Grundfos CUE Series Installation And Operating Instructions Manual page 27

When restarting, the pump will react in the following way:
1. If the flow is higher than the low-flow limit, the pump will return
to continuous operation at constant pressure.
2. If the flow is lower than the low-flow limit, the pump will
continue in start/stop operation. It will continue in start/stop
operation until the flow is higher than the low-flow limit. When
the flow is higher than the low-flow limit, the pump will return to
continuous operation.
2. Low-flow detection with flow switch
When the digital input is activated because there is low-flow, the
speed will be increased until the stop pressure (actual setpoint +
0.5 x ΔH) is reached, and the pump will stop. When the pressure
has fallen to start pressure, the pump will start again. If there is
still no flow, the pump will reach the stop pressure and stop. If
there is flow, the pump will continue operating according to the
setpoint.
Operating conditions for the stop function
It is only possible to use the stop function if the system
incorporates a pressure sensor, a non-return valve and a
diaphragm tank.
The non-return valve must always be installed
before the pressure sensor. See figs 39 and 40.
Caution
If a flow switch is used to detect low flow, the
switch must be installed on the system side after
the diaphragm tank.
Pressure sensor
Pump
Non-return
valve
Fig. 39 Position of the non-return valve and pressure sensor in
system with suction lift operation
Pressure sensor
Pump Non-return valve
Fig. 40 Position of the non-return valve and pressure sensor in
system with positive inlet pressure
Diaphragm tank
The stop function requires a diaphragm tank of a certain minimum
size. The tank must be installed as close as possible after the
pump and the precharge pressure must be 0.7 x actual setpoint.
Recommended diaphragm tank size:
Rated flow rate of pump
[m³/h]
0-6
7-24
25-40
41-70
71-100
If a diaphragm tank of the above size is installed in the system,
the factory setting of ΔH is the correct setting.
If the tank installed is too small, the pump will start and stop too
often. This can be remedied by increasing ΔH.
Diaphragm tank
Diaphragm tank
Typical diaphragm tank size
[litres]
8
18
50
120
180
10.7.11 Constant level with stop function (3.13)
Settings
The stop function can be set to these values:
• Active
• Not active.
The on/off band can be set to these values:
ΔH is factory-set to 10 % of actual setpoint.
•
ΔH can be set within the range from 5 % to 30 % of actual
•
setpoint.
A built-in low-flow detection function will automatically measure
and store the power consumption at approx. 50 % and 85 % of
the rated speed.
If Active is selected, proceed as follows:
1. Close the isolating valve to create a no-flow condition.
2. Press OK to start the auto-tuning.
Description
The stop function is used for changing between on/off operation
at low flow and continuous operation at high flow.
Start level
ΔH
Stop level
Fig. 41 Constant level with stop function. Difference between
start and stop levels (ΔH)
Low flow can be detected in two different ways:
1. With the built-in low-flow detection function.
2. With a flow switch connected to a digital input.
1. Low-flow detection function
The built-in low-flow detection is based on the measurement of
speed and power.
When low flow is detected, the pump will stop. When the level has
reached the start level, the pump will start again. If there is still no
flow, the pump will reach the stop level and stop. If there is flow,
the pump will continue operating according to the setpoint.
2. Low-flow detection with flow switch
When the digital input is activated because of low flow, the speed
will be increased until the stop level (actual setpoint – 0.5 x ΔH) is
reached, and the pump will stop. When the level has reached the
start level, the pump will start again. If there is still no flow, the
pump will reach the stop level and stop. If there is flow, the pump
will continue operating according to the setpoint.
Operating conditions for the stop function
It is only possible to use the constant level stop function if the
system incorporates a level sensor, and all valves can be closed.
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