Fault Finding - Grundfos DWK Series Service Instructions Manual

7. Fault finding

Warning
Before starting work on the pump, make sure that the
fuses have been removed or the mains switch has
been switched to off. It must be ensured that the
power supply cannot be accidentally switched on.
All rotating parts must have stopped moving.
For pumps with sensor, start fault finding by checking
the status on the GU01 or GU02 front panel. See
Note
installation and operating instructios for GU01 or
GU02.
Fault
1. Motor does not start,
fuses blow or motor
protector trips out
immediately.
Caution: Do not try to
start again.
2. Pump operates, but
motor protector trips out
after a short while.
3. The thermal switch of the
pump trips out after a
short while.
4. Pump operates at below-
standard performance
and power consumption.
5. Pump operates, but
gives no liquid.
6. Pump clogged.
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Cause
a) Supply failure; short-circuit; earth-leakage fault in
cable or motor winding.
b) Fuses blow due to use of wrong type of fuse
c) Impeller blocked by impurities.
d) Air bell, float switch or electrode out of adjustment
or defective.
e) Motor phase malfunction
a) Low setting of thermal relay in motor protector.
b) Increased current consumption due to large
voltage drop.
c) Impeller blocked by impurities.
d) Wrong direction of rotation.
a) Too high liquid temperature. Inadequate cooling.
b) Too high viscosity of the pumped liquid.
c) Fault in the electrical connection.
(Y-connection of pump to D-connection results in
considerable undervoltage)
a) Impeller blocked by impurities.
b) Wrong direction of rotation.
a) Air in pump.
b) Discharge valve closed or blocked.
c) Non-return valve blocked.
a) The liquid contains large particles.
b) A float layer has formed on the surface.
Remedy
Have the cable and motor checked and repaired
by a qualified electrician.
Fit fuses of the correct type.
Clean the impeller.
Check the air bells, float switches or electrodes.
Inspect motor and connections.
Set the relay in accordance with the
specifications on the pump nameplate.
Measure the voltage between two motor phases.
Tolerance: - 10 %/+ 6 %.
Clean the impeller.
Check the direction of rotation and possibly
interchange any two phases in the power supply.
Improve cooling or lower the liquid temperature.
Dilute the pumped liquid.
Check and correct the electrical connection.
Clean the impeller.
Check the direction of rotation and possibly
interchange any two phases in the power supply.
Vent the pump twice.
Check the discharge valve and possibly open
and/or clean.
Clean the non-return valve.
Select a pump with a larger size of passage.
Install a mixer in the tank.