Troubleshooting diaphragm boat
- 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,