English (GB)
28
16. Operating conditions
16.1 Maximum operating pressure
The pumps are designed for a maximum operating pressure of 16
bar.
16.2 Minimum inlet pressure
The minimum inlet pressure "H" in metres head required at the
suction port of the pump during operation to avoid cavitation in
the pump can be calculated from the following formula:
H = p
b
x 10.2 - NPSH - H
f
- H
v
- H
s
If the calculated value of "H" is positive, the pump can operate
with a maximum suction lift of "H" metres.
If the calculated value of "H" is negative, a minimum suction head
of "H" metres is required.
Relation between vapour pressure and liquid temperature t
m
Fig. 29
Vapour pressure scale
16.3 Maximum inlet pressure
The actual inlet pr closed-valve pressure must always be
lower than the maximum operating pressure. See section
16.1 Maximum operating pressure
The closed-valve pressure of the pump can be taken from the
data booklet of the pump set.
16.4 Minimum flow rate
In pump sets with a water-cooled diesel engine, a minimum flow
rate of the pump is ensured by a pipe connecting the pump
discharge port with the heat exchanger.
Pump sets with air-cooled diesel engine must be fitted with a
bypass pipe to ensure a minimum flow rate of 2 % (5 % for NKF
125-315) of the flow rate at maximum efficiency. The minimum
flow rate will help to lead away excess heat and thus protect the
pump against overheating.
16.5 Pump speed
The pump speed is stated on the nameplate.
16.6 Direction of rotation
The direction of rotation of the pump is clockwise when seen from
the drive end. The correct direction of rotation is indicated by an
arrow on the pump housing.
16.7 Liquid and ambient temperature
Liquid temperature
The pump is designed for liquid temperatures up to 120 °C.
Ambient temperature
The maximum permissible ambient temperature depends on the
driver and controller. See installation and operating instructions
for the driver and controller.
16.8 Relative air humidity
The relative air humidity must not exceed 80 %. Otherwise the
controller may be damaged. If humidity is a problem, install a
space heater with a hydrostat.
Caution
Do not charge the batteries by an external
charger when they are connected to the
controller.
p
b
Barometric pressure in bar.
(The barometric pressure can be set to = 1 bar.)
In closed systems, p
b
is equal to the system 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).
You can read it from the curves in the data booklet.
H
f
Friction loss in suction pipe in metres head.
H
v
Vapour pressure in metres head, with t
m
= liquid
temperature. See fig. 29.
H
s
NKF pumps according to EN
Safety margin = minimum 1.0 metres head.
TM
00 303
7 079
8
20
15
12
10
8,0
6,0
5,0
4,0
3,0
2,0
1,0
0,8
0,6
0,4
0,3
0,2
0,1
1,5
120
110
90
100
80
70
60
50
40
30
20
10
0
Hv
(m)
tm
(°C)
150
130
140
25
35
45
40
30
Caution
The pump must not run against a closed valve as
this may cause an unacceptable temperature
increase or formation of vapour.
Note
Pump set with water-cooled diesel engine:
The maximum liquid temperature depends on the
coolant temperature required to cool the diesel
engine. See installation and operating
instructions for the diesel engine.
