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Thread: low velocity...what the heck?

  1. #1
    Join Date
    Oct 2013
    Location
    Dayton OH
    Posts
    458

    low velocity...what the heck?

    here's a good one. so i bought my second automag not too long ago (older 68 automag air valve). aired it up and chronoed it, and it wouldn't go higher than 250 fps. so i tore it apart, thoroughly cleaned the regulator, installed a new piston o-ring and reg seat, put fresh oil / grease / anti-seize on the relevant parts. i tested it on my working automag (newer 68 automag classic) and it would chrono at 280 fps no problem. so back onto the older automag, and...250 fps.

    after swapping various parts around, i determined that the bolt was the issue. for whatever reason, using the old bolt resulted in a low velocity, while the newer bolt had no issues. so, i guess it was old and worn out? before i toss it, i get out the caliper just to compare measurements, and i hold it up to the light and notice the holes that the air pass through are much smaller on the old bolt than they are on the new bolt! also, that light could pass through a part inside the bolt.

    that's weird. i look closer and...there was an old regulator piston o-ring shoved inside the bolt! if that wasn't enough, there was an old power tube o-ring pushed all the way down the stem on my newer bolt. i pushed the o-rings out by shoving three tootsie-pop popsicle sticks down in there (they're paper, so it wouldn't scratch anything) until they came out of the back. i re-tested the bolt and there are no more velocity issues.

    so yeah, if you have low velocity problems on a classic valve, and you know it's not the regulator, check your bolt and make sure there's nothing weird inside there!


    as an aside, while i was overhauling the regulator, i noted a buna o-ring on the regulator piston (which is of course, not correct). i guess i found out where original piston o-ring disappeared to! LOL!

  2. #2
    Join Date
    Jan 2002
    Location
    Halifax, N.S., Canada
    Posts
    7,351
    There is no way a piston oring would make it through the valve. The old orings don't usually come out, even powertube orings. I'm betting that the old bolt had been stored in a box that had loose orings in it and one got inside. Then, the bolt got installed on a valve and the oring got pushed farther up inside.
    Except for the Automag in front, its usually the man behind the equipment that counts.

  3. #3
    Join Date
    Oct 2013
    Location
    Dayton OH
    Posts
    458
    well yeah, it got misplaced somehow. i was just surprised it was in there!

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