Technical information

11
consideration should be given to 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 rainwater goods may
be damaged by such discharges.
500mm Max.
300mm
Min.
Temperature & pressure
relief valve
Metal discharge pipe (D1) from
temperature & pressure relief valve.
to tundish.
Metal discharge pipe (D2) from tundish
with continuous fall. See Table 2 and worked
example.
Tundish
Fixed grating
Trapped gulley
Discharge below
fixed grating.
(see page 10 for
alternative points
of discharge).

Valve outlet size Minimum size of
discharge pipe D1*
Minimum size of
discharge pipe D2*
from tundish
Maximum
resistance allowed,
expressed as a
length of pipe (i.e.
no elbow or bends)
Resistance created
by each elbow or
bend
G 1/2 15mm 22mm
28mm
35mm
Up to 9m
Up to 18m
Up to 27m
0.8m
1.0m
1.4m
G 3/4 22mm 28mm
35mm
42mm
Up to 9m
Up to 18m
Up to 27m
1.0m
1.4m
1.7m
G 1 28mm 35mm
42mm
54mm
Up to 9m
Up to 18m
Up to 27m
1.4m
1.7m
2.3m
TABLE 2. Sizing of copper discharge pipe “D2” for common temperature valve outlet sizes.
WORKED EXAMPLE
The example below is for a G
1
/
2
temperature & pressure 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 2;
Maximum resistance allowed for a straight length of 22mm copper discharge
pipe (D2) from G
1
/
2
temperature & pressure valve is 9m. Subtract the resistance
for 4 no. 22mm elbows at 0.8m each = 3.2m. Therefore the maximum permitted
length equates to: 5.8m. As 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 G
1
/
2
temperature & pressure valve equates to: 18m. Subtract the resistance for 4 no.
28mm elbow at 1.0m each = 4m. Therefore the maximum permitted length
equates to: 14m
As the actual length is 7m, a 28mm (D2) copper pipe will be satisfactory.
FIG. 2.9