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9. Functions
The booster systems include application-optimized software.
9.1 General functions
9.1.1 Dry-running protection (optional)
When a pump is running in manual mode, it is not
protected against dry running.
To protect the pumps against damage from dry running, the
booster system incorporates a water shortage function. This
function is based on the monitoring of the inlet pressure or the
level in a possible tank on the inlet side.
The pressure or level can be monitored by one of the following
devices:
•
pressure switch
•
float switch
•
level switch
•
external electrode relay
•
analog sensor.
Dry-running protection with pressure switch, float switch,
level switch or external electrode relay
Set the monitoring device to the desired limit.
If a water shortage is detected for more than 5 seconds, the
system will stop, and the "WS" water shortage indicator light is
on.
When the water supply has been reestablished, the dry-running
fault is automatically reset.
Dry-running protection with analog sensor
The limit for the minimum inlet pressure in the inlet manifold is a
factory-set value which can only be changed by a Grundfos
service engineer.
If the sensor output is below the limit for minimum inlet pressure
for more than 5 seconds, the system will stop, and the "WS"
water shortage indicator light is on.
When the water supply has been reestablished, the dry-running
fault is automatically reset.
9.1.2 Automatic pump changeover
The automatic pump changeover function ensures an equal
number of operating hours of the pumps, but it also ensures that,
in case of an alarm on one pump, another pump is automatically
started.
There are three types of automatic pump changeover:
•
operation-dependent pump changeover
•
alarm-dependent pump changeover
•
time-dependent pump changeover.
Alarm-dependent pump changeover
If a pump stops due to an alarm, CU 323 will send a stop
command to the pump to prevent auto-restarting and start
another pump which is ready to start and which has the lowest
number of operating hours.
If the speed-controlled pump in an ES system is
stopped due to an alarm, the system will function as
an S-system.
See section
9.2.5 S-system mode (start/stop
Time-dependent pump changeover
In certain applications, the demand remains constant for long
periods and does not require all pumps to run. In such situations,
pump changeover does not take place naturally, and forced pump
changeover may thus be required.
Once every 24 hours, CU 323 checks if any of the running pumps
has a higher number of operating hours than the pumps that are
stopped. If this is the case, the pump will be stopped, and a pump
with a lower number of operating hours will start.
9.1.3 Minimum time between start and stop
This function ensures a delay between the start/stop of one pump
and the start/stop of another pump. The purpose is to prevent
hunting when pumps start and stop continuously.
If the system is stopped due to an alarm, the
minimum time between start and stop will be ignored,
and the pumps will be stopped immediately.
9.2 Functions for constant-pressure systems
9.2.1 Pump cascade control
The cascade function ensures that only the required number of
pumps is running. This means that the number of running pumps
always corresponds to the required flow at the entered setpoint.
The first pump is started if the pressure at the outlet manifold is
below the setpoint.
If the first pump is not able to keep the outlet pressure at the
setpoint, and the minimum time between start/stop has passed,
another pump is started.
During the start and stop of a pump, the speed of the
speed-controlled pump is controlled in such a way that the
pressure disturbance is kept as low as possible.
At decreasing demand, pumps will be stopped if the pressure
rises above the setpoint. Pumps will not be stopped until the
minimum time between start/stop has passed.
The last pump in operation
If only one pump is operating, this pump can be operated in
energy-saving on/off mode. See section
operation.
The number of possible starts/stops per hour for all pumps is
limited by the maximum number of starts per hour.
band).
9.2.4 Low-flow
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