looking at their 3500psi burst discs and 3000psi burst discs, they are actually the exactly same part and are rated at 5000psi burst. One of them is actually rated for 5250, but that is too high for the modern 3442 tanks.
All of that to say, just buy the ones for AL80's with a 5000psi burst and you'll be more than fine.


Tanks - Valves - Valves - Valve Repair Parts - Burst Discs - Scuba Valve Burst Discs - Page 1 - Northeast Scuba Supply Store

where did this 90% value come from??? Burst disks in the actual CFR are plus 0% to minus10% of TP

(3) For a specification 3, 3A, 3AA, 3AL, 3AX, 3AXX, 3B, 3BN, or 3T cylinder filled with gases in other than Division 2.2 (except oxygen and oxidizing gases transported by aircraft, see §§ 173.302(f) and 173.304(f)), beginning with the first requalification due after December 31, 2003, the burst pressure of a CG–1, CG–4, or CG–5 pressure relief device must be at test pressure with a tolerance of plus zero to minus 10%. An additional 5% tolerance is allowed when a combined rupture disk is placed inside a holder. This requirement does not apply if a CG–2, CG–3, or CG–9 thermally activated relief device or a CG–7 reclosing pressure valve is used on the cylinder.
https://www.govinfo.gov/content/pkg...df/CFR-2010-title49-vol2-part173-subpartG.pdf

SP14157 for all current Xscuba 3442psi cylinders references these CFR sections.

So they are AT LEAST 90% of test pressure and not to exceed TP​

3442psi tanks are hydro tested at 5250 (and are actually marked "TP5250") they get 5250psi disks just like 3500psi tanks.
2400psi * 5/3 = 4000psi
3000psi * 5/3 = 5000​

I have two HP (3500) Genesis 120 tanks. I have not had any problems getting full fills in the past but when I took them to a different shop for a vis, they only put 3000 in them. I was told the burst disk should be stamped 5250 for a 3500 fill. He then pointed out mine were stamped 3500. Since he did the vis on the tanks I assumed he knew what he was talking about. Or maybe not.

So if i understand correctly, the 3500 stamped on a burst disk is actually the (working) pressure of the disk and not the rating that it is expected to burst. The busting pressure would be somewhere around 5000?

You're fine

 

[tbone1004]

@rjack321 thanks for clarification, I thought I had read it was not to exceed 90% of test pressure.

 

[2airishuman]

3442 *modern HP steels*-5163
3500 *older HP steels*-5250

All the HP steels I've seen with a 3442 working pressure have a 5250 test pressure stamped on the neck and are equipped with 5250 PSI burst disks.

The other two standard ratings that are out there are 3750 PSI (for LP72s with a working pressure of 2250) and 3360 PSI (for some argon bottles and a few small, older LPs)

 

[tbone1004]

@2airishuman I thought I had seen lower ones on a couple of my pst's, but likely was wrong. Good catch