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Troubleshooting diaphragm boat

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  • William Abernathy
    I am building a pop-pop boat to resemble the one in Ponyo as a holiday gift to my daughter. I have scratchbuilt a boiler from a 1-5/8 -ish round copper pipe
    Message 1 of 1 , Dec 18, 2010
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      I am building a pop-pop boat to resemble the one in Ponyo as a holiday
      gift to my daughter. I have scratchbuilt a boiler from a 1-5/8"-ish
      round copper pipe cap end, about 3/8" deep, with a .003" brass diaphragm
      sweated to the top. There are two 1/8" copper tubes sweated to the front
      of the boiler, and the pipes extend down in a nice curve followed by
      about 6" of straight run out to the stern of the boat. I have tried to
      test-run the boiler, but have had no luck.

      The pipes and diaphragm are unobstructed and, as far as I can tell,
      tight (when I hold my finger over one pipe and blow in the other, I get
      an oilcan pop from the diaphragm). On early test runs, I could see flux
      emerging slowly from one of the tailpipes, and there are a few bubbles
      from time to time. Nonetheless, I can't get a good pop out of the boiler
      unless I hold my fingers over the outlets, and as soon as I let go,
      we're back to nothing.

      I wish I could add some photos, but the digicam is out of the house with
      my vacationing daughters right now.

      My theories so far:

      1) The copper pipe cap is too thick to be heated effectively
      2) The boiler is not properly primed with water (i.e., too much
      headspace in the boiler. I thought I'd done this right, but there's
      really no way to be sure)
      3) The brass diaphragm is too thick. I doubt this because I am within
      the range described by Jean-Yves's plans. Perhaps my soldering was too
      sloppy and this made the brass effectively thicker.
      4) The boiler is too big to be heated effectively by the heat source (a
      "tea light" candle)
      5) Something I haven't thought of yet!

      I would much appreciate it if those of you who've solved similar
      problems might let me know how better to understand this problem and go
      about fixing it.

      Thanks in advance,

      --
      William Abernathy
      Berkeley, CA
      http://yourwritereditor.com
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