DOMESTIC HEATING AND HOT WATER
EXPANSION VESSEL AND SYSTEM REQUIREMENTS
Safety Valve Setting 3 bar
Initial System Pressure 0.5 bar 1.0 bar 1.5 bar
Total Water Content of System TOTAL VESSEL VOLUME **
Litres Litres Litres Litres
25 2.1 2.7 3.9
50 4.2 5.4 7.8
75 6.3 8.2 11.7
100 8.3 10.9 15.6
125 10.4 13.6 19.5
150 12.5 ->[16.3]<- 23.4
175 14.7 19.1 27.2
200 16.7 21.8 31.2
225 18.7 24.5 35.1
250 20.8 27.2 39.0
FOR FURTHER INFORMATION CONSULT APPROPRIATE TRAINING MANUALS
AND BS 7074 PART 1, BS 5449, ETC
* * When calculating size of any additional expansion vessel required, remember to deduct
the boiler expansion vessel volume of 10 litres from the calculated
total system vessel volume required, as given in above table.
EXAMPLE: using above table
If ............................Total water content of system - 150 litres
And ....................Initial system pressure required is - 1.0 bar
Then ..................Vessel volume required [from above table] - 16.3 litres
But ......................Vessel supplied with boiler - 10.0 litres
Therefore ....Additional vessel required - 6.3 litres (minimum)
(For this system of 150 litres - total water volume)
..Nearest available stock size for additional vessel required, at 1 bar initial system pressure
(taken from above table) is 8 Litres.
It is emphasised that the installer should be fully acquainted with sealed system installation and
operation, calculation of total system water volume, determining of initial system pressure
required and calculation of any additional expansion vessel volume required.
NB .. Ensue that all expansion vessels in the same system are set at EQUAL air charge pressures.
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