4.6.2 Suction-piping checklist
Performance curve reference
Net positive suction head available (NPSH
A
) must always exceed NPSH required (NPSH
R
) as shown on
the published performance curve of the pump.
Suction-piping checks
Check
Explanation/comment
Checked
Check that the distance between the inlet
flange of the pump and the closest elbow
is at least five pipe diameters.
This minimizes the risk of cavitation in the suction in-
let of the pump due to turbulence.
See the Example sections for illustrations.
Check that elbows in general do not have
sharp bends.
See the Example sections for illustrations.
—
Check that the suction piping is one or two
sizes larger than the suction inlet of the
pump.
Install an eccentric reducer between the
pump inlet and the suction piping.
The suction piping must never have a smaller diame-
ter than the suction inlet of the pump.
See the Example sections for illustrations.
Check that the eccentric reducer at the
suction flange of the pump has the follow-
ing properties:
•
Sloping side down
•
Horizontal side at the top
See the example illustrations.
It is recommended that a commissioning
(temporary) suction strainer be used.
After commissioning it is recommended an
operating (permanent) suction strainer be
used.
Check that the strainer has at least three
times the area of the suction piping.
Check the location of the suction strainer is
at least 5 pipe diameters from the suction
nozzle.
Continuously monitor the pressure drop
across the suction strainer.
Limit the pressure drop across the strainer
to 68.9 kPa | 10 psi, or the vapor pressure
of the pumped fluid, or the resulting NPSHr
is not adequate.
After a period of time (24 hours minimum)
system flushing should be complete and
the commissioning (temporary) suction
strainer can be removed.
Suction strainers help to prevent debris from entering
the pump
Recommended commissioning (temporary) strainer
mesh size:
•
Viscosity≤100cP use 60 mesh
•
Viscosity>100cP use 40 mesh
•
Viscosity>300cP use 20 mesh
Recommended operating (permanent) strainer mesh
size:
•
Viscosity≤100cP use 40 mesh
•
Viscosity>100cP use 20 mesh
•
Viscosity>300cP use 12 mesh
If more than one pump operates from the
same liquid source, check that separate
suction-piping lines are used for each
pump.
This recommendation helps you to achieve a higher
pump performance and prevent vapor locking espe-
cially with specific gravity of liquid less than 0.60.
If necessary, make sure that the suction
piping includes a drain valve and that it is
correctly installed.
—
4.6 Piping checklists
Model 3700i API610 / Type OH2 Installation, Operation, and Maintenance Manual
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