Stop Functions - Grundfos CUE Series Product Manual

Functions

Stop functions

Constant pressure with stop function
The purpose of the stop function is to stop the pump
when low or no flow is detected.
When low flow is detected, the pump is in on/off opera-
tion. If there is flow, the pump will continue operating
according to the setpoint. See fig. 22.
Stop pressure
ΔH
Start pressure
Fig. 22 Constant pressure with stop function. Difference
between start and stop pressures (ΔH)
Low flow can be detected in two different ways:
• a built-in low-flow detection function
• a flow switch connected to a digital input.
Low-flow detection function
The low-flow detection function will check the flow reg-
ularly by reducing the speed for a short time. No or only
a small change in pressure means that there is low flow.
Low-flow detection with flow switch
When a flow switch detects low flow, the digital input
will be activated.
Operating conditions for the stop function
It is only possible to use the stop function if the system
incorporates these components:
• a pressure sensor
• a non-return valve
• a diaphragm tank.
22
On/off operation
Continuous operation
Note: The non-return valve must always be installed
before the pressure sensor. See figs 23 and 24.
Pressure sensor
Pump
Non-return valve
Fig. 23 Position of the non-return valve and pressure sen-
sor in a system with suction lift operation
Pressure sensor
Pump
Non-return valve
Fig. 24 Position of the non-return valve and pressure sen-
sor in a system with positive inlet pressure
Diaphragm tank
The stop function requires a diaphragm tank of a cer-
tain 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:
Rated flow rate of pump
gpm (m³/h)
0-25 (0-6)
25-100 (7-24)
100-175 (25-40)
175-300 (41-70)
300-450 (71-100)
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.
Grundfos CUE
Diaphragm tank
Diaphragm tank
Typical diaphragm tank size
gal (litres)
2 (8)
4 (18)
14 (50)
32 (120)
44 (180)