Grundfos NB Series, Installation And Operating Instructions Manual

Page: 23 / 52

23
14. Fault finding chart
Before removing the terminal box cover and before any removal/dismantling of the pump, make sure that the electricity sup-
ply has been switched off. It must be ensured that it cannot be accidentally switched on.
Fault Cause Remedy
1. The pump delivers no
or too little liquid. a) Wrong electrical connection (2 phases). Check the electrical connection and remedy, if neces-
sary.
b) Wrong direction of rotation. Interchange two phases of the mains supply.
c) Air in suction pipe. Vent the suction pipe or the pump and replenish.
d) Counter-pressure too high. Set the duty point in accordance with the data sheet.
Check the system for impurities.
e) Inlet pressure too low. Increase the liquid level on the suction side. Open the
isolating valve in the suction pipe. Make sure that all the
conditions in
6.7 Pipework are complied with.
f) Suction pipe or impeller blocked by impuri-
ties. Clean the pump.
g) Pump draws in air due to defective seal. Check the pipeline seals, pump housing gaskets and
shaft seals, and replace, if necessary.
h) Pump draws in air due to low liquid level. Increase the liquid level on the suction side and keep it
as constant as possible.
2. The motor-protective
circuit breaker has
tripped because the
motor is overloaded. a) Pump blocked by impurities. Clean the pump.
b) Pump running above the rated duty point. Set the duty point in accordance with the data sheet.
c) Density or viscosity of the liquid is higher
than specified when ordering.
If less flow is sufficient, reduce the flow on the discharge
side. Or fit a more powerful motor.
d) Motor-protective circuit breaker overload set-
ting is incorrect.
Check the setting of the motor-protective circuit breaker
and replace, if necessary.
e) The motor runs on 2 phases. Check the electrical connection. Replace the fuse, if
defective.
3. Pump makes too
much noise.
Pump runs unevenly
and vibrates. a) Inlet pressure too low (cavitation). Increase the liquid level on the suction side. Open the
isolating valve in the suction pipe. Make sure that all the
conditions in
6.7 Pipework are complied with.
b) Air in suction pipe or pump. Vent the suction pipe or the pump and replenish.
c) Counter-pressure is lower than specified. Set the duty point in accordance with the data sheet.
d) Pump draws in air due to low liquid level. Increase the liquid level on the suction side and keep it
as constant as possible.
e) Impeller out of balance (clogged impeller
blades).
Clean and check the impeller.
f) Inner parts worn. Replace defective parts.
g) Pump stressed by the pipework (thus causing
starting noise).
Mount the pump so that it is not stressed.
Support the pipes.
h) Defective bearings. Replace the bearings.
i) Defective motor fan. Replace the fan.
j) Foreign bodies in the pump. Clean the pump.
k) Frequency converter operation. See 8.2 Frequency converter operation .
4. Leakage in pump or
at connections.
Leakage in mechani-
cal shaft seal. a) Pump stressed by the pipework (thus causing
leaks in the pump or at connections).
Mount the pump so that it is not stressed.
Support the pipes.
b) Pump housing gaskets and gaskets at con-
nections defective.
Replace pump housing gaskets or gaskets at connec-
tions.
c) Mechanical shaft seal dirty or stuck together. Check and clean the mechanical shaft seal.
d) Mechanical shaft seal defective. Replace the mechanical shaft seal.
e) Shaft surface defective. Replace the shaft.
5. Too high temperature
in pump or motor. a) Air in suction pipe or pump. Vent the suction pipe or the pump and replenish.
b) Inlet pressure too low. Increase the liquid level on the suction side. Open the
isolating valve in the suction pipe. Make sure that all the
conditions in
6.7 Pipework are complied with.
c) Bearings lubricated with too little, too much
or unsuitable lubricant.
Replenish, reduce or replace lubricant.
d) The axial pressure is too high. Check the relief holes of the impeller and the lock rings
on the suction side.
e) Motor-protective circuit breaker is defective
or setting is incorrect.
Check the setting of the motor-protective circuit breaker
and replace, if necessary.
f) The motor is overloaded. Reduce the flow rate.