Grundfos CUE 150 hp Notice D'installation Et D'entretien page 32

Descriptions
The stop function is used for changing between on/off operation
at low flow and continuous operation at high flow.
On/off operation
Stop pressure
ΔH
Start pressure
Fig. 38 Constant pressure with stop function. Difference
between start and stop pressures (ΔH)
Low flow can be detected in two different ways:
1. A built-in "low-flow detection function" which functions if the
digital input is not set up for flow switch.
2. A flow switch connected to the digital input.
1. Low-flow detection function
The pump will check the flow regularly by reducing the speed for
a short time. If there is no or only a small change in pressure, this
means that 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 after a few
seconds. The pump will restart at the latest when the pressure
has fallen to the start pressure (actual setpoint – 0.5 x ΔH).
If the flow in the off period is higher than the low-flow limit, the
pump will restart before the pressure has fallen to the start
pressure.
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.
The check 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.
32
Continuous operation
Pressure sensor
Pump
Check valve
Fig. 39 Position of the check valve and pressure sensor in
system with suction lift operation
Pressure sensor
Pump Check valve
Fig. 40 Position of the check 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
[gpm]
0-26
27-105
106-176
177-308
309-440
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.
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.
Diaphragm tank
Diaphragm tank
Typical diaphragm tank size
[gallons]
2
4.4
14
34
62