Brochure

5252
3. Pumps operating in systems
3.4.1 Throttle regulation
Installing a throttle valve in serial with the pump it can
change the system characteristic, see figure 3.7. The resist-
ance in the entire system can be regulated by changing the
valve settings and thereby adjusting the flow as needed.
A lower power consumption can sometimes be achieved
by installing a throttle valve. However, it depends on the
power curve and thus the specific speed of the pump.
Regulation by means of a throttle valve is best suited for
pumps with a relatve high pressure compared to flow (low-
n
q
pumps described in section 4.6), see figure 3.8.
Figure 3.9: The bypass valve
leads a part of the flow
back to the suction line
and thereby reduces
the flow into the system.
Figure 3.10: The system characteristic is changed through bypass
regulation. To the left the consequence of a low-n
q
pump is
shown and to the right the concequences of a high n
q
pump is
shown. The operating point is moved from a to b in both cases.
3.4.2 Regulation with bypass valve
A bypass valve is a regulation valve installed
parallel to the pump, see figure 3.9. The bypass valve
guide part of the flow back to the suction line and con-
cequently reduces the head. With a bypass valve, the
pump delivers a specific flow even though the system is
completely cut o. Like the throttle valve, it is possible
to reduce the power consumption in some case. Bypasss
regulation is an advantage for pumps with low head
compared to flow (high n
q
pumps), see figure 3.10.
From an overall perspective neither regulation with
throttle valve nor bypass valve are an energy ecient so-
lution and should be avoided.
Figure 3.8: The system characteristic is changed through throttle
regulation. The curves to the left show throttling of a low n
q
pump and the curves to the right show throttling of a high n
q
pump. The operating point is moved from a to b in both cases.
Figure 3.7: Principle
sketch of a throttle
regulation.
System
Valve
H
H
loss,system
H
loss, throttling
H
Q
H
Q
Q
P
a
a
b
b
η
a
b
b
a
a
b
P
a
P
b
a
b
Q
Q
P
P
a
P
b
η
Q
H
Q
H
Q
Q
P
b
b
a
a
a
η
b
b
a
b
a
b
a
Q
Q
P
P
1
P
b
P
2
P
a
η
Q
System
flow
System
flow
Bypass
flow
Bypass
flow
H
Q
Q
bypass
Q-Q
bypass
Bypass valve
System
H
loss,system