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Which Scubapro piston 1st stage is the overall best?

Discussion in 'Regulators' started by Eric Sedletzky, Jun 2, 2021.

  1. couv

    couv Instructor, Scuba

    # of Dives: 1,000 - 2,499
    Location: 13th floor of the Ivory Tower
    6,152
    4,040
    ...
    IMG_1707.JPG
     
  2. 350xfire

    350xfire Instructor, Scuba

    909
    17

    I am actually taking the tech certification class for the Mk2 and asked what the differences are between the cheap and expensive regs. The Mk25 has a way bigger hole through the piston and it is a flow through design where the cheap Mk2 has a smaller hole(quite a bit smaller) and it is not a flow through it flows off to the side of the piston stem. This is how they get the higher flow rate. Now SP does have their reg CE tested and even the chap Mk2 exceed the CE requirments by 3 times...
     
  3. halocline

    halocline Contributor

    9,058
    3,502
    You're talking about something different; the MK2 is a totally different design than any of the balanced piston regs. Our discussion on this thread is about the differences between the various generations of the balanced piston, flow through design. Of course the flow-by (unbalanced) MK2 has lower flow rates, but there are some other benefits, like no dynamic o-rings subjected to HP air, and a very small teflon seat. This makes it an excellent design for high percentage 02.

    Nice to see that SP is making sure they put a little free advertising into their tech certification class.
     
  4. rhwestfall

    rhwestfall Woof! ScubaBoard Sponsor

    # of Dives: 200 - 499
    Location: "La Grande Ile"
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    One must realize that the true limiting factor in flow is the tank valve. These first stages all can pass a higher flow rate than the tank valve can...
     
    scrane likes this.
  5. Geo7

    Geo7 Contributor

    # of Dives: 2,500 - 4,999
    Location: Los Angeles
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    Yes, I think we all agree that all of the 1st stages in question flow more than enough air. Out of curiosity I brought up the question of how flow (ratings) can vary so widely with such a similarly dimensioned piston, which halocline explained. But I actually did not intend to imply that more flow is better. In the spirit of the OP's initial question, my preference is usually for simple designs. I was fine with the Mk2 for a long time, but like the hose routing of the balanced pistons best.
     
  6. halocline

    halocline Contributor

    9,058
    3,502
    The practical value of a high flow rate would be in IP recovery under heavy load at depth. The 1st stage has to flow enough air to re-stock the IP chamber without it dipping too low under demand, otherwise 2nd stage breathing effort, especially with an unbalanced 2nd stage will go up.

    That said, I have never noticed any appreciable difference while diving (even air sharing) between any of the SP 1st stages, including the MK2, until tank pressures get down well below 500 PSI.
     
    couv likes this.
  7. buddhasummer

    buddhasummer Bat sh.t crazy

    # of Dives: 1,000 - 2,499
    Location: Nanny State
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    Most often they have no rubber ring cosmetic or SPEC, either way to me looks like something is missing when it's not there. There's a million plus MK10 over here and I've only ever seen one with the rubber ring it was a MK10 plus that I bought and sold. I want to love them as they are easy for me to get. Given boredom is forever knocking on my door and money is tight perhaps I'll take another run at them.

    Scrap that idea, just remembered new pistons are NLA. I like amassing huge stocks of new parts that I'll never use and eventually sell at a massive loss.

    Morning madness.
     
  8. buddhasummer

    buddhasummer Bat sh.t crazy

    # of Dives: 1,000 - 2,499
    Location: Nanny State
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    4,743
  9. couv

    couv Instructor, Scuba

    # of Dives: 1,000 - 2,499
    Location: 13th floor of the Ivory Tower
    6,152
    4,040
    It is THE answer to the OP's question.

    Simple: No oddball bushing that one will not be able to source years from now. Homemade boot retaining readily available grease in the ambient chamber. The seat is still available from SP, aftermarket, or homemade. The seals are standard, easily sourced o-rings. The piston, if needed, can be dressed with emery cloth.

    The MK10 is a popular model found throughout the world so getting spares is not an issue.

    Reliably handles the high pressure (3500 psi) of my favorite cylinder. etc, etc...
     
    Kupu and Geo7 like this.
  10. Kupu

    Kupu Polliwog ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: USA
    954
    494
    Does that mean aftermarket MK10 boots can be purchased? I have seen a couple versions made by SB members, but did not think they were an item that was generally available. I considered going ghetto and trying a homemade inner tube boot but never got around to it.

    Difficulty finding the boot is one reason I stopped using the MK10 for salt water dives. It took a couple years searching to find an original MK10 boot at acceptable price. The quest to own sealed SP pistons has also resulted in a purchase of MK5 outfitted with environmental kit.

    SP enviromental kits-page-001.jpg
     

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