What is a Floor Trap (Nahni Trap)?
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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.
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.
Also Read: What is Trap & its Ideal Requirements
Foul gasses produced in the sewers, drains, waste-pipes may cause a nuisance by entering in houses through house-connecting pipes if their passage is not checked by some suitable devices. The appurtenances which are used to stop entering of foul gasses inside the houses are known as traps.
Floor trap is also called as Nahni Trap (Nahni in hindi means washing / bathing place). Nahni Trap is provided to prevent the foul gasses entering into the building by providing the water seal. Minimum 50 mm depth of water seal should be provided. Whether waste water is flowing or not, floor trap prevents the foul gases (bad smells) to enter in to the building.
To collect wastewater from the bathroom, wash area, wash basin, kitchen sinks etc., floor trap or Nahni trap is provided into the floor. Floor traps are available in PVC, UPVC and CI; they are without vent pipe but removable grating is provided at the top of Traps.
Floor traps or Nahni traps (Nahni means washing place) come in a variety of shapes, sizes and outlet conditions. Many do not have a water seal at all, and have a non-uniform and rough bore. Nahni traps are a source of major leakages due to their poor design, casting and poor quality. It is prevented by using only deep seal P traps with multi-inlet fitting/traps with connections from wash basins and other fitting to provide a positive joint.
Traps installed in the areas not in normal use may lose their water seal due to evaporation. Provision must be made to renew the seal by adding water periodically and this can be done by connecting a waste appliance to the trap (e.g. a wash basin, etc). Replenishment is also achieved by installing a sophisticated water supply valve with a back-flow prevention device that is connected to the trap. Care has to be taken to prevent installation of traps that are exposed to freezing conditions.
The length of floor trap is 310 mm, with minimum 80 mm diameter at the inlet end, 30 mm diameter near outlet end and 73 mm diameter outside the outlet of floor trap. And 95 mm grating size provided at the top of floor trap with 8 mm diameter holes.
Also Read: Different Types of Traps
Preventing cockroach from entering house through bathroom
By providing Nahni Trap with grating on the top it also prevents entry of bugs and insects (Cockroach) from sewer line to bathroom or toilet.