Grundfos CRE Installation And Operating Instructions Manual page 50

Pos. Description
1 Stop pressure
2 Start pressure
In start-stop operation, the pressure varies between the start and
stop pressures. See the figure above.
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 actual setpoint.
The pump changes to start-stop operation if the flow becomes lower
than the minimum flow.
The minimum flow is set in % of the nominal flow of the pump (see
the pump nameplate).
In "User-defined mode" ("Customised operating mode"), the
minimum flow has been factory-set to 10 % of nominal flow.
Factory setting
See the section on factory settings.
"Low-flow detection"
Low flow can be detected in two ways:
1. A built-in low-flow detection function which is active if none of
the digital inputs are set for flow switch.
2. A flow switch connected to one of the digital inputs.
1. Low-flow detection function: The pump checks 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 is increased until the stop pressure (actual setpoint + 0.5
x ΔH) is reached and the pump stops. When the pressure has
fallen to the start pressure (actual setpoint - 0.5 x ΔH), the pump
restarts.
• If the flow is higher than the set minimum flow, the pump
returns to continuous operation at constant pressure.
• If the flow is still lower than the set minimum flow (Q
pump continues in start-stop operation until the flow is higher
than the set minimum flow (Q
than the set minimum flow rate (Q
continuous operation.
2. Flow switch: When the digital input is activated for more than 5
seconds because there is low flow, the speed is increased until
the stop pressure (actual setpoint + 0.5 x ΔH) 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.
Always install the non-return valve before the pressure
Caution
sensor. See the two figures below.
3
4
Position of the non-return valve and pressure sensor in system
with suction lift operation
50
), the
min
). When the flow is higher
min
), the pump returns to
min
1
2
PT
Pos. Description
1 Diaphragm tank
2 Pressure sensor
3 Pump
4 Non-return valve
1 2
Position of the non-return valve and pressure sensor in a system
with a positive inlet pressure
Pos. Description
1 Pump
2 Non-return valve
3 Pressure sensor
4 Diaphragm tank
"Set minimum flow"
Set the minimum flow (Q ) in this display. This setting determines
min
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.
Factory setting
See the section on factory settings.
"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:
Rated flow rate 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)
Factory setting
See the section on factory settings.
Related information
9.2 Factory settings
4
3
PT
Typical diaphragm
tank size
[gal (liters)]
2 (7.6)
4.4 (16.7)
14 (53.0)
34 (128.7)
62 (234.7)
86 (325.5)