Shaft Seal Run-In Period; Number Of Motors Starting Or Stopping; Reference Readings Of Monitoring Equipment - Grundfos NB Installation And Operating Instructions Manual

5. Check the overload by measuring the motor
current consumption and comparing the value to
the rated current stated on the motor nameplate.
In case of overload, throttle the valve on the outlet
side until the motor is no longer overloaded.
If the pump is fitted with a motor with
an output selected on the basis of a
specific maximum flow rate, the motor
may be overloaded if the differential
pressure is lower than anticipated.
6. Always measure the motor current consumption
during startup.
At the moment of startup, the input
current of the pump motor is up to six
times higher than the full-load current
stated on the motor nameplate.

7.5 Shaft seal run-in period

The seal faces are lubricated by the pumped liquid,
meaning that there may be a certain amount of
leakage from the shaft seal. When the pump is
started for the first time, or when a new shaft seal is
installed, a certain run-in period is required before the
leakage is reduced to an acceptable level. The time
required depends on the operating conditions, that is,
every time the operating conditions change, a new
run-in period is started.
Under normal conditions, the leaking liquid
evaporates, and as a result, no leakage will be
detected.
Liquids such as kerosene do not evaporate, and
drops are visible, but it is not a shaft seal failure.
7.5.1 Mechanical shaft seals
Mechanical shaft seals are precision components. If
the mechanical shaft seal of a recently installed pump
fails, it normally happens within the first few hours of
operation. The main cause of such failures is
improper installation of the shaft seals and/or
mishandling of the pump during installation.

7.6 Number of motors starting or stopping

Maximum number of motor starts
Frame size
Number of poles
2
56-71 100
80-100 60
112-132 30
34
per hour
4 6
250 350
140 160
60 80
Maximum number of motor starts
Frame size
Number of poles
2
160-180 15
200-225 8
250-315 4
7.7 Reference readings of monitoring
equipment
We recommend that you take initial readings of these
parameters:
• vibration level - use SPM (shock pulse method)
measuring points (only for NK and NKG)
• inlet and outlet pressure - use pressure gauges.
The readings can be used as reference in case of
abnormal operation.
per hour
4 6
30 50
15 30
8 12