### Discussion :: Waste Water Engineering - Section 1 (Q.No.6)

Sandip Ghosh said: (Dec 9, 2014) | |

But actually 1 in 105 for a velocity of 0.9m/s & 1 in 150 for a velocity of 0.75m/s. |

Aman Gautam said: (Dec 10, 2014) | |

@Sandeep. Greater is the gradient, greater is the velocity. Thus your point is wrong and as for 225 mm diameter, velocity should be 1 m/s. So it would require the highest gradient. |

Manohar said: (Jul 9, 2015) | |

Yes, the gradient, 1 in 105 is greater than 1 in 150. |

Ganesh said: (Oct 29, 2015) | |

Which formula is used here to calculate self cleansing formula? |

Akash said: (Dec 26, 2015) | |

V-under root (8 beta under f multiply by (specific gravity of solids- 1)*g*diameter of solids). Find v and using manning or any other formula find slope. But data is not sufficient. |

Narayan said: (Jan 17, 2016) | |

Velocity of the sewer is 0.9 to 0.75 m^3/s. So assume velocity of sewer V = 0.9 m/s. And using the manning's formula: V = R^2/3*s^1/2/n but the wastage flow is not specify. |

Ritesh Dev Singh said: (Dec 20, 2016) | |

By Shield's Theory, Self - cleansing velocity (Vs), Vs= √ {8kgd'(G-1)}÷f], where, k= (1-n)sin θ. |

Vaibhav Gupta said: (May 9, 2017) | |

Explain the expression for self-cleaning velocity. |

Marwa said: (Jun 21, 2017) | |

Which formula is used? Please help me? |

Himajwala said: (Aug 21, 2017) | |

I didn't understand which formula was used. Can anyone help me? |

Sanjay said: (Sep 9, 2017) | |

Self cleaning velocity is 0.75 m/s to 0.9 m/s. So 100/120 =0.83. 100/60 =1.66. 100/100 =1. So right answer is 1 in 120. |

Dheeraj Singh said: (Sep 16, 2017) | |

The slope of sewer should be designed for min permissible velocity at min flow but in this case, a material made of sewer not given so can't be calculated if I assume brick-lined sewer then calculate slope by given velocity trial and error velocity (1to2.5). |

Gubendhiran said: (Jan 13, 2018) | |

Using Manning's formula. Vs=[(R^0.67)*(S^0.5)]/n. For circular sewer R=D/4=0.225/4=0.05625m. Vs=ranges from 0.45 to 0.8 m/s from S.K.GARG EEN Vol IIT. Take Max for design Vs=0.8 m/s. n=Manning's constant=0.015. 0.8=[(0.05625^0.67)*(S^0.5)]/0.015. (S^0.5)=0.08253. S=0.00681. S=1/147. So we can option 'C'. |

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