HYDRAULICS_4

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HYDRAULICS_4

• Design of Irrigation Systems
• by
• László Ormos

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DESIGN OF IRRIGATION SYSTEM

• Options
• The rule of 20 is applied to all the sprinklers
  on the same subplot. Any excess pressure over 20
  between subplots is controlled by flow pressure
  regulators.
• The rule of 20 is applied to a single lateral,
  and pressure regulators control the difference
  pressure between the laterals.(It is common in
  drip systems.)
• The difference pressure along the lateral exceeds
  the 20 head loss by any desired amount. Flow
  regulators inside the emitters or pressure
  regulator in the sprinkler riser control the
  excess pressure. (It enables the use of a longer
  lateral pipe or smaller diameter than permitted
  by options 1 or 2.)

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DESIGN OF IRRIGATION SYSTEM Option 1

• A PE lateral pipe with 10 micro-sprinklers is
  spaced 10m
• apart. The first sprinkler is 5m away from the
  inlet of lateral.
• The flow rate of selected sprinkler is qs120l/h,
  the required
• pressure head is hs20m. The riser height is
  0.15m. What
• is the appropriate lateral pipe diameter if
  options 1, 2, and 3
• are taken into consideration?
• The length of lateral is as follows
• The flow rate of the lateral pipe is

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DESIGN OF IRRIGATION SYSTEM Option 1

• For a 20mm PE pipe the hydraulic gradient out of
  a slide
• ruler or monograph is J19.
• 3. The head loss of a 20mm plain PE pipe is
• The head loss for 10 sprinklers is as follows
  where coefficient F100.384
• Since hf??hmax0.2 hs the diameter of lateral
  pipe is too small.

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DESIGN OF IRRIGATION SYSTEM Option 1

• For a 25mm PE pipe the hydraulic gradient out of
  a slide
• ruler or monograph is J6.2.
• 5. The head loss of a 25mm plain PE pipe is
• 6. The head loss for 10 sprinklers is as follows
  where coefficient F100.384
• Since hflt?hmax0.2 hs the diameter of lateral
  pipe is good.
• 7. The required inlet lateral pressure is

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DESIGN OF IRRIGATION SYSTEM Option 2

• The permitted pressure variation along the
  lateral can be 4m,
• therefore, a combination of different diameter
  pipes can be
• used. The applied pipes are 25mm and 20mm
  diameter
• ones.
• Pressure regulators will be installed by the
  inlets of laterals to
• compensate greater head loss than 20.
• Let the first 25mm diameter pipe be along 35m
  (n254) and 20mm diameter pipe be along 60m
  (n206) as it can be seen below

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DESIGN OF IRRIGATION SYSTEM Option 2

• 2. The flow rate for 25mm pipe along 60m is
  calculated as follows
• 3. The hydraulic gradient out of a table or slide
  ruler for 25mm pipe and flow rate of 0.72m3/h is
  2.5.

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DESIGN OF IRRIGATION SYSTEM Option 2

• 4. The head loss for 25mm pipe along 60m is as
  follows
• 5. The head loss for 6 sprinklers is as follows
  where coefficient F60.458
• 6. Previously the head loss for 25mm pipe along
  95m, 10pcs of sprinklers and Q1.2m3/h has been
  computed which was 2.261m (see Option 1), then
  the head loss for 25mm pipe along 35 with four
  sprinklers is

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DESIGN OF IRRIGATION SYSTEM Option 2

1. The flow rate for 20mm pipe along 60m with six
   sprinklers is as follows
2. The hydraulic gradient out of a table or slide
   ruler for 20mm pipe and flow rate of 0.72m3/h is
   8.
3. The head loss for 20mm pipe along 60m is as
   follows
4. The head loss for 20mm pipe with six sprinklers
   is

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DESIGN OF IRRIGATION SYSTEM Option 2

• The total head loss along the combined lateral
  pipe with 35m length of 25mm pipe and 60m length
  of 20mm pipe is as follows
• Since hf,95lt?hmax0.2 hs the diameter of lateral
  pipe is good.
• 12. The required inlet pressure by the last
  lateral is

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DESIGN OF IRRIGATION SYSTEM Option 3

• The lateral pipe can be designed either with flow
  regulators
• or pressure regulators in every emitters, the
  sprinklers or
• the drippers.
• Therefore, the diameter of pipe can be reduced.
  The cost
• of reduced pipe must be less than the additional
  cost for
• energy and regulators.
• Principal theory of Option 3 is that unlike
  Option 1 and
• Option 2, in case of Option 3 the entire head
  loss along
• lateral pipe is added to the lateral inlet
  pressure.
• In case of 20mm diameter, the head loss hf6.93m
  (see Option 1).
• Therefore, the required inlet pressure of the
  lateral pipe is as follows

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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