Stop Function (4.3 - Grundfos CONTROL MPC Installation And Operating Instructions Manual

11.7.22 Secondary functions (4.3)
Fig. 58 Secondary functions
Description
Functions that are secondary in relation to the normal operation
of the system can be set in this display. Secondary functions are
functions that offer additional functionality.
The display makes it possible to open these specific displays:
•

Stop function (4.3.1)

•
Soft pressure build-up (4.3.3)
•
Digital inputs (4.3.7)
•
Analog inputs (4.3.8)
•
Digital outputs (4.3.9)
•
Emergency run (4.3.5)
•
Min., max. and user-defined duty (4.3.14)
•
Pump curve data (4.3.19)
•
Flow estimation (4.3.23)
•
Control source (4.3.20)
•
Fixed inlet pressure (4.3.22).
11.7.23 Stop function (4.3.1)
Fig. 59 Stop function
Description
This function is typically used in constant pressure applications
and makes it possible to stop the last pump if there is no or a very
small consumption. The purpose is to
• save energy
• prevent heating of shaft seal faces due to increased
mechanical friction as a result of reduced cooling by the
pumped liquid
• prevent heating of the pumped liquid.
The description of the stop function applies to all booster systems
with variable-speed pumps. Control MPC-S will have on/off
control of all pumps as described in section 8. Overview of control
variants.
H
On/off band
H
set
Q
min
On/off
Normal operation
control
Fig. 60 On/off band
When the stop function is activated, the operation is continuously
monitored to detect a low flow rate. When the CU 351 detects no
or a low flow rate (Q < Q ), it changes from constant-pressure
min
operation to on/off control of the last pump in operation.
Before stopping, the pump increases the pressure to a value
corresponding to H + 0.5 x on/off band. The pump is restarted
set
when the pressure is H – 0.5 x on/off band. See fig. 61.
set
H [m]
A B
Stop
Start
Stop = H + 0.5 x on/off band
set
Start = H – 0.5 x on/off band
set
Fig. 61 On/off operation
The flow rate is estimated by the CU 351 when the pump is in the
stop period. As long as the flow rate is lower than Q
will run on/off. If the flow rate is increased to above Q
pump returns to normal operation, H
current setpoint. See section 11.4.4 Setpoint (1.2.2).
Detection of low flow rate
Low flow rate can be detected by means of
• direct flow measurement with a flowmeter or flow switch
• estimation of flow rate by measurement of pressure and
speed.
If the booster system is not connected to a flowmeter or flow
switch, the stop function will use the estimating function.
If the detection of low flow rate is based on flow estimation, a
diaphragm tank of a certain size and with a certain precharge
pressure is required.
Q
A: Normal operation
B: Pressure boosting
C: Stop
C B C
Time [sec]
, the pump
min
, the
min
. H is equal to the
set set
37