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Burst discs: Yes they burst when they shouldn't

Discussion in 'Tanks, Valves and Bands' started by 2airishuman, Jun 6, 2017.

  1. tbone1004

    tbone1004 ScubaBoard Supporter ScubaBoard Supporter

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    @Storker
    This is a "normal" fill whip end over here. It's identical to the 300bar regulator ends. The same yoke adapters spin on and off we go. It's quite nice. I have never seen a 200bar fill end, and I have only seen a handful of 200bar regulators so it isn't a common thing over here. We use a lot of 200bar valves, but they are identical to our 300bar valves with the face shaved back 2 turns so we can use a yoke plug to convert it
    Din Filler with Screw Bleed - Upgraded
    001-039c__07389.1481918101.1280.1280.jpg
     
  2. Akimbo

    Akimbo Lift to Freedom Volunteer Staff Member ScubaBoard Supporter

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    I'm confused. I understood that the 300 Bar din connections had more threads (longer) than 200 Bar. That would prevent a 200 Bar regulator or fill whip from making a seal on a 300 Bar valve but a 300 Bar fill whip would screw into and make a seal on a 200 Bar valve. True?

    It has been years but I seam to recall that DIN dominated Northern Europe and Scandinavia but yokes were very common in southern Europe, especially around the Med. Is that still the case? It is interesting here. Nobody actually checks blowout disk ratings here, even during VIPs and hydros. XS-scuba's valves are the only ones I have seen that clearly marks the pressure on the valve body.
     
  3. 2airishuman

    2airishuman Solo Diver

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    3/8" UNF is 24 threads per inch (chart).

    No, in fact, it is a recommended practice to do that.

    All (oddball exceptions aside) LP72s are 3AA-2250, not 3AA-2400 like most newer LP steels. The correct choice is a 3750 burst disc, which has been discontinued. Some dealer/distributor stock still exists but they are getting hard to find. The usual choices are 3360, which is what you probably encountered, or 4000. Which of those is safer is debatable. I have 3750s in mine so I don't have to choose.
     
  4. 2airishuman

    2airishuman Solo Diver

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    The photo shows a fill end that is deliberately designed to fit either 200 bar or 300 bar DIN.

    300 bar DIN fill whips have a post at the end. If you look at some 200 bar and 300 bar valves, you'll see that the 300 bar valves have a recess that will fit the post, but 200 bar "provalves" do not.

    https://www.nuvair.com/store/media/...9df78eab33525d08d6e5fb8d27136e95/a/1/a101.jpg


    The connection design is intended to accommodate interlocking for both filling and usage, so there are 2 possible valve-side connections:

    a) 200 bar
    b) 300 bar

    And 3 possible connections for the reg/fill side:

    1) 200 bar only
    2) 300 bar only
    3) either

    Some do. PSI requires it, from what I understand, and I've run into PSI inspectors who replace burst discs at every hydro.

    The new strategy is to mark the burst disc rating on the one-piece burst disc itself, since in theory there's no way to mis-assemble valves so that the wrong rating is displayed. Prior to that, with the 3 piece burst discs assemblies, XS scuba and maybe others marked the valve with the service pressure, so that at least the common scenario of valves being mixed up between cylinders of varying service pressures could be addressed.[/quote]
     
  5. BRT

    BRT Giant Squid

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    How do they do that? (I found the answer above)
     
  6. Storker

    Storker Divemaster

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    You've got it right about the threads. But a 300 bar fill whip also has a longer protruding thingy than a 200 bar whip, effectively preventing the whip from sealing in a 200/232 bar valve. The 200/232 bar protruding thingy is shorter and fatter.
     
    Akimbo likes this.
  7. Storker

    Storker Divemaster

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    The last years I've dived abroad in Italy, France and the canaries. All the ops used DIN.
     
    Akimbo likes this.
  8. KWS

    KWS ScubaBoard Supporter ScubaBoard Supporter

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    2air

    a little correction . I believe the burst disk used is required to blow between 90-100% of test pressure. an al80 tests at 5k so the disk should blow about 4600 psi a little over the 90%. Picky perhaps but i have had one blow. It was on a lp95 pumped to 3200 on the gage , however teh gage was in error and off about 250 psi. It actually had about 3500 in it and the heat raised it to a little over 3600 EST. and it blew. tp was 4000 on a lp tank. 35 degree increase in temp at 5 psi per is about 175 psi increase from temp. I have never crossed paths with a blown disk since. Over filling was the cause of the rupture. BTW i believe the vis and hydro is to include verification that the burst disk is undamaged and the correct size for the tank application. I have 3000 psi valves on my lp's (they have burst disks for 4500#) and I do not give the valves to the hydro shop. In the above diagram item 11 is not always an item the the disk can be separated from the bolt. If they insist on valves i put on the original 2400 psi thermo valves. Item 11 is not a cheap item (5-7$ a piece) when you vis a dozen tanks a year.
     
  9. tbone1004

    tbone1004 ScubaBoard Supporter ScubaBoard Supporter

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    @2airishuman I require a full valve rebuild including burst disc replacement at hydro if I'm going to sticker a tank for someone else
     
  10. KWS

    KWS ScubaBoard Supporter ScubaBoard Supporter

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    I think you have it backwards. a 300 bar whip will seal on a 300 and a 200 bar valve. the 200 bar regulator will not seal on the 300 bar valve, insuring the lower rated reg is not connected to the higher pressure source.
     

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