Howard wrote:

As I pointed out...... centrifugal pumps do not conform to conventional
logic which is based upon positive displacement..... actually restricting
flow beyond a certian point reduces pressure.... contrary to what one might
think.   Until you set up a centrifugal pump with a guage and play with it a
bit it is a bit difficult to relate to.   Needless to say a totally
unrestricted outlet leaves you with very little pressure.... as the outlet
is progressively restricted pressure rises, and then falls.   A nearly
stalled (outlet restricted) pump will have far less pressure than it would
have if it had more opening.  There is an optimum flow for max pressure....
above or below that point pressure drops......     This is easily observable
if illogical...

H.W.

We are mostly concerned with flow Howard. Any significant pressure difference 
across the pump is due to the restrictions in the flow. Rad, block, 
thermostate, etc.. 

BTW One inch of water is a pressure of .036 psi while the system pressure 
due to the radiator cap is 15 to 20 psi. 15 psi would equate to pumping water 
stright up to 35 feet or a three story building. Of course the pump does 
not see this as both sides see the 15 psi more or less. It would be 
interesting to put a pressure tap on both sides of the pump
but I would rather have a flow meter in the system.

Paul Lamar
 
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