Grundfos CMV, Инструкция по установке и эксплуатации

Страница: 12 / 22

En
gl
is
h (
G
B)
12
12.6 Maximum system pressure and permissible liquid temperature
* At liquid temperatures below 0 °C (32 °F), higher motor outputs may be needed due to increased viscosity,
for instance if glycol has been added to the water.
12.7 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
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 curves on
page 16 at the highest flow the pump will
be delivering).
H
f
= Friction loss in suction pipe in metres
head.
H
v
= Vapour pressure in metres head,
see fig. 10, page 17.
t
m
= liquid temperature.
H
s
= Safety margin = min. 0.5 metres 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 during
operation to avoid cavitation.
Example
p
b
= 1 bar.
Pump type: CMV 3, 50 Hz.
Flow rate: 4 m
3
/h.
NPSH (from fig. 8, page 16): 3.3 metres head.
H
f
= 3.0 metres head.
Liquid temperature: 90 °C.
H
v
(from fig. 10, page 17): 7.2 metres head.
H = p
b
x 10.2 - NPSH - H
f
- H
v
- H
s
[metres head].
H = 1 x 10.2 - 3.0 - 3.3 - 7.2 - 0.5 = -3.8 metres head.
This means that a suction head of 3.8 metres is
required during operation.
Pressure calculated in bar: 3.8 x 0.0981 = 0.37 bar.
Pressure calculated in kPa: 3.8 x 9.81 = 37.3 kPa.
12.8 Maximum inlet pressure
The actual inlet pressure plus the pressure when the
pump is operating against a closed valve should
always be lower than the maximum system pressure.
Shaft seal Permissible liquid temperature* Maximum system pressure
AVBx
-20 °C to +40 °C
+41 °C to +90 °C
(-4 °F to 104 °F)
(105.8 °F to 194 °F)
10 bar
6 bar
(145 psi)
(87 psi)
AQQx -20 °C to +90 °C (-4 °F to 194 °F) 10 bar (145 psi)