57
A FIELD PLOT SPRINKLER IREGATOR
J. P. Riley
J. W. Wolfe
Miscellaneous Paper No. 57
September 1958
Agricultural Experiment Station
Oregon State College
Corvallis
The research reported in this manuscript was sponsored
in part by Western Regional Research Project W-28, eleven
Western States, Hawaii, and U. S. Department of Agriculture,
cooperating.
A FIELD PLOT SPRINKLER IRRIGATOR
by J. P. Riley and J. W. Wolfe*
Introduction
Moisture control and evaporation is one of the most
difficult variables to control in irrigation research. This
difficulty has resulted from the usual methods and techniques
of applying irrigation water to field experimental plots.
These methods have usually employed conventional farm equipment
of rotary sprinklers or perforated pipe. These are satisfactory
at the farm level where precise amounts of water applied are not
critical, and inequalities of distribution are not apparent in
the over-all yield. In experimental purposes, where close
control of the variables is necessary, these methods have many
disadvantages.
Uniformity of water application by rotary sprinklers or
perforated pipe is not ideal for experimental work. This uniformity is further affected when the rate of application exceeds
the soil infiltration rate and puddling results, or the pattern
of distribution is altered by winds. Also, these methods require
large experimental plots or they must be spaced at great distances apart. The first alternative requires a split-plot
experimental design, while under, the second the soil variability
between plots is increased.
Because of the obvious need in irrigation research for a
tool which would apply a precise amount of water at a given rate
and at a high degree of uniformity to a small, rectangular,
experimental plot, the project described in this bulletin was
initiated in 1954.
Objectives
Basic requirements of the proposed plot were:
1.
To apply water uniformly to a small plot.
2.
To apply water at a rate of 0.20 inches per hour or less.
3.
To apply water uniformly to the edges of a rectangular
plot with no spillover onto the adjacent plot.
*Research Assistant and Associate Agricultural Engineer, respectively, Oregon Agricultural Experiment Station
-2-
4. To apply a precise amount of water.
To be portable and easily moved from plot to plot and
site to site.
6.
To be adaptable or readily modified in accordance with
both the height of the crop and the dimensions of the
plot as required by other factors.
7.
To have a relatively low construction cost.
Review of previous work
Previous work in the development of a plot irrigator is
limited. The first plot irrigator of this kind built in this
country was developed at Pennsylvania State College (1). This
machine was later modified and used for irrigation research in
Georgia (2). Both irrigators employed the principle of a
traversing boom mounted on rails. An air-cooled gasoline engine
produced the traverse movement of the boom. Water from nozzles
mounted on the boom sprayed down over the crop. A third precision plot irrigator has been developed in England by the
National Institute of Agricultural Engineers (3). This irrigator
also was equipped with a traversing boom with mounted low pressure drip nozzles. Each of these three machines satisfied many
of the requirements listed in the previous section. However,
work at Oregon State College was initiated in the hope of finding
a simpler, less costly design that met all of the requirements.
Irrigator design
Oscillating boom
The first step in the design of the irrigator was the testing
of several commercially-built lawn and agricultural sprinklers.
White Showers and Skinner oscillating sprinklers satisfied requirements most closely. Primary disadvantages were insufficient
uniformity of application for experimental work, lack of precise
boundary control, and lack of independent control between area of
coverage and rate of application.
From modifications of these units, various models of irrigators were designed based on the principle of an oscillating boom
mounted in one position at a height of 8 to 10 feet over the
center of the plot.
Complete coverage of the plot was achieved by moving the
nozzles through a certain arc. Trajectories of the streams from
these nozzles were required to be long enough to reach the
extreme ends of the plot, a horizontal distance of approximately
15 feet from the stand on which the nozzles were mounted. The
oscillating motion was imparted to the nozzle boom by means of a
double-acting water cylinder. Water passed from the supply line
to the cylinder and from the cylinder to the nozzles. The final
model of this type can be characterized by two essential features:
1. The linear velocity of the water driven piston was transformed into angular velocity of the boom by means of a
cam. The shape of this cam determined the rate of
angular rotation at any point in the wetting arc. Thus,
the rate of jet travel along the ground surface could be
regulated at any point along the length of the plot by
an adjustment of the cam shape. For a given height of
sprinkler above the ground surface and a given nozzle
size and operating pressure a cam shape could be
designed by test methods which would yield good uniformity of application along the line of the jet.
2. Through a ratchet drive mechanism the movement of the
water piston was utilized to impart lateral motion to
the boom. The boom was equipped with 0.10 gpm high
velocity jet nozzles spaced at a distance of 2I. inches.
This spacing was selected in order to produce a precipitation rate within the desired range of 0.15 to 0.20
inches per hour. The 0.10 gpm nozzles were found to be
the minimum size necessary for the spray to reach the
extreme ends of the plot and to avoid excessive wind
n drift. 11 Because of the lateral movement of the boom,
dry spots between the nozzles were eliminated and
uniformity of application across the plot was thus
considerably improved.
Tests were conducted on this irrigator under still-air conditions in the laboratory. Variables involved in these tests were
the nozzle size, pressure, spacing, maximum angle from the vertical, and height above the ground surface. Data from these tests
were obtained for the rate of precipitation, maximum horizontal
distance of jet travel, and uniformity of coverage. In order to
determine mechanical reliability of the machine and the influence
of wind upon the distribution pattern, extended tests were also
conducted in the field.
These tests indicated several disadvantages in the oscillating boom type of irrigator:
1. Streams of water issuing from the nozzles tended to
destroy structure of exposed surface soil. When the
irrigator was first proposed * it was-to be used only on
close growing crops such as pasture; however, the need
developed to irrigate small experimental plots on which
inter-tilled crops such as beans were being grawn.
Under these conditions, particularly in the area
directly beneath the boom, force of the water from jets
or nozzles tended to break up surface soil structure.
A more gentle stream of water would not have reached
the ends of the plot.
2.
Because of the long trajectories from the nozzles, wind
considerably influenced the uniformity of distribution,
particularly toward the ends of the plot.
3. The irrigator permitted very little variation in the
type and intensity of spray. It was felt that it would
be an advantage to be able to vary the intensity of
spray (and so the intensity of application) from almost
a fog to a heavy rain.
4.
The area of coverage could not be varied without
changing the uniformity of application.
5. It was mechanically complicated and unreliable. However, this situation could have been improved.
Traversing
boom
Although the principle of the oscillating boom sprinkler
appeared good, the machine contained several disadvantages. A
new type of design, now referred to as the Oregon Plot Irrigator,
was proposed, based upon the traversing boom principle. A line
drawing illustrating the various parts of this irrigator is
shown in figure 1. The design of the pilot model was based upon
a plot size of 20 by 25 feet. The following is a brief description of basic components of the machine:
1. Boom: Water is sprayed vertically downward from nozzles
mounted on a boom which traverses the entire length of
the plot (figure 2). The 20-foot boom is of 3/1-inch
outside diameter aluminum pipe fitted with commerciallYavailable tee jet nozzles spaced at 15 inches. The tee
jet nozzles may readily be changed to vary the intensity
and type of spray as required. (Those selected discharged water in a fan-shaped spray.) For a given
nozzle size, rate of application can be varied somewhat
by changing the regulated pressure to the boom. Two gay
wires consisting of 3/32-inch airplane cable anchored
to the carriage supports the boom ends.
2.
Carriage: The boom is slung from a 4-wheeled carriage
which traverses two cylindrical tracks (figure 3).
Wheels are cast aluminum. Rims are shaped to conform
to the outside diameter of the tracks.
3.
Tracks: Three-inch aluminum irrigation pipe in 30-foot
lengths forms the twin tracks (figure 2). Besides
being light and readily available, this pipe is effective in beam action. Two clamps at each end of the
pipe secure it to a frame consisting of welded steel
conduit and pipe (figures 3 and 4). Sag in the tracks
is eliminated by a cable supported truss stand placed
at the middle of the pipe (figure 2). The 3/32-inch
airplane cable is anchored to the frame at either end
of the irrigator. The aluminum pipe is not drilled or
otherwise damaged in any way.
4. Prime mover: A double-acting water cylinder produces
the movement of the carriage and boom (figure 5). The
reciprocating motion of this cylinder is converted to
rotational motion by means of two overrunning clutches
mounted on the same shaft. Since this arrangement produces rotation of the shaft for both the forward and
backward strokes of the water piston, the rotational
motion is nearly continuous.
Drive mechanism: A sprocket wheel mounted on the shaft
rotated by the water cylinder drives a number 48 roller
chain which in turn transmits the motion to the boom
carriage (figure 5). The chain is supported only at its
two extrane ends. The idler sprocket at the end of the
chain farthest from the water cylinder is adjustable to
enaDle tdfLhtening of the chain (figures 3 and 4). The
carriage is connected to the chain by means of a pivot
and sliding linkage which permits a reversal of the
boom travel at the ends of the plot (figures 3 and 5).
6. Water supply: Water under pressure from a source of
supply passes through a shut-off valve to the doubleacting cylinder (figure 5). From the exhaust of this
cylinder the water flows through a pressure regulator
valve and then is conveyed to the boom by means of a
light-weight 3/8-inch plastic garden hose (figures 2
and 5). This hose is suspended from a taut cable by
means of swivel snap hooks and is coiled and extended
by the reciprocating motion of the carriage. There is
no ftwaste n water. The boom pressure is adjusted and
held constant by means of the pressure regulator valve
which is also equipped with a pressure gage (figure 5).
Since the water cylinder is a positive displacement
mechanism, the speed of boom travel for a given plot
size is a function of the nozzle discharge rate. For an
application rate of 0.20 inches per hour and a plot size
of 20 by 25 feet the time required for the carriage to
travel the entire length of the plot is 9 minutes.
7. Standards: The entire irrigator mechanism and frame
is supported on four standards or legs consisting of
2-inch steel tubing (figures 3, 4, and 5). Position
of the frame on these legs is adjustable so that,
depending upon the type and stage of crop growth, the
boom height can be varied in a range from the ground
surface to a distance of 8 feet above the ground. A
slight lateral adjustment is also provided for the
legs in order to accommodate different row spacings.
At one end of the irrigator the legs are equipped
with 3-inch square metal ground pads, while attached
to the remaining two legs are wide-rimmed cast aluminum
wheels 16 inches in diameter. To facilitate moving
from one plot to another, Wheels can be adjusted to
turn in a direction either lengthwise or crosswise with
the plot. By carrying the pad equipped legs two men
can negotiate the irrigator from plot to plot as
required without difficulty. In order to transport the
irrigator from one experimental site to another the
aluminum ground wheels are exchanged for rubber-tired
wheelbarrow wheels. One end of the irrigator is placed
on the back of a truck, while the wheeled end is permitted to trail. The carriage and boom are removed
during this operation. The total weight of the
irrigator (25 foot model) is approximately 250 pounds.
Performance tests on the traversing-boom irrigator
The uniformity of application was evaluated for four different
tee jet nozzle sizes--80015, 80020, 80030, and 800140. Each size
was operated at three different pressures--6, 8, and 10 pounds per
square inch. For the larger nozzles tests were conducted for
approximately two hours while for the smaller nozzles the length
of test was approximately five hours. Water was caught in 46ounce cans spaced 7 1/2 inches in rows parallel to the boom and
5 feet perpendicular to the boom. Each test included a total of
84 can readings. The boom height during the tests was 6 feet.
Tests covered rates of application ranging from 0.15 inches
per hour to 0.37 inches per hour. These rates were based on a
plot size of 20 by 25 feet. For a given nozzle size and pressure
an increase or decrease in the length of plot would produce a
converse change in the rate of application. A typical test
result is shown by figure 6. (Table 1 summarizes the results of
all the tests. Each entry in the table is the mean of duplicate
trials.) The smaller nozzles operating at 10 pounds per square
inch and applying 0.20 inches per hour gave the highest uniformity
of application at 92.4%. Based on a total of 84 can readings, the
amount of water applied was measured to an accuracy of plus or
-7-
minus 0.0033 inches per hour. The large nozzles operating at
the lowest pressure of six pounds per square inch, and applying
water at 0.30 inches per hour gave the lowest uniformity
obtained at 81.1%. Here the amount of water applied was
accurately measured to an accuracy of plus or minus 0.0124 inches
per hour. These figures indicate that the irrigator was able to
apply a required quantity of water with a considerable degree of
accuracy.
Tests indicated that wind caused drift of the spray and somewhat lowered the uniformity of application. It was found however,
that this problem was not so serious in actual field operation as
in the test area because of the protection from air movement
afforded by the crop foliage.
After a thorough testing in the laboratory, the irrigator
was extensively operated under actual field conditions (figure 7).
As the result of these tests several mechanical difficulties
were detected and eliminated. A total of four machines were
then built and used during the entire irrigation season of 1957.
Figure 8 shows these in operation on sweet corn plots on one of
the college farms. During the season they irrigated a total of
30 plots which were in two separate projects about three miles
apart. A total of 112 plot irrigations were applied, or 28 per
irrigator. Amount of water applied at each irrigation ranged
from 1 to 6 inches. At a precipitation rate of 0.20 inches per
hour a 6-inch irrigation required 30 hours to apply.
Operation of the plot irrigators was very successful. They
were permitted to run unattended during the night with relatively
little difficulty. Temporary equipment failure occurred, however,
during 8 of the 112 irrigations. In each instance the design of
the equipment was modified to prevent a reoccurring stoppage of
each respective type. By the end of the season there were very
few stoppages. The irrigator is now being used in connection with
several irrigation research projects in Oregon and is functioning
very satisfactorily. For one of these projects at Hillsboro,
Oregon, the length of the irrigator was increased from 25 to 30
feet. This change required that the 3-inch aluminum pipe tracks
be substituted by 4-inch aluminum pipe, and also necessitated a
slight increase in the size of some of the members of the frame.
Complete working drawings are now available from the Department
of Agricultural Engineering, Oregon State College, for either the
25-foot or the 30-foot model.
Conclusions
The traversing boom irrigator described in this bulletin has
met he basic reuirements of an irrigation research tool to
apply water to field experimental plots.
1.
The uniformity coefficient of water application is high.
For the 80015 tee jet nozzles operating at 10 p.s.i.
and applying 0.20 inches per hour this coefficient was
found to exceed 90 per cent.
2.
The rate of application can go as low as 0.10 inches
per hour with nozzles that are available commercially.
This rate, however, is computed on the basis of the
entire plot. Since the boom traverses fairly slowly
from one end to the other, the application rate
directly under the boom is considerably higher than
the average application rate for the plot.
3.
The border zone at the edges of the rectangular plot
where the application rate tapers off to zero can be
made less than two feet in width.
A precise amount of water can be applied at each irrigation. No attempt has been made to measure any
change in the discharge characteristics of the nozzles
after they have been used.
5.
The machine is relatively portable and can be moved
without difficulty from plot to plot and site to site.
6.
The irrigator is adaptable to varying crops and plot
sizes. The height of the boom is readily adjusted.
The width of coverage can be increased by extending
the boom length, or decreased by plugging nozzles as
required. An increase in the length. of plot requires
longer track pipes and drive chain and perhaps stronger
component parts, while a decrease in plot length
entails only an adjustment at the track clamps and a
shortening of the drive chain.
7.
The cost of construction in 1958 in Ore g,on was approximately. $400. It is considered an excellent investment
because it will reduce the cost of irrigation research.
-9References
1.
Myers, Earl A. A field plot irrigator. Ponn. State College,
Progress Report No. 83. 1952.
2.
Sparrow, George N. and R. L. Carter. A field plot irrigator.
Paper presented at the Winter Meeting, American Society
of Agricultural Engineers, Chicago, Illinois,
December 11-12, 1955. (Mimeo)
3.
Bean, A. G. M., E. J. Winter, and D. A. Wells. Design of a
precision plot irrigator. The British Society for
Research in Agricultural Engineering, National Institute
of Agricultural Engineering, Report No. 30. Not dated.
Appendix
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Figure 2. Traversing boom and carriage motion near the center of
the tracks.
Figure 3. Traversing boom and carriage approaching the idler gear
mounted on an end frame.
Figure 4. Closeup of the end frame secured to the two pipe tracks.
Figure 5. This end frame supports the water motor, pressure control
valve, shutoff valve, sliding hose, drive sprocket, and one
end of the pipe tracks.
Figure 6. Plot sprinkler test
Tf, me
197
181
180
182
214
205
207
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216
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1 1
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193
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Total length 15 feet
with 12 nozzles
206 ..-14.
213
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11 194
Z,
.186
185
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208
183— 19 —191
- 5 ft. -- 5 ft.
5 ft.—
223
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1:00 am
6:00 am
5 hours
Nozzles
Type tee jet 80015
psi 10
Height above cans 61111
Spacing along boom 15n
Plot tested
4 ze
Si
I
196
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Start
Stop
Total
(-1
I
208
211
(North to south 13I9n
(East to west
1510n
Boom travel
—......................
Length of track
time 16 min. 58 sec.
Can spacing
5 1 0 n perpendicular with boom
7.5" parallel with boom
Precipitation
181
Coefficient of uniformity= 94.4%
Average precipitation rate =
0.1986 ..t 0.0024 in/hr
Precipitation figures are
in/hr X 1000
Figure 7. An Oregon Plot Irrigator applying water to an experimental sweet corn plot.
Figure 8. Four Oregon Plot irrigators operating in a sweet corn experimental area.