IDEAL istor HE260 Installation And Servicing page 14

6 SYSTEM REQUIREMENTS - Domestic Hot Water (continued)
the installation of an electronically operated device to
warn when discharge takes place.
Note.
The discharge will consist of scalding water and steam.
Asphalt, roofing felt and non-metallic rain water goods may be
damaged by such discharges.
Worked example of discharge pipe sizing
The example below is for a G1/2
temperature relief valve with a discharge
pipe (D2) having 4 No. elbows and length
of 7m from the tundish to the point of
discharge.
From Table 1:
Maximum resistance allowed for a straight
length of 22mm copper discharge pipe
(D2) from a G1/2 temperature relief valve
is 9.0m
Subtract the resistance for 4 No. 22mm
elbows at 0.8m each = 3.2m.
Therefore the permitted length equates to
5.8m.
5.8m is less than the actual length of 7m
therefore calculate the next largest size.
Maximum resistance allowed for a straight
length of 28mm pipe (D2) from a G1/2
temperature relief valves equates to 18m.
Subtract the resistance of 4 No.28mm elbows at 1.0m each:
4.0m.
Therefore the maximum permitted length equates to:14m.
As the actual length is 7m a 28mm min (D2) copper pipe will
be satisfactory.
WARNINGS
Under no circumstances should the factory fitted
temperature/pressure relief valve be removed other than
by authorised personnel. To do so will invalidate any
warranty claim.
Table 1. Sizing if copper discharge pipe (D2) for common
temperature relief valve outlet sizes.
Control and safety valves MUST NOT be tampered with.
14
GENERAL
The discharge pipe MUST NOT be blocked or used for
any other purpose.
The tundish must not be removed.
Electrical components must not be sited near the
tundish.
Valve Minimum Minimum
outlet discharge discharge
size pipe D1 pipe D2
from tunish pipe (i.e. no elbow or bends) or bend
22mm
G1/2 15mm 28mm
35mm
28mm
35mm
G3/4 22mm 42mm
35mm
G1 28mm 42mm
54mm
The boiler does not normally need a bypass but at least
some radiators on the heating circuit, of load of at least
10% of the minimum boiler output, must be provided
with twin lockshield valves so that this minimum
heating load is always available. See note regarding
thermostatic radiator valves on page 10.
Note.
Systems incorporating zone valves which could
completely cut off the flow through the system, must be
wired such that the boiler will not fire or continue to fire
when this occurs.
Maximum resistance
allowed, expressed
as a length of straight
up to 9m
up to18m
up to 27m
up to 9m
up to 18m
up to 27m
up to 9m
up to 18m
up to 27m
istor system store -
Installation and Servicing
Resistance
created by
each elbow
0.8m
1.0m
1.4m
1.0m
1.4m
1.7m
1.4m
1.7m
2.4m