6.0
SYSTEM DETAILS
12
Publication No. 5106451
6.7
Sealed Systems
(Fig. 11)
1.
SAFETY VALVE
- A safety valve complying with
the requirements of BS 6750 Part 1 must be fitted
close to the boiler on the flow pipe by means of a
horizontal or vertically upward connection with no
intervening valve or restrictions and should be
positioned to facilitate testing. The valve should be
pre-set and non-adjustable to operate at a pressure
of 3 bar (45 Ibf/in
2
). It must be arranged to discharge
any water or steam through a pipe to a safe outlet
position.
2.
PRESSURE GAUGE
- A pressure gauge of
minimum range 0-4 bar (0-60 Ibf/in
2
) with a fill
pressure indicator must be fitted to the system,
preferably at the same point as the expansion vessel
in an easily visible position.
3.
EXPANSION VESSEL
- An expansion vessel
complying with the requirements of BS 4814 must be
fitted to the system by means of a connection close
to the inlet side of the circulating pump in accordance
with the manufacturers instructions, the connecting
pipe being unrestricted and not less than 15mm (
1
/
2
in) nominal size. The volume of the vessel should be
suitable for the system water content and the
nitrogen or air charge pressure should not be less
than the system static head (See Table. 1).
Further details of sealed system design can be
obtained from BS 5449 and the British Gas
publication entitled 'Specifications for Domestic Wet
Central Heating Systems'.
4.
FILLING POINT
- A filling point connection on the
central heating return pipework must be provided to
facilitate initial filling and pressurising and also any
subsequent water loss replacement / refilling.
The sealed primary circuits may be filled or
replenished by means of a temporary connection
between the primary circuit and a supply pipe
provided a ‘Listed’ double check valve or some other
no less effective backflow prevention device is
permanently connected at the inlet to the circuit and
the temporary connection is removed after use.
The filling method adopted must be in accordance
with all relevant water supply regulations and use
approved equipment.
Your attention is drawn to, for GB: Guidance G24.2
and recommendation R24.2 of the Water Regulations
Guide. for IE: the current edition of I.S. 813
“Domestic Gas Installations”.
5.
MAKE UP SYSTEM
- A method of replacing water
lost from the system should be provided either by
means of a make up vessel of not more than 3 litres
(5 pints) capacity, mounted above the highest point of
the system, or by re-pressurisation of the system.
6.
VENTING
- A method of venting the system during
filling and commissioning must be provided by fitting
automatic air vents or by venting manually.
7.
HOT WATER STORAGE
- The hot water storage
vessel must be of the indirect coil type. All
components used in the system must be suitable for
operation at 110°C (230°F) and at the pressure
allowed by the safety valve.
Initial System
Pressure (Bar)
Vessel Charge
Pressure (Bar)
Multiply Total
Water Content Of
System By (Litres)
0.067
0.112
0.207
0.441
0.087
0.152
0.330
0.125
0.265
0.5
1.0
1.5
2.0
1.0
1.5
2.0
1.5
2.0
0.5
1.0
1.5
Example :-
Then :-
System Volume = 75 litres
Vessel Charge Pressure = 1.0 bar
Initial System Pressure = 1.5 bar
75 x 0.152 = 11.4 litres
Expansion Vessel Volume
Method of determining minimum
value of expansion vessel volume for
sealed systems using Baxi Boilers
NOTE
Where a vessel of the calculated size is not obtainable
then the next available larger size should be used.
Safety
Valve
Pressure
Gauge
Pump
Filling
Point
Air
Vent
3 Litre
Top Up Bottle
(if required)
Radiator
Circuit
Expansion
Vessel
System Drains
at Low Point
Max Boiler Flow
Temp = 82° C
Boiler
Fig. 11
Table. 1
Stop
Valve
Double
Check
Valve
DHW
Mains
Inlet
CH
Return
Temporary
Hose
Stop
Valve
Fig. 11a
