Grundfos CRE Series Installation And Operating Instructions Manual page 21

Three-phase pumps
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 still 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. 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 H) 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. 30 and
fig. 31.
Pressure sensor
Pump
Non-return
valve
Fig. 30 Position of the non-return valve and pressure sensor in
system with suction lift operation
Pressure sensor
Pump Non-return valve
Fig. 31 Position of the non-return valve and pressure sensor in
system with positive inlet pressure
Diaphragm tank
Diaphragm tank
DBP-1 - GRUNDFOS PUMP CRE - 99392005
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
1s, 1, 3
(0 - 5.9)
27 - 105
5, 10, 15
(6.1 - 23.8)
106 - 176
20, 32
(24.2 - 40)
177 - 308
45
(40.2 - 70.0)
309 - 440
64, 90
(70.2 - 99.9)
441 - 750
120, 150
(100 - 170)
If a diaphragm tank of the above size is installed in the system,
the factory setting of H 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 H.
10.3.9 Flow limit for the stop function
(only three-phase pumps)
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 customised set-
up and optimizing to the process.
Typical diaphragm
tank size [gal (liter)]
2 (7.6)
4.4 (16.7)
14 (53.0)
34 (128.7)
62 (234.7)
86 (325.5)
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