Flow Limit For The Stop Function - Grundfos CRE Instrucciones De Instalación Y Funcionamiento

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 fig.
Pressure sensor
Pump
Non-return
valve
Fig. 16 Position of the non-return valve and pressure sensor in
system with suction lift operation
Pressure sensor
Pump Non-return valve
Fig. 17 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 immediately after the pump and
the precharge pressure must be 0.7 x actual setpoint.
Recommended diaphragm tank size:
Rated flow of pump
CRE pump
3
[gpm (m h)]
0-26 (0 - 5.9) 1s, 1, 3
27-105 (6.1 - 23.8) 5, 10, 15
106-176 (24.2 - 40) 20, 32
177-308 (40.2 - 70.0)
309-440 (70.2 - 99.9) 64, 90
441-750 (100-170) 120, 150
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.
18
16 and 17.
Diaphragm tank
Diaphragm tank
Typical diaphragm
tank size
[gal (liter)]
2 (7.6)
4.4 (16.7)
14 (53.0)
45 34 (128.7)
62 (234.7)
86 (325.5)

4.4.9 Flow limit for the stop function

– Flow limit for the stop function only works if the
system is not set up for flow switch.
In order to set at which flow rate the system is to go from
continuous operation at constant pressure to start/stop operation,
select among these four values of which three are preconfigured
flow limits:
• Low
• Normal
• High
• Custom.
The default setting of the pump is Normal, representing approx.
10 % of the rated flow rate of the pump.
If a lower flow limit than normal is desired or the tank size is
smaller than recommended, select Low.
If a higher flow than normal is wanted or a large tank is used, set
the limit to High.
The value Custom can be seen in R100 but it can only be set by
means of the PC Tool E-products. Custom is for customized set-
up and optimizing to the process.
ΔH
Low
Normal
Fig. 18 Three preconfigured flow limits, Low, Normal and High
High