Lecture 13
Center Pivot Nozzling
I. Cen
e reduced closer to the
slower speed at inner points;
q
r
∝
r)
•
e required near the end of the center pivot, spray
nd the spray drops nearest the pivot
•
•
•
ter Pivot Nozzling
•
The wetted width of the application package can b
pivot point because the towers are moving at a
therefore, the application intensity (AR) is less (
Generally, if spray booms ar
drops can be used toward the center, a
point will produce something like a fine mist
At the far end of the lateral the application may be more like a torrential rain
Generally, impact and spray sprinklers would not be mixed on a center pivot
because the pressure requirements are substantially different
The minimum wetted width at any radius r along the pivot (for an elliptical
pattern) can be calculated as:
=
d
r
x
pa
8rU
w
60T AR DE
(274)
where AR
x
is the maximum permissible application rate (mm/min) according
, and vegetative cover; U
d
is in mm/day; T
pa
d as a fraction
es zero for r
→
0
m/min) at radius r at the ground using a device
with wetted diameter w
d
should be:
to limits imposed by the soil, slope
is in hrs/day; and DE
is expresse
•
Note that w
r
approach
•
A suitable application device can then be selected for radius r such that the
wetted diameter of the device, w
d
, is greater or equal to w
r
(w
d
≥
w
r
)
The actual application rate (m
•
'
d
e
e
r
d
rU R O
AR
7.5Tw
≤
(275)
•
unt for evaporation
and wind drift losses, and pipe leakage
0/8 = 7.5 and that we are using f = 1 day
Divide by R in the above equation to obtain AR at the nozzle
ing an elliptical pattern) along the
lateral is:
The term “R
e
O
e
” is included in the above equation to acco
•
Note that 6
•
e
•
The wetting time at any radius r (assum
(
)
f
t
Sprinkle & Trickle Irrigation Lectures
Page 155
Merkley & Allen
r
r
4D
t
AR
π
where D is the total cumulative application (d R
O
=
(276)
f
e
e
)

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