Dimplex SUTP Mid Range Installation Manual page 8

Sizing of copper discharge pipe "D2" for common temperature relief valve outlet sizes
Valve outlet Min size of
size, diameter discharge pipe
(inches) D1 in (mm)
1/2 15
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3/4 22
1 28
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Worked example
The example below is for a ½"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.
From
Maximum resistance allowed for a straight length of 22mm copper discharge pipe (D2) from a
½"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 ½"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.
Min size of
discharge pipe
D2 from tundish
in (mm)
22
28
35
28
35
42
35
42
54
Max resistance
allowed, expressed
as a length of
straight pipe, i.e.
no elbows or
bends.
up to 9
up to 18
up to 27
up to 9
up to 18
up to 27
up to 9
up to 18
up to 27
Resistance
created by
each elbow
or bend
(m)
0.8
1.0
1.4
----
----
1.7
1.4
1.7
2.3
8