Page 117 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Be st Practice 2 .24 Pump Best Practices

Fig 2.23.4 Speed change performance verification (Courtesy of Union Pump Company)

Best Practice 2.24

The use of variable speed motors in low voltage services is Lessons Learned
effective in terms of energy and reliability. Controlling centrifugal pumps with control valves is not
Consider a low voltage motor best practice of always using variable energy efficient, and can expose centrifugal pumps to re-
frequency driver motors to provide just the amount of power required liability issues due to control valve instability.
for process requirements. The writer has experienced large savings by using VFDs and not
Install a control system (level, pressure or flow) that will regulate using process control valves which typically have a pressure drop of 23
pump motor driver speed to meet set point requirements without the meters (75 feet) of head or more and expose the pump process control
use of a process control valve. system to valve instability and maintenance (valve packing and di-
This approach will reduce required power in low voltage applica- aphragm replacement).
tions (less than 600 volts) by as much as 25%.
At the present time, the additional installed cost of low voltage VFDs Benchmarks
can be paid for in less than three years by the energy savings pro- This best practice has been used since 2005, and has resulted in
duced.
significant energy savings and increased pump control system safety
and reliability.

B.P. 2.24. Supporting Material

See B.P. 2.2.6 and 2.2.21 for supporting material.

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