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Old 04-21-09, 11:14 AM   #26
Hugh Jim Bissel
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Default Very Cool (in more ways than one!)

I'm not a HVAC tech, nor do I play one on TV, but I just wanted to add my 2 (or 10) cents to the matter. Wanting to comment on this thread (and other ground-source heat/air threads) was what prompted me to reform my evil lurking ways and register.

A touch of background to start: The last year I've been helping to install a ground-source system at my place of employment. As a result, I've had some hands-on experience welding polyethylene pipe -- over 2000 welds of both butt and socket fusion.

So lets talk about the fusion: The butt fusion I was doing was in the 2-4" pipe size, with this machine <http://www.mcelroy.com/fusion/no14/>. We did socket fusion for the smaller stuff mainly because of all the tees used, I would guess, but for the scale you're talking about I wouldn't expect that you'll be needing many fittings.

Here are some things that come to mind about welding in general, and specifically about DIY welding:
- Most definitely make some sort of sliding jig to hold the pipes for heating and assembly.
- You want to keep both ends of the pipe parallel with each other.
- You want both ends of the pipe aligned with each other. like this: == not this: =---
- The ends of the pipe should cut be square (to each other, and to the heater) We had a contraption with rotating blades to square up the ends (and get to clean pipe)
- The ends of the pipes need to be cleaned (if not trimmed, but that wasn't an option for us: proper procedure was to ALWAYS trim/square (even if you've already trimmed and you just adjust the pipe in the clamps to align the ends))
- Our heater was set for about 500 deg F. Time-wise, I didn't do any butt fusion smaller than 2" (heating time was around 20 or 30 sec for 2", but not sure off the top of my head) so I don't know what to tell you about the time: experiment till you get a bead that's the right size
- There should actually be two beads - one from each pipe, and they should be about the same size (probably 1/8-1/4" for your pipe size) and even all the way round: if its a joint that counts (ie you can't cut it up to look at the cross section) the bead is how you tell if its likely to be a good weld or not.
- Practice before you do welds that'll be permanent: especially to determine your heating time. Then cut the pipe in half longways to look at the cross section of your welds: the bead should wrap around to the pipe, there should be no line: ie. if the bead wasn't there you shouldn't be able to tell where one pipe starts and the other ends. (also, before you cut, try bending the pipe back on itself to test strength)
- The evenness of your bead (or lack therof) will tell you if the end faces of the pipes were square to each other
- Let the joint sit and cool for awhile (3 min was specified) before you remove from the alignment jig to keep from putting stress on the joint until it's cooled some -- even after removal, be gentle with it until it's cool to the touch

This is getting longer than I intended, so let me leave it at that for now, and come back later. I'm definitely not trying to rain on your parade, just want to make sure you don't have to go leak hunting in a year or two.

Edit: I guess this doesn't address the original issue of what to use to do the welds, but it'll be important to keep in mind (IMO) as you build your alignment tool, and put it to use.

Good luck welding! I much preferred the butt fusion to the socket fusion: socket doesn't use an alignment machine. If you make yourself a good aligner you can take your time lining up and clamping, so the only thing you adjust in the heat of fusing is the pressure/distance of the pipes from each other. With socket, you have to align the pipe and fitting on the heater, then put them together and keep them aligned during cool down. Much more prone to error.

Have fun, but don't breathe the plastic smoke (anymore than you have to, at least)

Last edited by Hugh Jim Bissel; 04-21-09 at 11:25 AM.. Reason: additional points to ponder
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