Brochure

4949
Figure 3.1: Example of a closed system. Figure 3.3: Example of an open system
with positive geodetic lift.
Figure 3.4: The system characteris-
tics of an open system resembles a
parabola passing through (0,H
z
).
3.1 Single pump in a system
A system characteristic is described by a parabola due to
an increase in friction loss related to the flow squared. The
system characteristic is described by a steep parabola if
the resistance in the system is high. The parabola flattens
when the resistance decreases. Changing the settings of
the valves in the system changes the characteristics.
The operating point is found where the curve of the
pump and the system characteristic intersect.
In closed systems, see figure 3.1, there is no head when
the system is not operationg. In this case the system char-
acteristic goes through (Q,H) = (0,0) as shown in figure
3.2.
In systems where water is to be moved from one level to
another, see figure 3.3, there is a constant pressure dier-
ence between the two reservoirs, corresponding to the
height dierence. This causes an additional head which
the pump must overcome. In this case the system charac-
teristics goes through (0,H
z
) instead of (0,0), see figure 3.4.
Figure 3.2: The system characteris-
tics of a closed system resembles a
parabola starting at point (0.0).
H
operation
H
Q
Q
operation
H
loss,friktion
H
max
H
max
H
operation
H
z
H
Q
Q
operation
H
loss,friktion
Heat Exchanger
Boiler
Valve
Q
operation
H
operation
Buffer tank
Elevated tank
H
z
Q
operation
H
operation