Technical Data; Ambient Temperature And Altitude; Maximum Operating Pressure And Temperature Limits; Minimum Inlet Pressure - Grundfos CRT Serie Instrucciones De Instalación Y Funcionamiento

5. Technical data

5.1 Ambient temperature and altitude

Motor Motor
Motor
power efficiency
make
[kW] class
Grundfos
0.37 - 0.55
MG
Grundfos
0.75 - 18.5 IE3
MG
If the ambient temperature exceeds the above temperature
values or the pump is installed at an altitude exceeding the above
altitude values, the motor must not be fully loaded due to the risk
of overheating. Overheating may result from excessive ambient
temperatures or 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
rated output.
P2
[%]
100
90
80
70
60
50
20 25 30 35 40 45 50 55 60 65 70 75 80
1000
Fig. 2 Motor output depends on temperature/altitude
Example
Figure 2 shows that the load of an IE3 motor at an ambient
temperature of 70 °C must not be loaded more than 89 % of the
rated output. If the pump is installed 4750 metres above sea
level, the motor must not be loaded more than 89 % of the rated
output.
In cases where both the maximum temperature and the maximum
altitude are exceeded, the derating factors must be multiplied
(0.89 x 0.89 = 0.79).
For motor bearing maintenance at ambient
Note temperatures above 40 °C, see section
9. Maintenance.
5.2 Maximum operating pressure and temperature
limits
Maximum operating pressure: 25 bar.
Temperature range:
See also Appendix on page 128, which shows the relationship
between liquid temperature and maximum operating pressure.
The maximum operating pressure and liquid
Note
temperature ranges apply to the pump only.
Liquid temperatures above +120 °C may involve
Note the risk of periodic noise from the shaft seal and
reduce shaft seal life.
CRT pumps are not suitable for the pumping of liquids hotter than
+120 °C for long periods.
8
Maximum
Maximum
altitude
ambient
above sea
temperature
level
[°C]
[m]
- +40 1000
+60 3500
IE3, MG
t [°C]
2250 3500 4750 m
-20 °C to +120 °C.

5.3 Minimum inlet pressure

Hf
H
Pb
Fig. 3 Schematic view of open system with a CRT pump
The maximum suction lift "H" in metres head can be calculated as
follows:
H = p x 10.2 - NPSH - H - H
b f v
p = Barometric pressure in bar.
b
(Barometric pressure can be set to 1 bar.)
In closed systems, p
b
bar.
NPSH = Net Positive Suction Head in metres head (to be read
from the NPSH curve on page 131 at the highest flow the
pump will be delivering).
H = Friction loss in suction pipe in metres head at the
f
highest flow the pump will be delivering.
H = Vapour pressure in metres head.
v
See Fig. E on page 130.
t = Liquid temperature.
m
H = Safety margin = minimum 0.5 metres head.
s
If the calculated "H" is positive, the pump can operate at a suction
lift of maximum "H" metres head.
If the calculated "H" is negative, an inlet pressure of minimum "H"
metres head is required. There must be a pressure equal to the
calculated "H" during operation.
Example
p = 1 bar.
b
Pump type: CRT 16, 50 Hz.
3
Flow rate: 16 m /h.
NPSH (from page 131): 1.5 metres head.
H = 3.0 metres head.
f
Liquid temperature: +60 °C.
H (from Fig. E on page 130): 2.1 metres head.
v
H = p x 10.2 - NPSH - H - H
b f v
H = 1 x 10.2 - 1.5 - 3.0 - 2.1 - 0.5 = 3.1 metres head.
This means that the pump can operate at a suction lift of
maximum 3.1 metres head.
Pressure calculated in bar: 3.1 x 0.0981 = 0.304 bar.
Pressure calculated in kPa: 3.1 x 9.81 = 30.4 kPa.
NPSH
Hv
- H
s
indicates the system pressure in
- H [metres head].
s