Grundfos NB Installation And Operating Instructions Manual page 41

• The inlet conditions are poor.
• The operating pressure is low.
13.1.5 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
valve gives the highest operating pressure.
The NB pumps comply with IEC 60335-2-51 if the
maximum inlet pressure is equal to or less than 1.2
MPa (12 bar).
13.1.6 Minimum flow rate
The pump must not run against a closed valve as it
causes an increase in temperature and a formation of
steam in the pump. That may result in shaft damage,
impeller erosion, short life of bearings and damage to
the stuffing boxes or mechanical shaft seals due to
stress or vibration. The continuous stable flow rate
must be at least 10 % of the rated flow rate. The rated
flow rate is stated on the pump nameplate.
13.1.7 Maximum flow rate
Do not exceed the maximum flow rate, otherwise
there is a risk of cavitation or overload, for instance.
The minimum and maximum flow rates are indicated
either on the performance curve pages in the relevant
data booklets, or on a curve for a specific pump when
selecting it in the Grundfos Product Center. See
www.grundfos.com.
H
(m)
38
32
A
28
24
20
16
12
8
4
0
0 5 10 15
Example from Grundfos Product Center in
www.grundfos.com showing minimum and
maximum flow rate
NBG 50-32-160/163, 50Hz
Pumped liquid = Water
o
Liquid temperarure = 20 C
3
Density = 1000 kg/m
B
20 15 30 Q(m /h)
3
Pos. Description
A Minimum flow rate
B Maximum flow rate
Related information
• www.grundfos.com
41