Design of sprinkler laterals, design of main line, selection of pumps,
1. 1
Sprinkler Irrigation System:
Design of Sprinkler Laterals, Design of Main Line, Selection
of Pumps
Speaker
Dr. Jitendra Sinha
Associate Professor
Department of Soil and Water Engineering,
SVCAETRS, FAE, IGKV, Raipur
jsvenusmars@gmail.com
7000633581
2. Design of Laterals
• Laterals supply water to the Sprinklers
• Pipe Sizes are chosen to minimize the pressure
variations along the Lateral, due to Friction and
Elevation Changes.
• Select a Pipe Size which limits the total pressure change
to 20% of the design operating pressure of the
Sprinkler.
• This limits overall variations in Sprinkler Discharge to
10%.
4. • Sprinkler lateral has equally spaced sprinklers along its length.
• In the beginning the flow will equal the combined discharge of all
the sprinklers.
• This will decrease along the line until, at the farthest end, there
will be only the flow of the last sprinkler.
• Therefore, the friction loss in a lateral will be much less than if
the total flow were carried through the entire length of the line.
• However, many authorities advise against tapering of pipe
diameter in lateral as it then become necessary to keep the
various pipe sizes in the same relative position
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More discharge
Less discharge
Should be do this?
6. • It is recommended that the total pressure variation in the lateral,
when practicable should not be more than 20% of the higher
pressure. If the lateral runs uphill or downhill allowance for these
differences in elevation should be made in determining the
variation in head.
• If the water runs uphill then less pressure will be available at the
nozzle if it runs downhill there will be a tendency to balance the
loss of head due to friction.
• It is necessary to compute the friction loss in the lateral line where
flow decreases along its length.
• A simple approximate procedure devised by Christiansen has
become standard. First ascertain the friction loss with full flow to
the end of the line, using appropriate formulae are the values given
in appendix F, table F1 to F5.
• Next refer to table 12.5 for F factors by which the friction loss will
with full flow to the end of the line are multiplied to obtain the
approximate friction loss in the lateral. 6
8. Determine the friction loss Hf in 396 metres of a 15 cm diameter
aluminium pipe which coupler made of 12 metre sections having 22
sprinklers spaced 18 metres apart, each discharging 1.58 litres per
second. The first sprinkler is 18 metres from the main.
• Total discharge of the system = 22 x 1.58 = 34.7 lps
• From appendix F table F1 the friction loss in a 15cm aluminium
pipe with the discharge of 34.7 litre per second = 2.52 metres
per hundred metres.
• From this 3% is deducted for 12 metres length of sections (see
footnote on appendix F table F1)
• From table 12.5 the value of F factor for 22 sprinklers when the
first sprinkler is one sprinkler interval from the main = 0.357
• Hf =
396 𝑋 252 𝑋 97 𝑋 0.357
100 𝑋 100
= 3.45 metres
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10. • The design capacity for sprinklers on a lateral is based on the average
operating pressure. Where the friction loss, Hf, in the laterals is within
20% of the average pressure, the average head, Ha, for design in a
sprinkler line can be expressed approximately by: Ha = 𝐻0 +
𝐻 𝑓
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in which H0 is the pressure at the sprinkler on the farthest end. Thus,
the average pressure is equal to the pressure at the farthest and plus
one fourth the friction loss. Where the lateral is on nearly level land or
on the contour the head (pressure) Hn at the main is Hn = H0 + Hf
• By solving for H0 by substituting and by making allowance for differences
in elevation along the lateral : Hn = Ha + 3
𝐻 𝑓
4
+ 3
𝐻 𝑒
4
+ Hr
• He = maximum difference in elevation between the first and last
sprinklers on the lateral, in metres; Hr = the riser height, metres
• The term 3
𝐻 𝑒
4
is positive if the lateral runs up the slope and negative if
it runs down the slope. This term is an approximation since the
allowance for the difference in elevation varies with the number of
sprinklers on the lateral. 10
13. Lateral Discharge
• The Discharge (QL) in a Lateral is defined as
the flow at the head of the lateral where
water is taken from the mainline or submain.
• Thus: QL = N. qL Where N is the number of
sprinklers on the lateral and qL is the Sprinkler
discharge (m3/h)
14. Selecting Lateral Pipe Sizes
• Friction Loss in a Lateral is less than that in a Pipeline
where all the flow passes through the entire pipe
Length because flow changes at every sprinkler along
the Line.
• First Compute the Friction Loss in the Pipe assuming
no Sprinklers using a Friction Formula or Charts and
then:
• Apply a Factor, F based on the number of Sprinklers
on the Lateral (See Text for F Values)
15. Selecting Pipe Sizes of Submains and MainLines
• As a general rule, for pumped systems, the Maximum
Pressure Loss in both Mainlines and Submains should
not exceed 30% of the total pumping head required.
• This is reasonable starting point for the preliminary
design.
• Allowance should be made for pressure changes in the
mainline and submain when they are uphill, downhill or
undulating.
16. Main Line Pipe Size
• The main lines and sub man convey the required quantity of water at
the desired pressure to all lateral lines under maximum pressure
conditions.
• The selection should be based on economic considerations.
• Main line friction loss of about 3 metres for small systems and 12
metres for large systems may be allowed.
• The friction losses in main lines of the portable aluminium pipe can be
determined from the appendix F table F1 and F3.
• Semi rigid plastic irrigation pipelines manufactured of PVC or asbestos
compound are also used in sprinkler irrigation. In designing sprinkler
irrigation, water may be performed through low pressure reinforced
cement concrete pipes to a booster pump employed to pump water
directly in the laterals.
• Appendix F table f 4 and 5 provide respectively the fiction loss in PVC or
asbestos compound and asbestos cement pressure pipes. A nomograph
is used for plastic pipes.
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25. Pumping Requirements
• Maximum Discharge (Qp) = qs N Where:
• qs is the Sprinkler Discharge and
• N is the total number of Sprinklers operating at one
time during irrigation cycle.
• The Maximum Pressure to operate the system (Total
Dynamic Head, Pp) is given as shown.
27. • In selecting a suitable pump it is necessary to determine the
maximum total head against which the pump is working this
may be determined by
Ht = Hn + Hm + Hj + Hs
Ht = total design head against which the pump is working, m
Hn = maximum head required at the main to operate the sprinklers on the
lateral at the required average pressure including the riser height, m
Hm = maximum friction loss in the main and in the suction line, m
Hj = elevation difference between the pump and the junction of the
lateral and the main, m
Hs = elevation difference between the pump and the source of water after
drawdown, m
The amount of water that will be required is determined by multiplying the
number of sprinklers by the capacity of each. When the total head and rate
of pumping are known the pump may be selected from the rating curves or
tables furnished by the manufacturer.
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