Page 59 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Pump Best Practices Be st Practice 2.3

Fig 2.2.26 Example No. 3 NPSH reference
Fig 2.2.25 Application of vertical pump in condensate hot well
service

Best
Best Practice 2.3Practice 2.3
Accurately define all liquid and hydraulic conditions on the The pump operating conditions noted on the pump data sheet are
Centrifugal Pump Data Sheet. the result of hydraulic calculations performed prior to pump selection.
Completely define all possible operating conditions, by meeting The pump head required by the process is a function of inlet
with process engineering and site senior operations personnel during pressure, discharge pressure and specific gravity.
the process design phase to accurately determine: Centrifugal pump curve head rise (head at zero flow divided by head
at rated conditions) can be 5% or lower.
Flow rates Any significant change in the total head required during field op-
Head required eration can result in a centrifugal pump operating in a flow range that
Liquid properties will lower pump reliability and expose the pump to component failures
NPSH available (bearings, seals, impellers, wear ring seizure and shaft breakage).
Define the rated operating point to be as close to the pump best
efficiency point as possible; but not greater than 10% or less than 50% Benchmarks
from the potential pump best efficiency point for centrifugal pump Since the mid-1970s I have made a practice of reviewing all pump
without an inducer. operating conditions with a senior process engineer and plant opera-
tor, during the process design phase, to ensure that the conditions are
Lessons Learned specified as accurately as possible prior to pump selection. This
practice has resulted in trouble free pump start-up and continued
Small changes in operating conditions, especially resulting
operation at optimum levels of safety and reliability (Pump MTBFs
in higher than specified head required in the field, will
exceeding 80 months).
cause lower pump reliability and expose the plant to safety
issues in hydrocarbon services.

B.P. 2.3. Supporting Material in completing the sketch and system design include the
following:
Flow rate e All flow rates including minimum, normal and
Completely define the operating conditions rated should be listed in the data sheet. Normal flow is usually
the flow required to achieve a specific process operation. The
Correctly stated operating conditions are essential for proper rated flow is normally a set percentage increase over the normal
definition and subsequent selection of a specifictypeand flow and it usually includes consideration for pump wear and the
configuration of pump that will meet these specified type of operation within the process system. It can amount to as
conditions. much as ten (10) percent depending upon specific company
Once it is decided to install a pumping system, a sketch practice. The minimum flow is important to identify in order to
should be drawn to define all of the components which establish if a minimum flow bypass line is required for process or
are needed. Some of the factors which need to be considered mechanical design considerations.

33