Dear Community

I have a model for a City of 30,000 with a Water Treatment Plant. For High Service (HSP) Pump Elevations, there are elevations for suction side and discharge side and I use the suction side.

HSP discharge elevation: 958.50 ft

HSP suction pipe elevation: 940.00 ft

The reservoir elevation can be between 843-852 ft based on the control and I use 843 ft as the worst case scenario.

When I compared the pump head of actual and modeled HSP pumps during hydrant flushing tests with known water elevations at towers, the model results show always about 8-9 psi higher pump head than the actual.

The pump curve are correct so the HSPs pumps higher flow of water in the model.

What can be the cause of the 8-9 psi discrepancy? 

Also, I actually requested the City to provide the pump discharge pressure. However, they provided me the pump head instead. What is the disadvantage of comparing the pump head instead of pump discharge pressure?

Yoko