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 Shafts and Bearings
External motor pumps should be checked for shaft alignment and bearing wear. If
the shaft is out of alignment, bearings will wear quite rapidly. Listening to the pump
is one of the best ways to check these points.
Current Draw
Another excellent way to spot pump problems is by measuring the current draw of
the pump and comparing it to the manufacturer's specifications.
The following table gives a general indication of other things to inspect based on
current readings. "High" and "low" refer to the pump manufacturer's specifications.
TABLE 3-1 : Current Readings and Pump Problems
Inspect for:
If Ammeter Reads:
Power supply problem
Zero
Control problem
Relay or starter problem
Broken motor lead
Thermal overload tripped
Motor problem
Too low
Broken or slipping shaft
(1/4 to 1/2 times
specifications)
Airbound loop
Correct amount
Closed valve, backwards check
valve
Broken or slipping shaft
Direction of motor rotation
Misaligned shaft
Too high
Worn bearings
(1 1/4 to
Foreign matter in volute
1 1/2 times
Impeller against volute wall
specifications)
Motor problem
Locked rotor problem
Much too high
(2 or more times
specifications)
INSPECTION
80
3.1 INSPECTION PROCEDURES
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