9
British Gas 4100 & 4125 RD2 -
Installation & Servicing
GENERAL
Notes.
a.
Flow and return pipes should rise vertically on leaving the
boiler.
b.
Horizontal pipes should be ABOVE ceiling level and as short
as possible.
c.
A MINIMUM inclination of 25 mm per 3 m run (1" per 10') is
required to avoid air locks.
If the above conditions cannot be met pumped primaries should
be used.
1.
Separate flow and return connections are used for each
service. All possible configurations are given in Frame 12
and
ONLY those shown should be used.
2.
The schematic pipework graph is based on the assumption
that NO MORE than 8 elbows are used in the gravity loop,
including entry to the boiler.
3.
For each extra elbow in excess of 8 (R) MUST be reduced by
300 mm (12") or (H) increased by 100 mm (4")
4.
Whatever value is selected for (R), the value of (H) MUST be
at least that indicated by the graph.
(R)
=
the horizontal distance between the centre line of the
cylinder and the boiler tappings used - measured along
the pipe run.
(H)
=
the vertical distance between the top of the boiler and
the base of the cylinder.
3
MINIMUM REQUIREMENTS
Fully pumped systems
1.
Open vent and cold feed connections must be made to the
boiler flow and return tappings according to the options
shown in Frame 12.
2.
The boiler is assumed to be the highest point of the
circulating system.
3.
The circulating pump is positioned on the FLOW and the
vertical distance, between the pump and feed/ expansion
tank, must comply with the pump manufacturer's minimum
requirements, to avoid cavitation. Should these conditions
not apply, either lower the pump position or raise the feed/
expansion tank above the minimum requirements of
British Gas Services.
4.
The water velocity through the boiler flow / return pipes is
assumed to be below 1.5 m/s (5 ft./s), whilst the pump flow
rate is set to provide a temperature difference of
11
o
C (20
o
F) across the boiler flow / return, at design input.
5.
This information is intended as a GUlDE ONLY and cannot
take into account instantaneous changes in head caused
by the operation of motorised valves, pumps etc.
Due allowance MUST be made if surging is liable to occur.
If in any doubt, contact
British Gas Services.
4
GRAVITY HOT WATER & PUMPED CENTRAL HEATING
