Gravity Water Supply Design Monroe L Weber-Shirk School

Gravity Water Supply Design Monroe L. Weber-Shirk School of Civil and Environmental Engineering

Population Projection ä Example from Agua Para el Pueblo (Honduras) ä Count the houses ä Assume 6 people per house ä Assume linear growth for design period äN = design period ä K = growth rate

Water Demand ä Assume a per capita demand (this might be based on a governmental regulation) ä Multiply per capita demand by the future population to get design average demand ä Multiply average demand by scaling factors to get maximum day demand maximum hour demand

Distribution Storage Tank Size ä Based on 8 hours of storage at average demand ä These systems aren’t designed for fire protection

Design Flows ä Transmission Line Design flow ä ä Perhaps based on maximum daily demand or on maximum hourly demand Distribution system design flows Take peak hourly flow at the end of the system design life ä Divide that flow by the current number of houses to get a flow per house ä The flow in each pipe is calculated based on the number of houses downstream ä

Pipe Diameters ä How are pipe sizes chosen? ä Energy Equation ä An equation for head loss ä Requirement of minimum pressure in the system

EGL (or TEL) and HGL pressure head (w. r. t. reference pressure) ä ä velocity head elevation head (w. r. t. datum) downward The energy grade line must always slope ______ (in direction of flow) unless energy is added (pump) The decrease in total energy represents the head loss or energy dissipation per unit weight EGL and HGL are coincident and lie at the free surface for water at rest (reservoir) If the HGL falls below the point in the system for which it is plotted, the local pressures are _____ ______ lower than reference pressure

Energy equation Energy Grade Line Hydraulic G L velocity head static head pressure head z elevation pump z=0 datum

Transmission Line Design EGL Spring box Distribution Tank Air release valves HGL

Hydraulic Grade Line Minimum ä Avoid having the HGL below the point in the system for which it is plotted (negative pressure) ä Air will accumulate at intermediate high points in the pipeline and the air release valve won’t be able to discharge the air if the pressure is negative

Methods to Calculate Head Loss (Mechanical Energy Loss) ä Moody Diagram ä Swamee-Jain ä Hazen-Williams

Moody Diagram 0. 10 0. 08 0. 05 0. 04 0. 03 friction factor 0. 06 0. 05 0. 02 0. 015 0. 04 0. 01 0. 008 0. 006 0. 004 0. 03 laminar 0. 002 0. 001 0. 0008 0. 0004 0. 0002 0. 0001 0. 00005 0. 01 1 E+03 smooth 1 E+04 1 E+05 1 E+06 Re 1 E+07 1 E+08

Swamee-Jain ä ä 1976 limitations ä ä /D < 2 x 10 -2 Re >3 x 103 less than 3% deviation from results obtained with Moody diagram easy to program for computer or calculator use Each equation has two terms. Why?

Pipe roughness pipe material glass, drawn brass, copper commercial steel or wrought iron asphalted cast iron galvanized iron cast iron concrete rivet steel corrugated metal PVC pipe roughness (mm) 0. 0015 0. 045 0. 12 Must be 0. 15 dimensionless! 0. 26 0. 18 -0. 6 0. 9 -9. 0 45 0. 12

Pipeline Design Steps Find the minimum pipe diameter that will keep the HGL above the pipeline ä Round up to the next real pipe size ä Calculate the location of the HGL given the real pipe size ä ä If an intermediate high point constrained the design then investigate if a smaller size pipe could be used downstream from the high point.

Minor Losses ä Most minor losses (with the exception of expansions) can not be obtained analytically, so they must be measured ä Minor losses are often expressed as a loss coefficient, K, times the velocity head. High Re

Entrance Losses can be reduced by accelerating the flow gradually and eliminating the vena contracta

Head Loss in Valves ä Function of valve type and valve position ä The complex flow path through valves can result in high head loss (of course, one of the purposes of a valve is to create head loss when it is not fully open) What is the maximum value of Kv? ______

Solution Technique: Head Loss ä Can be solved explicitly

Solution Technique 1: Find D ä Assume all head loss is major head loss ä Calculate D using Swamee-Jain equation ä Calculate minor losses ä Find new major losses by subtracting minor losses from total head loss

Solution Technique 2: Find D using Solver ä Iterative technique ä Solve these equations Use goal seek or Solver to find diameter that makes the calculated head loss equal the given head loss. Spreadsheet

Exponential Friction Formulas ä Commonly used in commercial and industrial settings range of ____ ä Only applicable over _____ __ data collected ä Hazen-Williams exponential friction formula C = Hazen-Williams coefficient

Head loss: Hazen-Williams Coefficient C 150 140 130 120 110 100 95 60 -80 Condition PVC Extremely smooth, straight pipes; asbestos cement Very smooth pipes; concrete; new cast iron Wood stave; new welded steel Vitrified clay; new riveted steel Cast iron after years of use Riveted steel after years of use Old pipes in bad condition

Hazen-Williams vs Darcy-Weisbach ä Both equations are empirical ä Darcy-Weisbach is dimensionally correct, and ____. preferred ä Hazen-Williams can be considered valid only over the range of gathered data. ä Hazen-Williams can’t be extended to other fluids without further experimentation.

Air Release Valve http: //www. apcovalves. com/airvalve. htm http: //www. ipexinc. com/industrial/ airreleasevalves. html

Pipes http: //www. ipexinc. com/industrial/4080_pipe. html

Additional PVC Pipe Schedules Presión de Trabajo RD-13. 5 22. 4 kg/cm 2 315 psi RD-21 14. 0 kg/cm 2 200 psi RD-26 11. 1 kg/cm 2 160 psi RD-32. 5 8. 6 kg/cm 2 125 psi http: //www. prodigyweb. net. mx/pofluisa/pvc. htm#tuboce mentar

Surveying q Vertical angle Dx r Dz

Surveying using Stadia Vertical angle q Dx r Dz b c The reading is on a vertical rod, so it needs to be corrected to the smaller distance measured perpendicular to a straight line connecting theodolite to the rod. a

Horizontal Distance Trig identity M is the Stadia multiplier (often 100) c is the Stadia reading

Vertical Distance Trig identities

Pipe Length (along the slope)