Page 75 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Pump Best Practices Be st Practice 2.7

Fig 2.7.15 Centrifugal pump head vs. flow curve

seal chamber pressures and temperatures to change and lead to
premature seal wear and/or failure. Note that the stated EROE
1. The EROE flow range is + 10% and 50% of the pump best
efficiency point (BEP) flow low flow range can be reduced if the pump or fluid have any of
2. All ‘bad actor pumps’ (more than one component failure per the characteristics noted in Figure 2.7.18.
year) should be checked for EROE.
3. To determine that the pump is operating in EROE:
Calculate the pump head required
Measure the flow
Plot the intersection of head and flow on the pump shop test Pumps with suction specific speeds > 8,000 (customary units)
curve Double suction pumps
Water pumps with low NPSH margin
Fluids with S.G. < 0.7
Pumps with Inducers
Fig 2.7.16 EROE Facts
If a flow meter is not installed, Figure 2.7.17 defines the
options that are available to determine the pump flow, so the Fig 2.7.18 Factors that can reduce low flow EROE range
EROE can be obtained.
The flow values in Figure 2.7.17 can be determined by hand Therefore, we always recommend that the first step in
calculations using the equations available in any pump text seal condition monitoring be determination of pump opera-
(power equation and pump temperature rise equation). tion within its EROE. If the ‘bad actor’ pump is operating
It can be seen that the EROE will provide a reasonable guide outside its EROE, we recommend the action shown in
that usually will eliminate hydraulic disturbances that can cause Figure 2.7.19.
If seal reliability does not improve when operating within the
EROE, further investigation is required concerning the process
1. Measure motor amps and calculate power conditions in the seal chamber and/or flush system.
2. Record control valve position, valve differential pressure, fluid
S.G. and calculate valve flow (pump flow).
3. Measure pump pipe differential temperature and calculate
pump efficiency Consult operations to determine if process changes can be
4. Obtain an ultrasonic flowmeter to measure flow made to operate in EROE
5. For items 1 and 3, locate the calculated value (power or Define target EROE parameters for operations (flow, amps,
efficiency) on the pump test curve to determine pump flow control valve postion, delta T)

Fig 2.7.17 Available pump flow determination options Fig 2.7.19 If a centrifugal pump is outside its EROE

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