Page 416 - 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

IMPROVE YOUR MATHS
Let’s look at how Table 6.12 works.
The temperature and pressure relief valves both have ½-inch BSP outlets. Therefore, the D1 pipework, as can be
seen from the table, can be installed in 15 mm tube. The discharge pipe run is 6 m long to the final termination
and there are six elbows installed in the run of pipe.
Using the first row in the table, the first option has to be 22 mm because the D2 pipework must be at least one
pipe size larger than the D1 pipework. The maximum length of 22 mm pipe is 9 m but there are six elbows in the
run and each of these has a resistance of 0.8 m.

6 × 0.8 = 4.8 m
If we add the original length of 6 m, we get:
4.8 + 6 = 10.8 m
The maximum length of 22 mm discharge pipe, as we have already seen, is 9 m so, at 10.8 m, 22 mm pipe is
not large enough for the discharge pipe run. Another pipe size will have to be chosen.
Looking at 28 mm, we see that the maximum run of pipe is 18 m but the 28 mm elbows now have a resistance of
1 m and there are six of them. Therefore:

6 × 1 = 6 m
Add this to the original length of 6 m:

6 + 6 = 12 m
In this case, the discharge pipework is well within the 18 m limit and so 28 mm discharge pipework can be installed.

ACTIVITY
A customer wishes to have an unvented hot water storage system installed. You
have been asked by the site supervisor to size the discharge pipework. The
temperature and pressure relief valves both have ½-inch BSP outlets. Therefore,
the D1 pipework can be installed in 15 mm tube. The discharge pipe run is 9 m
long to the final termination and there are 5 elbows installed in the run of pipe.
What size of discharge pipework should be installed?

Correct termination of the discharge pipework
A risk assessment is likely to be needed where any termination point for the
discharge pipework is to be considered. This will determine whether any special
requirements are needed in relation to the termination point and its access.
Points to be considered here are:

● areas where the public may be close by or to which they have access
● areas where children are likely to play or to which they have access
l areas where the discharge may cause a nuisance or a danger
l termination at height
● the provision for warning notices in vulnerable areas.
The Building Regulations Approved Document G3 states that the discharge pipe
(D2) from the tundish must terminate in a safe place, with no risk to any person
in the discharge vicinity. Acceptable discharge arrangements are:
(a) To trapped gully with pipe below gully grate but above the water seal.
(b) Downward discharges at low level up to a maximum 100 mm above
external surfaces, such as car parks, hard standings and grassed areas,
are acceptable provided a wire cage or similar guard is provided to
404 prevent contact, whilst maintaining visibility.

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