Precharge Pressure Setting; Pressure Relief Valve; Product Introduction; Product Description - Grundfos CU 301 Notice D'installation Et De Fonctionnement

2.4 Precharge pressure setting

The precharge pressure of the diaphragm tank must
be set to 70 % of the pressure setting in order to use
the tank to the limit of its capacity. This is of course
especially important when the tank volume is limited
to 8 litres.
Use the values in the following table:
Setting
[bar]
2
2.5
3
3.5
4
4.5
5
If the precharge pressure is higher than the pressure
setting, the system is not able to control the
pressure.
If the user wants to adjust the pressure without
changing the precharge pressure of the diaphragm
tank, the precharge pressure must be equal to the
lowest pressure setting used. This means that the
control works but that the pressure fluctuations might
increase. In such cases, we recommend that you use
a larger diaphragm tank, for example a tank of
double size.

2.5 Pressure relief valve

In order to provide protection against the possibility
of an overpressurization, a pressure relieve valve
must be installed down stream of the well head. The
setpoint of the pressure relief valve must be at least
30 psi above the pressure setting. See section
5. Setting the product.
If a relief valve is installed, we recommend that its
outlet is plumbed into an appropriate drainage point.
Precharge pressure
[bar]
1.4
1.8
2.1
2.5
2.8
3.2
3.5

3. Product introduction

3.1 Product description

The system maintains a constant pressure within the
maximum pump performance in spite of a varying
water consumption.
Figure 5 shows an example of an installation with
constant-pressure control.
1
4
Fig. 5
Pos. Description
1 CU 301
2 Diaphragm tank
3 Pressure sensor
4 SQE pump
The pressure is registered by means of the pressure
sensor, which transmits a signal to CU 301. CU 301
adjusts the pump performance accordingly by
changing the pump speed.
Mains borne signalling
The communication between CU 301 and the pump
is effected via the power cable.
This communication principle is called mains borne
signalling, or power line communication. Using this
principle means that no additional cables to the
pump are required.
The communication of data is effected by means of a
high-frequency signal transmitted to the power cable
and led into the electronics unit by means of signal
coils incorporated in the motor and CU 301
respectively.
In situations where multiple CU 301 pump power
cables are run parallel in wiring trays or conduit and
less than 25-30 cm apart, the possibility for
undesired communication between units exists.
When this occurs, intermittent or continuous "No
contact" is typically seen. Other unexpected errors
may also be seen.
Figure 6 shows the principle of mains borne
signalling between CU 301 and the pump.
2
3
7