EXPANSION VESSEL
3.17
A diaphragm type expansion vessel, conforming to the current issue of
BS4814 (see also BS7074 Part 1 and 2) must be connected at a point
close to the inlet side of the circulating pump, see the diagrammatic
layout, figure 7 unless laid down differently by the manufacturer.
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.
Example:
For an initial design pressure of 0.7 bar, the minimum total
vessel volume required is 0.063 x Total System Volume.
7
SEALED WATER SYSTEM
Expansion Vessel Requirements
Vessel charge and initial
system pressure
Total water content for
system using 8L (1.54 gal)
capacity expansion vessel
supplied with appliance
For systems having a
larger capacity, multiply
the total system capacity in
litres (gallons) by these
factors to obtain the total
minimum expansion vessel
capacity required in litres.
bar
0.5
0.75
1.0
1.5
L
96
84
73
50
0.0833 0.093
0.109
0.156
The charge pressure must not be less than the static head of the system,
that is, the height of the highest point of the system above the expansion
vessel.
The water content of the boiler is given in 2.3 General Specifications.
PRESSURE GAUGE
3.18
A pressure gauge with a set pointer and covering at least 0 to 4 bar (0 to
60 lb/in) shall be fitted permanently to the system in a position where it
can be seen when filling the system.
WATER MAKEUP
3.19
Provision should be made for replacing water loss from the system
using a make up bottle mounted in a position higher than the top point
of the system, connected through a non-return valve to the return side
of either the heating circuit or the hot water cylinder.
Alternatively, provision for make up can be made using a filling loop.
FILLING A SEALED WATER SYSTEM
3.20
Provision for filling the system at low level must be made, see figure 8.
There must be no permanent connection to the mains water supply, even
through a non-return valve.
CONTROLS.
As a minimum it is recommended that a room thermostat
be installed to control the appliance. Thermostatic radiator valves may
be fitted to the system, however they must not be fitted in the room
where the room thermostat is fitted. There must be at least one radiator
installed with lock shield valves that should not be closed. Further
guidance can be obtained from the Domestic Heating and Hot Water
Guide to the building regulations.
Note:
A higher initial design pressure requires a larger volume
expansion vessel.
ROOM THERMOSTAT
TANK
THERMOSTAT
HOT
WATER
CYLINDER
RETURN
FLOW
DRAIN
COCK
CH/DHW
SWITCHED LIVE
CH/DHW
2 CHANNEL
PROGRAMMER
APPLIANCE
EXPANSION
VESSEL
TERMINAL
BLOCK
SAFETY
VALVE
LOCKABLE
BALANCING
VALVE “A”
PUMP
PRESSURE
GAUGE
3-WAY
VALVE
FILL POINT
NON-RETURN
VALVE
SYSTEM
BYPASS
MOTORISED
VALVE
AIR RELEASE
VALVE
NON RETURN
VALVE
AUTOMATIC
AIR VENT
MAKE UP BOTTLE
Observe minimum
static head requirements
NOTE:
No automatic by-pass required. However,
it is recommended to leave one radiator open and
to fit a system by-pass in the DHW circuit to ensure
pump over-run functionality.
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