Pumping Duration VS Pump Life
Pumping Duration VS Pump Life
(OP)
I work for a water utility which predominantly supplies water to storage reservoirs via gravity flow, however, for about 10% of our systems we pump water from a tank at low elevation to a reservoir at a higher elevation. The pumps used are typically vertical multistage centrifugal pumps such as the CRN series manufactured by Grundfos and pumping is done daily to match the total daily demand for the area to be served.
Most of these systems, however, have been designed so that only about 4 hours of pumping is necessary to fill the reservoirs. As you know larger pumps mean higher capital costs including larger pipes to accommodate the flow rates. For some of our new designs we've discussed using smaller pumps and longer pumping times.
My question is what would be the trade-off, if any, with regard to the life of the pumps and frequency of maintenance given that over a specific extended period the smaller pumps would have run for a much longer time. I know this is not something that's easy to calculate/simulate, so I'd like to hear from anyone who's had experience with both scenarios. I also realise that it would also depend on the quality of the pumps with regard to materials, bearing design, lubrication, etc. Thanks.
Most of these systems, however, have been designed so that only about 4 hours of pumping is necessary to fill the reservoirs. As you know larger pumps mean higher capital costs including larger pipes to accommodate the flow rates. For some of our new designs we've discussed using smaller pumps and longer pumping times.
My question is what would be the trade-off, if any, with regard to the life of the pumps and frequency of maintenance given that over a specific extended period the smaller pumps would have run for a much longer time. I know this is not something that's easy to calculate/simulate, so I'd like to hear from anyone who's had experience with both scenarios. I also realise that it would also depend on the quality of the pumps with regard to materials, bearing design, lubrication, etc. Thanks.





RE: Pumping Duration VS Pump Life
RE: Pumping Duration VS Pump Life
It is normally supposed that a high number of starts and stops decreases motor (if not pump also) lifetime. Many pump manufacturers give a recommended maximum number of starts/stops per hour for their lighter duty pumps.
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RE: Pumping Duration VS Pump Life
RE: Pumping Duration VS Pump Life
As pointed by others, large pumps draw high start up curents and high maximum demand. Power tarriffs are usually based on the actual units consumed plus peak demand. The later is charged regardless of your unit consumption. As such, your power costs may be significantly higher for short duration pumping using large pumps.
Your curve of capital, plus maximum demand costs , plus power consumption costs , plus maintenance costs will have a minimum value which is the optimum level.
RE: Pumping Duration VS Pump Life
That's because frequent starts are more severe than continuous duty.
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RE: Pumping Duration VS Pump Life
Steve Wagner
RE: Pumping Duration VS Pump Life