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6. Operating conditions
6.1 Inlet pressure
The minimum inlet pressure is according to the
NPSH curve plus a safety allowance of at least 2 m.
The maximum inlet pressure is limited by the maxi-
mum operating pressure.
6.1.1 Minimum inlet pressure - NPSH
Calculation of the inlet pressure "H" is recommended
when
• the liquid temperature is high
• the flow is significantly higher than the rated flow
• water is drawn from depths
• water is drawn through long pipes
• inlet conditions are poor.
To avoid cavitation, make sure that there is a mini-
mum pressure on the suction side of the pump. The
maximum suction lift "H" in metres head can be cal-
culated as follows:
H = p
x 10.2 – NPSH – H
b
Barometric pressure in bar.
p
b
(Barometric pressure can be set to 1 bar.)
In closed systems, p
pressure in bar.
NPSH Net Positive Suction Head in metres head.
(To be read from the NPSH curve at the
highest flow the pump will be delivering.
See page 285.)
Friction loss in suction pipe in metres
H
f
head. (At the highest flow the pump will be
delivering.)
Vapour pressure in metres head. (To be
H
v
read from the vapour pressure scale. "H
depends on the liquid temperature "T
See page 285.)
H
Safety margin = minimum 2 metres head.
s
If the "H" calculated is positive, the pump can oper-
ate at a suction lift of maximum "H" metres head.
If the "H" calculated is negative, an inlet pressure of
minimum "H" metres head is required.
H
f
H
P
b
H
v
Fig. 3
Schematic drawing of an open system
Check that the pump is not and will not
Caution
be exposed to cavitation.
12
– H
– H
f
v
s
indicates the system
b
"
v
".
m
NPSH
6.2 Ambient temperature, motor
Ambient temperature: Maximum +60°C.
If the ambient temperature exceeds +60°C or if the
motor is installed more than 3500 metres above sea
level, the rated motor output (P2) will fall 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
2250
Fig. 4
Motor P2 depends on temperature/
altitude
6.3 Liquid temperature
0°C to +90°C.
The maximum liquid temperature is marked on the
pump nameplate.
6.4 Operating pressure
At +90°C: Max. 1.6 MPa (16 bar).
The maximum operating pressure depends on the
liquid temperature.
6.5 Minimum flow rate
A minimum flow rate equal to 10% of the flow rate at
maximum efficiency is needed at all times. Flow rate
and head at maximum efficiency are stated on the
pump nameplate.
6.6 Maximum flow rate
To prevent cavitation and overload, the maximum
flow rate must be according to the NPSH curve and
must not exceed the values for each individual pump
stated on page 285.
6.7 Frequency of starts and stops
Maximum 20 per hour.
t [°C]
3500
m
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