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Hydraulic Structures in Irrigation Distribution Systems

Hydraulic Structures in Irrigation Distribution Systems. Chapter 5. Valves in pipe networks. On-Off valves Throttling valves Pressure Regulating Valves Check Valves Surge Control Valves Pressure Relief Valves Vacuum relief valves (Air release valves. Pressure regulating valve.

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Hydraulic Structures in Irrigation Distribution Systems

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  1. Hydraulic Structures in Irrigation Distribution Systems Chapter 5

  2. Valves in pipe networks • On-Off valves • Throttling valves • Pressure Regulating Valves • Check Valves • Surge Control Valves • Pressure Relief Valves • Vacuum relief valves (Air release valves

  3. Pressure regulating valve

  4. Flow measurements in pipelines • differential pressure flow meters • Venturi meters • Orifice meters • Elbow meters Rotating mechanical flow meters Bypass flow meters Ultrasonic flow meters Magnetic Flow meters

  5. Magnetic flow meters

  6. Ultrasonic flow meters

  7. Control structures in open channels • Intake structures • Check structures • Check-drops • Drop and chute structures

  8. Flow measurements in open channels • Volumetric method • Velocity area method • Using float method • Current meters • Control sections • Thin plate weirs • Broad Crested weirs • Flumes

  9. Thin plate weirs

  10. Assumptions • no head losses (E1 = E2) (the means no significant turbulence) • water surface elevation remains constant, note: this is physically impossible, but actual errors are small • pressure at crest (station 2) = Patmo throughout depth.

  11. Thin weirs- full width

  12. For Cd=0.611, weir equation becomes: • For SI units, g= 9.81 m/s2, or • For foot units, g=32.2 ft/s2, or • In general, discharge could be given by: • Where, C is a weir coefficient.

  13. Contracted rectangular weir

  14. Triangular weir

  15. Broad crested weir

  16. Weirs • Advantages: • Accurate measurement. • Simple and easy to construct with non-obstruction by moss (type of algae) or floating materials. • Durable • Disadvantages: • Require considerable fall of water surface. • Deposition of sand, gravel and silt upstream of weirs

  17. Example • An end-contracted weir of total length 286 ft and crest height 5 ft is used to discharge water without exceeding a head of 2.5 ft from a tank 300 ft wide. The weir carries piers that are 10 ft clear distance apart and 2 ft wide, to support the footway. Determine the discharge. Cd = 0.6

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