• Welcome to ScubaBoard


  1. Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

    Benefits of registering include

    • Ability to post and comment on topics and discussions.
    • A Free photo gallery to share your dive photos with the world.
    • You can make this box go away

    Joining is quick and easy. Login or Register now by clicking on the button

Scubapro D300, D350 & D400 Overhaul: Theory and Practice

Discussion in 'Repairing your own Gear' started by rsingler, Nov 10, 2020.

  1. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    4,758
    5,992
    113
    The very last model of the D400 included big changes, discussed in Service Bulletin #268 (attached below). The "improvements" included a redesign of the housing, eliminating the fragile metal knife edge in favor of a new housing with a replaceable "techno- polymer" orifice.
    20201120_185041.jpg
    20201116_190415.jpg
    The lever was also changed to increase poppet opening and air flow by effectively doubling the mechanical advantage of the short arm of the lever.
    20201119_173712.jpg
    IMG_20201130_193350.jpg
    Most significant was the change in knife edge. The "techno-polymer" edge was durable, no doubt about it. Only the new D420 plastic knife edge seems to be better. But its contour was decidedly rounded, and it was rare to be able to seal at less than 0.8"WC. The seat material in later poppets seems to have become harder, IMO. With a smooth but dull plastic orifice, that made for a better mating at lower cracking effort. The earlier, softer seats would better tolerate a nicked metal knife edge, but those same poppets would require too much spring tension to seal against a duller edge (with its larger total surface area). It became a Catch-22 to experiment with multiple seats to get best performance. As noted above, using @Kupu 's technique with the proper Duro 2-104 o-ring may be the solution to all this:
    solution for D-series poppet seat DIY?

    With regard to the lever, the sharper contact point where the new style lever contacted the nib at the bottom of the poppet made for slightly increased friction, although total valve opening was improved. The mechanics are suggested by the diagram below:

    poppets.png
    In any case, it is occasionally possible to "downgrade" to an older metal orifice, and lots of smooth D400 levers are around. It's worth experimenting to see if you can identify a difference in performance.

    From a service standpoint with the very last D400 model, the only new challenge is getting the orifice out of the housing without damaging it, for there are no more available techno-polymer orifices on the market that I have seen.

    To remove the orifice, use a small flat blade screwdriver to lever up on the two tabs in the oval holes in the side of the housing.
    IMG_20201120_185532.jpg
    Then, using a straight blunt pick, carefully engage the side of the orifice from below through the stem of the housing, and carefully push up.
    IMG_20201120_185753.jpg
    If the pick is engaged, the orifice will slide out. If not, it will slip and likely scratch your knife edge.

    The static o-rings that seal the orifice to the housing are spec'ed by Scubapro as AS568 5-179 duro 70. However, this is roughly a 1x6mm oring, and the lands in the techno-polymer orifice measure 8.37mm diameter. A 1x6mm therefore requires significant stretch, and I am surprised at the specification. A 1mm x 7mm duro 70 fits quite well and is my choice, but as a static oring it probably makes little difference either way, as long as you can insert the orifice and it seals in the housing.
    Replacing the orifice requires careful, symmetric downward pressure on the knife edge with nothing harder than your thumb. Resurfacing this knife edge will be discussed in an upcoming D-series restoration thread.

    Well, that's about all I have to offer on this reg. I hope the tips above have been helpful. As always, this is just one guy's opinion, and with @Kupu 's poppet invention as an example, new ideas are always appearing for keeping this old beauty in service. I welcome any new ideas or differing opinions regarding service or performance of this regulator.
     

    Attached Files:

  2. Jacobyz

    Jacobyz Angel Fish

    # of Dives: 200 - 499
    Location: Palm Beach Gardens, FL
    31
    11
    8
    Wow, Rob, this is great!! Unbelievably detailed. I am now prepared to give servicing one of my “new” 400’s a try. Wish me luck!!
    Best
     
    rsingler likes this.
  3. lexvil

    lexvil ScubaBoard Sponsor ScubaBoard Sponsor

    # of Dives: 1,000 - 2,499
    Location: jamestown, ca.
    3,508
    3,285
    113
    This should be a sticky!
     
    Andrew Dawson and axxel57 like this.
  4. Kupu

    Kupu Polliwog ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: NC
    841
    366
    63
    Thanks for this information! So many helpful details and tips.
     
  5. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    4,758
    5,992
    113
    Here are the initial posts as a series of PDF's, to make it easier to navigate.
    I appreciate all your support.

    EDIT: corrected Service Guide uploaded 11/27
     

    Attached Files:

    couv, TTPaws, Kupu and 3 others like this.
  6. axxel57

    axxel57 Solo Diver

    649
    456
    63
    F.....g great job, Rob!

    Alone this work gets you also in my personal SB Hall of Fame!:)
     
    Andrew Dawson and rsingler like this.
  7. halocline

    halocline Solo Diver

    8,761
    3,032
    113
    Amazingly detailed and informative thread. Great job, Rob!
     
    rsingler likes this.
  8. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    4,758
    5,992
    113
    Well, nuts! Found a mistake in the Guide. You'll have a little trouble inserting the inlet tube "hose end first", lol! Five of you need to download a revised Guide. I've uploaded it into post #15 above. If you already happen to have printed it out, then just reprint page #24. My apologies. I hope I don't find too many more silly mistakes. If any of you do, sing out!
     
  9. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    4,758
    5,992
    113
    I knew I'd find it in the shop eventually.
    Post #11 above now has a pic of the very last model lever, for those that wondered what they did to increase mechanical advantage.
    Cheers!
     

Share This Page