Page 414 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

The City & Guilds Textbook: Plumbing Book 1

There are three sections to the discharge pipework:

1 D1 pipework arrangement
2 the tundish
3 D2 pipework arrangement.

As we have already established the role of the tundish earlier in the chapter, we will
concentrate specifically here on the D1 and D2 sections of the discharge pipework.
To ensure that there is no damage to the property, the discharge pipework
should be positioned in a safe but visible position, and should conform to the
following.
● The discharge must be via an air break (tundish) positioned within 600 mm
of the temperature relief valve.
● The tundish must be located within the same space as the hot water storage
vessel.
l It should be made of metal or other material capable of withstanding the
temperature of the discharged water. The pipe should be clearly and permanently
marked to identify the type of product and its performance standards.*
l The discharge pipe must not exceed the hydraulic resistance of a 9 m straight
length of pipe without increasing the pipe size.
l It must fall continuously throughout its entire length with a minimum fall
of 1 in 200.
l The D2 pipework from the tundish must be at least one pipe size larger than
the D1 pipework.
l The discharge pipe should not connect to a soil discharge pipe unless the pipe
material can withstand the high temperatures of discharge water, in which
case it should:
● contain a mechanical seal (such as a Hepworth HepvO valve), not
incorporating a water trap, to prevent foul air from venting through the
tundish in the event of trap evaporation
l be a separate branch pipe with no sanitary appliances connected to it
l where branch pipes are to be installed in plastic pipe, be either
polybutylene (PB) to class S of BS 7291–2:2006 or cross-linked
polyethylene (PE-X) to Class S of BS 7291–3:2006
● be marked along the entire length with a warning that no sanitary
appliances can be connected to the pipe.
● The D1 pipework must not be smaller than the outlet of the temperature
relief valve.
l The D1 discharge from both the pressure relief and temperature relief valves
may be joined by a tee piece, provided that all of the points above have been
complied with.
● There must be at least 300 mm of vertical pipe from the tundish to any bend
in the D2 pipework.
* Paragraph 3.9 of Approved Document G3 Guidance specifies metal pipe for the discharge pipework.
However, G3 itself states only that hot water discharged from a safety device should be safely conveyed
to where it is visible but will not cause a danger to persons in or about the building. Since many types of
plastic pipe are now able to withstand the heat of the discharge water, the responsibility for the choice
of material rests with the installer, the commissioning engineer and the local Building Control Officer to
ensure that G3 is complied with. It is also important that, if plastic pipes are used, the type of plastic is
clearly indicated for future reference when inspections and servicing are carried out.
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