SDI burial depth CropBurial DepthLine spacing Trees and grapes>16 inches (0.4m)As per row spacing Berries, Vines> 8 inches (0.2m)As per row spacing Row crops – corn, cotton ≥ 12 inches (0.3m) 24 – 80in (0.6 -2.03m) Raised beds – single row Tomatoes, melons 2-4 inches (0.05 – 0.1m)One line 4- 6 inches (0.1 - 0.15m) from center of bed Raised beds – double row Onions, peppers, strawberries 2-4 inches (0.05 – 0.1m)One line down center of bed Raised beds – double row > 30 inch (0.75m) bed width 3-6 inches (0.075 -0.15m)Two lines spaced ½ the bed width apart
Tape orientation ◦ One tape or more per bed ◦ Holes upward Tape thickness ◦ Trend toward thicker Tape materials ◦ Stretch vs. breakage
Lateral Line Design Important lateral characteristics ◦ Flow rate ◦ Location and spacing of manifolds ◦ Inlet pressure ◦ Pressure difference
Standard requires Pipe sizes for mains, submains, and laterals shall maintain subunit (zone) emission uniformity (EU) within recommended limits Systems shall be designed to provide discharge to any applicator in an irrigation subunit or zone operated simultaneously such that they will not exceed a total variation of 20 percent of the design discharge rate.
Design objective Limit the pressure differential to maintain the desired EU and flow variation What effects the pressure differential ◦ Lateral length and diameter Economics longer and smaller ◦ Manifold location ◦ slope
Allowable pressure loss (subunit) This applies to both the lateral and subunit. Most of the friction loss occurs in the first 40% of the lateral or manifold Ranges from 2 to 3 but generally considered to be 2.5 D P s =allowable pressure loss for subunit P a = average emitter pressure P n = minimum emitter pressure
Manifold spacing Spacing is a compromise between field geometry and lateral hydraulics Lateral length is based on allowable pressure - head difference. Have the same spacing throughout the field in all crops
Manifold Location More efficient to place in middle two laterals extend in opposite directions from a common inlet point on a manifold, they are referred to as a pair of laterals. Manifold placed to equalize flow rates on the uphill and downhill laterals
Or Or use equation Where Fe= equivalent length of lateral, ft) K = 0.711 for English units) B = Barb diameter, in D = Lateral diameter, in
Adjusted length L’ = adjusted lateral length (ft) L = lateral length (ft) Se = emitter spacing (ft) fe = barb loss (ft)
Barb loss More companies are giving a K d factor now days
Example Given: lateral 1 diameter 0.50”, qave=1.5gpm,Barb diameter 0.10” lateral 2 diameter 0.50”, q ave =1.5gpm, k=.25 Both laterals are 300’ long and emitter spacing is 4 ft Find: equivalent length for lateral 1 and h etotal for lateral 2
Design Considerations Select emitter/flow rate Determine required operating pressure Calculate friction loss ◦ Quick estimate use multiple outlet factor ◦ Manufacture’s software ◦ Built spreadsheet Decide whether to use single or paired laterals Make adjustments Determine Δh and hose EU
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