En
gl
is
h (
G
B)
22
In start-stop operation, the pressure varies between
the start and stop pressures. See fig.
.
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
flowrate becomes lower than the minimum flow rate.
The minimum flow rate is set in percentage 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.
"Low-flow detection"
Low flow rate can be detected in two ways:
1. A built-in low-flow detection function which is
active if the digital input is set for flow switch.
2. A flow switch connected to the digital input.
1. 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 a low flow rate. The speed is
increased until the stop pressure (actual setpoint
+ 0.5 x
Δ
H) is reached and the pump stops.
When the pressure has fallen to the start
pressure (actual setpoint - 0.5 x
Δ
H), 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. 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
se 0.5 x
Δ
H) 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.
Fig. 27
Position of the non-return valve and
pressure sensor in system with suction
lift operation
Fig. 28
Position of the non-return valve and
pressure sensor in a system with a
positive inlet pressure
"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 rated flow rate.
"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.
In order 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 x actual setpoint.
Recommended diaphragm tank size:
Always install the non-return valve before
the pressure sensor. See figs
.
TM
03
85
8
2
19
07
TM
03
85
8
3
19
07
Rated flow rate of
pump
[m
3
/h]
Typical diaphragm tank
size
[litres]
0-6
8
7-24
18
25-40
50
Pressure sensor
Diaphragm tank
Non-return
valve
Pump
Diaphragm tank
Pressure sensor
Pump Non-return valve
