Verifying pump operating point when using the Implicit, Explicit or GVF-Convex solver

Applies To
Product(s): SewerGEMS, SewerCAD, CivilStorm
Version(s): V8i, CONNECT Edition
Area: Output and Reporting
Original Author: Mark Pachlhofer, Bentley Technical Support Group

Problem Description

How do I verify if my pump is adding the correct pump head when using the Implicit, Explicit or GVF-Convex solver in SewerGEMS, CivilStorm or SewerCAD?

Steps to Resolve

1) Move your time browser to a time when the pump is on in your simulation

2) Take the hydraulic grade upstream of your pump (this is displayed in the pump property results) and subtract that from the crown (top) elevation of the conduit immediately upstream of the first manhole after the pressure pipe. (where the pressure pipes transition to the gravity network)

3) Add the headloss you are getting in your pressure pipes and that should give you very close to the total dynamic head needed to be added by the pump.

For example,  If the upstream hydraulic grade of the pump is 1,117.04 ft. The crown of conduit is 1158.16 ft. and the headloss in pressure pipe is 15.89 ft.

Therefore:

1158.16 ft. - 1117.04 ft.  = 41.12 ft.

41.12 ft. + 15.89 ft. = 57.01 ft. of head the pump needs to add.

If the pump is not operating near this point, the model may be unstable (see below links for tips). Typically the Implicit or GVF-Convex solver is best for models with complex pumping, with a small calculation timestep.

See Also

Troubleshooting unstable SewerGEMS and CivilStorm results using the implicit solver

Troubleshooting unstable SewerGEMS and CivilStorm model results using the Explicit SWMM Solver

Troubleshooting Air Valves at High Points with the GVF Convex (SewerCAD) Solver

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