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Centrifugal Pump Driver Sizing

INERTANCE shares the engineering calculator for centrifugal pump driver sizing (motor capacity), which is one of possible root cause for site trouble shooting works. The suitable driver sizing such as hydraulic power has to be considered during design phase, when mechanical engineer evaluates the technical bid for centrifugal pump. Driver capacity has to be mainly determined by process condition such as flow rate, head, specific gravity of pumping liquid, which information is included in pump performance curve. And, it is possible to increase the driver power as per pump efficiency, service factor as specified in API 610 11th. This engineering calculator for driver sizing includes the information with hydraulic power, brake horse power with incorporating API service factor.

How to use this calculator

  1. Input the flow rate in m3/hr unit for pumping liquid.
  2. Input total head in meter (m) unit based on process condition.
  3. Input the specific gravity (S.G) for pumping liquid.
  4. If engineer input above three (3) input data, the hydraulic power (Hyd.P, kW) can be calculated.
  5. Pump efficiency (%) should be input, which data can be found from pump performance curve.
  6. Based on pump efficiency input, the brake horse power (BHP1, kW) can be automatically calculated.
  7. As per para 7.1.4 of API 610 11TH, the service factor shall be considered, in case the customer’s pump is designed as per API standard.
  8. Then, the brake horse power (BHP2 kW) can be calculated with consideration of API  service factor.
Pump Driver Sizing
Pump Driver Sizing

Pump Motor Capacity Calculator

The drivers for centrifugal pump shall be sized to meet the maximum specified operation conditions. It shall have the nameplate power ratings at least equal to the percentages of power at pump rated conditions given in below table as per para. 7.1.4 of API 610 11th. This service factor should be considered as well as possible process condition specified in pump datasheet.

API Service Factor
API Service Factor

Example for Driver Sizing

Driver capacity can be increased as per project requirements, which to be carefully checked by mechanical engineer for procurement, and see below example with various driver sizing with hydraulic power of same performance curve by different requirements.

Pump performance curve for sizing

* Rated point for pump operation in above performance curve

– Flow rate: 104.5 m3/hr

– Total Head: 42.4 m

– Speed: 1450 rpm (Fixed speed with induction motor)

– Specific gravity: 0.919

– Pump efficiency: 66%

1) Rated condition

Firstly, the Centrifugal driver capacity can be initially calculated at rated condition as follows;

Rated condition
Rated condition

2) Head increase

Sometimes, pump shall have capable of at least a 5% head increase at rated condition by replacement of the impeller(s) with one(s) of larger diameter for different hydraulic design for future condition. 5% head increase of total head (42.4m) has to be input (42.4m x 105% = 44.52m)

Head increase
Head increase

3) End of curve

– Sometimes, Centrifugal pumps have to operate around end of curve by transient condition of parallel operation, and/or some of project specifications request to have lager driver capacity to cover up to end of curve point. The operating point at end of curve has to be input.

End of curve
End of curve

* End of curve point for pump operation in above performance curve

– Flow rate: 128 m3/hr

– Total Head: 37.0 m

– Specific gravity: 0.919

– Pump efficiency: 62%

 

4) Test condition

– Sometimes, the driver has to be tested with driven equipment together for design reliability at manufacturer’s shop as per project specific requirements. In this case, higher specific gravity (water = 1.0) has to be considered, which cause the driver sizing increasing for test condition.

Test condition
Test condition

* Test condition for shop inspection

– Flow rate: 104.5 m3/hr

– Total Head: 42.4 m

– Speed: 1450 rpm (Fixed speed with induction motor)

– Specific gravity: 1.0

– Pump efficiency: 66%

Based on above steps for driver sizing, we can understand that the motor capacity can be various and increased by different specific requirements. These kinds of variation can effect under or over-estimated for centrifugal pump driver motor sizing. Mechanical engineer need to consider this matter carefully.

INERTANCE has a capability regarding noise and vibration engineering, and our experts are familiar with assessment of related design. For further information, please contact us at (mountain@inertance.com).

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