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• The connection for the expansion vessel must be on the
RETURN line, stepped off the pump station.
• The expansion vessel must always be placed 500mm
or more BELOW the pump station.
• If it is not possible to position the expansion vessel below the
level of the pump station, an intermediary vessel should be
installed between the pressure vessel and pump station. This
is also referred to as a cooling vessel.
• Use a 3/4” / 22mm copper or stainless steel pipe spur line.
This should
NOT
be insulated.
NOTE:
Before filling the system, the gas side (air or nitrogen) of the expansion vessel must be charged at
approximately 0.2 bar lower than the intended cold fill pressure (normally 2 bar) of the solar system. As the
initial cold filling pressure is set slightly higher than the vessel gas pressure, some fluid is pushed into the
vessel. This provides an allowance for fluid losses between maintenance cycles and protects the expansion
vessel membrane from potential jets of steam during the operational phases.
9.9.2 Intermediate expansion vessel
High temperature fluid in the expansion vessel for long periods of time
has the effect of shortening its useful life - ultimately causing
premature failure of the diaphragm.
To avoid this situation, an additional “flow-through” expansion vessel
is recommended when the fluid volume between the collector and the
expansion vessel is approx. 50% or less than the “wet” side volume
(between the expanded diaphragm and the vessel inlet). This approach
is covered by European directive VDI 6002.
The intermediate vessel should be installed without insulation. As
well as dissipating heat before it reaches the diaphragm in the main
expansion vessel, the heat is also diluted into the cooler volume of
the vessel, while expansion continues to occur in the main vessel,
but at a lower temperature than might otherwise occur.
The following table highlights recommended intermediate
vessel sizes with respect to main expansion vessel size.
Solar expansion vessel
Intermediate vessel size
18 litre
5 litre
24 litre
8 litre
35 litre
12 litre
50 litre
18 litre
Intermediate
vessel
Auto shut-off
valve
Solar expansion
vessel
Connection to system
INSTALLATION
