Lecture6 wastewater systems-3

172 views

Published on

sanitary

Published in: Engineering
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
172
On SlideShare
0
From Embeds
0
Number of Embeds
1
Actions
Shares
0
Downloads
13
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Lecture6 wastewater systems-3

  1. 1. Gravity Sewer Collection System Design ‐ Design Criteria ‐ FLOW • Usually we design for Q/Qfull to be not more than 91% or d/dfull to be not more than 75% 21.1 Partial Flow Curves Q &V d / D
  2. 2. Gravity Sewer Collection System Design ‐ Design Criteria ‐ HINTS • In normal practice, the ground slope is used as a first trial for selecting the slope of the pipe. However, there are number of exceptions: A) if the ground is flat, select the minimum slope to achieve the minimum velocity with the sewer flowing pipe B) If the ground slope yields a velocity greater than the maximum velocity (2.5 m/sec), the select a lower slope and drop manholes could be used. C) Because LS & PS are expensive to build, operate and maintain, avoid them as much as possible.
  3. 3. Sewer Layout
  4. 4. Flow Select Ø and slope that will  carry flow while flowing full Is pipe  Ø<200mm? Select 200mm Select pipe Slope = Ground Slope Is slope<min. slope Select Min. Slope Check velocity for design flow Is Velocity> Min.  Velocity STOP Is increase in slope  reasonable? Is pipe  Ø>200mm? STOP Increase  Pipe size YES YES YES 1 1 NO YESIncrease  Slope NO NO Sewer Design Flow Chart for selecting pipe size
  5. 5. Example 1 Determine the velocity of 0.0081 m3/sec flow in a 200 mm diameter  sewer at a slope of 0.004 m/m. The pipe is VCP.  Solution n for VCP = 0.013 For full flowing pipe; R = D/4 Vfull = 1/n R2/3 S0.5 = 1/(0.013) * (D/4)2/3 (0.004)0.5 = 0.66m/sec A full = πD2/4 = π* (0.2)2/4 Qfull = A * Vfull = 0.0208 m3/sec Q/ Qfull = 0.0081/0.0208 = 0.39 From chart V/Vfull = 0.9 V = 0.9 * 0.66 = 0.6 m/sec
  6. 6. Example2: For population = 50000 persons  and  sewer flow Rate = 160 L/cap/d Design the dia. of the sewer  pipe when dmax /D = 0.67 . Assume Peak Factor = 2 S = 0.004 Solution • Qav = 160  * 50 000  = 8000 000 L/d  =  0.093 m3 / sec . • Qmax = PF * Qav =  2 * 0.093 = 0.186 m3 / sec . • d max / D=  0.67  from chart  Qmax / Qfull = 0.78 & Vmax / Vfull= 1.11 • Q full  = Qmax / 0.78 = 0.186 / 0.78 = 0.238 m3/ sec • S = 0.004 • Qfull = A/n R2/3 S0.5 = A/(0.013) * (D/4)2/3 (0.004)0.5  • D = 499 mm  = 500mm
  7. 7. Example3: Design a VCP sewer to connect 2 businesses to an existing sewer main at MH No.48  at an invert elevation of 177.98m. The distance between manholes is marked on the  below plan. The peak flow rates for Koffee Au Noir and Elsie’s Kreamer are 20.2 l/sec  and 14.5 l/sec respectively.  Design.xls

×