Traps are fittings at the end of soil and waste pipes that retain water to prevent foul gases from entering buildings. Traps should be self-cleaning and allow waste water to scour their walls. Modern traps made of plastic can be easily dismantled for cleaning. Traps come in different shapes, including P-traps, Q-traps, and S-traps. Intercepting traps prevent foul gases in larger sewers from entering house drainage systems and remove harmful pathogens. Trap seals can be lost through evaporation, capillary attraction, momentum discharge, leakage, wavering from wind pressure, compression, induced or self-siphonage.

1. TRAPS
• 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

2. TRAPS
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 cleaning.

3. Traps And Pipes and other components
of 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 surface area.
• 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.

4. Classification of Traps
• Depending upon the shapes the traps are classified
as:
• P-Trap
• Q-Trap
• S-Trap
• 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.

5. P, Q and S Traps
P Trap Q Trap S Trap

6. P, Q and S Traps

7. Nahni Trap

8. Gully Trap

9. Intercepting Traps

10. Advantage of Intercepting 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.

11. Loss of Trap Seals If a trap seal loss,
smells from the
sanitary appliances
would enter the
building. Therefore the
water seal in the trap
must be maintained
under all
circumstances.

12. 1) Evaporation
When trap is not being used, the rate of water
evaporation 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

13. 2) Capillary attraction
Is another rare occurrence
which 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 : Capillary
attraction

14. 3) Momentum 4) Leakage
This is caused by a sudden It is caused by a fault in the
discharge of water from a trap or plumbing installation
bucket. Due to velocity water and water on the floor would
is discharged and it shoots be apparent.
around the trap bend and
goes down the waste pipe,
leaving no seal.
5) Wavering out
This is caused by the effect of the
wind which passes over the top of
the ventilation pipe and thus causes
pressure fluctuations. See Figure
3.8.
Figure 3.8 : Wavering out

15. 6) Compression or back pressure
This occurs in high rise buildings. When water is discharged down to
the main discharge stack, air is compressed at the base of the stack. A
waste pipe connected to the stack in the pressure zone may have the
seal of the trap lost by the compressed air forcing out the water.
Detergent foam increases the risk of compression. See Figure 3.9 .

16. 7) Induced siphonage
This is caused by discharge of water from another sanitary
appliance connected to the same discharge pipe. In either a
vertical or horizontal main waste pipe, as water flows down the
pipe and passes the branch pipe connected to it, it draws air
from it, thus creating a partial vacuum and subsequently
siphonage of the trap takes place. See Figure 3.10.

17. 8) Self siphonage
This is caused by
appliances such as wash
basins and other small
appliances, due to their
curved shape, and is
caused by a moving plug
of water in the waste
pipe. A partial vacuum is
created at the outlet of
the trap, thus causing
siphonage action takes
place. See Figure 3.11.

18. Thank you