7
5.2 Inlet pressure
Minimum inlet pressure
Fig. 1
Schematic view of open system with a CRNE-HS
pump
The maximum suction lift "H" in metres head can be calculated as
follows:
H = p
b
x 10.2 – NPSH – H
f
– H
v
– H
s
p
b
= Barometric pressure in bar.
(Barometric pressure can be set to 1 bar.)
In closed systems, p
b
indicates the system pressure in
bar.
NPSH = Net Positive Suction Head in metres head (to be read
from the NPSH curve on page 23 at the highest flow the
pump will be delivering).
H
f
= Friction loss in suction pipe in metres head at the
highest flow the pump will be delivering.
H
v
= Vapour pressure in metres head, see Fig. B on page 23.
t
m
= Liquid temperature.
H
s
= Safety margin = minimum 0.5 metres head.
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
b
= 1 bar.
Pump type: CRNE 1 HS.
Flow rate: 2 m
3
/h.
NPSH (from page 23): 2.0 metres head.
H
f
= 3.0 metres head.
Liquid temperature: +60 °C.
H
v
(from Fig. B, page 23): 2.1 metres head.
H = p
b
x 10.2 – NPSH – H
f
– H
v
– H
s
[metres head].
H = 1 x 10.2 – 2.0 – 3.0 – 2.1 – 0.5 = 2.6 metres head.
This means that the pump can operate at a suction lift of
maximum 2.6 metres head.
Pressure calculated in bar: 2.6 x 0.0981 = 0.255 bar.
Pressure calculated in kPa: 2.6 x 9.81 = 25.5 kPa.
Maximum inlet pressure
•
10 bar (static pressure).
•
25 bar (pressure during operation).
Maximum operating pressure
50 bar.
5.2.1 Pressure test
The pump may be tested at a static pressure of 55 bar.
To lock the pump shaft, proceed as follows:
1. Remove the motor.
2. Lift the chamber stack as far as possible and fit a bracket
(fig. 2) to the pump shaft and the pump head.
The bracket must be ordered separately (product number
96465853).
Fig. 2
Bracket for locking the pump shaft
5.3 Minimum flow rate
5.4 Shaft seal
The shaft seal is fitted on the suction side of the pump. As the
shaft seal is not affected by the discharge pressure, the choice of
shaft seal is only determined by the inlet pressure as well as the
chemical properties and temperature of the liquid to be pumped.
5.5 Start/stop of pump
The number of starts and stops via the mains supply must not
exceed 4 times per hour. When switched on via the mains supply,
the pump will start within 5 seconds.
If a higher number of starts and stops is desired, the input for
external start/stop must be used when starting/stopping the
pump.
When started/stopped via an external on/off switch, the pump will
start immediately.
The maximum number of starts and stops is 200 times per hour.
6. Installation
See the installation and operating instructions for the CR, CRI,
CRN pumps.
In order to maintain the UL/cUL approval, additional installation
procedures must be followed. See page 22.
6.1 Motor cooling
To ensure cooling of motor and electronics, the following must be
observed:
•
Place the pump in such a way that sufficient cooling is
ensured.
•
Keep the temperature of the cooling air below 40 °C.
•
Keep motor cooling fins and fan blades clean.
T
M
0
2
01
18
38
00
Caution
The actual inlet pr the maximum pump
pressure (at no flow) must not exceed 50 bar.
Caution
The pump must not run against a closed
discharge valve.
Hv
H
NPSH
Pb
Hf
Note
During the test, the pump shaft must be locked to
prevent axial movement.
TM
0
3
0
504
0
1
05
Pump type
Liquid temperature
Up to +80 °C
+80 to +90 °C
CRNE 1 HS
0.5 m
3
/h
1.0 m
3
/h
CRNE 3 HS
0.5 m
3
/h
1.0 m
3
/h
Caution
Do not use rapid-closing valves, e.g. rapid-
closing spray guns, as these may cause water
hammering.
