Information for installation
Corrosion
33
on the primary side. In order to achieve optimal flow
based on the flow temperature, the use of a two-way
control valve (see graphic above) is recommended.
Additionally, the primary pump should be designed
with differential pressure control. A system separation
module with these specifications is available from ETA.
Fig. 7-9: ETA system separation module
No open expansion tanks
Open expansion tanks improperly allow air into the
system. Existing systems with open expansion tanks
must be redesigned or physically separated from the
boiler.
Pressureless buffer storage may not be attached
directly to the boiler. If it is not possible to replace
this buffer, there must be a physical separation
between the boiler and the pressureless buffer.
Install automatic bleed valves
Automatic bleed valves in the boiler flow, at the highest
point in the distribution network and at the top of the
buffer significantly reduce the danger of rust and also
the frequency of radiator bleeding.
7.5
Corrosion
Initial protection with corrosion inhibitors
These agents line the new and still uncoated internal
surfaces with a protective film. This is only possible in
a new system. If corrosion has already begun, these
agents can no longer be of help. Use corrosion
inhibitors sparingly.
For systems with buffers with a large water volume
relative to the internal surfaces, it is preferable to use
half rather than double the quantity specified by the
manufacturer.
Corrosion protection
To limit corrosion with softened water, the pH value
should be adjusted to between 8 and 9 using suitable
inhibitors (trisodium phosphate).
7.6
Pressure equalisation
An expansion tank or pressure maintaining device
is required
To equalise pressure in the system, a diaphragm
expansion tank with a gross capacity of around 10% of
the system volume is required, or a pressure
maintaining device.
If the pressure difference between cold and warm
heating system (buffer fully loaded if installed) is
greater than 1.0 bar for a single-storey system or 0.5
bar for a three-storey system, then the expansion tank
is too small and absolutely must be replaced with a
larger one. If the installed expansion tank is not large
enough, the system sucks in air when cooling, which is
absorbed by the cold water and transported to the
boiler. At the point of highest temperature, the air
separates from the water again. This usually takes
place in the boiler, and the inevitable result is that the
boiler wall will rust through in these spots.
Adjust expansion tank preset pressure
Most expansion tanks are delivered with primary
pressure of 1,5 bar. Adjust the pressure by releasing
nitrogen so that it is 0.3 bar higher than the static
pressure at the installation location, but make sure the
pressure does not fall below 0.9 bar.
•
Example 1:
height difference between expansion tank and
highest point in the system pst = 11 m = 1.1 bar:
1.1 bar + 0.3 bar = 1.4 bar pressure setting.
•
Example 2:
height difference between expansion tank and
highest point in the system pst = 5 m = 0.5 bar:
0.5 bar + 0.3 bar = 0.8 bar -> 0.9 bar pressure
setting.
Here, the minimum pressure of 0.9 bar must be
selected. The factory setting of 1.0 bar for the cut-
off pressure is compatible with this minimum
pressure setting.
Protect the expansion tank against shut-off
All shut-off valves along the path from the expansion
tank to the boiler and to the buffer storage tank must
be capped valves, or the hand wheels or levers must
be removed from the valves (hang on the valve with a
wire), to ensure that they cannot be closed inadver-
tently.
