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© Irrigation Association
Effect of Irrigation
© Irrigation Association
Calculate Hydraulic
Requirements
Chapter 4:
© Irrigation Association
Predicting Friction Losses
Calculating friction lossesHead (pressure) required at the
pivot pointBased on what the pivot “thinks” it is
irrigatingCalculating pressures, sprinkler by
sprinklerMainline layout and sizing
Page 59
© Irrigation Association
Supply (Main) Line – 1,000 gpm – 8” (approx) pipe
© Irrigation Association
1,000 gpm Total – Identical Outlets at 40’ – 8” (approx.) Pipe
© Irrigation Association
1,000 gpm total – 125 gpm end gun – sprinklers at 20’ 8” (approx) pipe
Page 62
© Irrigation Association
Practice Session on Friction Loss
Hydraulic Length Lateral Size (single
size) C = 145 (why?) Lateral friction loss Span Lengths
(Obstacles?)
Page 66
Friction Loss
• Hazen-Williams equation
© Irrigation Association
1.852 1.852
4.87
1002.207f
QH
C D
01
00
20
03
00
40
05
00
60
07
00
80
09
00
10
00
11
00
12
00
13
00
13
23
13
20
14
000100200300400500600700800900 GPM w/o Endgun
GPM w/Endgun
System Length (feet)
Gal
lon
s P
er M
inu
te
Center Pivot Flow Rate Distribution
• In a system having an end gun, the flow rate at the end of the pipe is equal to the discharge of the end gun, rather than zero
© Irrigation Association
Hyrdualic length
where:
Lh = the equivalent hydraulic length of the center-pivot lateral, ft (or m)
L = the physical length of the center-pivot lateral, ft (or m)
Qb = the “base” discharge for the basic circle, gpm (or L/s)
Qs = the discharge for all of the area irrigated by the center pivot lateral, gpm (or L/s) (generally, Qs = Qb + Qg)
Qg = the discharge of the end gun, if one is present, gpm (or L/s).
© Irrigation Association
b
gbh
b
sh Q
QQLLor
Q
QLL
© Irrigation Association
Multiple Sized Laterals
8 inch 6-5/8 inch
Page 66-78
© Irrigation Association
Additional Hydraulic Calculations
Calculating Velocity & Velocity HeadPressure Required at the Pivot
PointSimple Energy ConservationImpact of Pressure Regulators
Elevation Considerations
Page 80
© Irrigation Association
Friction Losses at Tower Joint?H-W “C”?
Page 84
Energy Balance EquationBernoulli
Accounts For Total Energy of water between two points
• Pressure head• Elevation head• Velocity head• Friction head
Energy Balance EquationBernoulli - Head
P1 + z1 + V12 / 2g = P2 + z2 + V2
2 / 2g – Hf 1-2 EQ. 4-16
Where:P1 = Pressure head at point 1, feet Z1 = Elevation head at point 1, feetV1
2 / 2g= Velocity head at point 1, feetP2 = Pressure head at point 1, feet z2 = Elevation head at point 1, feetV2
2 / 2g= Velocity head at point 1, feetHf 1-2 = Friction loss between points 1 and 2, feet
© Irrigation Association
Practice ExampleDesign Project
Minimum Sprinkler Pressure
Elevation Rise Nozzle Height Above
Ground Pivot Pressure at
Ground Level
Page 88
© Irrigation Association
• Look at each section of one-diameter pipe separately
• Compare to a pivot with all that size pipe
• Add the friction losses together
Calculating PressureSection by Section
Page 89
© Irrigation Association
Section-by-section
50
52
54
56
58
60
62
64 P
ressure
, P
SI
0 200 400 600 800 1000 1200 Distance along lateral, feet
Line (Lateral) Pressure Nozzle Pressure (drops)
Section-by-Section Calculation
© Irrigation Association
0 2 4 6 8
10 12 14 16
Nozzle
Dis
charg
e, gpm
0 200 400 600 800 1000 1200 Distance along lateral, feet
Required Est. (Manuf.)
Est. (Calc.) Est. (Complete.)
Section-by-Section Calculation Method
Nozzle discharge
© Irrigation Association
End Guns & Corner Systems Have Significant Effects on Hydraulics
© Irrigation Association
Varying Pivot Flow Rates(Affects Pump Selction)
© Irrigation Association
Affect on Pumping Requirements
© Irrigation Association
Mainline Layout and Sizing
Layout of clusters Economic vs.
hydraulically “best” solution
More small diameter pipe vs. less larger pipe
Page 89
© Irrigation Association
Mainline Configuration
a. Length of feeder pipe = 6 x lateral length
b. Length of feeder pipe
= 7.7 x lateral length
Page 90
© Irrigation Association
Supply (Main) Line Selection
Friction Losses in Supply (Main) LinePressure required at start
Pipe diameter (velocity method)Friction lossesSizing using economic criteriaSurge Pressures (Water hammer)
Appendix DValve placement, Air-vac, Pressure relief,
Sediment traps
© Irrigation Association
Screening Requirements
© Irrigation Association
Practice Example
Pages 94-96