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Servicing your own regulators

Discussion in 'Regulators' started by Rick Warren, Feb 20, 2021.

Would you take a Manufacturer Approved Class on regulator servicing if offered?

Poll closed Feb 27, 2021.
  1. Yes

    92.3%
  2. No

    7.7%
  1. halocline

    halocline Solo Diver

    9,001
    3,401
    Since the inline tool operates pressurized, the seat is only touching the orifice with enough pressure to barely make the seal. Turning the orifice with the tool is less likely to damage the seat than doing so unpressurized and without the purge depressed.

    But, I usually get the 2nd stage pretty close manually as you describe, then connect the inline tool for the last bit of fine adjustment.
     
  2. Angelo Farina

    Angelo Farina Marine Scientist

    # of Dives: 1,000 - 2,499
    Location: Parma, ITALY
    1,831
    2,849
    This is a common misconception. The pressure forcing the seat against the orifice is much larger when the reg is pressurized, as the compressed air goes into the balance chamber and presses the seat against the orifice. Instead, when not pressurized, there is just a very weak spring pushing the seat against the orifice. Of course unbalanced regs works differently, but they are mostly disappeared nowadays...
    And it is always recommended to press the purge button while acting on the orifice for screwing it in or out, so that the seat is not in contact with it...
     
    Open Ocean Diver likes this.
  3. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    5,880
    7,627
    I'm sorry, Angelo, but you are mistaken that the seat pressure increases when the reg is pressurized. It actually decreases very slightly.

    Yes, the Intermediate Pressure applied through the center of the poppet down into the balance chamber and back up against the seat increases force in that direction. The total force applied is a function of the cross sectional area of the balance chamber times the IP.

    BUT, countering that is the simultaneous application of force against the seat by the IP directly. Since the area inside the knife edge is fractionally larger than the cross-sectional area of the balance chamber, the sum of the two vectors is in favor of less pressure against the seat.

    That's why even a balanced second still acts as a safety valve in the event of runaway IP. The increasing net vector in favor of seat opening eventually causes the second stage to freeflow.

    @halocline 's comment that the seat is "barely touching" the knife edge when pressurized, was perhaps a little misleading. He is correct that seat pressure goes down when pressurized, but the active cracking effort and thus poppet spring pressure is the determinant of how hard the seat presses. So while "barely touching" is a correct statement when cracking effort is light, the orifice can still cut the seat, and you are correct that lifting the seat with the purge button is the technique that both you and @halocline follow to reduce that risk.
     
  4. The Chairman

    The Chairman Chairman of the Board Staff Member

    # of Dives: I just don't log dives
    Location: Cave Country!
    62,355
    30,938
    Only balanced second stages have that and they are few and far between.
     
  5. Angelo Farina

    Angelo Farina Marine Scientist

    # of Dives: 1,000 - 2,499
    Location: Parma, ITALY
    1,831
    2,849
    Well, I admit that I was wrong.
    Thanks @rslingler for showing me the error!
    The whole concept of a "balanced" second stage means that the pressure of the seat against the orifice is almost constant, whatever the intermediate pressure (IP). And yes, it decreases VERY SLIGHTLY at increasing of IP, to the point that beyond a maximum IP value the valve opens and the reg free flows.
    On the opposite, an unbalanced second stage (but they still make them for primary regs???) has a large pressure exerted by the spring when the reg is NOT pressurized. The IP pressure counterbalances the spring action almost entirely, so, when the reg is pressurized, the force pushing the seat against the orifice is much smaller.
    Still I do not find a good idea to act on those in-line tuning tools without pressing the purge button...
     
    Open Ocean Diver and rsingler like this.
  6. Open Ocean Diver

    Open Ocean Diver ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 100 - 199
    Location: Lauderdale-by-the-Sea
    1,310
    869
    Thanks for today’s lesson boys, now have better understand of balancing. :)
     
  7. halocline

    halocline Solo Diver

    9,001
    3,401

    It's just the cracking pressure (which is the same as 'sealing' force) that is pushing the seat against the orifice when pressurized. Since I use the inline tool only for fine adjustments, basically to remove the last bit of free flow, I have no concern that the seat is getting cut as the orifice is slightly rotated with the inline tool. There's less than an inch of water pressure differential between the downstream and upstream forces, and it the seat would get cut with that amount of force, it wouldn't stand a chance in storage.

    I'm not sure how you would use the inline tool while pressing the purge button. I think the whole point is to be able to adjust while pressurized, and of course you couldn't do that with the purge depressed.

    Thank you for clearing up the issue that Angelo raised.
     
    Open Ocean Diver and rsingler like this.
  8. Jim Lapenta

    Jim Lapenta Dive Shop

    # of Dives: 500 - 999
    Location: Canonsburg, Pa
    17,217
    9,326
    The service class was actually being developed around that time. I got my Reg Tech Instructor Cert from the guy who put the manual together at DEMA in 2011.
     
  9. Jim Lapenta

    Jim Lapenta Dive Shop

    # of Dives: 500 - 999
    Location: Canonsburg, Pa
    17,217
    9,326
    That gauge works but I've had a couple from scubatools not be as accurate as I like. It also makes the tool a bit unwieldy and when you are tuning it while breathing the reg vs pushing the purge button, you can't see it anyway. Better to put a larger known gauge on the LP inflator hose.
     
  10. halocline

    halocline Solo Diver

    9,001
    3,401
    Angelo, I'm not sure you are fully understanding the difference in seating forces between balanced and unbalanced 2nd stages, or at least you are not articulating it well. Yes, an unbalanced reg has more force against the seat when not pressurized than a balanced reg. But there is no difference when they are pressurized; they both have exactly the force needed to seal the seat at a given cracking pressure. When the reg is adjusted to the point of barely freeflowing, that means that the seat is not pressing against the orifice with sufficient force to close the valve. It doesn't matter whether it is just a large spring (unbalanced) or a small spring and a portion of IP (balanced) providing that force against the downstream force of the air coming from the 1st stage.

    It makes no sense to use an inline tool with the purge pressed, because the whole point of the inline tool is to be able to adjust the 2nd stage while pressurized. Once you press the purge, it no longer functions in that way. You could, I guess, attach everything, then turn off the tank, purge to empty the pressure out of the regulator, press the purge, then turn the orifice with the inline tool, then turn the tank back on, check for freeflows, and repeat this process over and over until you have it set where you want it. But that's not really different than simply removing the hose and adjusting the orifice with a screwdriver.
     

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