User notification "Pump exceeds the maximum operating point specified for the pump curve"

  Applies To 
  Product(s):
WaterGEMS, HAMMER, WaterCAD
  Version(s): 08.11.XX.XX, 10.XX.XX.XX
  Original Author: Mark Pachlhofer, Bentley Technical Support Group

Problem

My pumps are operating at a much higher rate than the design point. How do I fix this?

OR

What does the user notification "Pump exceeds the maximum operating point specified for the pump curve" mean?

Solution

The first step to solving this problem starts with understanding how pumps function in the hydraulics and hydrology products. You can find that explanation in this wiki

The second step is to check the pump curves for the pumps that are adding too much flow or head and make sure the curves are correct. If the curves are correct check the head and flow being output by the pump is on the pump curve.   

Next, check the demands in your model for the junctions, hydrants, tanks, and the HGL on your reservoirs that are downstream of the pump.  The best way to check your demands on downstream elements is to make a selection set of all those nodes and then open your flextable based on that selection set. There are directions in the wiki found here that explain how to do this. With the flextable open add the column called "Demand" if it's not already. This wiki article will explain how to do that. Once that column is added you can right click on the column header and choose statistics to see the total sum of the demand and other important information. At this point you can also sort that column by right clicking on it and choosing Sort > Descending because you are likely looking for values in the column that are to high. After doing this you should scan all the demands to make sure they are correct. Note that for the reservoir there is no "demand" column. You should be checking the hydraulic grade in reservoirs to make sure that it is set correctly. 

Finally, if you are checking the demands for an EPS simulation you should use the time browser to choose the time step where the pumps are operating higher than the design point and then use the steps above to check the appropriate tables for the demands.   

What does the user notification "Pump exceeds the maximum operating point specified for the pump curve" mean?

Pumps in water and storm water product line operate by adding enough head to system to balance the hydraulic grade in the system, namely by overcoming the losses and elevation differences between your upstream and downstream boundary conditions. The head and flow rate is defined on your pump definition curve. In the water products, like WaterGEMS and WaterCAD, the pumps need to also add enough flow to be able to fulfill the demand.     

This warning message usually indicates that the pump is operating beyond the user-entered pump characteristic curve (pump definition). This will happen when the pump definition is not defined all the way out to zero head. WaterCAD and WaterGEMS will use extrapolation on the pump curve, so that it extends all the way to zero head. The pump can operate past the user entered range if the system conditions warrant it. The pump curve that you see in the system head curve viewer is an extrapolated pump curve. 

The warning message may indicate that the real pump may not be able to operate correctly in this condition. Basically, the system conditions are such that the head the pump needs to add is less than the lowest head value in your pump curve. 

You can always check the operating point and extrapolated pump curve by right clicking the pump and selecting "Pump Curve".

You should compare the operating point to the actual pump curve that you have defined under Components > Pump Definitions, and not to the system head curve window.

Sometimes you may also get this message if you are using a multiple point pump curve with large gaps between flow values.  If this is the situation you're facing, the issue can usually be resolved by adding one or two flow values with its corresponding head value to make the gaps between consecutive values smaller.

See Also

Pump cannot deliver flow or head user notification

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