13
INSTALLATION
Expansion Vessel Capacity
Note the internal 5 litre expansion vessel might not accommodate the entire system volume.
A second diaphragm type expansion vessel, conforming to the current issue of BS4814 might be required. The
expansion vessel must be connected to the systems at a point close to the inlet side of the circulating pump.
The expansion vessel volume depends on the total water system volume and the initial system design
pressure. For any system an accurate calculation of vessel size is given in the current issue of BS5449 and
BS7074 Part 1.
The water content of the boiler is given in the technical specification. Note a higher initial design pressure
requires a larger volume expansion vessel.
The charge pressure must not be less than the static head of the system, which is the highest point of the
system above the expansion vessel.
NOTE: Failure to ensure the correct vessel size could result in premature failure of the expansion vessel
which in turn may adversely affect other components in the system i.e. circulating pump and diverter valve.
Capacity of Expansion Vessel
Where design information is not complete the following chart can be used for selecting the size of the
vessel, it should be noted that the size given in the table take account of fault conditions.
Safety valve setting (bar gauge)
3 Bar
Vessel charge and initial system pressure (bar
gauge)
0.5
1.0
1.5
Total water content of system (litre)
Vessel volume (litre)
25
2.3
3.3
5.9
50
4.7
6.7
11.8
75
7.0
10.0
17.7
100
9.4
13.4
23.7
125
11.7
16.7
29.6
150
14.1
20.1
35.5
175
16.4
23.4
41.4
200
18.8
26.8
47.4
System Temperature
The normal running temperature of the heating system is 75°C, if a fault was to occur then the safety device
would allow the system temperature to rise to 100°C. It is recommended that this figure be used in the
calculations of vessel size.
Pressure Gauge
A 0 to 4 bar pressure gauge is fitted within the unit.
Drain Tapping
A drain tapping is provided on the boiler. An additional tapping must be provided at the lowest point of the
system, which will allow the entire system to be drained.
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