3. C factor
Pipe Material C
Plastic (4-in diameter or larger) 150
Plastic (2- to 3-in diameter) 140
Aluminum (with couplers every 30 ft) 130
Galvanized steel 130
Epoxy-coated steel 145-150
Polyethylene lined steel 135-145
Steel (new) 130
Steel (15 years old) 100
Butyl rubber drop tubes 150
Rigid drop tubes 145
4.
5. Multiple outlet factor
ο Christiansen's equation for computing
the reduction coefficient (F) for pipes
with multiple, equally spaced outlets
where the first outlet is Sl from the
mainline is:
F = Reduction factor
N= number of sprinklers
M= exponent depends on which friction equation is
6. Caveats
ο For pipes that have no flow past the last
outlet (sprinkler)
ο Cannot be directly applied to the estimation
of friction losses only partway down the
lateral pipe.
ο Assumes that each outlet has a constant
discharge,
ο Equations are for use with laterals having
nearly constant discharge per outlet, such as
for hand lines, wheel-lines, solid set (fixed),
and linear-move systems.
ο The value of F approaches 0.36 when N >
35, which is often the case with sprinkler
laterals.
7. Applying Irrigation Water in Circles (vs. squares)
Why itβs a little trickier?
In a rectangular system each
sprinkler applies water to an
Identically sized Area (A)
In a circular system the area
increases as the radius increases
Hence, each sprinkler applies
water to a differently sized Area (A)
1 4
3
2
A1 = A2 = A3 = A4 A1 < A2 < A3 < A4
1 2 4
3
8. Center pivot reduction factor
ο Outlet discharge varies with distance from the center
pivot
ο Flow rate in the pipe decreases more slowly at the
upstream end
ο Average velocity along the length of the lateral is
higher.
ο F value is higher on a center-pivot lateral than on
laterals for other types of sprinkler systems
ο For center pivot F = 0.555 (> than 35 sprinklers)
10. Hydraulic length
ο No flow past the last outlet
β¦ End gun?
Lh = Hydraulic length (ft)
L = Base pivot length (ft)
Qb = base pivot flow rate (gpm)
Qg = end gun flow rate (gpm)
πΏβ = πΏ
ππ + ππ
ππ
