In start-stop operation, the pressure varies between the start and
stop pressures. See the figure above.
In User-defined mode (Customised operating mode), ΔH has
been factory-set to 10 % of the actual setpoint. ΔH can be set within
the range from 5 to 30 % of the actual setpoint.
The pump changes to start-stop operation if the flow becomes lower
than the minimum flow rate.
The minimum flow rate is set in percentages of the nominal flow
rate of the pump. See the pump nameplate.
In User-defined mode (Customised operating mode), the
minimum flow rate has been factory-set to 10 % of the nominal flow
rate.
Factory setting
See the section on factory settings.
Low-flow stop function
A low flow rate can be detected in two ways:
1. A built-in low-flow detection function which is active if none of
the digital inputs are set for flow switch.
• Low-flow detection function: The pump checks the flow rate
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 rate. The speed is increased until the stop pressure
(actual setpoint + 0.5 × ΔH) is reached and the pump stops.
When the pressure has fallen to the start pressure (actual
setpoint - 0.5 × ΔH), the pump restarts.
• If the flow rate is higher than the set minimum flow rate, the
pump returns to continuous operation at constant pressure.
• If the flow rate is still lower than the set minimum flow rate
(Q
min
), the pump continues in start-stop operation until the
flow rate is higher than the set minimum flow rate (Q
min
).
When the flow rate is higher than the set minimum flow rate
(Q
min
), the pump returns to continuous operation.
2. A flow switch connected to one of the digital inputs.
• Flow switch: When the digital input is activated for more than
5 seconds because there is a low flow rate, the speed is
increased until the stop pressure (actual setpoint + 0.5 x ΔH)
is reached, and the pump stops. When the pressure has
fallen to start pressure, the pump restarts. If there is still no
flow, the pump quickly reaches the stop pressure and stops.
If there is flow, the pump continues operating according to the
setpoint.
Operating conditions for the low-flow stop function
You can only use the stop function if the system incorporates a
pressure sensor, a non-return valve and a diaphragm tank.
Always install the non-return valve before the pressure
sensor.
See the figures below.
TM038582
Position of the non-return valve and pressure sensor in system
with suction lift operation
Pos. Description
1 Non-return valve
2 Pump
3 Pressure sensor
4 Diaphragm tank
TM038583
Position of the non-return valve and pressure sensor in a system
with a positive inlet pressure
Pos. Description
1 Pump
2 Non-return valve
3 Pressure sensor
4 Diaphragm tank
Set minimum flow
Set the minimum flow rate (Q
min
) in this display. This setting
determines at which flow rate the system is to change from
continuous operation at constant pressure to start-stop operation.
The setting range is 5 to 30 % of the rated flow rate.
Factory setting
See the section on factory settings.
Diaphragm tank volume
The stop function requires a diaphragm tank of a certain minimum
size. Set the size of the installed tank in this display.
To reduce the number of start-stops per hour or to reduce the ΔH,
install a larger tank.
Install the tank immediately after the pump. The precharge pressure
must be 0.7 × actual setpoint.
Recommended diaphragm tank size:
CRE pump
Typical diaphragm tank size
[gal (liters)]
1s, 1, 3, 5 2 (8)
10 4.4 (17)
15, 20 10.3 (39)
32 14 (53)
45 20 (76)
64 34 (129)
95 44 (167)
125 62 (235)
155 81 (307)
Factory setting
See the section on factory settings.
Related information
10.57 Factory settings for Grundfos GO
10.23
Stop at min. speed
This stop function can be utilised in for example constant level
applications where a boost of pressure is not needed. It is a
different type of stop function than low-flow stop but the purpose is
the same. The pump stops if there is no or low consumption.
50
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