Worked Example

www.tradeplumbing.co.uk Call Sales On 08708034288

connected. If unvented hot water storage systems are installed where discharges from safety devices may not be apparent i.e. in dwellings occupied by the blind, infirm or disabled people, 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

Temperature & pressure	Metal discharge pipe (D1) from
relief valve	temperature & pressure relief valve.
	to tundish.

Tundish

500mm Max.

300mm

Min.

Metal discharge pipe (D2) from tundish with continuous fall. See Table 2 and worked example.

FIG. 2.9

Discharge below fixed grating. (see page 10 for alternative points of discharge).

Fixed grating

Trapped gulley

TABLE 2. Sizing of copper discharge pipe “D2” for common temperature valve outlet sizes.

Valve outlet size	Minimum size of	Minimum size of	Maximum	Resistance created
	discharge pipe D1*	discharge pipe D2*	resistance allowed,	by each elbow or
		from tundish	expressed as a	bend
			length of pipe (i.e.
			no elbow or bends)

G 1/2	15mm	22mm	Up to 9m	0.8m
		28mm	Up to 18m	1.0m
		35mm	Up to 27m	1.4m
G 3/4	22mm	28mm	Up to 9m	1.0m
		35mm	Up to 18m	1.4m
		42mm	Up to 27m	1.7m
G 1	28mm	35mm	Up to 9m	1.4m
		42mm	Up to 18m	1.7m
		54mm	Up to 27m	2.3m

be damaged by such discharges.

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 www.tradeplumbing.forco4 no.uk. 22mmCallelbowsSalesat 0.8m eachOn= 3.2m08708034288. Therefore the maximum permitted length equates to: 5.8m. As 5.8m is less than the actual length of 7m therefore