What do you mean by a "feed pipe"?

Stand pipe, open or closed.  It is in lue of the real world expansion tank.

If you are talking about a stand pipe open on the
top that is not an option in a real system. In order for an open  stand

pipe

to develop significant pressure on the inlet side of the pump it would
have to be ten feet tall. One foot head is .45 psi. Ten feet would be 4.5
psi.

If you are talking about a sealed pipe with air in it the system
will reach some sort of equilibrium with air bubbles mixed with the fluid
equaling the pressure in the closed pipe be it positive or negative.
My guess is it will be negative if it is on the suction side of the pump.

If it is negitive, why would the stand pipe on the suction side have to be
10 feet tall?

Bob Darrah

I learn more from a good arguement than if I agreed.

Here is a little experiment for both you and Vance. Get a soda straw. Stick
it in a glass of water. Put your thumb over the end of the straw.
Lift the straw out of the glass of water. 

Does the water run out of the straw?

If not why not?

Remove your thumb.

Does the water now run out of the straw?

Why?

Why do I spend half of my life teaching elementary physics? :)
Must be a problem with our schools!

Paul Lamar
 
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