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Emitter Selection

Emitter Selection . Emitter types. Long path emitters, Short orifice emitters, Vortex emitters, Pressure compensating emitters, Porous pipe or tube emitters. Further classification. Point source Line source Sprays. Microsprinkler /Sprays. Orifice control emitters

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Emitter Selection

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  1. Emitter Selection

  2. Emitter types • Long path emitters, • Short orifice emitters, • Vortex emitters, • Pressure compensating emitters, • Porous pipe or tube emitters.

  3. Further classification • Point source • Line source • Sprays

  4. Microsprinkler/Sprays Orifice control emitters • Flow rate at any given pressure is governed primarily by the orifice diameter • Turbulent flow devices - flow rate is regulated by dissipating energy. • Flow velocities are greater and the potential for clogging is less than for laminar flow devices. • Flow rates are less sensitive to pressure (emitter exponent is about 0.5) and less sensitive to water temperature than are laminar flow devices. • Vortex Control Emitters • Less sensitive to pressure variations than laminar or turbulent flow emitters (emitter exponent is about 0.4). • Low pressure area formed in the center where the orifice is located caused by vortex – reducing energy of water at the discharge point & a controlled flow rate. • Emitter flow rate is controlled by vortex design and orifice diameter. • Pressure Compensating Emitters • Excess inlet pressure used to deform a diaphragm to control the flow rate. • As the pressure increases, the diaphragm restricts the passage diameter. • Pressure compensating emitters are designed to discharge at a fairly constant rate over a wide range of pressures (emitter exponent is normally less than 0.1). • Drawbacks - the elasticity of the diaphragm may change over time. • Diaphragms often retain some moisture when the pressure is off and bacteria growth ants seeking food source may result in clogging or destruction of diaphragm.

  5. Stake Assemblies • Stake assemblies raise emitter 8 inches above the ground. • larger wetting pattern • water dispersed over weeds and grass. • 4 mm ID tubing made of vinyl or polyethylene (PE). • Spaghetti tubing length depends on grower preference, but typically is 2 to 4 ft long

  6. Wetting Patterns spinner • Important consideration in sandy soils or where root zones are shallow. • Larger wetting patterns are often preferred for tree crops. • Emitters flow needs to correspond with diameter to manage them effectively. • When discharge is ≤0.08 in/hr, it requires very long run times to move the water into the mid and lower root zone. • Potential for more wind drift, evaporation, and wetting of non-productive areas as the diameter increases. • High density plantings • Most effective to provide each tree with a smaller pattern emitter than to install larger pattern emitters on every other tree. • Wetting pattern from larger diameter emitters is often distorted by interference from tree trunks and low branches • However, small wetting patterns associated with low flow rates can lead to more plugging problems, particularly with the orifice control emitters. spray

  7. (a) spinner Catch distribution patterns • Spinners have much higher application uniformities than the spray-type emitters. • Both types have higher uniformity with high pressure 20 psi or higher compared 15 psi. • Spinners - most of the wetted area receiving near-average application depths, with nearly continuous wetting throughout the pattern. • Spray- wetted spokes radiating from the emitter with 50-75% of the area within the coverage diameter receiving little or no wetting. • Lateral movement of water in the soil may help compensate for this in the root zone to varying degrees depending on the soil type (b) spray

  8. Class Activity

  9. Emitter Selection Criteria 1. Inexpensive 2. Closeness of discharge-pressure relationship to design specifications. 3. Easy to Install 4. Susceptibility to clogging 5. Pressure compensating 6. Not affected by temperature and solar radiation 7. Reliablityof discharge-pressure relationship over a long period of time

  10. Manufacturing variation • The variations in emitter passage size, shape, and surface finish that do occur are small in absolute magnitude but represent a relatively large percent variation.

  11. Emitter manufacturing variability Coefficient of manufacturing variation (CV) is a statistical description of how uniformly the flow rate of each manufactured emitter is in relation to one another

  12. Example

  13. Flow rate • Flow is characterized by the following equation

  14. Emitter Exponent • is important and critical to the design, management and uniformity of the Micro system • The exponent (x) measures the flatness of the discharge-pressure curve.

  15. Flow rate/pressure relationship for a laminar flow emitter(X=1.00)

  16. Flow rate/pressure relationship for a turbulent flow emitter (X=0.50)

  17. Flow rate/pressure relationship for a pressure compensated flow emitter (X=0.0)

  18. PC emitters • Even the best PC emitters only have a certain range of pressures over which they provide good pressure compensation. • A PC emitter may retain its compensating abilities at very high pressures. But when pressures exceed 35 psi or so, emitters tend to pop off the hose, or hoses tend to pop out of their fittings

  19. System EU for a PC emitters • The EU for a PC emitter is still dependent on the manufacturing variation CV • They do not have a discharge exponent of exactly 0.0, even though that is what is claimed

  20. How to get x and K • K and x may be obtained from manufacture or calculated • For sprinkler x is nearly always 0.5 • For pressure compensating x ~ 0.0

  21. Example Given: q1 = 1.5 gph, q2 = 2.0 gph, P1 = 12 psi, P2 = 20 psi Find: x and K

  22. Solution

  23. Practice problem

  24. Emitter spacing

  25. Optimum Spacing • Optimum spacing is approximately 80% of the wetted area (7.2*.8= 5.76ft)

  26. Wetted area overlapWhat is the optimum emitter spacing?Closest together? Farther away?

  27. The optimum area is a rectangle

  28. Soil wetted area 1 Based on an emitter flow rate of 1 gph (3.785 L), the estimated Aw is given as a rectangle with the wetted width (Sw) equal to the maximum expected diameter of the wetted circle and the optimum emitter spacing (S’e) equal to 80 percent of that diameter.

  29. Some times two or more rows are needed

  30. Number and spacing of emitters. • …..shall be adequate to provide water distribution to the plant root zone and percent plant wetted area (Pw).

  31. Example problem Given: Tree spacing of 24’x24’, Root depth 4’ Single drip hose Loam soil ( medium texture, Homogeneous) Desired wetted area 50% Find: # of emitters and emitter spacing

  32. Solution Number of emitters From table 7-14 Emitter wetted area = 7.2 Tree area = 24x24 =576 Desired wetted area = 576 *.5 =288 Required emitters = 288/7.2= 40

  33. Practice problem

  34. System capacity. • ….shall be adequate to meet the intended water demands during the peak use period • ….shall include an allowance for reasonable water losses (evaporation, runoff, and deep percolation) during application periods. • …shall have the capacity to apply a specified amount of water to the design area within the net operation period.

  35. System capacity Continued • should have a minimum design capacity sufficient to deliver the peak daily irrigation water requirements in 90% of the time available, but not to exceed 22 hours of operation per day.

  36. Emitter Flow rate qa

  37. Watering strategies • Select emitter based on water required • Calculate set time

  38. Adjust flow rate or set time • If Ta is greater than 22 hr/day (even for a single-station system), increase the emitter discharge • If the increased discharge exceeds the recommended range or requires too much pressure, either larger emitters or more emitters per plant are required.

  39. Select the number of stations • If Ta ≈ 22 h/d, use a one-station system (N = l), select Ta < 22 hr/day, and adjust qa accordingly. • If Ta <11 h/d, use N = 2, select a Ta <11, and adjust qa accordingly. • If 12 < Ta < 18, it may be desirable to use another emitter or a different number of emitters per plant to enable operating closer to 90 percent of the time and thereby reduce investment costs.

  40. Determine average emitter pressure head (Pa) Where: qa= average emitter flow rate (gph) Pa = average pressure (psi) x = emitter exponent K = flow constant

  41. Average depth applied Where: Fn = Average applied (in) e = number of emitters qa=average emitter flow rate (gph) Ta = set time (hrs) Sp = Plant spacing (ft) Sr = Row spacing (ft)

  42. Determine total system flow rate Where: A = field area, ac. e = number of emitters per plant. N = number of operating stations. qa = average or design emission rate, gph. Sp = plant spacing in the row, ft. Sr = distance between plant rows, ft

  43. Practice problem

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