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How do I check that my pump design is correct and optimal (for pumping water to multiple overhead tanks)?

Dear all,

I have a situation where pipe network is laid upto 12 overhead tanks. Now I need to design pump to feed water to this network, so that daily demands at the tanks are met. So far, what I have tried is- defined a 1 design point pump with an approximate head and exact cumulative demand of the 12 tanks. When I run the system, it gives no error and the ESRs show positive residual head. So I guess the pump is working. However, the head I entered is approximate. And I need to place purchase order for the pump. How do I know that the pump definition is optimal for the network? How do I design a pump such that I am not over-sizing / under-sizing it?

I would gladly share my model if anyone's willing to have a look at it.

Regards,

Pankhuri

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  • Here's a generic approach.

    Determine the peak demand for the planning horizon . Let's say its 300 L/s with an average day around 150 L/s. You should meet this flow with one unit out of service which would mean 2 300 L/s pumps or 3 150 L/s pumps. The 3 pump option gives you more operator flexibility.

    To determine the head required, generate system head curves for a range of conditions such as a peak demand when tanks are at low level and low demand when tanks are nearly full. This will give you a range of heads you will need to provide  at the design flow.

    Then go through pump catalogs to find a pump(s) that have a best efficiency point (BEP) at the design flow rate and can provide that head.

    Put the candidate pump into the model and see how it works. The actual operating point should fall close to the BEP.

    Since the actual demand will generally be less than the peak demand, investigate different control rules for turning the pumps on/off based on tank water levels.

  • Thank you for the answer!

    I tried running System Head Curve with maximum flow as my desired flow (say 300 L/s from your example). The result is showing lot of negative heads (-62,50,000 to -6,87,50,000). The two curves - system head curve and pump curve are not crossing each other. pump curve is at 0m.

    I ran the model afterwards and checked residual heads at junctions and head on pump. They are coming within expected range (pressure at pump discharge: 39m, residual head between 3m and 40m).

    I expected the System Head Curve tool to show similar range of head. But it isn't. Where might have I gone wrong?

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  • Thank you for the answer!

    I tried running System Head Curve with maximum flow as my desired flow (say 300 L/s from your example). The result is showing lot of negative heads (-62,50,000 to -6,87,50,000). The two curves - system head curve and pump curve are not crossing each other. pump curve is at 0m.

    I ran the model afterwards and checked residual heads at junctions and head on pump. They are coming within expected range (pressure at pump discharge: 39m, residual head between 3m and 40m).

    I expected the System Head Curve tool to show similar range of head. But it isn't. Where might have I gone wrong?

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