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o-ring sizes question

Discussion in 'Vintage Equipment Diving' started by GreyhoundsAreFast, Dec 22, 2018.

  1. GreyhoundsAreFast

    GreyhoundsAreFast Angel Fish

    # of Dives: 50 - 99
    Location: Micronesia
    67
    11
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    Hey guys, the local dive shop wouldn't service my MK5/R109/R156 set-up so I sent it off-island.

    Got the regulators back, and started connecting the hoses, but before I got very far I realized I should replace the o-rings on the hoses. Can you help me order the right o-rings?

    What size o-ring for the LP hose connecting the MK5 to the BCD inflator?

    What size o-rings for the LP hose connecting the MK5 to the R109?

    What size o-rings for the LP hose connecting the MK5 to the R156?

    And I know this is a dumb question for anyone that knows what they're doing... but both sides of the hose need an o-ring, right? (one on the 1st stage side of the hose, one on the second stage side)

    Thanks in advance.
     
  2. Scubagaskets

    Scubagaskets Nassau Grouper

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    You searched for Hose - Premium O-rings Provider for Scuba Diving
     
  3. Scubagaskets

    Scubagaskets Nassau Grouper

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  4. Pao

    Pao Manta Ray

    # of Dives: 200 - 499
    Location: Manila, Philippines
    983
    206
    43
    That will be an 010 for the 1st stage end and another 010 for the 2nd stage end. The 2nd stage end is quite tricky. An o-ring pick with a looped end is quite helpful.
     
  5. herman

    herman Divemaster

    # of Dives: 500 - 999
    Location: Raleigh,North Carolina
    9,453
    2,000
    113
    Here is a chart with them all.
    The first stage end of the low pressure hoses are 011 (although many use 010s) , the second stage end is a 010 and the oring inside the LP inflator (a pain to replace) is also a 010. All of these orings should be 70 durometer. The HP hose is an 012 (again, some use 011) these should be 90 durometer but a 70 durometer will usually work OK.
     

    Attached Files:

    JamesBon92007 and Pao like this.
  6. Scubagaskets

    Scubagaskets Nassau Grouper

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    you can use the 6,75 x 1,78 for the side that connects to the first stage L.P. Plug O-rings NBR Sh70-610 this is size 610.
    you can use the 6.35 x 1,78 for the side that connects to the second stage Scuba O-Rings NBR 70Sh 6.35x1.78 - Premium O-rings Provider for Scuba Diving
    and the 012 You searched for 012 - Premium O-rings Provider for Scuba Diving for the hp that connects to the first stage

    we had some discussion over the years about those o-rings since many people used the 010 or 011 for those applications. the exact match is what i wrote above .
    merry christmas to everyone
    Nicolas
     
    JamesBon92007 likes this.
  7. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: U.S. East Coast
    7,320
    4,723
    113
    Caveat Emptor. Double-check any o-ring size info you are given on the internet. There is some bad info out there, even from those who sound quite certain.
     
  8. Pao

    Pao Manta Ray

    # of Dives: 200 - 499
    Location: Manila, Philippines
    983
    206
    43
    MK5 Annotated schematic
     

    Attached Files:

    couv likes this.
  9. herman

    herman Divemaster

    # of Dives: 500 - 999
    Location: Raleigh,North Carolina
    9,453
    2,000
    113
    If we really want to get it right, the actual orings for this gland design, which is a straight thread oring port design (SAE J1926 if you want to look it up), are 903 for the LP (and old HP) and 904 for the newer HP hose. Most are unfamiliar with these orings and fall back on the more common sizes. If you dig back into older reg parts list, a few actually listed the orings as 011 (LP)and 012 (HP) or at least vaguely disguised the fact that these were what they were.
    Orings must have a small amount of crush/squeeze to properly seal which means the oring needs to be slightly larger than the hole it fits in. Drop a 010 into a LP fitting and it's pretty obvious it's not big enough and to make matters worse, once it's installed on a hose or port plug it's cross section reduces a bit more. Does it work? Most of the time yes but that does not mean it's the proper oring. The proper 903 (for LP fitting) has an ID of .301 and an OD of .429, the 011 has the same ID but a slightly bigger OD of .442. This extra OD is OK since it is within the given range of acceptable crush amounts for orings. Now compare that to the .250 ID and .375 OD of the 010 which is nowhere near big enough to provide any amount of crush when installed, esp when you take into account the extra reduced cross section due to it being over stretched when installed on the hose/plug. The same idea holds for the HP port as well.
    Bottom line, neither 010, 011 or the 012 are the correct orings but the 011 and 012 are close enough.
     
  10. Scubagaskets

    Scubagaskets Nassau Grouper

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    34
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