Technical Booklet P Sanitary Appliances Unvented Hot Water Storage and Scalding·Page 16·Table 2.1
Sizing of copper discharge pipe D2 for temperature relief valves
Table specifying minimum discharge pipe sizes (D2 from tundish) and maximum allowable resistance lengths based on valve outlet size (G1/2, G3/4, G1), with resistance values for elbows and bends to be subtracted from maximum straight pipe lengths.
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 straight pipe (i.e. no elbows or bends) Resistance created by each elbow or bend
G1/2 15 mm 22 mm / 28 mm / 35 mm up to 9 m / up to 18 m / up to 27 m 0.8 m / 1.0 m / 1.4 m
G3/4 22 mm 28 mm / 35 mm / 42 mm up to 9 m / up to 18 m / up to 27 m 1.0 m / 1.4 m / 1.7 m
G1 28 mm 35 mm / 42 mm / 54 mm up to 9 m / up to 18 m / up to 27 m 1.4 m / 1.7 m / 2.3 m
* See paragraphs 2.9(b), Section 2 and Diagram 2.1.
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