Hi Tim,
I definitely recommend the HDPE ("High Density PolyEthylene") for durability
and ease of installation. With the flow rates you mention I'd recommend 4"
pipe, butt-welded on site using a "fusion welder" machine that you can rent
from the pipe supplier. It comes in 40' lengths. You'll need a small
generator to run the end trimmer and the heater element for the welding
machine.
I have built two penstocks with welded HDPE now and after also using steel
and PVC for other projects I'm convinced that the poly is the way to go.
Just this fall I installed 600' of 6" HDPE on a 30 degree rock and scree
slope in two easy days with just three people. We used a small gas-powered
winch to pull the pipe up the hill as we welded it together. If you can
get the pipe lengths dropped at the intake and pull it down the hill as you
weld, that is even easier. (thats the way we did it at my house)
I'm also in Western WA so if you want help with design, materials sourcing
or installation, let me know off-list.
Eric
Rainshadow Solar, Inc.
Orcas, WA
----- Original Message -----
From: "Timothy Crawford" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Friday, November 25, 2005 9:27 PM
Subject: [microhydro] Penstock decision
>I am also a newbie, this being my first post. I would appreciate some
>perspective on what would be the most sensible type of piping for a
>penstock on my potential site. On my property is a small, year-round
>spring-fed creek running at an estimated 100 - 300 gpm, depending upon
>amount of added flow from local runoff after rains (...it rains a lot here
>in Western Washington). I estimate the available gross head (I haven't
>surveyed it) at 60 ft. The run of the penstock pipe would approximate
>600 - 800 feet. I would like to extract as much AC production as I
>reasonably can from the site, as my state and utility encourages net
>metering, and my house uses a lot of power, even though I have installed
>geothermal heat pumping.
> My question is this: the stream is in a fairly steep, heavily wooded
> ravine, and the going is tough because of the irregular terrain and brush.
> Because of the expected difficulty of installing and properly bedding a 4
> or 5" PVC pipe, I wonder if (1or several) 2" or larger polyethylene
> pipe(s) would make sense instead. I am afraid that the joints on the PVC
> could fail from the stress of the uneven terrain. Since freezing isn't an
> issue, I think poly pipe could just be laid on the ground (with necessary
> tethering). Would this be more appropriate given the difficulty of the
> terrain, or would PVC be cheaper and acceptably rugged?
> Thank you so much for your advice.
> Respectfully,
> Tim Crawford
> Montesano, Washington, USA
>
>
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