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How to size a centrifugal pump in SewerCAD?

Hi there.

I come from the pumping industry in Australia and trialing the use of SewerCAD at the moment, we use steady-state modeling via excel sheets and also some of the other modeling tools available in the market. 

I have gone through the exercises available on Youtube and also from your learn server, where it doesn't actually represent a real-life problem, the pump curves are not just available for a project as you show, and in most cases, for a model it is the responsibility of the designer to choose the pump/s with the help of suppliers, for this, the designer is expected to provide a duty point ie. flow and required head. 

please see attached for a simplified real-life problem where we are required to work the pump duty point so we can select a pump. We can do this in various other ways as I have mentioned above and what I want to please know is how to tackle this from SewerCAD. How would you model a system to work out the pump's duty point without placing the pump? 


PDF

explanation of the scenario:

we have a wet well and the pump sets are submersible centrifugal sewer pumps. 

the incoming gravity pipework is 225mm Ductile Iron pipework, ID is 240mm. The peak incoming flow is 12L/s, and our requirement is the match this flow via the pump selection. ie. the pump flow rate has to be min 12L/s. The levels are provided in the model and based on this flow rate we have selected the forced main as 125mm PE100 PN16 (ID is 102mm)

In some of the other modeling tools, we can place the pump as a fixed flow pump and when we run the model it would develop the required duty point.

while searching about this topic, I had come across this: https://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/16879/estimating-a-pump-curve-for-a-model but not too sure if this works or not. 

your help in this regard is appreciated and believe this will help many. 

Cheers,

Imran

Parents
  • The overall steps work like this.

     

    1. Pick a design flow for the pump. The value should be a little higher than the peak inflow. The inflow will vary over time and will rarely high the peak.

     

    1. Size the force main such that the velocity is greater than 2 ft/s and less than 8 ft/s when the pump is on.

     

    1. Generate the system head curve for the pump. Generate the system head curve. You need to use the GVF-Convex solver for this. This calculation will show you the head you need to provide at you design flow rate.

     

    1. Now pick several alternative pumps which produce that flow at that head. Run each through the model (use scenario manager). Determine the operating point of reach pump and see what the pump efficiency is at that operating point.

     

    1. Check the operation by running an extended period simulation to see how the pump will cycle, not just at peak time but on normal days. If it is cycling too frequently, you may need to upsize the wet well or downsize if the cycle is too slow.

     

    1. Those steps should get you a reasonable pump. However, to do a really want to pick the best pump use WaterGEMS’ scenario energy costing tool to determine the present worth of energy cost. The biggest component of life cycle cost is usually energy and sometimes the least expensive pump is the most costly to run.
  • For the benefit of other forum viewers, you can use WaterCad to do exactly what you describe above.

    I have used WaterCad to successfully design many sanitary pumping stations.  It's a great tool and easy to use.  Once you have a library of pump curves it's almost a trivial exercise to see which pump works the best for a given configuration.

    WaterCad is also useful for designing and modeling manifolded wastewater pumping stations (which are essentially vastly simplified water distribution systems).

  • Thanks Gary. I agree. WaterCAD (WaterGEMS) . It has more tools than SewerCAD for things like system head curves, combination pump curves and energy costing. You just need to separate out the portion of the system from the wet well to the final discharge point.

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