Quantum IOT Series, Installation And User Instructions Manual

7

It is strongly recommended that only metal pipe-

work should be used. No responsibility will be 

taken for any damage caused from discharges.

The discharge pipe D2 should be at least one pipe 

size larger than the nominal outlet size of the 

safety device unless its total equivalent 

hydraulic resistance exceeds that of a straight 

pipe 9m long, i.e. for discharge pipes between 9m 

and 18m the equivalent resistance length should 

be at least two sizes larger than the nominal 

outlet size of the safety device; between 18 and 

27m at least 3 sizes larger than the nominal outlet 

size of the safety device; between 18 and 27m at 

least 3 sizes larger, and so on; bends must be 

taken into account in calculating the flow 

resistance. See Figure 1, Table 2  and the worked 

example.

Note: An alternative approach for sizing 

discharge pipes would be to follow Annex D, 

section D.2 of BS 6700:2006 + A1:2009).

Trapped

gully

Fixed

grating

Discharge below

fixed grating 

tundish

Metal discharge pipe (D1) from

temperature relief valve to tundish

Metal discharge pipe (D2) from tundish,

with continuous fall. See Table and

worked example

300mm

minimum

600mm maximum

Safety device

(eg. temperature

relief valve)

Figure 1: Typical Discharge Arrangement

Valve Outlet 

Size      [-]

Minimum size of 

discharge pipe before 

tundish   [mm]

Minimum size of 

discharge pipe after 

tundish   [mm]

Maximum allowed length 

of pipe after tundish    [m]

Length to be subtracted 

for each elbow or bend   

[m]

22

9

0.8

28

18

1.0

35

27

1.4

28

9

1.0

35

18

1.4

42

27

1.7

35

9

1.4

42

18

1.7

54

27

2.3

15

22

28

G1/2 

G3/4

G1

Table 2: Sizing of copper discharge pipe “D2” 

for common temperature relief valve outlet sizes

Pre-Installation

This example is for a G½ temperature relief valve 

with a discharge pipe (D2) (as fitted on 125l to 

300l cylinders) having 4 No. 22mm elbows and 

length of 7m from the tundish to the point of dis-

charge.

From Table 2, the maximum resistance allowed for 

a straight length of 22mm copper discharge pipe 

(D2) from a G½ 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, which is less than the actual length of 

7m, therefore calculate the next largest size.

Maximum resistance allowed for a straight length 

of 28mm copper discharge pipe (D2) from a G½ 

temperature relief valve equates to 18m.

Subtract the resistance for 4 No. 28m.m elbows at 

1.0m each = 4m. 

Therefore the maximum permitted length equates 

to 14m.

As the actual length is 7m, a 28mm (D2) copper 

pipe will be satisfactory.

•  Where a single common discharge pipe serves   

more than one system, it should be at least 

one pipe size larger than the largest individual 

discharge pipe (D2) to be connected.

•  The discharge pipe should not be connected to 

a soil discharge stack unless the soil discharge 

stack is capable of safely withstanding temper-

atures of the water discharged, in which case, 

it should:

      - contain a mechanical seal, which allows  

                water  into  the  branch  pipe  without  allowing                                                                                                                                

        foul air from the drain to be ventilated  

        through the tundish. 

      - there should be a separate branch pipe with 

        no sanitary appliances connected to it. 

      - if plastic pipes are used as branch pipes 

        carrying discharge from a safety device, 

        they should be either polybutalene (PB) or 

        cross-linked polyethylene (PE-X) complying 

        with national standards. 

      - be continuously marked with a warning that 

        no sanitary appliances should be connected 

        to the pipe.

5.4.2 

Worked Example