Method of Ventilation of House Drains System
The entire sewerage system of a house is ventilated by providing vent pipes and anti-siphonage pipes and sometimes by fresh air inlet. Following is the method of ventilation of house drains:
Fresh air inlet
The ventilation is usually achieved by providing a fresh air inlet. It is connected to the house drain through the lowermost manhole (inspection chamber). Fresh air from the atmosphere enters through this inlet and finally goes out through the vent pipes.
A one-way valve (the mica flap valve) is provided at the head of the fresh air inlet. This valve opens inside to admit fresh air. But it closes in case of reverse flow of gases from the manhole.
Water seals of traps in multi-storied buildings or houses may sometimes get broken due to siphonic action. To overcome this difficulty, a separate pipe of smaller diameter is fitted to the traps, which connects the trap with the vent pipes. This pipe is known as an anti-siphonage pipe. It supplies air at the time of suction. It also acts as a vent pipe.
Purpose of Ventilation of House Drains System
The ventilation system is required to serve the following purposes:
1) To relieve the pressure of foul gases developed in the house drains.
2) To prevent the breakage of trap’s seal by siphonic action.
3) To dilute the foul gases in the drains and to reduce their harmful effects.
Methods of Ventilation in Tunnels
Secondary Sedimentation Tank or Clarifier