Page 114 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Pump Best Practices Best Practice 2 .22

Fig 2.21.4 Speed change performance verification (Courtesy of Union Pump Company)
true. However, it is good practice to verify the mechanical in- The data used for this example are taken from an actual
tegrity of the pump coupling and driver with the vendor before pump operating at 1150 rpm. The affinity law calculation results
proceeding with the change. The mechanical design of the compare favorably with the same pump operating at 1750 rpm
process system must also be confirmed for the revised pressures (refer to Figure 2.21.4).
and flow rates (refer to Figure 2.21.3).

Best Practice 2.22

Require a plant pump spare changeover philosophy to Lessons Learned
ensure optimum pump MTBF. Lack of a plant spare changeover philosophy has been
All pumps are subjected to the highest component forces and responsible for low pump MTBFs, safety issues and pro-
changes during transient (start-up and shut down) operation. cess unit shutdowns.
Whilst it is true that spare pumps must be periodically checked to Many plants either do not have a stated change over philosophy, or
ensure safe and reliable operation when required, the periods between
do not implement the stated policy. In cases where pumps operate on
checks should be optimized.
fluids with a high vapor pressure, too frequent changeover (less than
We have found that the changeover period which results in the
3 months) has resulted in low mechanical seal MTBFs (less than
highest possible pump MTBF is between 3 and 6 months in most pump
12 months).
applications. Notable exceptions are firewater pumps (weekly e for
safety) and seawater pumps (to eliminate corrosion).
Benchmarks
This best practice has been followed since the mid-1990s to optimize
pump safety and maximize pump MTBFs (in excess of 80 months).