Page 599 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

Chapter 9 Sanitation systems

Capillary action
INDUSTRY TIP
Capillary action generally occurs only in ‘S’ traps, when long fibres or long hairs
get lodged over the weir of the trap. Capillary action draws the water out of the Capillary action is covered
trap and down the lodged material, and the trap water slowly drips away. in Chapter 3, Scientific
principles, page 161.

Strand of material or hair hanging
over the trap weir draws water out
of the trap by capillary action
Loss of
seal depth

p Figure 9.85 Capillary action

Momentum

Loss of trap seal by momentum occurs only when a large amount of water is
suddenly discharged down the trap of an appliance. The force of the water will
dislodge most of the water in the trap in a similar way to self-siphonage.

Water poured at high speed
directly above outlet

Momentum of water carries away the water seal

p Figure 9.86 Momentum

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