• Traps are defined as fittings at the end of soil pipes of waste pipes to
prevent foul gases coming out of the soil pipe/ waste pipe
Traps are an integral part of a modern sanitary
system, being designed to retain a small quantity
of the waste water from the discharge of fitting to
which they are attached as a barrier to prevent
foul air entering the building as shown in Figure
Traps should be self-cleaning, that is to say , they
should be designed so that their walls are scoured
by the discharging water. One of the advantages
of modern traps constructed of plastic materials is
the ease with which they may be dismantled for
Traps And Pipes and other components
house Drainage System
Following are the main components of House drainage system.
Traps: Good Traps should have following Qualities:
Should provide enough water seal ( around 50 mm) with large
• Interiors surface should be smooth so that the flow is not
obstructed which enables self cleansing.
• An assess door should be provided for cleaning the trap.
• It should be made of non- adsorbent material.
Depending upon the shapes the traps are classified as:
Above three types of traps are shown in the following figures.
The depth of a Trap Seal would depend upon the usage of a
pipe. The trap seal varies from 25 to 75 mm deep.
and SS Traps
• Foul Gases of larger municipal sewers are prevented from
entering house drainage system.
• Harmful pathogens are not entered in house drains.
• Well designed and contructed interceptors can quickly remove
foul matter of house drain to muncipal sewers.
If a trap seal loss,
smells from the
enter the building.
water seal in the
trap must be
When trap is not being used, the rate of water
depends upon the relative
humidity of the air in the room. The rate is
approximately 2.55 mm per week, so a 25 mm
seal would last for 10 week. See Figure 3.6.
Figure 3.6 : Evaporation occur
when trap not being used
2) Capillary attraction
Is another rare
happens in ‘S’ trap
when a piece of porous
material being caught
over the bend of a trap
absorbs water and
deposits it down the
waste discharge pipe.
See Figure 3.7.
Figure 3.7 :
This is caused by a
It is caused by a fault
sudden discharge of
in the trap or plumbing
water from a bucket.
installation and water
Due to velocity water is
on the floor would be
discharged and it shoots apparent.
around the trap bend
and goes down the
waste pipe, leaving no
5) Wavering out
This is caused by the effect
of the wind which passes
ventilation pipe and thus
causes pressure fluctuations.
See Figure 3.8.
Figure 3.8 : Wavering out