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Steve - Travis - et al
<P> Travis - you may have a good idea - it was my first
response too - I started an e-mail - then I thought about it - it ain't
so simple.
<BR> You tell me - normal practice on low head is to
use a standpipe that is open to atmosphere near the top of the penstock
and below the intake - this eliminates the possibility of pulling
a vacuum in the penstock if the intake is closed off either by a valve
or major trash blockage. Maybe you don't need this with small pvc lines
on high head - perhaps the penstock will withstand the possible 14 or so
pounds per square inch external - I truly don't know - but I would never
build a system without a standpipe. I've actually seen a 6' diameter riveted
steel penstock that collapsed - it was only on 32 ft of head.
<BR> So here is the rub - If you use a standpipe - the
nozzel size on the turbine becomes critical and hard to calculate. No matter
how short the 2" diameter section of pipe there will be some friction (head
loss) this friction will increase with velocity - say as you use a larger
nozzel and increase discharge at the bottom of the penstock. You may risk
sucking air in through the standpipe if your nozzel size is too large or
you add a second nozzel when you have the water.
<BR> Another way to go is to use a large vaccine relief valve
in place of the standpipe - most have a spring you can change out to adjust
the point at which the valve opens to relieve vacuum. This could work and
solve your problem - but in cold climates the can freeze up and put your
penstock at risk.
<BR> So Steve - what do you think? Does he need a standpipe?
I have never worked with PVC this small.
<BR> Best Ron
<P>Steve Willey, Backwoods Solar wrote:
<BLOCKQUOTE TYPE=CITE>By jolley, Travis, you have an answer there.
You ARE a hydro expert! I had
<BR>never run up against that kind of rules, but I would think that your
idea
<BR>might satisfy them if you explain the reasoning. But caution
to check first
<BR>and see if they accept that usage of irrigation water. Sometimes
it could
<BR>be prohibited as to application of water intended for crops.
I have known
<BR>people doing that that state they are not telling what they use it
for. And
<BR>of course you can actually water crops with the water coming out of
the
<BR>hydro to satisfy that requirement.
<P>And a lot of these systems do great with less than a few hundred watts.
50
<BR>watts and up is very usable for some life-styles, a huge change from
zero
<BR>watts.
<P>Steve Willey www.backwoodssolar.com
<BR>Backwoods Solar Electric Systems
<BR>A catalog business on a mountain
<BR>2 miles from utility lines,
<BR>powered entirely by our catalog products.
<BR>IF UTILITY POWER IS 1/2 MILE OR MORE FROM YOUR SITE,
<BR>get our free 160 page solar-electric Planning Guide/Catalog.
<BR>(Your postal address required - Our list is never given or sold).
<BR>Phone(208)263-4290 Fax (208) 265-4788 in Idaho, USA
<P>----- Original Message -----
<BR>From: Travis Creswell, Ozark Solar <ozsolar@ipa.net>
<BR>To: <RE-wrenches@topica.com>; <RE-wrenches@topica.com>
<BR>Sent: Friday, September 08, 2000 5:53 AM
<BR>Subject: Re: help with hydro site calcs [RE-wrenches]
<P>> Steve,
<BR>>
<BR>> I haven't done any micro hydro but I have looked at several potential
<BR>sites
<BR>> so take that I really have no idea what I am talking about.
Around here
<BR>> most of the sites I've looked at would need major land work just
to get a
<BR>> few hundred watts.
<BR>>
<BR>> What if you started out with a few feet of 2" pipe to meet
the
<BR>restrictions
<BR>> then stepped up to 4" for the remainder of the run to the nozzles?
<BR>>
<BR>> Travis Creswell
<BR>> Ozark Solar
<P>>
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For info contact list moderator by email:
michael.welch@homepower.com</PRE>
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