Page 72 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Be st Practice 2 .7 Pump Best Practices

Fig 2.7.2 Centrifugal pump

Figure 2.7.7 shows that all types of mechanical failures can
occur based on where the pump is operating based on the
Pumps produce the pressure required by the process
process requirements.
The flow rate for the required pressure is dependent on the
pump’s characteristics Since over 95% of the pumps used in this refinery are cen-
trifugal, their operating flow will be affected by the process.
Figure 2.7.8 shows that centrifugal pump reliability and flow
Fig 2.7.3 Pump performance rate is affected by process system changes.
At this point it should be easy to see how we can condition
monitor the centrifugal pump operating point. Refer to
Figure 2.7.9.
Driver reliability (motors, steam turbine and diesel engines)
can also be affected by the process when centrifugal driven
Variable flow
Fixed differential pressure produced for a specific flow ∗ equipment (pumps, compressor and fans) are used.
Does not require a pressure limiting device Refer to Figure 2.7.10 and observe a typical centrifugal pump
Flow varies with differential pressure (P 1 –P 2 ) and/or specific curve.
gravity Since the flow rate will be determined by the process
∗ ensuring specific gravity is constant
requirements, the power (BHP) required by the driver will also
1
be affected. What would occur if an 8 / 2 " diameter impeller
Fig 2.7.4 Centrifugal pump characteristics were used, and the head (differential pressure) required by the
process was low? Answer: Since the pressure differential
1
required is low, the flow rate will increase and for the 8 / 2 "
diameter impeller, the power required by the driver (BHP) will
increase.
Therefore, a motor can trip out on overload, a steam turbine’s
speed can reduce or a diesel engine can trip on high engine
temperature. These facts are shown in Figure 2.7.11.
Auxiliary system reliability is also affected by process
changes. Auxiliary systems support the equipment and their
components by providing clean, cool fluid to the components
at the correct differential pressure, temperature and flow
rate.
Typical auxiliary systems are:
Lube oil systems
Seal flush system
Seal steam quench system
Fig 2.7.5 A centrifugal pump in a process system Cooling water system

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