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WaterGEM the System Head is lower than the pump curve settings

I am updating an existing water system model for a city with about 20,000 population.  I am having two problems. I have searched the Bentley Community forum, but I have not be able to fix the two problems listed below. I'd appreciate the advice from expertise.

1. There are four pumps pumps at higher flow rate outside the pump curve due to low system head (see the attached 'User Notification' and 'Pump Result').

2. Fire flow test results were computed to calibrate the model. The difference between the actual and model result of the static pressure are greater than 5 psi (between 4-6 psi.)(The residual reading difference between the actual fire flow test and the model results are 2-4 psi.)

Following is a list of updates that have been made:

1. Imported new piping, wells, pumps, storage tanks using Model Builder from AutoCAD. All pipe's C-values were updated based on the construction years.

2. Update pump curves for new pumps

3. Realized that the elevations near the river banks do not match with an USGS map. Imported elevation using TRex, then subtracted 8' using Global Edit in Junction Flex Table. Made sure the elevation of pumps, wells, and tanks remained the same.

4. Added the hydrants where the fire flow tests were conducted. Set the elevations of the hydrants to be 9.25' above the watermain

Please let me know if I should provide more data.  Thank you in advance for reviewing my questions.

Parents
  • Hello Yoko,

    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 that the pump needs to add is less than the lowest head value in your pump curve.

    The following link has more information on this user notification: communities.bentley.com/.../24830.pumps-are-operating-at-a-much-higher-rate-than-the-design-point-pump-exceeds-the-maximum-operating-point-specified-for-the-pump-curve

    You should take a look at the demands in the system, as well as elevations at tanks or reservoirs downstream of the pumps. Demands and hydraulic grade at boundaries will have an impact of the pump results.

    If that doesn't help, let us know. We may need to see a copy of the model files. There are two options for sharing your model on Communities, whichever you choose please be sure to zip your files first. The first option is to attach the zip file containing your model to your reply on the forum using the Advanced Reply Editor (you'll find the link below and to the right of the reply box). If your data is confidential please use the instructions in the link below to send it via Bentley Sharefile. Files uploaded to Sharefile can only be viewed by Bentley employees.

    communities.bentley.com/.../7079.be-communities-secure-file-upload

    If you upload the file to Sharefile, please post here with the name of the file so that we know it is available.​

    Regards,
    Scott
Reply
  • Hello Yoko,

    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 that the pump needs to add is less than the lowest head value in your pump curve.

    The following link has more information on this user notification: communities.bentley.com/.../24830.pumps-are-operating-at-a-much-higher-rate-than-the-design-point-pump-exceeds-the-maximum-operating-point-specified-for-the-pump-curve

    You should take a look at the demands in the system, as well as elevations at tanks or reservoirs downstream of the pumps. Demands and hydraulic grade at boundaries will have an impact of the pump results.

    If that doesn't help, let us know. We may need to see a copy of the model files. There are two options for sharing your model on Communities, whichever you choose please be sure to zip your files first. The first option is to attach the zip file containing your model to your reply on the forum using the Advanced Reply Editor (you'll find the link below and to the right of the reply box). If your data is confidential please use the instructions in the link below to send it via Bentley Sharefile. Files uploaded to Sharefile can only be viewed by Bentley employees.

    communities.bentley.com/.../7079.be-communities-secure-file-upload

    If you upload the file to Sharefile, please post here with the name of the file so that we know it is available.​

    Regards,
    Scott
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