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The expansion vessel protects the solar system during pressure changes and temperature
fluctuations. For example, in very hot conditions when energy is not being drawn off, the system may
overheat causing the glycol to expand.
Technical information (Standard 18L Vessel):
Maximum pressure: 10 bar
Working pressure: 3.0 - 4.0 bar (20
o
C)
Gas pressure: 2.5 bar
Maximum working temperature: 130
o
C
Membrane: Nytril (butyl) rubber
Resistance: 40% glycol
Sizing
It is of critical importance to have the correct size of expansion vessel in your solar system. The
volume of the expansion vessel is determined by the number of RM Solar solar panels connected
within the one solar heating system. Approximately for one collector 6 litres of expansion vessel
volume is required. When fitting a system larger than 3 panels RM Solar should be consulted on
expansion vessel sizing.
Location
The pressure vessel should be located in a position where it can be easily accessed. It should be
fitted with isolating valve for ease of replacement. The isolating valve should not be accessible
without a tool so that an unqualified person cannot shut it off. The expansion vessel should be fitted
on the return run of the system.
Where the expansion vessel is sited at the same level as the panels or above, a thermal loop should
be present.
Maintenance
Once an expansion vessel is pressurised correctly it will require yearly maintenance and a visual
inspection by a qualified person. Monthly checking of the pressure gauge on a double pump station
is also very important, as well as pressure testing the expansion vessel at each maintenance
inspection. A pressure drop might indicate:
• A leak on the pipes connections or
• A leak on the panels connections or
• A faulty expansion vessel or loss of pressure in the expansion vessel
In the case of any unexpected changes, the customer must contact the installer immediately and the
installer should inform the customer of this when explaining the system.
Important
When installing your expansion vessel ensure that you have not mixed the expansion vessel with
another one from somewhere else. The solar expansion vessel has been carefully designed to work
with glycol without corrosion. The solar expansion vessel should be clearly marked as being a solar
expansion vessel.
Section 5 - Expansion V
essel
Expansion Vessel
