Piping choices for 140 PSI hydro system

[randallburns]

I own a small hydro system in Southwestern Washington. We recently had a line break followed by a unusual freeze-and I lost 100 feet of line. Right now I'm using 3" PVC pipe(above ground). I'm planning to redo some things, so I wanted a fast, inexpensive way to replace that 100 feet of line(even if I couldn't generate full power right away-putting PVC pipe together in the cold is a pain). Does anyone have experience using polyethylene pipe for hydro applications? I've seen the 160 psi stuff. I'd need to use it at the higher level of its rating. Does anyone know of a good writeup on how to attach fittings to this stuff?

Thanks!

 

[jimovonz]

I use MDPE pipe for my hydro, but only at 50psi. We do however use 2" MDPE for water reticulation up to 350psi. At this pressure there were no fittings available and we had to get the joins welded on site. The available fittings went up to 16 bar (~230psi) and are simple enough to use, consisting of a sleeve, O ring and a threaded  cap. The fitting goes entirely on the outside of the pipe (no flow restriction).

[randallburns]

Can you point me to any links on the fittings you are using? There are 3 ways of fastening this stuff I've seen:

1. exterior metal bands that you screw to tighten
   
2. a copper band that you tighten with a specialized crimping tool
   
3. a "fusor" that uses heat to wield the polyethelene
   
   

I'm under the impression the last two are prefered for high pressure applications. I've only used this stuff with lower pressure(50-60). I want to find out as much as I can about higher pressure approaches before I do this. Thanks in advance.

[jimovonz]

I have not found any fittings for PE pipe that go beyond 16bar (including electrofusion) which is why we had to get the plastic welder in. The pipe itself had to be specially made for us by RXPlastics and had a wall thickness around 1/3". Anyway, the brand of fitting we use for under 16bar is Plassim. You can find technical specs  for each fitting on their site along with installation instructions.

[GaryGary]

Hi,

The Endot site has quite a bit of test data on PE pipe:

 http://www.endot.com/support/installation.asp

My recollection is that the burst pressure tests go several times the advertised working pressure, so I would think that 160psi rated pipe would be fine for 140 even if you have some higher bumps.

The biggest think with PE pipe is to keep the temperature down -- the pressure it will withstand goes down with increasing temperature, and its not worth much of anything above 130 or 140F.  There is data on pressure degradation with temperature on the Endot site.  Black pipe sitting in the sun with no flow can get this hot.  

Gary