Equipment and Calibration Circular 1192

Equipment and Calibration Circular 1192
This circular is the first in a series of kublications dealing with application equipment and the calibration of low-pressure sprayers, granular applicators, highpressure sprayers, air-carrier sjjrayers, small-capacity sprayers and dusters, and
aerial sprayers and granular applicators.
The calibration method described here has three important advantages over
most other methods. First, it allows the operator to select the number of gallons
to apply per acre and to complete almost all of the calibration before going to the
field. Second, it provides a simple means for frequently adjusting the calibration to
compensate for changes because of nozzle wear. Third, it can be used for broadcast, band, directed, and row-crop spraying.
We wish to thank Stephen L. Pearson of the Department of Agricultural Engineering for reviewing the material in this circular and making many helpful
L. E. Bode
13. J. ButEt~
Equ ipmen t
pairability, and efficient operation at tractor power
take-off (PTO) speeds. Roller pumps are positivedisplacement pumps, and are self-priming. There is a
wide assortment of roller pumps from which to choose,
with normal outputs ranging from 5 to 30 gallons per
minute and maximum pressures ranging from 150 to
300 psi.
Roller pumps have a slotted rotor that revolves in
an eccentric (nonsymmetrical) case. Rollers in the
slots seal the spaces between the rotor and the wall
of the case. As the rollers pass the pump inlet, the
spaces around the rollers enlarge and are filled with
liquid drawn through the suction hose. When the
rollers approach the pump outlet, the spaces become
smaller, and the fluid is forced through the o u t l e t .
Pump output is determined by the length and diameter
of the case, its eccentricity, and the speed of rotation.
Roller pumps are usually constructed with cast iron
or corrosion-resistant housings and rotors; nylon, Teflon, or rubber rollers; and Viton, rubber, or leather
seals. The type of material selected depends upon the
chemical being pumped.
Nylon or Teflon rollers have proved to be the most
resistant to agricultural chemicals, and are recommended for multipurpose sprayers. Rubber rollers are
preferable when the pump is to be used only for water
solutions and wettable powder slurries at pressures
under 100 psi. Sand or scale is abrasive to the rollers,
and the solution being pumped must not contain these
Polypropylene rollers wear better than either nylon
or rubber rollers when applying weak solutions or
solutions with little or no lubricating qualities. Some
operators have had problems with excessive wear of
the rollers, especially when using wettable powders.
Other operators have maintained long pump life by
operating the pump at all times when using wettable
powders, by proper maintenance and storage of the
pump, and by keeping abrasive materials out of the
More pesticides are applied with low-pressure
sprayers than with any other kind of equipment. These
sprayers apply chemicals to control weeds, insects, and
diseases in field crops, ornamentals, turf, fruits, vegetables, rights-of-way, etc. Tractor-mounted, pull-type,
and self-propelled sprayers are available in many
models. Spray pressures range from nearly 0 to about
200 psi, and application rates can vary from 10 to
over 100 gallons per acre. All low-pressure sprayers
have several basic components: a pump, a tank, an
agitation system, a flow-control ‘assembly, and a distribution system.
The pump is the “heart” of the sprayer. Although
diaphragm pumps are popular overseas, only roller
and centrifugal pumps are used extensively on lowpressure sprayers in the United States.
Regardless of type, the pump must provide the
necessary flow rate at the desired pressure. It should
pump enough spray liquid to supply the gallons per
minute (GPM) required by the nozzles and the tank
agitator, with a reserve capacity of 10 to 20 percent
to allow for some flow loss as the pump becomes worn.
Pumps are not 100 percent efficient. They have
losses because of drive friction, leakage, etc. When estimating the pump horsepower needed for an application, an efficiency (Eff) of 50 to 60 percent should be
used. The horsepower required to drive the pump can
be estimated by using the following formula:
GPM X psi
1,714 x Eff
Example: How much Hp is required to run a
pump if the maximum output of the pump is 50 GPM
at 40 psi? Assume a pump efficiency of 50 percent.
Centrifugal Pumps
50 X 40
1,714 x 0.50 = 2.33
Centrifugal pumps are the most popular type used
for low-pressure sprayers. They are durable, simply
constructed, and can readily handle wettable powders
and abrasive materials. Because of the high output of
centrifugal pumps (70 to 130 GPM ), the spray solution can be agitated sufficiently even in large tanks.
The initial cost of a centrifugal pump is somewhat
higher than that of a roller pump, but its long life and
low maintenance make it an economical choice.
Centrifugal pumps develop pressure as a result of
centrifugal force. In most centrifugal pumps, the
Because of inefficiencies of the drive units, electric
motors should be about one-third larger than the calculated horsepower. Gasoline engines should be from
one-half to two-thirds larger than the pump horsepower required.
Roller Pumps
Roller pumps are popular for smaller sprayers because of their low initial cost, compact size, easy re-
Roller Pump Spraying System
Boom control levers
Pressure relief valve
Centrifugal Pump Spraying System
Tank lid with screen
Boom control
Hydraulic agitato
Shut-off valve
spray material is fed into the center of a high-speed
impeller, and is thrown outward, radially, into the
pump casing. The high-velocity spray material is
forced out the pump outlet, generating pressure in the
outlet line. Efficiency in developing outlet pressure
depends upon the design of the pump, especially the
diameter and speed of the rotating impeller.
Centrifugal pumps for low-pressure spraying are
capable of developing pressures up to 70 psi when
the impellers are running between 3,000 and 4,500
r p m The output volume drops off rapidly when the
outlet pressure is above 30 to 40 psi. This decrease in
volume can be an advantage because it permits controlling nozzle pressure without a relief valve.
The need to operate at high impeller speeds requires
some kind of step-up speed mechanism when operating
centrifugal pumps from power take-off (PTO) shafts.
The simplest and least expensive is a belt-and-sheave
assembly. Other step-up mechanisms have planetary
gears that are completely enclosed and mounted
directly on the PTO shaft. Another method of driving
a centrifugal pump is with a close-coupled, high-speed
hydraulic motor. Using the tractor hydraulic system to
drive the pump keeps the tractor PTO shaft free for
other uses. Pumps can also be driven by direct-coupled
gasoline engines when other drive mechanisms cannot
be used.
Single-stage centrifugal pumps designed to operate
at speeds up to 6,000 rpm and generate pressures up
to 150 psi are now available. Although these pumps
supply the higher pressures required for some foliar
applications, they require more care in pressure control to prevent damage to other components when the
boom is closed. Multiple-stage centrifugal pumps will
provide high pressures at lower speeds, but they are
much more expensive than single-stage centrifugal
Turbine pumps are also available for low-pressure
sprayers. These pumps are similar to centrifugal pumps
except that they can provide the normal capacity and
pressures up to 70 psi when mounted directly on a
l,OOO-rpm PTO shaft, eliminating the need for stepup mechanisms.
The capacity of centrifugal pumps varies directly
with the speed; the pressure varies as the square of the
speed; and power consumption varies as the cube of
the speed. Since centrifugal pumps are not self priming, they should be mounted below the supply tank
to aid in priming. In addition, a small vent tube
should be installed from the top of the pump housing
to the supply tank. This positive vent line allows the
pump to prime itself by “bleeding off” trapped air
when the pump is not operating and upon starting.
The inlet of a centrifugal pump should never be
restricted. A partially clogged suction strainer, c o l lapsed suction line, or a suction line with insufficient
capacity will result in a loss of pressure control and
possible damage to the pump. Since centrifugal pumps
can handle small pieces of foreign material without
damage, a suction strainer is not always required. If
a suction strainer is used, it must be capable of
handling the large capacities of the pump with a
minimum drop in pressure across the strainer, and
must be cleaned frequently.
Sprayer tanks should be large enough so that they
do not need to be refilled frequently. They also should
be corrosion-resistant, easy to fill and clean, shaped
suitably for mounting and effective agitation, and have
adequate openings for pump and hydraulic or mechanical agitation connections.
The capacity at various levels should be clearly
marked on the tank. If the tank is not transparent, it
should have a sight gage or other external means of
determining the fluid level. Sight gages should have
shutoff valves at the bottom to permit closing in case
of failure. The opening of the tank should be fitted
with a cover that can be secured to avoid spills or
splashes The opening should be large enough to facilitate cleaning the tank. The drain should open through
the bottom so that the tank can be completely emptied.
Fiberglass tanks are widely used on all types of
sprayers and applicators and as nurse tanks. Fiberglass
is strong and durable, but it will break or crack under
impact. One advantage of fiberglass over polyethlene
is that repair kits are available for “on-farm” use, or
a spray-equipment, dealer can make repairs. Fiberglass
tanks are about equal to aluminum in cost, and can
be used with most chemicals. They may, however, be
affected by certain kinds of solvents.
Stainless steel tanks are strong, durable, and resistant to corrosion by any crop chemical. Because
stainless steel is the most expensive material used for
pesticide and fertilizer applicator tanks, only equipment with high annual use is commonly equipped with
stainless steel tanks.
Gaivanized steel tanks are inexpensive, and can be
constructed in almost any size or shape. They are easy
to repair or modify. Corrosion is the biggest drawback.
Even with protective coatings, chemicals can cause
rapid rusting. Rust flakes off, plugging the nozzles,
clogging the strainers, and damaging the pumps. Galvanized tanks and recycled barrels are suitable for
most pesticides, but they should not be used with the
Typical Centrifugal Pump (Cutaway)
Typical Roller Pump (Cutaway)
Outlet port
Inlet port
Performance Curve
trifugal pump (6,000 rpm)
ntrifugal pump (4,200 rpm
Roller pump (1,000 rpm
more corrosive liquid fertilizers insecticides, and
Aluminum tanks are moderate in cost, resist corrosion, and are suitable for many chemicals. They should
not, however, be used for liquid nitrogen solutions with
a phosphoric acid base. A few pesticides can also cause
rapid corrosion. These pesticides usually have proper
warnings on the label.
Polyethylene tanks are relatively inexpensive and
are available in many sizes and shapes. The development of high-quality polyresins provides improved control of stress cracking and assures compatibility with
commonly used agricultural chemicals. Polyethylene
tanks are tough and durable. If a tank is cracked or
broken, however, it must be replaced because there is
no effective way to repair it. Because polyethylene
breaks down under ultraviolet light, inhibitors are
added for protection against sunlight. Nonetheless, it is
best to keep these tanks out of direct sunlight when not
in use.
W h e n barrels or small metal tanks are used, the tank
mounting is not critical. Polyethylene and fiberglass
tanks must be properly mounted on a “saddle” that
supports the tank over a large area. Without a saddle,
the weight of the liquid could break the tank as the
sprayer bounces over obstructions or rough terrain.
should receive fluid from a separate line on the discharge side of the pump and not merely from the bypass line.
The amount of flow needed for agitation depends
upon the chemical used, as well as upon the size and
shape of the tank. For a simple orifice jet agitator,
a flow of 6 GPM for every 100 gallons of tank capacity
is usually adequate. There are several types of siphon
attachments available that will help stir the tank with
less flow. If these are used, the agitator flow from
the pump can be reduced to 2 to 3 GPM for every
100 gallons of tank capacity. Foaming can occur if the
agitation flow rate remains constant as the tank
empties. This condition can be prevented by using a
control valve to gradually reduce the amount of agitator flow.
Hydraulic Agitators
Agitation requirements depend largely upon the
formulation of the chemical being applied. Soluble
liquids and powders do not require special agitation
once they are in solution, but emulsions, wettable
powders, and liquid and dry flowables will usually
separate if they are not agitated by some means. Separation causes the concentration of the pesticide spray
to vary greatly as the tank empties. For this reason,
thorough agitation is essential. Either mechanical paddles or hydraulic jets can be used to agitate the spray
Mechanical agitators are propellers or paddles
mounted on a shaft near the bottom of the tank. The
shaft usually rotates at 100 to 200 rpm. Excessive agitator speeds can cause foaming in some spray mixtures.
Hydraulic agitation is most commonly used on lowpressure sprayers. The fluid is circulated by returning
a portion of the pump output to the tank and discharging it under pressure through holes drilled in a
pipe running the entire length of the tank or through
special agitator nozzles. Jet agitation is simple and
effective provided that the device is installed correctly
and there is sufficient flow. The agitator orifices
A roller pump or other positive-displacement pump
usually has a flow-control assembly consisting of a bypass-type pressure regulator or relief valve a control
valve, a pressure gage, and a boom shut-off valve. B y pass pressure-relief valves usually have a spring-loaded
ball, disc, or diaphragm that opens with increasing
pressure so that excess flow is bypassed back to the
tank, preventing damage to the pump and other components when the boom is shut off.
When the control valve in the agitation line and the
by-pass relief valve in the by-pass line are adjusted
properly, the spraying pressure will be regulated. To
adjust the system properly, follow these steps: ( 1 )
close the control valve in the agitation line and open
the boom valve; (2) start the sprayer and run the
pump at operating speed; then adjust the relief valve
until the pressure gage reads about 10 psi above the
desired spraying pressure; and (3) slowly open the
control valve (agitation line) until the spraying pres-
inch. Strainers with high mesh numbers have smaller
openings than strainers with low mesh numbers.
Coarse basket strainers set in the tank-filler opening
prevent twigs, leaves, and other debris from entering
the tank as it is being filled. A 16- or 20-mesh tankfiller strainer will restrain Iumps of wettable powder
until they are broken up, helping to give uniform tank
A suction-line strainer should be used between the
tank and a roller pump to prevent rust, scale, or other
material from damaging the pump. A 40- or 50-mesh
strainer is recommended. A suction-line strainer is
not usualIy needed to protect a centrifuga1 pump except against Iarge pieces of foreign material.
The inlet of a centrifugal pump must not be restricted. If a strainer is used , it should have an effective
straining area several times larger than the area of the
suction line, be no smaller than 2O-mesh, and should
be cleaned frequently. A line strainer (usually 50mesh) should be located on the pressure side of the
pump to protect the spray nozzles and agitation
Small-capacity nozzles must have a strainer of the
proper size to stop any particle that may plug the
nozzle orifice. These strainers vary in size, depending
upon the size of the nozzle tip used, but they are
c o m m o n l y 50- or lOO-mesh. Nozzle catalogs list a
recommended mesh size for each nozzle tip.
In general, 1 00-mesh strainers are recommended
for most nozzles w i t h a flow rate below 0.2 G P M and
50-mesh strainers for nozzles with a flow rate between
0.2 and 1 G P M if a good line strainer is used, no
nozzle strainer is needed for nozzles with flow rates
above 1 CPM. When applying wettable powders do
not use nozzles with a flow rate less than 0.2 GPM.
Use 50-mesh or larger strainers to prevent clogging the
screens with the powder. Finer strainers, such as lOOmesh, can be used to protect small nozzles when applying liquid concentrates, emulsions, and soluble powders.
sure is reduced to the desired level. If the pressure
cannot be lowered sufficiently even with the control
valve open, use larger orifice caps in the jet agitator,
or use an agitator tube with larger orifices.
If there is insufficient a g i t a t i o n e v e n w h e n t h e
spraying pressure is correct and the relief valve is
closed, install a smaller orifice in the agitator. Agitation
is increased because the control valve can be opened
wider at the same pressure.
Because the output of a centrifugal pump can be
completely closed without damage to the pump, a
pressure-relief valve and separate by-pass line are
not needed. The spray pressure can be controlled with
simple gate or globe valves.
It is preferable, however, to use special throttling
valves that are designed to control the spraying pressure
accurately. Electric-controlled throttling valves are
becoming popular for remote pressure control. These
valves are especially useful for enclosed cabs.
The spray pressure is controlled with two throttling
or control valves-one in the agitation line and the
other in the spray boom line - permitting control of
agitation flow independently of nozzle flow. To adjust
for spraying, follow these steps: ( 1) prime the pump
with all valves open; (2) close both valves and, with
the pump runnin, open the boom control valve until
the pressure gage indicates the desired spray pressure;
and (3) open the agitation line valve until you have
sufficient agitation. If the agitation Ilow has lowered
the pressure, readjust the boom control valve to restore the desired pressure.
A pressure gage must be included in every sprayer
system because nozzles are designed to operate within
certain pressure limits. The importance of a good
pressure gage cannot be overemphasized. The pressure
gage must be used for calibrating and while operating
in the field. Select a gage for the pressure range that
you will be using. A range of 0 to 60 psi is adequate
for herbicides and most other pesticides. When a 150psi gage is used for operating at 20 psi, accurate pressure adjustment is difficult, if not impossible.
A quick-acting boom cut-off or control valve allows the sprayer boom to be shut off while the pump
and the agitation system continue to operate. Electric
solenoid valves, which eliminate inconvenient hoses
and plumbing, are also available.
Line Strainers
Three types of strainers are commonly used on lowpressure sprayers.* tan k-filler strainers, line strainers,
and nozzle strainers. The strainer numbers (20-mesh,
50-mesh, etc.) indicate the number of openings per
Pressure Relief Valves (Roller Pumps)
Throttling Valves (Centrifugal Pumps)
Boom Cu t-off Va lves
Boom stability is important in achieving uniform
spray application. The boom should be relatively rigid
in all directions, Swinging back and forth or up and
down is undesirable. The breakaway hinge arrangement of th e boom should be dampened so that the
boom is rigid in the fore and aft direction. The boom
should be constructed to permit folding for transport.
Check for interference of the folded booms with tractor cabs and roll bars. The boom height should be adjustable from about 1 to 4 feet above the ground.
Certain commonly used chemicals will react with
some plastic materials. Check with the sprayer manufacturer and the chemical manufacturer for compatibility.
All hoses and fittings should be of a suitable quality
and strength to handle the chemicals at the selected
operating pressure. They should be chosen on the basis
of composition, construction, and size.
A good hose is flexible, durable, and resistant to
sunlight, oil, chemicals, and general abuse such as
twisting and vibration. . The hose must be resistant to
the chemical action of spray materials. The outer
coating of the hose should be chemically resistant because spray may occasionally ycontact it. Two widely
used materials that are generally chemically resistant
are ethylene vinyl acetate (EVA) and ethylene propylene dione monomer ( EPDM ) . A special reinforced
hose must be used for suction lines to prevent collapsing.
Peak pressures are often encounter-cd that are much
higher than average operating pressures. These peak
pressures usually occur as the spray boom is shut off.
For this reason, the sprayer hoses and fittings must b e
in good lcondition to prevent a possible break and the
operator being covered with the spray chemical.
Spray lines and suction hoses must be the proper
size s for the system. The suction hoses should be airtight, noncollapsible, as short as possible , and as large
as the pump intake. A collapsed suction hose can restrict flow and "starve"” a pump, causing decreased
flow and damage to the pump or pump seals. When
you cannot maintain spray pressure, check kthe suction
line to be sure that it is not restricting flow.
Other lines, especially ythose between the pressure
gage and the nozzles, should be as straight as possible,
with a minimum of restrictions and fittings. The
proper size of these lines varies with the size and
capacity of the sprayer. A high but no t excessive fluid
velocity should be maintained throughout the system.
If the lines are too large, the velocity will be so low
that the pesticide will settle out and clog the system.
If the lines are too small, an excessive drop in pressure
will occur. A flow velocity of 5 to 6 feet per second is
recommended. The suggested hose sizes for various
pump flow rates are listed below.
The proper selection of nozzle type and size is the
most important part of pesticide application. The nozzle determines the amount of spray applied to a particular area, the uniformity of the applied spray, the
coverage obtained on the sprayed surfaces, and the
amount of drift. You can minimize the drift problem
by selecting nozzles that give the largest drop size,
while providing adequate coverage at the intended
application rate and pressure. Although nozzles have
been developed for practically every kind of spray application, only a few types are commonly used on lowpressure sprayers.These types are described below.
Regular Flat-Fan Nozzles
Regular flat-fan nozzles are used for most broadcast
spraying of herbicides and for certain insecticides when
foliar penetration and coverage are not required. These
nozzles produce a tapered-edge, flat-fan spray pattern,
and are available in several selected dspray-fan angles,
although 80-degree espray-angle tips are most commonly used. The nozzles are usually on 20-inch centers at a boom height of 10 to 23 inches. The boom
heights for various spray angles are shown below.
Spray angle
65. . . . . . . . . . . . . . . . . . . . 21-23
73................... .20-22
80 . . . . . . . . . . . . . . . . . . . .17-19
llO.................... 10-12
Hose sizes
Pump output
1-3 . . . . . . . . . . . . .
‘/ 2
3-6 . . . . . . . . . . . . .
6-12 . . . . . . . . . . . . .
12-25 . . . . . . . . . . . . . 1
25-5 0 . . . . . . . . . . . . . 1%
50-100 . . . . . . . . . . .
When applying herbicides with flat-fan nozzles,
the operating pressure between 15 and 30 psi. At
these pressures flat-fan
nozzles produce medium-tocoarse drops that are not as susceptible to drift as
the finer drops produced at pressures of 40 psi and
higher. Regular flat-fan nozzles are recommended for
Boom height,
20-inch spacing
1 l/4
Hollow-Cone Nozzles (Disc and Core Type)
some foliar-applied herbicides at pressures from 40 to
60 psi. These high pressures will generate fine drops
for maximum coverage on the plant surface.
Because the outer edges of the spray pattern have
tapered or reduced volumes, adjacent patterns along
a boom must overlap in order to obtain uniform coverage. For maximum uniformity, this overlap should
be about 40 to 50 percent of the nozzle spacing.
The LP or “low-pressure” flat-fan nozzle is available from the Spraying Systems Company. This nozzle develops a normal fan angle and distribution pattern at spray pressures from 10 to 25 psi. Operating at
a lower pressure results in larger drops and less drift
than the regular flat-fan nozzle designed to operate at
pressures of 15 to 30 psi.
Hollow-cone nozzles are used primarily when plant
foliage penetration is essential for effective insect and
disease control, and when drift is not a major concern.
At pressures of 40 to 80 psi, hollow-cone nozzles produce small drops that penetrate plant canopies and
cover the undersides of leaves more eflectively than
other nozzles. If penetration is not required, the pressure should be limited to 40 psi or less. The most
commonly used hollow-cone nozzle is the two-piece,
disc-core, hollow-cone spray tip. The core gives the
fluid a swirling motion before it is metered through the
orifice disc, resulting in a circular, hollow-cone spray
Whirl-Chamber Hollow-Cone Nozzles
Even Flat-Fan Nozzles
Whirl-chamber nozzles have a whirl chamber above
a conical outlet. These nozzles produce a hollow-cone
pattern with fan angles up to 130 degrees, and are
used primarily on herbicide incorporation kits. The
recommended pressure range is 5 to 20 psi.
Even flat-fan nozzles apply uniform coverage across
the entire width of the spray pattern. They should be
used only for banding pesticides over the row, and
should be operated between 15 and 30 psi. Band
width is determined by adjusting nozzle height. The
band widths for various nozzle heights are shown
Raindrop nozzles have been designed by the Delavan Corporation to produce large drops in a hollowcone pattern at pressures of 20 to 60 psi. The RD
Raindrop nozzle consists of a conventional disc-core,
hollow-cone nozzle to which a Raindrop cap has been
added. The RA Raindrop nozzle (a whirl-chamber
nozzle with the Raindrop cap) is used for herbicide
incorporation, and the RD Raindrop nozzle for foliar
spraying. When used for broadcast application, these
nozzles should be rotated 30 to 45 degrees from the
horizontal to obtain uniform distribution.
Nozzle height
Band width
. . . . . . . . . .
. . . . . . . . .
. . . . . . . .
. . . . . . . .
Hollow-Cone Nozzles
Flooding Flat-Fan Nozzles
Flooding flat-fan nozzles produce a wide-angle, flatfan pattern, and are used for applying herbicides and
mixtures of herbicides and liquid fertilizers. The nozzle
spacing for applying herbicides should be 60 inches or
less. These nozzles are most effective in reducing drift
when they are operated within a pressure range of 8
to 25 psi. Pressure changes affect the width of spray
pattern more with the flooding flat-fan nozzle than
with the regular flat-fan nozzle. In addition, the distribution pattern is usually not as uniform as that of
the regular flat-fan tip. The best distribution is achieved
when the nozzle is mounted at a height and angle to
obtain at least double coverage or loo-percent overlap.
Flooding nozzles can be mounted so that they spray
straight down, straight back, or at any angle in between. Position is not critical as long as double coverage
is obtained. You can determine nozzle position by rotating the nozzle to the angle required to obtain double coverage at a practicable nozzle height.
Material s
Nozzle tips are available in a wide variety of materials, including hardened stainless steel, stainless steel,
nylon, and brass. Hardened stainless steel is the most
wear-resistant material, but it is also the most expensive. Stainless steel tips have excellent wear resistance
with either corrosive or abrasive materials. Although
nylon and other synthetic plastics are resistant to corrosion and abrasion, they are subject to swelling when
exposed to some solvents. Brass tips are the most common, but they wear rapidly when used to apply abrasive materials such as wettable powders, and are corroded by some liquid fertilizers. Brass tips are probably
the most economical for limited use, but other types
should be considered for more extensive use. The figure
on page 10 shows the wear rates of a regular flat-fan
nozzle constructed of various materials.
Flooding Nozzle Operating Positions
Spray Overlap ( 50 Percent)
p--- 20"---1
Spray Overlap (100
Wear Rates of Various Materials (Regular Flat-Fan Nozzle)
cation rate (GPA) over a range of ground speeds.
The pressure is changed to vary the nozzle flow rate
according to changes in ground speeds. These systems
require calibration at a set ground speed. In the field,
speed changes must be limited to a range that maintains the nozzle pressure within its recommended range.
The performance of any pesticide depends upon the
proper application of the correct amount of chemical.
Most performance complaints about agricultural
chemicals are directly related to errors in dosage or to
improper application. The purpose of calibration is to
insure that your sprayer is applying the correct amount
of material uniformly over a given area.
Sprayed Width per Nozzle
The effective width sprayed per nozzle also affects
the spray application rate. Doubling the effective
sprayed width per nozzle decreases the gallons per
acre (GPA) applied by one-half. For example, if
you are applying 40 CPA with flat-fan nozzles on 20inch spacings, and change to flooding nozzles with
the same flow rate on 40-inch spacings, the application rate decreases from 40 GPA to 20 CPA.
The gallons of spray applied per acre can be determined by using the following equation:
GPM x 5,910
(Equation 1) GPA = --MPH x W
GPM = output per nozzle in gallons per minute
MPH = ground speed in miles per hour
W = effective sprayed width per nozzle in inches
5,940 = a constant to convert gallons per minute,
miles per hour, and inches to gallons per
Three variables affect the amount of spray mixture
applied per acre: ( 1) the nozzle flow rate; (2) the
ground speed of the sprayer; and (3) the effective
sprayed width per nozzle. To calibrate and operate
your sprayer properly, you must know how each of
these variables affects sprayer output.
Nozzle Flow Rate
The flow rate through a nozzle varies with the size
of the tip and the nozzle pressure. Installing a nozzle
tip with a larger orifice or increasing the pressure will
increase the flow rate. Nozzle flow rate varies in proportion to the square root of the pressure. Doubling
the pressure will not double the flow rate. To double
the flow rate, you must increase the pressure four
times. For example, to double the flow rate of a nozzle
from 0.28 GPM at 20 psi to 0.56 GPM, you must increase the pressure to 80 psi (4 X 20).
Pressure cannot be used to make major changes in
application rate, but it can be used to correct minor
changes because of nozzle wear. To obtain a uniform
spray pattern and minimize drift hazard, you must
keep the operating pressure within the recommended
range for each nozzle type. Remember - if you use
check valves to prevent nozzle drip, the pressure at the
nozzle is 5 to 7 psi lower than the boom pressure indicated on the pressure gage.
There are many methods for calibrating low-pressure sprayers, but they all involve the use of the variables in Equation 1. Any technique for calibration
that provides accurate and uniform application is
acceptable. No single method is best for everyone.
The calibration method described below has three
advantages. First, it allows you to select the number
of gallons to apply per acre and to complete most of
the calibration before going to the field. Second, it provides a simple means for frequently adjusting the
calibration to compensate for changes because of nozzle wear. Third, it can be used for broadcast, band,
directed, and row-crop spraying. This method requires a knowledge of nozzle types and sizes and the
recommended operating pressure ranges for each type
of nozzle used.
Ground Speed
The spray application rate varies inversely with the
ground speed. Doubling the ground speed of the
sprayer reduces the gallons of spray applied per acre
(GPA) by one-half. For example, a sprayer applying
20 GPA at 3 MPH would apply 10 GPA if the speed
were increased to 6 MPH and the pressure remained
Some low-pressure field sprayers are equipped with
control systems that maintain a constant spray appli-
The size of the nozzle tip will depend upon the application rate (GPA) , ground speed (MPH), and
effective sprayed width (W) that you plan to use.
Some manufacturers advertise “gallons-per-acre” nozzles, but this rating is useful only for standard conditions (usually 30 psi, 4 M P H and 20-inch spacings).
The gallons-per-acre rating is useless if any one of your
conditions varies from the standard.
A more exact method for choosing the correct nozzle tip is to determine the gallons per minute (GPM)
required for your conditions; then select nozzles that,
when operated within the recommended pressure
range, provide this flow rate. By following the five
steps described below, you can select the nozzles required for each application well ahead of the spraying
Step 1. Select the spray application rate in gallons
per acre (GPA) that you want to use. Pesticide labels
recommend ranges for various types of equipment.
The spray application rate is the gallons of carrier
(water, fertilizer, etc.) and pesticide applied per
treated acre.
Step 2. Select or measure an appropriate ground
speed in miles per hour (MPH) according to existing
field conditions. Do not rely upon speedometers as an
accurate measure of speed. Slippage and variation
in tire sizes can result in speedometer errors of 30
percent or more. If you do not know the actual
ground speed, you can easily measure it (see Measuring Ground Speed, page 17 ) .
Step 3. Determine the effective sprayed width per
nozzle ( W) in inches.
For broadcast spraying, W = the nozzle spacing;
For band spraying, W = the band width;
For row-crop applications, such as spraying from
drop pipes or directed spraying,
row spacing; (or band width)
number of nozzles per row (or band)
Step 4. Determine the flow rate required from each
nozzle in gallons per minute (GPM) by using a nozzle catalog, tables, or the following equation:
(Equation 2) GPM =
Example 1: You want to broadcast a herbicide at
15 GPA (Step 1) at a speed of 7 MPH (Step 2), using flooding nozzles spaced 40 inches apart on the
boom (Step 3 ) . What nozzle tip should you select?
The required flow rate for each nozzle (Step 4) is
as follows:
15x 7 x40
5,940 0.71
The nozzle that you select must have a flow rate of
0.71 GPM when operated within the recommended
pressure range of 8 to 25 psi. The table on page 14
shows the GPM at various pressures for several Spraying Systems and Delavan nozzles. For example, the
Spraying Systems TK5 and Delavan D5 nozzles have
a rated output of 0.71 GPM at 20 psi (Step 5). Either
of these nozzles can be purchased for this application.
Example 2: You want to spray an insecticide on
corn plants growing in 30-inch rows, using two nozzles
per row. The desired application rate is 15 GPA at
6 MPH. Which disc-core hollow-cone nozzle should
you select?
Because two nozzles spray each 30-inch row, W =
2= 15 inches. The required flow rate for each noz-
zle is as follows:
G P M = 15 X 6 X 15
= 0.23
Either a Delavan DC3-25 or a Spraying Systems
D3-25 disc-core nozzle (see table on page 14) has a
rated output of 0.23 GPM at 60 psi. This output is
within the recommended pressure range of 40 to 80 psi.
GPM =gaIlons per minute of output required from
each nozzle.
GPA = gallons per acre from Step 1.
MPH = miles per hour from Step 2.
W= inches sprayed per nozzle from Step 3.
5 , 9 4 0 = a constant to convert gallons per minute,
miles per hour, and inches to gallons per
After making sure that your sprayer is clean, install
the selected nozzle tips, partially fill the tank with clean
water, and operate the sprayer at a pressure within
the recommended range. Place a container (for example, a quart jar) under each nozzle. Check to see
whether all of the jars fill at about the same time.
Replace any nozzle that has an output of 5 percent
more or less than the average of all the nozzles, an
obviously different fan angle, or a nonuniform appearance in spray pattern.
To obtain uniform coverage, you must consider
the spray angle, spacing, and height of the nozzle.
The height must be readjusted for uniform coverage
with various spray angles and nozzle spacings. Do not
Step 5. Select a nozzle that will give the flow rate
determined in Step 4 when the nozzle is operated
within the recommended pressure range. You should
obtain a catalog listing available nozzle tips. These
catalogs may be obtained free of charge from equipment dealers or nozzle manufacturers. If you decide
to use nozzles that you already have, return to Step 2
and select a speed that allows you to operate within
the recommended pressure range.
Liquid pressure Capacity
Delavan Spraying Systems
Liquid pressure Capacity
Delavan Spraying Systems
use nozzles with different spray angles on the same
boom for broadcast spraying.
Worn or partially plugged nozzles produce nonuniform patterns. Misalignment of nozzle tips is a
common cause of uneven coverage. The boom must
be level at all times to maintain uniform coverage.
Skips and uneven coverage will result if one end of
the boom is allowed to droop. A practicable method
for determining the exact nozzle height that will
produce the most uniform coverage is to spray on a
warm surface such as a road and observe the drying
rate. Adjust the height to eliminate excess streaking.
Step 6. Determine the required flow rate for each
nozzle in ounces per minute (OPM). To convert the
GPM (Step 4) to OPM use the following equation :
(Equation 3) OPM = GPM X 128
( 1 gallon = 128 ounces)
From Example 1, page 13, the required nozzle flow
rate = 0.71 GPM.
OPM = 0.71 x 128 =91
From Example 2, page 13, the required nozzle flow
rate = 0.23 GPM.
OPM = 0.23 x 128 = 29
Now that you have selected and installed the proper
nozzle tips (Steps 1 to 5, page 13) you are ready to
complete the calibration of your sprayer (Steps 6 to 10
below), Check the calibration every few days during
the season or when changing the pesticides being applied. New nozzles do not lessen the need to calibrate
because some nozzles “wear in,” and will increase their
flow rate most rapidly during the first few hours of
use. Once you have learned the following method, you
can check application rates quickly and easily.
An alternative method for determining the OPM
is to use the table on page 15. Locate the GPA selected
in Step 1 in the lefthand column of the table. Follow
this line across to the column indicating the ground
speed that you determined in Step 2. The value shown
at the intersection of these two columns is the number
of ounces per minute (OPM) per inch of spray width.
To determine the output required per nozzle, multiply
this value by the inches of sprayed width per nozzle.
From Example 1, page 13, GPA = 15 ; MPH = 7 ;
W = 40 inches.
From the table, the value for OPM = 2.26. For a
nozzle spacing of 40 inches, the required flow rate =
2.26 x 40 = 90.4 OPM.
Step 7. Collect the output from one of the nozzles
in a container marked in ounces. Adjust the pressure
until the ounces per minute (OPM) collected is the
same as the amount that you determined in Step 6.
Check several other nozzles to determine if their
outputs fall within 5 percent of the desired OPM.
If it becomes impossible to obtain the desired output
within the recommended range of operating pressures,
select larger or smaller nozzle tips or a new ground
speed, and then recalibrate. It is important for spray
nozzles to be operated within the recommended pressure range. (The range of operating pressures is for
pressure at the nozzle tip. Line losses, nozzle check
valves, etc. may require the main pressure gage at
the boom or at the controls to read much higher.)
Step 8. Determine the amount of pesticide needed
for each tankful or for the acreage to be sprayed (see
Mixing Pesticides, page 17). Add the pesticide to a
partially filled tank of carrier (water, fertilizer, etc.) ;
then add the carrier to the desired level with continuous agitation.
Step 9. Operate the sprayer in the field at the
ground speed that you measured in Step 2 and at
the pressure that you determined in Step 7. You will
be spraying at the application rate that you selected in
Step 1. After spraying a known number of acres, check
the liquid level in the tank to verify that the application rate is correct.
Step 10. Check the nozzle flow rate frequently.
Adjust the pressure to compensate for small changes
in nozzle output resulting from nozzle wear or variations in other spraying components. Replace the nozzle
tips and recalibrate when the output has changed 10
percent or more from that of a new nozzle, or when
the pattern has become uneven.
Keep foreign materials out of the sprayer. These
materials can clog the nozzles and damage the pump
and other components. Thoroughly clean the spray
equipment to prevent injury to crops susceptible to a
previously applied pesticide. Some pesticides will cause
the equipment to deteriorate if they remain in the
sprayer for an extended period of time. The following
practices will help you to maintain and clean your
spray equipment properly.
1. Use only water that appears clean enough to
drink. Small particles often found in the water from
ditches, ponds, or lakes can clog nozzles and strainers.
If you are in doubt, filter the water as you fill the tank.
2. Check and clean the strainers daily. Partially
plugged strainers will create a pressure drop and reduce the nozzle flow rate. Most sprayers contain
strainers at three locations. The first location is on
the suction hose to protect the pump. The second is in
the line between the pump and the boom. The third,
which has the smallest openings, is in the nozzle body.
3. Do not use a metal object for cleaning nozzles.
When a nozzle becomes clogged, always remove it and
clean it. The nozzle orifice is precisely machined to
close tolerances, and the use of a metal object for
cleaning will destroy the orifice.
4. Flush a new sprayer before using. A new sprayer
invariably contains metal chips and dirt from the
manufacturing process. Remove the nozzles and
strainers; then flush the sprayer and boom with clean
water. Thoroughly clean each nozzle before reinstalling.
5. Clean your sprayer according to the formulation
of pesticide used.
To remove residues of oil-based herbicides, such as
esters of 2,4-D and similar materials, rinse the sprayer
with kerosene, diesel fuel, or a comparable light oil.
Do not use gasoline.
After rinsing the equipment with oil or a waterdetergent, fill the tank 1/4 to 1/2 full with a waterammonia solution ( 1 quart of household ammonia to
25 gallons of water) or a water-trisodium phosphate
Ground speed (MPH)
5 . . . . . . . . . . . . . . . . 0.32
10. . . . . . . . . . . . . . . . 0.65
l!i...................... 0.97
20...................... 1.29
30...................... 1.94
40...................... 2.59
(OPM per 1 inch of spray width)
(TSP) solution (1 cup TSP to 25 gallons of water).
Circulate the solution through the system for a few
minutes, letting a small amount go through the nozzles.
Allow the remainder of the solution to stand at least
6 hours; then pump it through the nozzles. Remove
the nozzles and strainers and flush the system twice
with clean water.
Equipment in which wettable powders, amine forms,
or water-soluble liquids has been used should be
thoroughly rinsed with a water-detergent solution (2
pounds of detergent in 30 to 40 gallons of water).
Water-soluble materials should be treated as watersoluble liquids. Allow the water-detergent solution to
circulate through the system for several minutes. Remove the nozzles and strainers and flush the system
twice with clean water .
6. When it is time to store your sprayer, add 1 to 5
gallons of lightweight oil, depending upon the size of
your tank, before the final flushing. As water is pumped
from the sprayer, the oil will leave a protective coating
inside the tank, pump, and plumbing. To prevent
corrosion, remove the nozzle tips and strainers, dry
them, and store in a can of light oil, such as diesel
fuel or kerosene.
7. Corrosive fertilizer solutions should not be used
in certain sprayers. Liquid fertilizers are corrosive to
copper, galvanized surfaces, brass, bronze, and steel.
You can damage an ordinary sprayer irreparably by
one use of a liquid fertilizer. Sprayers made completely
of stainless steel or aluminum are available for applying
liquid fertilizers. Aluminum is satisfactory for some
nitrogen fertilizers but not for mixed fertilizers.
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