Fault Finding; Frequency Converter - Grundfos NK Serie Montage- Und Betriebsanleitung

15. Fault finding

Warning
Before removing the terminal box cover and before
removing/dismantling the pump, make sure that the
power supply has been switched off and that it
cannot be accidentally switched on again.
Fault Cause
1. Pump delivers no or a) Wrong electrical connection, for instance two
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 running above rated duty point.
tripped because the
c) Density or viscosity of liquid higher than
motor is overloaded.
d) Motor-protective circuit breaker overload
e) Motor runs on two phases.
3. Pump makes too a) Inlet pressure too low, i.e. pump cavitates.
much noise.
Pump runs unevenly
and vibrates.
b) Air in suction pipe or pump.
c) Counter-pressure lower than specified.
d) Pump draws in air due to low liquid level.
e) Impeller out of balance or clogged impeller
f)
g) Pump stressed by pipework thus causing
h) Defective bearings.
i)
j)
k) Foreign bodies in pump.
l)
4. Leaking pump, a) Pump stressed by pipework thus causing
connections, shaft
seal or stuffing box.
b) Pump housing gaskets and gaskets at
c) Mechanical shaft seal dirty or stuck together. Check and clean the mechanical shaft seal.
d) Mechanical shaft seal defective.
e) Stuffing box defective.
f)
30
phases.
Suction pipe or impeller blocked by
impurities.
specified when ordering.
setting incorrect.
blades.
Inner parts worn.
starting noise.
Defective motor fan.
Defective coupling.
Frequency converter operation
leaks in pump housing or connections.
connections defective.
Shaft surface or shaft sleeve defective.
Remedy
Check the electrical connection and remedy, if
necessary.
Interchange two phases of the power supply.
Vent and fill the suction pipe and pump.
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 section 7.4 Pipework
Clean the suction pipe or 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 flow is sufficient, 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 section 7.4 Pipework
Vent and fill the suction pipe or pump.
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 the 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 section 7.3.2 How to align the
Clean the pump.
See section

9.2 Frequency converter

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
box.
Replace the shaft or the shaft sleeve. Replace the
packing rings in the stuffing box.
are complied with.
are complied with.
unit.
operation.