•
Air pockets can form in the top of the reducer and the pipe when operating on suction lift.
Never use a concentric reducer in a horizontal line.
Piping checklist
Check
Explanation/comment
Checked
Check that the elbows in the suction piping
for horizontal double-suction pumps are in-
stalled per the Hydraulics Institute Stand-
ards since there is always an uneven turbu-
lent flow around an elbow.
When there is an elbow in a position other than the
vertical when in relation to the pump suction nozzle,
this causes more liquid to enter one side of the impel-
ler than the other. The result is highly unequalized
thrust loads that overheat the bearings and cause
rapid wear, which adversely affects the hydraulic per-
formance. See the Example of unbalanced loading
figure.
Check that pipe reducers on the inlet side
have no more than one pipe diameter re-
duction in a single reducer.
This avoids excessive turbulence and noise.
When operating on a suction lift, check that
the suction pipe slopes upward to the pump
nozzle.
A horizontal suction line must have a gradual rise to
the pump. Any high point in the pipe can become fil-
led with air and prevent proper operation of the pump.
(Optional) You can install a short section of
pipe adjacent to the suction flange such as
Dutchman or a spool piece that is designed
so that it can be readily dropped out of the
line.
This facilitates the cleansing of the liquid passage of
the pump without dismantling the pump. With this ar-
rangement, anything that clogs the impeller is acces-
sible with the removal of the spool piece or pipe sec-
tion.
Example of unbalanced loading
CAUTION:
Risk of excessive axial load or cavitation. Do not install an elbow directly before the suction of
a double suction pump if the plane of the suction is parallel to the pump shaft. Alternatively,
install an elbow with straightening vanes to help evenly distribute the flow.
This figure shows the unbalanced loading of a double-suction impeller due to the uneven flow around an el-
bow that is adjacent to the pump:
1
2
3
4
5
1.
Pump casing
2.
Impeller
3.
Pump suction flange
4.
Suction elbow
5.
Water velocity increases here and causes a greater flow to one side of the impeller.
4.5 Piping checklists
28
Model 3409 Installation, Operation, and Maintenance Manual
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