Grundfos NB Installation And Operating Instructions Manual page 38

Fault
2. The motor-protective circuit
breaker has tripped because the
motor is overloaded.
3. The pump makes too much noise.
The pump runs unevenly and
vibrates.
4. The pump, connections or
mechanical shaft seal are leaking.
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Cause
a) The pump is blocked by
impurities.
b) The pump is running above rated
duty point.
c) The density or viscosity of the
liquid is higher than specified when
ordering.
d) The motor-protective circuit
breaker overload setting is
incorrect.
e) The motor runs on two phases.
a) The inlet pressure is too low, that
is the pump cavitates.
b) There is air in the inlet pipe or
pump.
c) The counterpressure is lower
than specified.
d) The pump draws in air due to
low liquid level.
e) The impeller is out of balance or
the impeller blades are clogged.
f) The inner parts are worn.
g) The pump is stressed by the
pipes thus causing starting noise.
h) The bearings are defective.
i) The motor fan is defective.
j) There are foreign bodies in the
pump.
k) Frequency converter operation.
a) The pump is stressed by the
pipes thus causing leaks in the
pump housing or at connections.
b) Pump housing gaskets and
gaskets at connections are
defective.
c) The mechanical shaft seal is
dirty or stuck together.
d) The mechanical shaft seal is
defective.
e) The shaft surface is defective.
Remedy
Clean the pump.
Set the duty point in accordance
with the data sheet.
If less flow is sufficient, reduce the
flow on the outlet side. Otherwise,
fit a more powerful motor.
Check the setting of the motor-
protective circuit breaker and
adjust it, if necessary.
Check the electrical connection.
Replace the fuse, if defective.
Increase the liquid level on the inlet
side. Open the isolating valve in
the inlet pipe. Make sure that all
the conditions in section Pipes are
complied with.
Vent the inlet pipe or the pump.
Set the duty point in accordance
with the data sheet.
Increase the liquid level on the inlet
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.
Clean the pump.
See section Frequency converter
operation.
Mount the pump so that it is not
stressed. Support the pipes.
Replace the pump housing gaskets
or gaskets at connections.
Check and clean the mechanical
shaft seal.
Replace the mechanical shaft seal.
Replace the shaft.