09
such discharges.
SIZING OF COPPER DISCHARGE PIPE “D2” FOR COMMON TEMPERATURE RELIEF VALVE OUTLET SIZES
Valve outlet size
(diameter, inches)
Min size of
discharge pipe D1
(mm)
Min size of
discharge pipe D2
from tundish (mm)
Max resistance
allowed, expressed
as a length of
straight pipe, i.e. no
elbows or bends
Resistance created
by each elbow or
bend (m)
G�
15
22
28
35
up to 9
up to 18
up to 27
0.8
1.0
1.4
G�
22
28
35
42
up to 9
up to 18
up to 27
1.0
1.4
1.7
G1
28
35
42
54
up to 9
up to 18
up to 27
1.4
1.7
2.3
Worked example
The example below is for a �”diameter temperature relief valve with a discharge pipe (D2) having
4 22mm elbows and a length of 7 m from the tundish to the point of discharge.
The maximum resistance allowed for a straight length of 22mm copper discharge pipe (D2) from
a �”diameter temperature relief valve is: 9.0 m.
Subtract the resistance for 4 No 22mm elbows at 0.8 m each = 3.2 m.
Therefore, the maximum permitted length equates to: 5.8 m.
5.8 m is less than the actual length of 7 m, therefore, calculate the next largest size.
Maximum resistance allowed for a straight length of 28mm pipe (D2) from a �”diameter
temperature relief valve equates to: 18 m.
Subtract the resistance for 4 No 28mm elbows at 1.0 each = 4 m.
Therefore the maximum permitted length equates to 14 m.
As the actual length is 7 m, a 28mm diameter copper pipe will be satisfactory.
