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Symptom
Not enough liquid being delivered
G&L Pumps Series A-C 8300 Base Mounted Centrifugal Pump INSTRUCTION MANUAL
Cause
Air leaks in suction piping
The motor speed is too low.
Discharge head too high
Suction lift too high
Impeller partially plugged
Cavitation; insufficient NPSH
(depending on installation)
Defective impeller.
Foot valve too small or partially
obstructed.
Suction inlet not immersed deep
enough.
Too small impeller diameter.
Probable cause if none of above)
7 Troubleshooting
Remedy
If liquid pumped is water or other
non-explosive, and explosive gas or
dust is not present, test flanges for
leakage with flame or match, or by
plugging inlet and putting line under
pressure. A gauge will indicate a leak
with a drop of pressure.
Check whether motor is directly
across-the-line and receiving full
voltage. Or frequency may be too low;
motor may have an open phase.
Check pipe friction losses. Large
piping may correct condition. Check
that valves are wide open.
If no obstruction at inlet, check for
pipe friction losses. Static lift may be
too great. Measure with mercury
column or vacuum gauge while
pump operates. If static lift is too
high, liquid to be pumped must be
raised or pump lowered.
Dismantle pump and clean impeller.
1. Increase positive suction head on
pump by lowering pump.
2. Sub-cool suction piping at inlet to
lower entering liquid
temperature.
3. Pressurization suction vessel.
Inspect impeller, bearings and shaft.
Replace is damaged or vane sections
badly eroded.
Area through ports of valve should be
at least as large as area of suction
pipe — preferable 1½ times. If
strainer is used, net clear area should
be 3 to 4 times area of suction pipe.
If inlet cannot be lowered, or if eddies
through which air is sucked persist
when it is lowered, chain a board to
suction pipe. It will be drawn into
eddies, smothering the vortex.
Check with factory to see if a larger
impeller can be used; otherwise, cut
pipe losses or increase speed — or
both, if needed. Be careful not to
seriously overload drive.
45
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