Assembled Pop Bottle Attachment
The attachment that shown here
looks more complicated that it needs to be. The simplest form is seen
here.
The reason for making this device out of threaded pipe and not just
"welded" pipe is because the pop bottle lids seem to always fail and
fracture. This leads to the necessity for them to be replaceable as
seen here.
It also seems wise to have a spare of this piece too, as when testing
the "weld" cracked once and would take a few minutes and tools to fix.
The heat from welding will destroy the thermocouple so you must be
able to remove the thermocouple or the part to be fixed.
To get the thermocouple through a wooded wedge and epoxy were. This
created a good seal. However air will leak though the outer casing of
the thermocouple wire, and since the casing seems to fragment when the
pop bottle detonates it may be best to expose the wires where they run
through the epoxy to ensure the seal. You will know if you have failed
to do this.
The last word of caution is that the must be made of pipe that can
handle the pressure. From my testing at least 1700kPa (250psi). Pop
bottles can hold a lot of pressure when they are frozen.