Help! Micro hydro pipe expansion

[Ktm rider]

So I have doing a micro hydro project to power and heat my home. I laid 900 ft of 8” PVC pipe in extremely rocky soil just beside my creek. i haven’t buried it as of yet because I am installing the turbine side of the build and want to pressure test the pipe. My problem is the pipe is expanding and contracting and pulling our of a few random joints.
My question is this. Will the expansion/ contraction stop once I have water running continually through the pipe even though it’s still exposed? Or should I bury it before I do anything else? I would really like to be able to check for leaks before I cover it but I guess it if has a major leak when covered up I’ll know it regardless. Any suggestions?

 

[MossRoad]

First thoughts would be incorrect glue, improper joint prep, pipes not pushed in far enough and held in place while glue dries.... that kind of stuff. The joints shouldn't come apart ever once they're glued.

 

[MossRoad]

Also, what's the air temp in your location? Are they sitting in hot sun?

 

[Ktm rider]

Also, what's the air temp in your location? Are they sitting in hot sun?

I started this project in the fall and it ran into 5he winter.so the temp varied wildly . I did find a chart online that shows the amount of expansion/ contraction to expect and this seems like a common problem.

 

[Ktm rider]

Am I wrong in thinking once the water is ran through the pipe continually that the expansion/ contraction would settle down when the pipe temp stabilizes from the water temp?

 

[scootr]

Sunshine greatly affects expansion. Shading the pipe with a few inches of dirt may help as will filling it with running water (and shading it) - I have seen PVC pipe roll over when heated up in the sun.

 

[IndyIan]

I guess to late now, but 8" is a big pipe, and needs to be pretty thick to handle a lot of water pressure. What's your calculated static pressure at the bottom?

 

[Ktm rider]

I guess to late now, but 8" is a big pipe, and needs to be pretty thick to handle a lot of water pressure. What's your calculated static pressure at the bottom?

Around 24 psi.

 

[IndyIan]

Around 24 psi.

Oh not that much head then, so you do need the big pipe, cool project though, post some pics and specs. I have 40m of elevation at our place, but no water source at the top of the hill. I don't think pumped hydro micro storage really pencils out but I think it would be fun to mess around with when I have time.

 

[MAX-24-Dean]

In general, if you have a delta temp. change of 25 degrees F you will need to use expansion joints on your 900 foot run. (EDIT Covering with backfill may take care of this.)
If you back fill the trench (if there is a trench) so the pipe is covered and shaded you can reduce the temp variation imposed on it. The more backfill depth the less temperature change on the pipe.

On long runs it is best practice to install it all within a delta change of 20° F so the glued fittings are installed at the approximately the same temperature. I have worked on a few jobs that this was written into the specifications for installing PVC.