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Expansion tank
The expansion tank evens out the effects of the changes in water volume. It ensures that there is a sufficient
amount of water also in the topmost circuits of the heating circuit.
The expansion tank is divided into a water space and gas space by a rubber diaphragm. The gas space is
filled with nitrogen gas. When an expansion tank comes from the factory, its pre-charge pressure can be
anywhere from 0.5 to 2.5 bar. The pre-charge pressure of each expansion tank must be checked and set
according to the characteristics of the building's heating system.
Use the table on the next page to check the correct expansion tank pre-charge pressure for the building in
question, based on the number of storeys. Set the pre-charge pressure according to the table before
pressurising the heating system.
When measuring the pre-charge pressure, the water side of the expansion tank must be free of pressure. If
you check the pre-charge pressure before connecting the expansion tank to the heating circuit, or if the
expansion tank is disconnected from the heating circuit for the duration of the check, use the "pre-charge
pressure without static pressure" value in the table.
The pre-charge pressure can be checked when the expansion tank is connected to a filled heating system. In
such a case, free expansion in the heating system must be ensured when checking the pre-charge pressure.
Open a valve at the highest point of the heating system for the duration of the check. Use the "pre-charge
pressure, with static pressure taken into account" value in the table for setting the expansion tank pre-
charge pressure.
The table below shows the expansion tank pre-charge pressure, cold water filling pressure and heating
system minimum operating pressure by the number of storeys of the building:
Number of storeys
Static head of the building, H
Heating system static pressure, P
Expansion tank pre-charge pressure without static
pressure (bar)
Expansion tank pre-charge pressure, with static pressure
considered, P
Cold water filling pressure (bar)
Heating system minimum operating pressure, P
Heating system maximum operating pressure, P
Safety valve opening pressure, P
Heating system pressure
Set the pressure in the water side of the heating system after setting the expansion tank pressure.
If the heating system is filled for the first time, use the "cold water filling pressure (bar)" value in the table.
The heating system pressure increases as the temperature of the heating circuit increases. Check the final
pressure when the heating system reaches its normal operating temperature.
The heating system pressure varies between summer and winter as the temperature of the heating circuit
varies. In the summer, when the operating temperature of the heating system is at its lowest, the pressure
must be at least the "heating system minimum operating pressure" value specified in the table. In the
winter, when the operating temperature of the heating system is at is highest, the pressure must not exceed
the "heating system maximum operating pressure" value specified in the table.
Gebwell G-Power® substation installation manual
(m)
st
(bar)
st
(bar)
e
(bar)
sv
1
0
0
0.5
0.5
0.8
(bar)
1.0
min
(bar)
2.0
max
2.5
2
3
3
6
0.3
0.6
0.3
0.3
0.6
0.9
0.9
1.2
1.1
1.4
2.0
2.0
2.5
2.5
6
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