Page 594 - 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

Anti-vac and resealing (anti-siphon) traps

There is no substitute for a well-planned, well-designed system of sanitary
pipework. If the system is designed in accordance with BS EN 12056, then
problems with trap seal loss should not occur. Anti-vac (anti-vacuum) and
resealing traps are not an alternative to a good sanitary pipework system, but
they can reduce the problems that occur with existing systems due to upgrades
to appliances and additions to the system.

Anti-vac (anti-vacuum) traps

Anti-vac traps use a small air admittance valve that is located after the water
p Figure 9.72 Washing machine seal. The valve opens if a drop in pressure occurs when the appliance is used,
trap
and this allows air into the system to break any siphonic action that may
occur.
INDUSTRY TIP
Resealing traps
Fitting an anti-vac trap is not
recommended on new systems Externally, resealing traps are identical to a normal bottle trap. Internally,
as they have a habit of not however, they are quite different: the trap has a bypass within the body of the
holding an air test at the bottle trap, allowing air to enter the trap, via a dip pipe, in the event of siphonic
installation and testing stage. action occurring. They are available only as a bottle trap and so are not suitable
for all installation situations.

Self-sealing traps

The self-sealing trap is a waterless valve that uses a thin neoprene rubber
membrane to create an airtight seal preventing foul air from entering
the dwelling, while maintaining equal pressure within the soil and vent
system.
p Figure 9.73 Swivel-type 50 mm
seal bath trap The membrane opens under the pressure of water from an appliance, closing
again when the water discharge has finished.

p Figure 9.74 38 mm seal bath trap Vertical closed Vertical open

Horizontal closed Horizontal open

p Figure 9.75 Bottle trap p Figure 9.76 The operation of the self-sealing trap

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