British Gas RD1
-
Installation & Servicing
9
GENERAL
Minimum Requirements
Note.
The pump manufacturers minimum
requirements must be complied with
System
return
Connections
to boiler
Inverted cold
feed entry
System
flow to
pump
150 (6")
Max
15mm
Cold
feed
450 (18")
Mimimum
450 (18")
Mimimum
22mm
Open vent
Feed / expansion
cistern
Water
level
(cold)
Surge
arrester
75 (3)
Min.
450
(18)
Min.
200
(8)
Min.
Highest
point of
flow or
return
150
(6)
Max
Max. practical
length
To pump
Cold
water
level
Feed / expansion
cistern
75 (3) Min.
Flow
Return
22 (3/4)
Open vent
All dimensions in mm (in.). N.B. Imperial dimensions are approximate
4
LOW HEAD INSTALLATIONS
The system should be vented directly off the boiler flow
pipe, as close to the boiler as possible. The cold feed
entry should be inverted and MUST be positioned
between the pump and the vent, and not more than
150mm (6") away from the vent connection.
There should be a minimum height - 450mm (18") - of
open vent above cistern water level. If this is impossible
refer below.
The vertical distance between the highest point of the
system and the feed/expansion cistern water level MUST
not be less than 450mm (18").
The pump MUST be fitted on the flow side of the boiler.
A suitable pump is a domestic circulator capable of
providing an 11°C (20°F) temperature differential (e.g.
Grundfos UPS 15/50 or equivalent). The vertical distance
between the pump and feed/expansion cistern MUST
comply with the pump manufacturers minimum
requirements to avoid cavitation. Should these conditions
not apply, either lower the pump position or raise the
cistern above the minimum requirement specified by
British Gas Services.
Note.
A cold water feed must be available back to the
boiler, when all automatic valves are in the closed position
(refer to BS. 6798) and when close coupled the feed must
not be in a vertical leg.
The range of boilers can be installed in
low head situations by fitting a 'surge
arrester' in the expansion pipe as shown.
The following conditions MUST be
observed:
1. The surge arrester must be at least
42mm in diameter x 150mm long,
thus ensuring a MINIMUM air gap
and a MINIMUM depth of water
below the static water level (cold) of
75mm.
2. The static water level (cold) must be
at least 200mm above the top of the
horizontal flow pipe, fitted as shown.
The vent connection MUST NOT be
made immediately off the top of the
boiler, as venting is made less
efficient.
3. The maximum practical length of
15mm cold feed pipe should be used
in order to reduce the effective
volume of system water expanding
into the feed/expansion cistern to a
minimum.
3
OPEN VENT SYSTEM REQUIREMENTS - FULLY PUMPED
