I am developing system head curves for high service pumps. I am generating a few curves to cover various flow ranges. I have noticed that the system curve starting point is lower than the head required to pump to the desired hydraulic grade line.
For instance, in one system curve I am using a suction side hgl of 957 feet and a discharge side hgl of 1067 feet and my flow requirement is 7 mgd. This would mean that at least the pump would need to produce 110 feet of lift to meet the discharge side hgl. However, the curve I generated in watergems starts out at 0 mgd and the head is calcuated at 98 feet.
I guess my question is why would the system curve ever dip down below the minimum static head?
Respectfully,
Aqueduct
Hello,
This could happen if the downstream boundary is supplying demands. Consider the below example network:
You might expect the "static" head (point on the system head curve at zero flow) to be 150 - 100 = 50, but when the pump is off (flow = 0) the difference between the suction and discharge HGL is only 48 feet. The reason is because when the pump is off, the tank supplies the demand at J-2. The flow from the tank induces head losses in the pipe between the tank and J-1, reducing the HGL on the suction side of the pump.
If this doesn't help, I would suggest submitting your model to technical support or explaining a bit more about how your network is set up.
Regards,
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
Jesse:
That makes perfect sense. Thanks!
Respecfully,