help with hydro site calcs [RE-wrenches]

[Steve Willey, Backwoods Solar]

No, I think a standpipe will work.  The only way he can draw air in is if
the intake screen is plugged, which will happen with any standpipe, or if he
tries to allow more flow than the 2 inch legal restriction pipe will allow.
The purpose of the 2" pipe here is to not allow drawing more than legal flow
of water, so air in the line is a signal that you need to reduce the nozzle
size,  or clean the screen at intake.  That is true in any system whether
uniform pipe size or not.

Steve Willey   www.backwoodssolar.com
Backwoods Solar Electric Systems
----- Original Message -----
From: Ron Macleod <microhydro at dplus.net>
To: <RE-wrenches at topica.com>
Sent: Friday, September 08, 2000 8:37 PM
Subject: Re: help with hydro site calcs [RE-wrenches]


>     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.
>     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.
>    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.
>     So Steve - what do you think? Does he need a standpipe? I have never
worked with PVC this small.
>     Best Ron
>


- - - - - - -
To send a message:
 RE-wrenches at topica.com

The archive of previous messages: 
 http://www.topica.com/lists/RE-wrenches/

To unsubscribe send a message to: 
 RE-wrenches-unsubscribe at topica.com

To check out the other RE-Wrench participants:
 www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine: 
 www.homepower.com

For info contact list moderator by email:
 michael.welch at homepower.com
___________________________________________________________
T O P I C A  The Email You Want. http://www.topica.com/t/16
Newsletters, Tips and Discussions on Your Favorite Topics