Grundfos NK Montage- Und Betriebsanleitung Seite 34

12. Service
Warning
If a pump has been used for a liquid which is
injurious to health or toxic, the pump will be
classified as contaminated.
If Grundfos is requested to service such a pump, Grundfos must
be contacted with details about the pumped liquid before the
pump is returned for service. Otherwise Grundfos can refuse to
accept the pump for service.
Possible costs of returning the pump are paid by the customer.
12.1 Service kits
Service kits for NK, NKG, see www.Grundfos.com (WebCAPS),
WinCAPS or Service Kit Catalogue.
13. Calculation of minimum inlet pressure
The minimum inlet pressure "H" in metres head required 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.)
pb
In closed systems p
b
bar.
Net Positive Suction Head in metres head (to be read
from the NPSH curve, page 725, at the highest flow the
NPSH pump will be delivering).
The maximum flow rate must not exceed the values
stated for the individual pump on page 713.
H Friction loss in suction pipe in metres head.
f
Vapour pressure in metres head, see page 731,
H
v
where t = liquid temperature.
m
H Safety margin = min. 0.5 metres head.
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. The calculated value of H must be
present during operation.
Example:
p = 1 bar.
b
Pump type: NK 50-200/219, 2-pole, 50 Hz.
Flow rate: 70 m³/h.
NPSH (read on page 725): 2.35 metres head.
H = 3.0 metres head.
f
Liquid temperature: +90 °C.
H (read on page 731): 7.2 metres head.
v
H = p x 10.2 - NPSH - H - H
b f v
H = 1 x 10.2 - 2.35 - 3.0 - 7.2 - 0.5 = -2.85 metres head.
This means that a suction head of 2.85 metres is required during
operation.
The inlet pressure calculated in bar: 2.85 x 0.0981 = 0.28 bar.
The inlet pressure calculated in kPa: 2.85 x 9.81 = 28 kPa.
34
- H
s
indicates the system pressure in
- H [metres head].
s