Operating Conditions; Ambient Temperature And Altitude; Liquid Temperature; Maximum Operating Pressure - Grundfos NK Serie Montage- Und Betriebsanleitung

6. Operating conditions

6.1 Ambient temperature and altitude

The ambient temperature and the installation altitude are
important factors for the motor life as they affect the life of the
bearings and the insulation system.
If the ambient temperature exceeds the recommended maximum
ambient temperature or the installation altitude exceeds the
recommended maximum altitude above sea level, see fig. 4, the
motor must not be fully loaded due to the low density and
consequently low cooling effect of the air. In such cases, it may
be necessary to use a motor with a higher output.
P2
[%]
100
90
80
70
60
50
20 25 30 35 40 45 50 55 60 65 70 75 80
1000
Fig. 4 The maximum motor output depends on the ambient
temperature and altitude
Legend
Pos. Description
1 0.25 - 0.55 kW MG motors
0.75 - 22 kW MG motors, IE2/IE3
2
0.75 - 450 kW MMG-H motors, IE2
3 0.75 - 462 kW Siemens motors, IE2
Example: A pump with a 1.1 kW IE2 MG motor: If this pump is
installed 4750 m above sea level, the motor must not be loaded
more than 88 % of the rated output. At an ambient temperature of
75 °C, the motor must not be loaded more than 78 % of the rated
output. If the pump is installed 4750 m above sea level at an
ambient temperature of 75 °C, the motor must not be loaded
more than 88 % x 78 % equal to 68.6 % of the rated output.

6.2 Liquid temperature

-40 - +140 °C.
The maximum liquid temperature is stated on the pump
nameplate. It depends on the shaft seal chosen.
For EN-GJL-250 cast iron pump housings, local regulations may
not allow liquid temperatures above +120 °C.

6.3 Maximum operating pressure

Maximum operating pressure, i.e. pressure
above atmospheric pressure
Pump pressure
Inlet pressure
Fig. 5 Pressures in the pump
The inlet pressure + the pump pressure must be lower than the
maximum operating pressure stated on the pump nameplate.
Operation against a closed discharge valve gives the highest
operating pressure.
10
3
2
1
t [°C]
2250 3500 4750 m

6.4 Minimum inlet pressure

Pay attention to the minimum inlet pressure to avoid cavitation.
The risk of cavitation is higher in the following situations:
• The liquid temperature is high.
• The flow rate is considerably higher than the pump's rated flow
rate.
• The pump is operating in an open system with suction lift.
• The liquid is sucked through long pipes.
• The inlet conditions are poor.
• The operating pressure is low.

6.5 Maximum inlet pressure

The inlet pressure + the pump pressure must be lower than the
maximum operating pressure stated on the pump nameplate.
Operation against a closed discharge valve gives the highest
operating pressure.

6.6 Minimum flow rate

The pump must not run against a closed discharge valve as this
will cause an increase in temperature/formation of steam in the
pump. This may cause shaft damage, impeller erosion, short life
of bearings and damage to stuffing boxes or mechanical shaft
seals due to stress or vibration. The continuous flow rate must be
at least 10 % of the rated flow rate. The rated flow rate is stated
on the pump nameplate.

6.7 Maximum flow rate

The maximum flow rate must not be exceeded as otherwise there
is a risk of for instance cavitation and overload.
The minimum and maximum flow rates can be read either from
the performance curve pages in the relevant data booklets or
from a curve for a specific pump when selecting it in Grundfos
Product Center.
Minimum flow rate
Maximum flow rate
Fig. 6 Example from Grundfos Product Center showing
minimum and maximum flow rate