7
NOTE: If the pressure gauge indicates 2.65 bar or greater
when the appliance is at maximum temperature with all
radiators in circulation an extra expansion vessel is
required.
2.7.3 Pressure gauge
A pressure gauge is mounted on the appliance facia panel.
2.7.4 Safety valve
A safety valve set at 3 bar (43.5 psi) is fitted to the appliance
and a discharge pipe is routed to outside of the appliance.
This discharge pipe should be extended to terminate safely
away from the appliance and where a discharge would not
cause damage to persons or property but would be detected.
The pipe should be able to withstand boiling water, be a mini-
mum of 15 mm in diameter, and installed with a continuous fall.
2.8 D.H.W. SYSTEMS
– Check that the mains supply pressure is within the pre-
scribed limits (
Table 4
).
If necessary, a pressure reducing valve should be fitted to
the mains supply before the D.H.W. inlet connection.
– A maximum D.H.W. flow rate of: 14 l/m (3.1 gpm) is rec-
ommended. Higher flow rates will not damage the appli-
ance but may lower the water temperature below an
acceptable level.
– If the appliance is installed in an area where the tempo-
rary hardness of the water supply is high, say over 150
ppm, the fitting of an in line scale inhibitor may be an
advantage. Consult the Local Water Undertaking if in
doubt.
– Devices capable of preventing the flow of expansion water:
e.g. non return valves and/or loose-jumpered stop cocks
should not be fitted unless separate arrangements are
made for expansion water.
– For specific information relating to fittings (eg. Showers,
washing machines etc.) suitable for connection in the
D.H.W. circuit, consult the Local Water Undertaking, how-
ever the following information is given for guidance.
2.8.1 Domestic hot/cold water supply
taps and mixing taps
All equipment designed for use at mains water pressure is
suitable.
2.8.2 Showers
If a shower control is supplied from the appliance it should be
of the thermostatic or pressure balanced type.
Thermostatic type shower valves provide the best comfort
and guard against water at too high temperature.
Existing controls may not be suitable, refer to the shower
valve manufacturer.
Vessel charge and initial system
pressure
Total water content of system
using 8 l (1.76 gal) capacity expan-
sion vessel supplied with appliance
For systems having a larger capaci-
ty multiply the total system capacity
in litres (gal) by the factor to obtain
the total minimum expansion vessel
capacity required litres (gal)
bar
psi
l
gal
0.5
7. 3
96
21.1
.0833
1.5
21.8
51
11. 2
.15 6
1.0
14.5
74
16.2
.1 0 9
TABLE 6
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