Specifications

9
Warning Notice – The discharge will consist of scalding water and steam. Asphalt, roofing felt and
non-metallic rainwater goods may be damaged by such discharges.
Typical discharge pipe arrangement.
Fig 7.2
Valve outlet size Min. size of Min. size of
Max. length of Resistance created
Diameter Discharge pipe D1 Discharge pipe D2
Straight pipe by each elbow
from Tundish
Or bend
22mm
Up to 9m 0.8m
½” 15mm 28mm
Up to 18m 1.0m
35mm
Up to 27m 1.4m
28mm
Up to 9m -
¾” 22mm 35mm
Up to 18m -
42mm
Up to 27m 1.7m
35mm
Up to 9m 1.4m
1” 28mm 42mm
Up to 18m 1.7m
54mm
Up to 27m 2.3m
Fig 7.3
Worked example
The example below is for a ½”diameter temperature relief valve with a discharge pipe (D2) having 4
elbows and a length of 7m from the tundish to the point of discharge.
From the table above the maximum resistance allowed for a straight length of 22mm copper
discharge pipe (D2) from a ½”diameter temperature relief valve is: 9.0m.
Subtract the resistance for 4 No 22mm elbows at 0.8m each = 3.2m.
Therefore, the maximum permitted length equates to: 5.8m.
5.8 m 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 ½”diameter temperature
relief valve equates to: 18m.
Subtract the resistance for 4 No 28mm elbows at 1.0 each = 4m.
Therefore the maximum permitted length equates to 14m.
As the actual length is 7m, a 28mm diameter copper pipe will be satisfactory.