You can use silver solder for quick testing, I generally braise with silphos, a lot more reliable than any soft solder, you require an oxy acetylene torch or similar, I have a Multiplaz 3500 plasma welder which doesn't require any bottled gas to run.
To use R22, make a small delivery tank about 1-2% volume of the heat pipe, evacuate it and the heat pipe, fill the delivery tank then use it to gas the heat pipe.
As a coincidence I'm also using heat pipes for extracting heat from the shower drain water, pre-heating the incoming cold water to the shower mixer.
You can use water in the pipes rather than R22, at 50 microns water boils at -40c, so at waste water temp 28 c should work quite well. Still experimenting with this. Have just bought a new vacuum pump and a digital vac gauge as borrowed items had to be returned. A digital gauge is a must, its impossible to work out what is happening with a mechanical gauge. You have to use boiled water, I found after a few days dissolved gasses come out of the water and kill the vacuum enough to stop the pipe working at low temperatures.
Current heat exchanger is a drain pipe with 6m 12mm soft copper tube wound in a spiral, sitting inside; the waste water flows over the coils carrying the cold water to the mixer, sort of illegal but works very well. You have to make a filter for it that easily cleaned of especially hair, it gets caught in the coils and after 6 months stops working.
Cheers
Mike
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