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Measure valve thread, please ?

Discussion in 'Tanks, Valves and Bands' started by Externet, Sep 12, 2019.

  1. Externet

    Externet Nassau Grouper

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    Hello.
    Anyone with a valve removed from the tank at the moment; can you please measure the thread in your valve, not what the documents/specs may show on a web site link ? (a parallel one, not tapered)
    Is it 0.700" or 0.740" or other ?

    Measure.png
     
  2. herman

    herman Divemaster

    # of Dives: 500 - 999
    Location: Raleigh,North Carolina
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    There are at least 4 straight threads that I am aware of that were used in scuba tanks, 1/2 NPT, 3/4NPT, 3/4 BSPP and M25. All are different and the last 3 are pretty close to each other so you need to be very careful when trying to figure out which you have.
     
    rjack321 and txpolo like this.
  3. txpolo

    txpolo Garibaldi

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    In addition to Herman's comment (He's usually right from what I've seen here on SB. He knows his stuff.) there is also the slightly less common 7/8 straight thread that is on some of the 3500 psi tanks. Ironically it's actually smaller than the 3/4 NPT thread... go figure. It's 0.875-14 UNF which seems larger than what you're measuring... you sure it's not a tapered thread?
     
  4. Externet

    Externet Nassau Grouper

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    Thanks, fellows. Is not tapered. To add confusion, Wikipedia mentions a thread 3/4" x 16 UNF, which I have to suspect the 3/4" is not from measuring the thread, but one of those plumbing 'nominal' names.
    What cylinders use the 3/4" x 16 UNF ? Do you know ?

    Is there a valve for such 3/4"x16UNF ?
    Seems there is nothing NPT
    Diving cylinder Wiki.png
     
  5. runsongas

    runsongas Great White

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  6. Externet

    Externet Nassau Grouper

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    Thank you, runsongas. Interesting a medical oxygen cylinder being listed in Wikipedia under diving cylinders.
     
  7. Bob DBF

    Bob DBF Solo Diver

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    Some people don't know what they have, and guess. Buy a foreclosed storage area, or clear out a relatives house. I've got some good deals because s seller, from his POV, is just getting rid of crap.


    Bob
     
    dead dog likes this.
  8. herman

    herman Divemaster

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    3/4-16 UNF would be .750 since the UNF indicates its a screw thread dimension rather than a pipe thread.
    I forgot about the 7/8. You have to be careful with valves since some will "almost work". If I remember correctly, the M25 will loosely thread into a 3/4 NPS but will come out under pressure. The 3/4 BPS will thread into a 3/4 NPS a few turns but stop......took me days to figure this one out. The size looks the same but the 55 deg threads jam after a few turns, you have to look hard to see the difference in 55 and 60 degree thread.
     
  9. captain

    captain Captain

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    Herman is correct 3/4-16 UNF is a bolt thread just as 3/8-28-4 UNF used on PL hose connections is the same as what is commonly referred to as a fine thread as opposed to course thread. A 3/8-16 UNC is coarse thread.

    UNC and UNF - Unified Inch Screw Threads
     

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