5.4.8 Stop function
The stop function can be set to these values:
• Active
• Not active.
When the stop function is active, the pump will be stopped at very
low flows. The controller will stop the pump to protect the pump as
follows:
• avoid unnecessary heating of the pumped liquid
• reduce wear of the shaft seals
• reduce noise from operation.
TM007744
Difference between start and stop pressures (ΔH)
Pos. Description
1 Stop pressure
2 Start pressure
ΔH is factory-set to 10 % of actual setpoint.
ΔH can be set within the range from 5 % to 30 % of actual setpoint.
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. When the pressure has fallen to the start pressure (actual
setpoint - 0.5 x ΔH), the pump will restart.
When restarting, the pumps will react differently according to pump
type:
Three-phase pumps
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 still 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. Flow switch
When the digital input is activated for more than 5 seconds 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 quickly reach 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 the figures below.
TM081973
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 system
with positive inlet pressure
Pos. Description
1 Pump
2 Non-return valve
3 Pressure sensor
4 Diaphragm tank
Diaphragm tank
The stop function requires a diaphragm tank of a certain minimum
size. The tank must be installed immediately after the pump and the
precharge pressure must be 0.7 x actual setpoint.
Recommended diaphragm tank size:
18
English (US)
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