Title Page
 Table of Contents

Title: Calibration of pesticide applicators
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00049930/00001
 Material Information
Title: Calibration of pesticide applicators
Translated Title: Circular / Agricultural Extension Service ; no. 275 ( English )
Physical Description: Book
Language: English
Creator: Harrison, D. H.
Orsenigo, J. R.
Jutras, P. J.
Publisher: Agricultural Extension Service, University of Florida
Publication Date: 1965
 Record Information
Bibliographic ID: UF00049930
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.

Table of Contents
    Title Page
        Page 1
    Table of Contents
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
Full Text








3 What Determines Variables on Boom and Other Type Sprayers?

6 Sprayer Calibration General Procedure for Broadcast Spraying.

8. Boomless Sprayer Calibration

8 Calibration for Spraying Lawns or Ornamentals Using a V-jet or
Multiple Nozzle Boom.

10 Calibration of Row Crop Sprayers, Using Multiple Drop Nozzles or
Clusters of Nozzles on Boom

10 Calibration for Band-Spraying of Liquid Pesticides

12 Calibration of Granular Band Applicators

14 Calibration of Air-Blast or Air Carrier Sprayers (Orchard or Grove)

16 Calibration of Dusters

18 Appendix (Abbreviation of Symbols)

Calibration of Pesticide Applicators
D. S. Harrison, J. R. Orsenigo, and P. J. Jutras1
Proper calibration of pesticide applicators is essential for
safe, economical and effective pest control. Users should cali-
brate an applicator prior to its initial use and periodically dur-
ing operation. Many factors cause variation in the rate of
What Determines Variables on Boom
and Other Type Sprayers?
Four factors govern the amount of spray applied. Each of
these can be varied:
Nozzle spacing on the boom
Nozzle orifice size
Pressure at the nozzle
Ground speed of the spray machine
The following formulas may be used in calibration when
some of the variables are known:
For determination of ground speed where a certain
gallonage per acre is desired, and ground speed can be
mph = 495 x gal. per min., per nozzle
Nozzle spacing (ft.) x gpa
where 495 is a constant.
Example: How fast should the sprayer travel if each nozzle
delivers 0.067 gallons per minute, the nozzle spacing is 20
inches (1.67 feet) and it is desired to spray 5 gallons per
mph = 495 x 0.067 = 33.17 = 3.98 (or 4 mph)
1.67 x 5 8.35
For determination of gallonage output per acre where
ground speed is constant, and gallons per acre can be varied:
mph ~ 495 x gal. per min., per nozzle
Nozzle spacing (ft.) x speed (mph)
Example: How many gallons per acre will be sprayed if
each nozzle delivers 0.067 gallons per minute, the nozzle
SAssociate Agricultural Engineer, Agricultural Extension Service, Gaines-
ville; Associate Horticulturist, Everglades Experiment Station, Belle
Glade; and former Assistant Agricultural Engineer, Citrus Experiment
Station, Lake Alfred.

spacing is 20 inches (1.67 feet) and the desired ground
speed is 4 miles per hour?

gpa = 495 x 0.067 = 33.17 = 4.98 (or 5 gal.)
1.67 x 4 6.68

For determination of nozzle capacity (gpm) required:

gpm = Rate appl. (gpa) x speed (mph) x nozzle spacing (inches)
where 5,940 is a constant.

Example: Pesticide is to be applied at a rate of 20 gallons
per acre (gpa), the nozzle spacing on the boom is 20 inches,
and the sprayer will travel at 5 mph; what capacity nozzle
(in gpm) is required?

gpm = 20 x 5 x 20 = 0.34
Consult nozzle manufacturer specifications for selection
of proper nozzle.

To check ground speed the spray machine should be run
over a course of known length, for example, 500 feet.
Following is a table showing minutes and seconds requir-
ed to cover 500 feet at the different ground speeds:

Table 1. Time Required to Travel 500 Feet at Various Field Speeds
Required Speed Time for 500 feet
mph Minutes plus Seconds
1.00 5 41
1.50 3 47
2.00 2 50
2.50 2 16
3.00 1 53
3.50 1 37
4.00 1 25
4.50 1 16
5.00 1 8
6.00 0 56
7.00 0 49
8.00 0 43
9.00 0 38
10.00 0 34

There is a definite relationship among various factors such
as ground speed, pump capacity, nozzle size, length of boom, and
pressure. These are demonstrated in the following example:

Length boom (ft.) = 43560 x acres to be sprayed
Percent time spent spraying x
number working hrs. x 5280 x speed (mph)

Example: What length of boom is required on a sprayer
operating at 5 miles per hour to permit spraying an 80 acre
field in 8 working hours (70 percent of time spent in actual
spraying; 30 percent in filling tank, turning, etc.)?
Length of boom = 43560 x 80
0.7 x 8 x 5280 x 5
= 23.6 feet (use closest standard size of boom)
According to a general rule of thumb, at 5 mph for three
working days each foot of boom length will cover approxi-
mately 10 acres. Thus a 250 acre field could be covered in
three days at 5 mph with a 25-foot boom.

To determine pump output in gpm:
gpm = Sq. ft. per min. x Gal. per sq. ft. or
to be covered to be applied
gpm = Ft. per min. x boom length x gal. per sq. ft., or
gpm = 5280 x mph x boom length x gpa
60 x 43560

Example: (1) What minimum size pump is required to apply
a spray at 10 gallons per acre with a sprayer operated at
5 mph and equipped with a boom 25 feet long? (Pump capa-
city must be great enough to accommodate by-pass agitation,
unless mechanical agitation is to be provided.)

Pump output or capacity (gpm) = 5280 x 5 x 25 x 10
60 x 43560
Pump output or capacity (gpm) = 2.5

(2) What is the maximum rate of application in gallons
per acre of a sprayer equipped with a 7 gpm pump and a
boom 20 feet long when operated at 5 mph, assuming
20 percent loss to by-pass agitation? From the above
relationship we have:
Gallons per acre = pump output in gpm
acres covered per minute
Gallons per acre = Net pump output (gpm) x 60 x 43,560
5280 x speed (mph) x length boom (ft.)
Gallons per acre = 5.6 x 60 x 43560 = 27 gpm
5280 x 5 x 20

To apply the spray material at a higher rate with this
sprayer either (a) reduce the ground speed, (b) space noz-
zles closer, (c) increase pressure, or (d) increase nozzle size.
Nozzle discharge does not vary linearly with pressure, but
varies with the square root of pressure. For this reason,
it is not advisable to try to increase spray rate of herbicides
by raising pressure; drift is increased greatly but there is
little effect on rate. For example, if it is necessary to raise
the pressure from 20 psi to 80 psi to double the spray rate,
the higher pressure might give excessive drift.
Output per nozzle in gpm = pump output in gpm
number of nozzles
Output per nozzle in gpm = pump output x nozzle spacing
length of boom
Output per nozzle in gpm = gal. per acre x mph x 5280 x
43560 60
nozzle spacing (inches)
Example: What capacity nozzle should be used for an ap-
plication of 20 gallons per acre with the sprayer traveling
5 mph and the nozzles spaced 20 inches apart on the boom?
gpm per nozzle = 20 x 5 x 5280 x 20
43560 x 60 x 12
= 0.337 gpm

Sprayer Calibration General Procedure for
Broadcast Spraying
Initial calibration of a sprayer may be accomplished easily
as follows:
1. Adjust nozzles, spraying pressure and ground speed as
they are to be operated in the field.
2. Fill sprayer tank completely with water.
3. With tractor operating as in 1 above, spray water over
a measured course of several hundred yards in a field prepared
for planting.
4. Determine amount of water required to refill tank to
replace that sprayed over the measured course. (Make sure
tank is in same position as in first filling, to minimize errors).
5. Calculate area sprayed: boom spread, in feet, times dis-
tance traveled, in feet.

6. From 4 and 5 above calculate quantity of water applied
per acre:
gpa = 43560 sq. ft. x gallons of water sprayed (#4)
area sprayed (#5)
7. Rate of application per acre can be decreased by smaller
nozzle tips, lower pressure or greater speed.
8. Rate of application per acre can be increased by larger
nozzle tips, greater pressure or slower speed.
9. Complete calibration by repeatedly adjusting and testing
unit until desired gallonage per acre is reached.
Example: A sprayer carries a swath 20 feet wide. When driven
over 870 feet it sprays 20 gallons of water.
gpa = 43560 sq. ft. x 20 gallons = 50
20 ft. x 870 ft.
10. Add desired quantity of pesticide per acre to amount of
water applied per acre when filling spray tank.
11. Keep a running check on calibration by occasional test-
ing and by records of amount of pesticide used to treat each
block. Calibration may also be checked with the information
contained in Table 2.
Example: Nozzles are spaced 18 inches apart on a spray boom.
A single tip delivers 68 ounces of spray solution in a 300 foot
run across a field. Locate 68 in the left-hand column of Table 2
and read across to the 18 inch spacing column to find that out-
put was 51 gpa. Check more than one tip to ensure correct

Table 2. For Checking Sprayer Calibration in Broadcast Boom Application
Volume of spray Gallons applied per acre
delivered by 1 when nozzle tip spacing on boom is
nozzle in 300 ft. 15 inches 18 inches 21 inches
24 ounces 22 -
28 25 21 -
32 (1 quart) 29 24 21
36 ounces 32 27 23
40 36 30 26
44 40 32 28
48 (1/2 quarts) 44 36 31
52 ounces 47 39 34
56 51 42 36
60 54 45 39
64 (2 quarts) 58 48 42
68 ounces 62 51 44
72 65 55 47
76 69 57 49

Boomless Sprayer Calibration
For calibration of a boomless type sprayer, determine:
(1) the gallons discharged in the time it takes to drive 660 feet,
and (2) the width of the swath covered by the spray pattern.
To determine the gallons discharged in 660 feet, first find
the time that it takes to drive 660 feet; then run the sprayer in
a stationary position, catching the spray, for that amount of
time. When testing, use the engine speed and pressure setting
that will be used in actual spraying.
Gallons per acre can be read directly from Table 3, after
determining swath width and gallons discharged in 660 feet.

Calibration for Spraying Lawns or Ornamentals Using a V-Jet
or Multiple Nozzle Boom
1. Fill the sprayer tank completely or to a predetermined
level with water.
2. Select the speed to be used by the sprayer operator. This
speed must be fairly constant to allow for uniform application
of the spray.
3. Set the pressure regulator at a pressure recommended
for the most efficient use of the nozzle.
4. Spray a known area (length times width of sprayed swath)
at the above recommended pressure.
5. Determine the number of gallons applied by refilling the
tank to the predetermined mark by adding water from a meas-
uring container.
6. Compute the gallons applied per acre by dividing the area
sprayed (sq. ft.) into 43,560 and then multiplying by the number
of gallons used.
gpa = 43,560 x gal. applied on area
Area sprayed

If the gallonage applied per acre is too high or low, it can
be corrected by:
a. Changing the speed of the sprayer or operator
(when walking)
b. Changing the nozzle pressure
c. Changing to different size nozzle tips

Table 3. Boomless Sprayer Calibration Table

per Width of Swath (in feet)
660 feet 20' 25' 30' 35' 40' 45' 50' 55' 60' 65' 70'
Gallons Per Acre




3.3 2.9
4.1 3.7
4.9 4.4
5.8 0.1
6.6 5.9
7.4 6.6
8.3 7.3
9.1 8.1
9.9 8.8
10.7 9.6
11.6 10.3
12.4 11.0
13.2 11.8
14.1 12.5
14.9 13.2
15.7 14.0
16.5 14.7
17.3 15.4
18.2 16.2
19.0 16.9
19.8 17.6

3.3 3.0 2.7 2.5 2.3
3.9 3.6 3.3 3.0 2.8
4.6 4.2 3.9 3.5 3.3
5.3 4.8 4.4 4.0 3.8
5.9 5.4 4.9 4.5 4.2
6.6 6.0 5.5 5.1 4.7
7.3 6.6 6.0 5.6 5.2
7.9 7.2 6.6 6.1 5.7
8.6 7.8 7.1 6.6 6.1
9.3 8.4 7.7 7.1 6.6
9.9 9.0 8.3 7.6 7.1
10.6 9.6 8.8 8.1 7.5
11.2 10.2 9.4 8.6 8.0
11.9 10.8 9.9 9.1 8.5
12.6 11.4 10.4 9.6 9.0
13.2 12.0 11.0 10.1 9.4
13.9 12.6 11.5 10.7 9.9
14.6 13.2 12.1 11.2 10.4
15.2 13.8 12.6 11.7 10.8

8.3 6.6
9.9 7.9
10.8 9.2
13.2 10.6
14.8 10.9
16.5 13.2
18.2 14.6
19.8 1l.8
l2.4 17.2
23.1 18.5
24.7 19.8
26.4 21.2
28.1 22.5
29.6 23.8
31.4 25.1
33.0 26.4
34.6 27.8
36.2 29.0
38.0 30.5

Remember, to increase gallons per acre:
1. Increase pressure at nozzle, or
2. Change to larger size nozzle tips, or
3. Decrease the speed of the sprayer, or
4. Add more nozzles to the boom, or
5. Space nozzles closer on boom
Sprayer calibration should be checked frequently in the field
because certain pesticides, particularly wettable powders, may
cause rapid wear of spray nozzle tips and pumps. With a field
or lawn of known length, the amount of spray needed for a
given gallonage for a certain number of rounds can be calculated,
and the amount actually applied can be determined when the
tank is refilled.

Calibration of Row Crop Sprayers, Using Multiple Drop
Nozzles or Clusters of Nozzles on Boom
For determination of gpa applied:
gpa = 495 x gpm x nn
v (mph) x rs (feet)
where gpa = gallons per acre applied
495 = a constant
gpm = capacity of each nozzle (gpm)
nn = number nozzles per row
rs = row spacing (feet)
v = speed (mph)
Example: Applying a fungicide on sweet corn spaced on 3-foot
rows, using a speed of 4 mph, 6 nozzles per row and a nozzle
capacity of 0.3 gpm, what is the gallonage applied per acre?
gpa = 495 x gpm x nn
vx rs
gpa = 495 x 0.3 x 6 = 891 = 74
4x3 12
This same formula can be used to find any other unknown
variables. For example, if we know the recommended gallon-
age per acre, the number of nozzles per row, the speed we want
to spray at, and the row spacing, we can use this same formula
to find the nozzle capacity in gpm.

Calibration for Band-Spraying of Liquid Pesticides
This table will help determine sprayer output in gallons per
acre on a band-sprayed basis. Band width is governed by the
angle of nozzle pattern and height of nozzle.

To use: Have sprayer equipped with proper nozzle tips and
have nozzles, ground speed and spraying pressure adjusted as
they will be operated in the field.
Then drive unit in field and collect spray liquid discharged
by one or more nozzle tips over a distance of 300 feet. Several
tips collected separately and averaged are better than one.
Measure the liquid sprayed by one tip in ounces. Locate this
figure in left column of Table 4 and read directly the gallons per
acre rate under the band-width column which applies to the unit.

Table 4. Calibration Table for Band-Spraying of Liquid Pesticides
delivered by AT BAND WIDTH OF:
1 tip in 300 ft. 9" 12" 15" 18"
/2 pt. or 8 oz. 12.1 -
10 15.1 11.3
12 18.1 13.6 10.9
14 21.2 15.9 12.7 10.6
1 pt. or 16 oz. 24.2 18.2 14.5 12.1
18 27.2 20.5 16.3 13.6
20 30.2 22.7 18.2 15.1
22 33.3 25.0 20.0 16.6
24 36.3 27.2 21.8 18.2
26 39.3 29.5 23.6 19.7
28 31.8 25.4 21.2
30 34.0 27.2 22.7
1 qt. or 32 oz. 36.3 29.0 24.2

Note: If two nozzle tips are used per row the value for one
tip will have to be doubled to give the correct gallons per acre
total. If two tips are used it would be desirable to calibrate the
unit to discharge in the area above the dotted line in the table.
Example: One nozzle per row; a sprayer is set up with
one tip spraying 12 inch bands on the row. When run
down the field at operating speed and pressure, a nozzle
tip discharges 26 ounces of solution in 300 feet. The
gallons per acre rate is found in the 12 inch column
opposite 26 ounces: 29.5 gpa.

* Faulty or irregular pattern-Remove obstructions from nozzle
tips. Never use a hard object for cleaning nozzle tips. Use
air pressure or a toothpick.
* Lack of pressure-Pump not primed. Increase pump speed for

a few seconds. Check hose connections and tighten securely.
Check pump condition.
Band too wide-Lower the nozzle.
Band too narrow-Raise the nozzle.
Excessive drift-Reduce pressure. Change to larger nozzle
tips, if necessary, to maintain spraying pressure.below 40
Pressure regulator fails to adjust low enough-Pressure regu-
lator may be stuck or insufficient material is being by-
passed. Use a larger by-pass hose or add a second by-pass.
Failure to get proper nozzle discharge at recommended pres-
sure-Check nozzle size; nozzle orifice may be plugged or
nozzle screens may be clogged.

Calibration of Granular Band Applicators
Most granular applicators use gravity flow with a rotating
agitator to meter the granules through an adjustable orifice.
It is difficult to design a granular applicator that is relatively
inexpensive and yet capable of accurately applying many differ-
ent chemicals over a wide range of field conditions. Several
factors can cause variation in the application rate, including:

Area of the metering orifices
Speed of the agitator
Ground speed of the applicator
Nature and size of granules
Roughness of the field.
Relative humidity and temperature

Use the following calibration steps:
1. Adjust delivery openings on applicator unit(s) at esti-
mated or approximate settings and fill hopper with granules to
be applied.
2. Set tractor or unit speed as it will be operated in the field.
3. Operate the unit over a measured distance of several
hundred yards in a freshly prepared seedbed. Collect the gran-
ules discharged over this course with pails or buckets under the
delivery openings (remove delivery tubes if necessary.)

4. Accurately weigh the amount of chemical delivered by
each outlet: units should be set or adjusted to deliver identical
5. Calculate the area that would have been treated over the
course: multiply individual band width in feet times number of
rows times distance covered in feet. This value equals the area
of the measured treated course, in square feet.
6. From No. 4 and No. 5 calculate the amount of granules
applied per acre (application rate) at follows:

Pounds/A = 43560 x pounds granules applied over course
area of measured course in square feet

This value is pounds per acre (lb/A) of granular formulation
applied. To determine amount of active ingredient applied
multiply pounds per acre by percent active ingredient and divide
by 100 as follows:

Pounds/A (active) = lb/A granules from above x 5% active

7. Complete calibration by repeatedly adjusting and testing
unit until desired quantity of granules is delivered. All indivi-
dual delivery spouts should have the same output.

Example: A granular chemical applicator treats bands one foot
wide on 5 rows (5 rows x 1 foot = 5 feet treated). When driven
over a distance of 870 feet each of the five openings delivered
4/10 pound of granules (5 rows x 4/10 pound = 2 pounds) at
the setting used.

Pounds/A = 43560 sq. ft. x 2 pounds granules = 20 lb/A granules
5 ft. x 870 ft.

If the active ingredient concentration of the granules was
20 percent the rate of active material applied per acre would be:

Pounds/A = 20 lb/A granules x 20 = 4 lb/A active ingredient

8. Keep a running check on calibration by occasional testing
and by records of amount of pesticide used to treat each block
of crops.

Calibration of Air-Blast or Air Carrier Sprayers
(Orchard or Grove)
These sprayers are equipped with either centrifugal pumps,
piston pumps or metering pumps. Some are designed for single
side delivery only, others for either single or double side deliv-
ery. These sprayers are designed and used mainly for orchards
and groves.

Make a test run to determine ground speed desired and use
the following formula:
mph = tree spacing (feet) x number trees passed per minute.
or, mph = s x n

Where mph = miles per hour
s = tree spacing (in feet)
n = number of trees passed in one minute

Example: If trees are on 20-foot centers and tractor passes 4.4
trees in one minute, then
20 x 4.4 = 1 mile per hour

Table 5 will be helpful in setting tractor speed.

Table 5. Information For Calibration Of Grove Sprayers
Speed of Tractor Tree Spacing, feet
Feet per 15 18 20 22 25 30 35
mph minute Number of trees passed per minute
1 88 5.9 4.9 4.4 4 3.5 2.9 2.5
11/2 132 8.8 7.3 6.6 6 5.3 4.4 3.8
2 176 11.7 9.8 8.8 8 7.0 5.9 5.0

The gallonage discharged by centrifugal pumps is varied by
selection of nozzle size and/or the number of nozzles. The dis-
charge pressure will vary depending on the amount of material
being discharged through the nozzles and the condition of the

It is important to check occasionally engine speed and pump
drive belts for slippage since these two factors affect pump
operating pressure. Pump pressure should be checked at the
discharge manifold rather than at the pump. Other factors that
affect pump operating pressure include:

Clogged strainer
Air leaks into pump suction line
Worn nozzle discs
Worn pump
Pump by-pass cut-off valve opened too much

The discharge of piston-type pumps is also varied by the
proper selection of nozzle size and/or the number of nozzles,
but can be varied also by changing the pressure regulator ad-
Metering pumps are adjustable and the output of each sec-
tion feeding a nozzle can be varied.

To determine gallonage of spray material required for:
One Side Delivery Two Side Delivery
gpm = g x v x 44 gpm = g x v x 88
zxs zxs

Where gpm = Gallons per minute of spray material
g = Gallons per tree (based on dilute gallonage)
v = Tractor speed in miles per hour
z = Spray concentration desired (use 1 for dilute)
s = Tree spacing in the rows

Example: If trees on 25-foot spacing, require 20 gallons of
dilute spray, and tractor speed is 1 mph, the gallons per minute,
per side at 4-x concentration should be:

gpm = 20 x 1 x 44 = 8.8
4 x 25

The rate of discharge per nozzle (in gpm) with a specific
nozzle and pressure can be obtained from the catalog of the
equipment manufacturer.
Nozzles should be arranged so they discharge approximately
50 percent of the total spray gallonage in the upper one-third

of the tree and 67 percent of the total spray gallonage in the
upper half of the tree.
In order to verify output per tree, make a trial run with the
equipment in operation. First, fill the tank with water, set the
tractor throttle for desired speed and spray a predetermined
number of trees. Then measure the amount of water necessary
to refill the tank. From the information obtained, calculate
the number of gallons used per tree. If the gallonage sprayed
does not agree with the desired gallonage, make the necessary
changes as described above.

Calibration of Dusters
Because of the wide variation in dust materials, calibration
checks are needed for each new batch of materials used, and/or
for each new application rate. Accuracy is important to prevent
possible damage from over-dosage and to assure application of
sufficient material for pest control.
The amount of material applied per acre depends on (1) the
ground speed of the duster, (2) blower speed, (3) type of dust
used and prior handling (4) depth in the hopper, and (5) size
opening in the bottom of the hopper or discharge port adjust-
ment. Ground speed, blower speed and dust handling should be
kept as constant as possible. Refill hopper when half of contents
have been applied.
With all other factors constant, use the hopper discharge
opening to calibrate the machine.
The only practical method for duster calibration is by a trial
and error that becomes quite methodical by following these
1. Measure off a test area of at least one-half acre (21,780
square feet) or eight 38-inch rows, 860 feet long.
2. Fill duster hopper and level the material in hopper.
3. Dust the measured area at normal tractor-operating speed.
Full throttle in the desired gear is recommended. If less than
full throttle is used note the exact throttle setting. If a tacho-
meter is available, a fast idle motor speed of 200 to 500 rpm
below full throttle in the desired gear may help facilitate cali-
bration. (Fast idle motor speed is the motor rpm recorded at

some throttle setting between one half and full throttle with
the tractor out of gear.)
4. After dusting the test area, carefully weigh the amount
of dust needed to refill the hopper to its original level.
5. Convert the number of pounds of dust required to refill,
to pounds per acre by multiplying by two. (Example: 17 pounds
per 1/2 acre equals 34 lb/A)
6. If the rate is more than desired, either increase the trac-
tor speed or decrease hopper discharge opening. If the rate is
'ess, reduce the tractor speed or increase the hopper opening.

7. Repeat dusting the test area after making adjustments
until correct speed and hopper discharge opening settings are
determined. Note these adjustments.
8. This calibration process should be repeated each time the
machine is used even though the same material is being applied
at the same application rate. Flow rate will vary with differ-
ences in density and dust particle relationships. Flow gauges
on dusters are unreliable.
If a motor tachometer is available on the tractor, a short
cut in calibration may be used. Example: On the first run where
34 lb./A was applied at approximately 1350 rpm motor speed, and
40 lb./A is the desired rate, then use the following formula:
Desired tachometer reading = rpm X test rate
desired rate
Desired tachometer reading = 1350 rpm X 34 lb/A
40 lb/A
Desired tachometer reading = Approx. 1150 rpm

Set the throttle speed at 1150 rpm and make a re-run in the
same gear. To be consistent, use tachometer readings at fast
idling speed before each run. Motor rpm is reduced somewhat
under load in field operation.
Remember, that as engine rpm is increased pto speed in-
creases which, in turn, increases the blower speed and agitation,
so that this proportion is not exact. The fact that the discharge
port adjustment remains the same should make delivery ap-
proximately in the same proportion. Ten percent variation is
an acceptable duster adjustment.


ft. = feet
gpa = gallons per acre
gpm = gallons per minute
lb/A = pounds per acre
mph = miles per hour
rpm = revolutions per minute
psi = pressure, pounds per square inch
sq. ft. = square feet
gal. = gallons)
g = gallons per tree (grove or orchard use)
n = number trees passed in 1 minute (grove or orchard
nn = number nozzles per row
rs = row spacing
s = tree spacing (feet) (grove or orchard use)
v = tractor or sprayer speed (mph)
z = spray concentration desired (dilute = 1)
495 = a conversion factor or constant
5,940 = a conversion factor or constant
1 acre = 43560 square feet
1 mile = 5280 feet
1 mph = 88 feet per minute

(Acts of May 8 and June 30, 1914)
Agricultural Extension Service, University of Florida,
Florida State University and United States Department of Agriculture, Cooperating
M. O. Watkins, Director

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