Page 598 - 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

Water
discharging
from
above

Water blown back into appliance
Positive pressure
Bend too tight in soil
system or at foot of stack

p Figure 9.82 Compression

Wavering out
KEY TERM
Wavering out is caused naturally by the wind. In high winds or exposed
Wavering out: the process of positions, the effect of the wind blowing across the top of the vent pipe will
water in traps in appliances cause the water in the traps of appliances to move with a wave-like motion
moving with a wave-like
motion because of pressure because of pressure fluctuations. This momentum can often cause water to
fluctuations due to exposure disappear over the top of the trap, resulting in trap seal loss. It can be prevented
to winds. by fitting a wind cowl onto the top of the vent pipe.

Evaporation
Evaporation is a natural form of trap seal loss caused by lack of use of the
INDUSTRY TIP appliance. Traps, to some extent, rely on the appliance being used regularly to

keep the trap ‘topped up’ with water. When the appliance is not used, the water
The rate of evaporation can in the trap will begin to evaporate away until all the water is gone.
vary but, on average, the rate
of evaporation is about 2.5 Evaporation
mm of trap seal per week,
increasing when the weather Average UK seal loss
is hot and dry. Wind direction 2.5 mm per week
Positive or negative pressure
zone depending upon
wind direction

Air movement

Loss of water
depth due to
pressure
fluctuation Loss of seal depth

p Figure 9.83 Wavering out p Figure 9.84 Evaporation

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