Grundfos NK Montage- Und Betriebsanleitung Seite 35

14. Fault finding
Warning
Before removing the terminal box cover and before any removal/dismantling of the pump, make sure that the power
supply has been switched off.
Fault Cause
1. The pump delivers no a) Wrong electrical connection (2 phases).
or too little liquid.
b) Wrong direction of rotation.
c) Air in suction pipe.
d) Counter-pressure too high.
e) Inlet pressure too low.
f)
g) Pump draws in air due to defective seal.
h) Pump draws in air due to low liquid level.
2. Motor-protective a) Pump blocked by impurities.
circuit breaker has
b) Pump runs over the dimensioned duty point.
tripped out due to
c) Density or viscosity of the liquid is higher
overload of the motor.
d) Overload setting is incorrect.
e) The motor runs on 2 phases.
3. Pump makes too a) Inlet pressure too low (cavitation).
much noise.
Pump runs unevenly
and vibrates.
b) Air in suction pipe or pump.
c) Counter-pressure is lower than specified.
d) Pump draws in air due to low liquid level.
e) Impeller out of balance (clogged impeller
f)
g) Pump stressed by the pipework (thus causing
h) Defective bearings.
i)
j)
k) Foreign bodies in the pump.
l)
4. Leakage in pump or in a) Pump stressed by the pipework (thus causing
connections.
Leakage in
b) Pump housing gaskets and gaskets at
mechanical shaft
seal.
c) Mechanical shaft seal dirty or stuck together. Check and clean the mechanical shaft seal.
Leakage in stuffing
d) Mechanical shaft seal defective.
box.
e) Stuffing box defective.
f)
Suction pipe clogged or impeller blocked by
impurities.
than specified when ordering.
blades).
Inner parts worn.
starting noise).
Defective motor fan.
Defective coupling.
Frequency converter operation
leaks in the pump housing or connections).
connections defective.
Shaft surface or shaft sleeve defective.
Remedy
Check the electrical connection and remedy, if
necessary.
Interchange two phases in the power supply.
Vent the suction pipe or the pump and replenish.
Set the duty point in accordance with the data sheet.
Check the system for impurities.
Increase the liquid level on the suction side. Open the
isolating valve in the suction pipe. Make sure that all the
conditions in 6.4 Pipework are complied with.
Clean the pump.
Check the pipeline seals, pump housing gaskets and
shaft seals, and replace, if necessary.
Increase the liquid level on the suction side and keep it
as constant as possible.
Clean the pump.
Set the duty point in accordance with the data sheet.
If less power suffices, reduce the flow on the discharge
side. Or fit a more powerful motor.
Check the setting of the motor-protective circuit breaker
and replace, if necessary.
Check the electrical connection. Replace the fuse, if
defective.
Increase the liquid level on the suction side. Open the
isolating valve in the suction pipe. Make sure that all the
conditions in 6.4 Pipework are complied with.
Vent the suction pipe or the pump and replenish.
Set the duty point in accordance with the data sheet.
Increase the liquid level on the suction side and keep it
as constant as possible.
Clean and check the impeller.
Replace defective parts.
Mount the pump so that it is not stressed.
Support the pipes.
Replace the bearings.
Replace the fan.
Replace the coupling. Align the coupling.
See 6.3.2 How to align the unit.
Clean the pump.
See 8.2 Frequency converter operation.
Mount the pump so that it is not stressed.
Support the pipes.
Replace pump housing gaskets or gaskets at
connections.
Replace the mechanical shaft seal.
Retighten the stuffing box. Repair or replace the stuffing.
Replace the shaft or the shaft sleeve. Replace the
packing in the stuffing box.
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