What is a Trap and Its Ideal Requirements?

For proper and effective functioning of the sewerage system, Sewer appurtenances are necessary. These include man-holes, lamp holes, various types of traps, intercepting chambers, flushing tanks, ventilating shafts, street inlets, siphons, venture flumes, leaping wires etc.

Traps are an important component of a plumbing system. They prevent ingress of foul air, insects and vermin from the sewers into the building and resist the spread of disease. Traps are constructed, so that they retain a body of water which acts as a water seal.

Terminology of Traps
Courtesy - joeynovak

Traps should be of the self-cleansing type. They should generate enough velocity from the available flow to have a self-cleansing effect, a smooth finish and a full uniform bore.

Some manufactured fixtures, e.g. water closets, bed pan washers and certain models of urinals have integral traps built within the body of the fixture.

Also Read: Different Type of Traps?

Trap can be defined as fittings at the end of soil pipes or waste pipes to stop foul gases (smell) coming out of the soil pipe or waste pipe.

It is a part of the drainage (sanitary) system. It is developed or designed such that it retains a small quantity of waste water from discharge of fitting to which it is attached as a barrier to prevent foul gases or air entering the building.

The Requirements of an Ideal Trap are Listed Below:

  • Trap must work without mechanical help and shall be able to pass waste water freely.
  • Whether sewage is flowing or not, trap must be able to prevent foul gases (bad smells) in either direction.
  • Trap must be self cleansing.
  • Trap must have a water seal, preferably not less than 50 mm deep.
  • Trap must be strong and also proof against leakage from either if gas or liquid.
  • Trap should be made available with a clean-out or other means of access to interior in the event of chock. The cover must be gas tight and watertight.
  • Trap must have no internal projections to catch and hold hair, lint, bits of matches, etc.; but must have a smooth inner surface every part of which is automatically scoured by the flow of the sewage or sewer air leakage.
  • Where necessary it must be back – vented.
  • Trap must not have concealed partitions, tubes or other invisible parts as defects in construction might permit sewer air to enter the house.
Also Read: What is Floor Trap/Nahni Trap?
Water Flow Direction in Trap
Courtesy - 123rf

Water Seal in Traps:

A trap is fitting, or a part of sanitary appliance, which is designed to hold a quantity of water. This water is called the water seal. Water Seal acts as barrier to prevent air from passing out of the waste pipe and into room. Therefore, soil and waste pipe work is installed carefully and water seal is not destroyed under all conditions of discharge.

Water closets and in some cases urinals are provided with integral traps. All other fixtures shall be provided with external traps with adequate water seal. Diameter of the trap shall in no case be smaller than the diameter of the outlet of the fixture to which it is connected. Traps shall be of self-cleansing design with uniform bore and shall not be dependent on internal partitions or other movable parts for retention of water seal. Connection of a trap into another trap should not be practiced. Diameter of outlet pipe from a floor trap shall not be less than size of the trap outlet.

No traps or drainage connections should be made inside cold storages, walk-in freezers or stores for food and medicines as there is a danger of water freezing in the trap and breaking it. All precautions need to be taken to prevent any contamination hazards in handling installations.

Also Read:

What are the Different Types of Traps?
What is a Floor Trap or Nahni Trap?
What is Septic Tank and Soak Pit?

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