Grundfos CU 301 - Positioning the Pressure Sensor; Precharge Pressure Setting; Pressure Relief Valve

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1.4 Positioning the pressure sensor
Pressure losses often cause inconvenience to the
user. The CU 301 keeps the pressure constant in the
place where the pressure sensor is positioned, see
fig. 7.
Fig. 7
In fig. 7, tap 1 is placed close to the pressure sensor.
Therefore, the pressure will be kept nearly constant
at tap 1, as the friction loss is small. At the shower
and tap 2, the friction loss is bigger. This, of course,
depends on the piping. However, old and furred-up
piping may cause inconvenience due to friction loss.
Example: A person is in the shower. Tap 2 is
opened. The increased flow will cause pressure loss
in the pipe, and even though the CU 301 is keeping
the pressure constant at the pressure sensor, the
person in the shower will feel the pressure loss.
If the pressure sensor is placed closer to the shower
tap, the CU 301 will increase the pressure when the
flow is increased. Then the pressure at the shower
and tap 2 will be kept constant, but the pressure at
tap 1 will be increased.
Therefore, it is recommended that the pressure sen-
sor be positioned as close to the places of consump-
tion as possible.
1.5 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:
Note: If the precharge pressure is higher than the
pressure setting, the system will not be able to con-
trol 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 will work but that the pressure fluctuations
might increase. In such cases, it is recommended to
use a larger diaphragm tank, e.g. a tank of double
size.
1.6 Pressure relief valve
In order to provide protection against the possibility
of an overpressurization, a pressure relieve valve
should be installed down stream of the well head.
The setpoint of the pressure relief valve should be at
least 30 psi above the pressure setting, see section
2.3.
If a relief valve is installed, it is recommended that its
discharge be plumbed into an appropriate drainage
point.
TM01 7862 4999
Setting [bar] Precharge pressure [bar]
21.4
2.5 1.8
32.1
3.5 2.5
42.8
4.5 3.2
53.5
Tap 1 Tap 2