Grundfos NBS Serie Notice D'installation Et De Fonctionnement page 20

Fault Cause
a) The inlet pressure is too low,resulting in
cavitation in the pump.
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.
3. The pump makes too much
e) The impeller is out of balance or the
noise. The pump runs
impeller blades are clogged.
unevenly and vibrates.
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 causes
noise.
a) The pump is stressed by the pipes which
causes leaks in the pump housing or at
connections.
b) Pump housing gaskets and gaskets at
4. The pump, connections or
connections are defective.
mechanical shaft seal is
leaking. c) The mechanical shaft seal is dirty or stuck
together.
d) The mechanical shaft seal is defective.
e) The shaft surface is defective.
a)There is air in the inlet pipe or pump.
b) The inlet pressure is too low.
5. The temperature in the
c) The bearings are lubricated with too little,
pump or motor is too high.
too much or unsuitable lubricant.
d) The axial pressure is too high.
e) The motor-protective circuit breaker is
defective or the setting is incorrect.
f) The motor is overloaded.
20
Remedy
• 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 according to the flow and head that the
pump is selected for.
• Increase the liquid level on the inlet side and keep it as
constant as possible.
1. Clean the impeller.
2. Check the impeller blades, clean them if necessary.
• 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.
• Find the different remedies in Frequency converter
operation section. 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.
1. Vent the inlet pipe or the pump.
2. Fill up the inlet pope and the pump again.
• 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.
• Replenish, reduce or replace the lubricant.
1. Check the relief holes of the impeller on the inlet side.
2. Clean the holes, if necessary
1. Check the setting of the motor-protective circuit breaker.
2. Replace the circuit breaker if necessary.
• Reduce the flow rate.