Pump Set; Operating Conditions; Maximum Operating Pressure; Minimum Inlet Pressure - Grundfos Fire NKF Montage- Und Betriebsanleitung

8.2 Pump set

See technical data in the installation and
Note
operating instructions for the controller and
driver.
Weight: See nameplate.
Sound pressure level
Note
The sound pressure level depends on the driver.
Pump set with diesel engine:
The silencer supplied is designed for the
Note
requirements of the industrial market. If you have
stricter noise level requirements, you can order
and install another silencer.

9. Operating conditions

9.1 Maximum operating pressure

NKF pumps are designed for a maximum operating pressure of
16 bar.
NKF pumps with VdS approval:
Note
To comply with VdS requirements, the pump
head must not exceed 120 metres (12 bar).

9.2 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 x 10.2 - NPSH - H - H
b f v
Barometric pressure in bar.
(The barometric pressure can be taken as = 1 bar.)
p
b
In closed systems, p
b
bar.
Net Positive Suction Head in metres head (to be read
from the NPSH curve at the highest flow the pump will
NPSH
be delivering).
It can be read from the curves in the data booklet.
Friction loss in suction pipe in metres head.
H
f
Vapour pressure in metres head,
H
v with t = liquid temperature (see fig. 9).
m
NKF pumps according to EN and DBI:
Safety margin = minimum 0.5 metres head.
H
s NKF pumps according to VdS CEA 4001:2010-11 (04):
Safety margin = minimum 1 metre head.
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.
14
All manuals and user guides at all-guides.com
- H
s
is equal to the system pressure in
Relation between vapour pressure and liquid temperature t
tm
(°C)
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Vapour pressure scale
Fig. 9

9.3 Maximum inlet pressure

The actual inlet pressure + closed-valve pressure must always be
lower than the maximum operating pressure.
See section 9.1 Maximum operating pressure.
The closed-valve pressure of the pump can be taken from the
data booklet of the pump set.

9.4 Minimum flow rate

Warning
The pump must not run against a closed valve as
Caution
this may cause an unacceptable temperature
increase or formation of vapour.
In pumps with water-cooled diesel engine, a minimum flow rate is
ensured by a pipe connecting the discharge port with the heat
exchanger.
Pumps with electric motor and 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.
m
Hv
(m)
45
40
35
30
25
20
15
12
10
8,0
6,0
5,0
4,0
3,0
2,0
1,5
1,0
0,8
0,6
0,4
0,3
0,2
0,1