Definition

A trap is bent or depressed sanitary fitting which always remain full of water.

Water which remains in trap in water seal, which is measured as the vertical distance between crown and dip of trap.

The depth of water seal in practice various from 25mm to 75mm.

Function

1. The main function of trap in drainage system is to prevent the passage of foul air or gases through it

2. Also it allows the sewage to flow through it.

Quality of good trap

1. It should be simple construction.

2. It should pass adequate water seal.

3. It must be easily connected with drain.

4. It should pass self-cleaning property.

5. Along the internal and external surface should be smooth finish.

Types – the trap are classified in the following two ways.

1. According to shape

2. According to use

1. According to shape

According to shape trap is classified as

a. P- trap

b. Q-trap

c. S- trap

a. P-trap

Trap which has shape of letter P is known as P- trap.

The leg of trap is at right angles to each other.

b. Q-trap

Trap which has shape of letter Q is known as Q- trap.

The leg of trap meets at angles other than right angle.

c. S-trap

Trap which has shape of letter S is known as S- trap.

The leg off trap is parallel.

2. According to use

According to use trap is classified as

a. Floor trap

b. Gully trap

c. Intercepting trap

a. Floor trap

Floor trap is also known as nahni trap.

A cast iron cover is grated is provided at top so as to prevent entry of solid matter

The cover has been removed from cleaning of trap

Location- Nahni trap located in bathroom.

b. Gully trap

Gully trap is usually made of stoneware and a cast iron grating is provided at it top.

It is fitted inside the masonry chamber.

A water seal is provided at a height of 60 to 70mm

It is kept at floor or pavement or ground level.

Its lead the sewage either to sewer or to inspection chamber or to manhole.

A CI cover is provided at it top so as cleaning can be done by lifting the cover.

Location

1. The gully trap form the starting point of horizontal flow of sewage.

2. It is usually situated near the external face of wall and it is kept slightly higher than ground level.

c. Intercepting trap

The main idea for providing intercepting the trap is to prevent the entry of sewer gases from public sewer line into the house drains.

This trap has water seal of 100mm.

Trap contains and intercepting arm for purpose of cleaning or interception.

The interception arm is kept closed by a plug or lid.

A fresh air inlet is also provide in the manhole contain the intercepting trap.

Location

Intercepting trap is provided in the last manhole at the junction of house drain and public sewer line.