HYDRAULICS_3

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HYDRAULICS_3

• Design of Irrigation Systems
• by
• László Ormos

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Lateral pipes

• The hydraulic gradient of a lateral is like a
  pipe with multiple
• outlets with even sections.
• Feature of lateral pipe decreasing discharge
  along the flow.
• Calculation of head loss
• head loss is calculated as a pipe without
  outlets,
• then outcome is multiplied by the coefficient F
  which depends on the number of outlets n.

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Lateral pipes

• Features of the lateral
• the average head (ha ) along the lateral pipe is
  equal to the head (hs ) of selected equipment ,
• the selected equipment is located on the first to
  fifths of a lateral pipe, as it seems
• three quarter of lateral head loss dissipates
  along the first two fifth section.

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Lateral pipes

• A flat field, 360x360m, is irrigated with a hand
  moved
• aluminium lateral pipe (C140). The laterals
  water szupply
• is from a submain crossing the center of field.
  The selected
• sprinkler is Naan 233/92 with nozzle of 4.5mm,
  the required
• pressure hs25m?2.5bar,and the flow rate
  qs1.44m3/hr.
• The space between sprinklers is d12m apart, and
  the
• location of the first sprinkler is 6m away from
  the lateral
• inlet. The riser height to the sprinkler is 0.8m,
  and the
• diameter is ¾.
• What a diameter of lateral is required?
• How much is the required pressure head at the
  lateral inlet?

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Lateral pipes

• The topography
• The number of sprinklers is as follows

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Lateral pipes

• The length of lateral pipe is as follows
• The flow rate of the lateral pipe is
• The maximum head loss (20) throughout the field
  is as follows

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Lateral pipes

• For a 2 aluminium pipe the hydraulic gradient
  out of a
• table or a ruler is J165.
• The head loss in 2 plain aluminium pipe is
• The head loss for 15 sprinklers is as follows
  where coefficient F150.363
• Since ?hf? ?hmax the diameter of lateral pipe is
  too small.

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Lateral pipes

• For a 3 aluminium pipe the hydraulic gradient
  out of a
• table or a ruler is J25.
• The head loss of a 3 plain aluminium pipe is
• 9. The head loss for 15 sprinklers is as follows
  where coefficient F150.363
• Since ?hf ? ?hmax the diameter of lateral pipe is
  good.
• The reserved head loss for the head loss of
  submain is the difference
• of ?hf and ?hmax
• ?hmax- ?hf 5m-1.579m3.421m.

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Lateral pipes

• The pressure head ?hu at the lateral inlet is
  determined by the following
• expression
• where
• hu is the lateral inlet pressure head,
• hs is the pressure head of selected sprinkler (or
  dripper),
• hf is the head loss along lateral,
• hr is the riser height from the lateral to the
  sprinkler.
• The required pressure head at the inlet of 3
  lateral pipe is the following

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Lateral pipes

• Pressure requirement on slope
• Once a lateral is laid out along a slope with
  difference elevation between
• its two ends. The required pressure at the
  lateral inlet is computed as
• follows
• where
• means the adjustment for upward slope,
• means the adjustment for downward slope.

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Lateral pipes

• Following the previous example, let us take into
  consideration 2
• downward slope and a 2 upward slope.
• The difference elevation between the two ends of
  lateral is as follows
• Inlet pressure with 2 downward slope
• 3. Inlet pressure with 2 upward slope

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Lateral pipes

• The 20 Rule
• In order to maintain up to 10 difference in flow
  rate between any
• emitters within a plot, then the pressure
  difference inside a plot should
• be up to 20.
• The relationship between pressure and flow rate
  is as follows
• 
  ,
• where
• Q is the flow rate,
• C, K are constant values depended on the type of
  emitter,
• A is the cross section area of a nozzle,
• H is the pressure head,
• x is the exponent which depends on the flow
  pattern inside a nozzle usually x0.5 for
  sprinklers, x0 for emitter with flow regulator,
  x0.5 for turbulence flow type like the
  labyrinth emitters, xlt0.5 for very low flow rate
  emitter, and x1 for laminar flow type emitter.

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Lateral pipes

• The question is, what the expected difference
  discharge is
• between the two ends of the lateral sprinkler
  when the
• hydraulic gradient along the lateral pipe is 20?
• The flow rate of a sprinkler is as follows
• The relationship between two identical sprinklers
  which have a same constant K, and 20 pressure
  difference is the following
• , and since

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Lateral pipes

• A PE lateral pipe, grade 4, has n10
  micro-sprinklers at
• ds10m apart. The selected sprinkler has a flow
  rate
• qs120 l/h at hs20m pressure head. The risers
  height is
• hr0.15m. What is the appropriate diameter of
  pipe?
• Length of lateral
• The total flow rate for one lateral is as
  follows
• The maximum allowable head loss in the entire
  plot is

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Lateral pipes

• The hydraulic gradient out of a slide rule or
  monograph for a 20mm PE pipe and Q1.3m3/h is
  J19, and coefficient F100.384.
• Since ?hfgt ?h therefore, a larger pipe is
  required.
• Let the larger pipe is a 25mm PE pipe which has
  hydraulic gradient J6.2 at Q1.2m3/h.
• Since ?hflt?h therefore, the pipe is useful.

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Lateral pipes

• 6. The required pressure at the lateral pipe
  inlet is

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References
Azenkot, A.(1998)Design Irrigation System.
Ministry of Agricul- ture Extension Service
(Irrigation Field service), MASHAV Israel Dr.
Avidan, A.(1995)Soil-Water-Plant Relationship.
Ministry of Agriculture Extension Service
(Irrigation Field service), CINADCO, Ministry of
Foreign Affairs, MASHAV, Israel Sapir, E.-Dr. E.
Yagev (1995)Drip Irrigation. Ministry of
Agricul- ture and Rural Development, CINADCO,
Ministry of Foreign Affairs, MASHAV,
Israel Sapir, E.-Dr. E. Yagev (2001)Sprinkler
Irrigation. Ministry of - culture and Rural
Development, CINADCO,Ministry of Foreign
Affairs, MASHAV, Israel Eng. Nathan, R.
(2002)Fertilization Combined with Irrigation
(Fertigation). Ministry of Agriculture and Rural
Development, CINADCO,Ministry of Foreign Affairs,
MASHAV, Israel