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11.7.10 Constant pressure with stop function (3.14)
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 the actual setpoint.
• ΔH can be set within the range from 5 % to 30 % of the actual
setpoint.
Operating conditions for the stop function
It is only possible to use the stop function if the system
incorporates a pressure sensor, a check valve and a diaphragm
tank.
Description
The stop function is used for changing between on/off operation
at low flow and continuous operation at high flow.
Fig. 49 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.
Fig. 50 Position of the non-return valve and pressure sensor in
system with suction lift operation
Fig. 51 Position of the non-return 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:
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.
TM03 8477 1607
Stop pressure
ΔH
Start pressure
Continuous operation
On/off operation
The check valve must always be installed before
the pressure sensor. See figs 50 and 51.
If a flow switch is used to detect low flow, the
switch must be installed on the system side after
the diaphragm tank.
TM03 8582 1907TM03 8583 1907
Rated flow rate of pump
[gpm (m
3
/h)]
Typical diaphragm tank size
[gallons (liters)]
0-26 (0-6) 2 (8)
27-105 (7-24) 4.4 (18)
106-176 (25-40) 14 (50)
177-308 (41-70) 34 (120)
309-440 (71-100) 62 (180)
Pressure sensor
Diaphragm tank
Non-return
valve
Pump
Diaphragm tank
Pressure sensor
Pump Non-return valve
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