Remember that air charge pressure must be equal in
both vessels (attached to the same system). In the above
example this is 1 bar. air charge pressure is the air
pressure in the expansion vessel before the system is filled.
It is measured with a tyre gauge attached to a Schrader
valve on the vessel.
N.B. The second red zone is between 2.5 and 4 bar
pressure. When the heating system is up to
full working temperature, if the pointer on the
pressure gauge should enter this red zone showing
a final system design pressure of more than 2.5 bar,
it is likely that:
(a)
total system water content is greater than that
calculated and if an additional expansion vessel
has been fitted, it should be replaced with a
larger unit
or if only an integral boiler expansion vessel
is used, then an additional expansion vessel is
required.
(b) Static head may be higher than calculated. In
this case it is necessary to re-measure the static
head and revise expansion vessel air charge
pressure.
(c) expansion vessel size is incorrect or the air
charge pressure is incorrect.
refer to Bs 7074
Part 1 and Bs 5449 for further information.
4
4.2 systeM BoIler - Installer guIdelInes
The nearest available stock size for the additional vessel
required at 1 bar initial system pressure (taken from table),
is 5 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. the warranty is void
if the boiler is installed in a system with insufficient
expansion.
NB. ensure that all expansion vessels in the same system are
set at eQUaL air charge pressures.
systeM FIllIng, testIng and Make-uP
Introduction
Mains cold water is supplied through the boiler drain/fill
valve.
Heating Circuit
This is the heating system including the boiler which is filled
from the mains supply via a flex filling loop to a pressure
determined from the system static head, expansion vessel
size and system water volume. This flexible filling loop
should be disconnected when boiler and system are filled
and checked.
note: there shall be no direct connection to the
mains, even with the use of a non-return
valve without the permission of local water
authority.
*
It is recommended that an inhibitor be added at
the time of final fill to protect the System from
corrosion. ensure that this is carried out in accord-
ance with inhibitor manufacturers instructions.
Installer should ensure that inhibitor used is suit-
able and that it will have no adverse effect on
expansion Vessels diaphragms or any other part
or component of the system.
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, BS 7074-1: 1989, BS eN 12828: 2012 + a1: 2014 aND aNY
OTHeR ReLeVaNT STaNDaRDS & RegULaTIONS.
* * When calculating the size of any additional expansion
vessel, remember to deduct the boiler expansion vessel volume
of 12 litres from the calculated total system vessel volume
required, as given in the above table.
eXaMPle: using above table
If total water content of system is
- 150 litres
and initial system pressure required is
- 1.0 bar
then vessel volume required is
- 16.3 litres
[from above table]
the vessel supplied with boiler is
- 12.0 litres
therefore an additional vessel of
- 4.3 litres
is required
(minimum)
(For this system of 150 litres - total water volume)
15
