R. P. Cromwell
Much equipment used in aquatic herbicide applications is similar to that used
in agricultural
applications. However, modifications are made to adapt equipment to unique situations such as
applying from boats and injection of herbicides into deep water. This chapter discusses the use
of
conventional herbicide application equipment and adaptations for use with aquatic
herbicides.
Liquid Formulations
The majority of aquatic herbicides are formulated as liquids. The equipment needed for
applying liquids depends on which of the two methods below is used:
b. Direct metering into pump suction. The herbicide is
metered into the suction side of the pump at the rate needed to apply the correct
amount per acre. The diluent needed to ensure adequate coverage is drawn directly
from the body of water being treated.
Aquatic weeds are treated from boats with outboard engines, airboats, fixed-wing aircraft and
helicopters. The type of application equipment used is dictated to some degree by which vehicle
is
used.
Spraytank Applications
Figure 3 shows a typical sprayer used to apply herbicides from a boat. Features of the sprayer
components are described below.
Tank.
Agitation system
A well-designed hydraulic agitation system that uses a venturi device for stirring is adequate
for keeping wettable powders in suspension. However, this type of agitator will not stir the
mixture
enough to form invert emulsions or mix polymers. To function properly, the hydraulic agitation
line
must be tapped into the high-pressure side of the pump (Figure 3). When using a hydraulic
agitator,
the pump must have the capacity to simultaneously deliver the required flow to the boom or
handgun
and the agitator. If the maximum pressure that can be achieved after completely closing off the
pressure regulator is lower than the pressure needed, the agitator orifice size must be reduced.
Mechanical or paddle wheel agitators are probably the best type of agitator. Well-designed
mechanical agitators stir the mixture vigorously and allow the use of both polymers and invert
emulsions. Sometimes a clutch is added to the agitator drive, and the operator can keep the
mixture
at the desired consistency by agitating only when needed.
Hoses
A pressure hose must be strong enough to withstand the maximum pressure within its length
without bursting. Pressure varies at different points along the hose, with the greatest pressure
occurring at the pump. Hose size is important because the pressure loss in the hose depends on
the
hose inside diameter (ID), length and flow rate (Figure 5). For example, a 1/2-in. ID hose loses 1
psi
per foot at a flow rate of 10 gal per/min.
Pressure loss in relatively short hoses is not very important, but it is important to choose the
proper hose size when extremely long hoses are used, such as in some handgun spraying work.
Recommendations for hose sizes are presented in Table 3.
Table 3. Recommendations for hose sizes.
Suction hoses are under a partial vacuum; they will not burst but they can collapse. Choose
a suction hose that is reinforced to prevent collapsing. A collapsed suction hose can restrict flow
of
liquid and starve a pump. This will cause decreased outflow and greatly accelerated wear. As a
rule
of thumb, suction hose diameters should be at least as large as the pump inlet port.
Polyvinyl chloride (PVC) pipe works well for rigid plumbing, however, caution should be
used in selecting the valves. For example, a 1-in. valve can be plumbed to a 1-in. pipe, but the
opening inside the valve may be restricted to 0.5 in. in diameter.
Pumps
Most pumps used for applying liquid herbicide
formulations are of five general types: roller, piston, centrifugal, diaphragm and gear. Each type
has
certain capabilities and limitations that determine when it should be chosen. Characteristics of
the
various pumps are listed in Table 4.
Table 4. Characteristics of the various pumps.
Roller Pumps have the advantage of being relatively
inexpensive. They are widely used in agriculture on general-purpose crop sprayers. However,
roller
pumps are not often used for aquatic weed control work because they do not produce the high
pressures needed for handgun spraying. While a pressure capability of 300 psi is stated for a
roller
pump (see tabulation above), which is adequate for handgun spraying, the pump would not be
able
to sustain high pressure very long because the rollers wear and fluid leaks back past the rollers.
Figure 6 shows how to plumb a liquid application system using a roller pump. The system has a
hydraulic agitator that would only be suitable for systems not used to apply invert emulsions or
sprays
containing polymers.
Piston Pumps are often used in aquatic weed control because
they can deliver high pressure for hand-gun spraying. These pumps are dependable, long lived,
and
highly adaptable to most types of service. Their primary disadvantages are that they are
expensive
and deliver relatively low volume, although the volume is usually sufficient for aquatic
applications.
A piston pump is a positive displacement pump, which means that the output depends on the
displacement of the piston in the cylinder. Output is proportional to speed and virtually
independent
of the pressure needed to force the flow through the orifice area on the system.
Output from a piston pump is not steady. It comes in spurts because the distance that the
piston travels in the pump cylinder varies with time. This problem can be eliminated through the
use
of a surge dampener. Pulsation is especially noticeable for pumps with a small number of
pistons
(small pumps often have two pistons). The pulsing nature of the flow makes a surge tank
desirable.
The system should also be equipped with a glycerine-filled pressure gauge (glycerine dampens
movement of the gauge needle). These gauges last longer and can be read more easily than
nondampened gauges on piston pump-equipped systems.
Figure 7 shows how to plumb a system equipped with a piston pump. The system includes
an unloader valve that is especially useful when spraying with a handgun. When the gun is shut
off,
the system pressure rises until it is sufficient to overcome the spring force on the unloader valve.
The
valve will crack open and bypass fluid back to the tank. Without the unloader valve, the pressure
would continue to rise until a hose bursts. The plumbing system shown in Figure 7 is
appropriate
for
all of the positive displacement pumps, including diaphragm and gear pumps, as well as the
piston
type.
Centrifugal Pumps deliver high flow rates when working
against a low pressure. These pumps are especially useful for transferring fluids from one tank to
another or from the body of water into the tank when refilling.
Centrifugal pumps are not suitable for most systems used in aquatic weed control because of
the inability to generate high pressures. Small centrifugal coupled to a small two-stroke cycle
engine
are sold by some manufacturers and are particularly useful for tank refilling.
Diaphragm pumps are now used in many applications instead
of piston pumps. Benefits of diaphragm pumps include relatively low cost, low maintenance and
small size compared with other pumps with similar flow and pressure ratings. Like piston
pumps,
diaphragm pumps are positive displacement pumps so the pump output depends on pump speed
and
remains constant regardless of the pressure it is working against.
Gear pumps are used in a number of applications and are
positive displacement pumps capable of high pressure. The corrosive chemical comes in contact
with
the pumping gears, so maintenance can be a problem. Gear pumps are becoming less popular
and
are being replaced by diaphragm and piston pumps in many installations.
Nozzles
The spray nozzle forms the spray pattern, determines
the droplet size and meters the flow rate. Nozzle selection is based on a balance of these three
functions. Many types of nozzles are used in terrestrial weed control. However,
because of the
nature of aquatic weed control, the variety of nozzles used in aquatic spraying is much less. The
method of application (submersed or surface) determines the nozzle type selected. The four primary
application methods and nozzle considerations in aquatic weed control are:
2. Subsurface injection just below the water surface for submersed weed
control:
Usually short hoses are spaced at approximately 2-ft intervals on a short, bow or
stern-mounted boom. Hoses are just long enough to place the nozzle at the water
surface or just below it (Figure 8). The nozzle body contains a disk that meters the
flow into the water.
3. Bottom placement or deep-water injection: Nozzles are located at the
end of long
hoses that trail from a boom on the bow of the boat. Hoses are usually weighted to
keep the herbicide placement deep within the weed mat or near the bottom (Figure
9). A common arrangement involves constructing a nozzle by drilling small holes in
a piece of galvanized pipe. The length of the pipe depends on how much weight is
needed to lower the hose to the desired depth. Pipe length varies from 9 to 30 in.
The pipe is capped on one end and attached to the hose on the other. Deep-water
injection hoses must not have any clamps or protrusions that will catch and hold
plants.
4. Aerial applications: Aerial applications normally use hollow cone or flat
fan nozzles
to improve coverage with the smaller volume of spray solution applied per acre. A
specialized aerial boom designed to produce a large droplet size at low pressure and
low volume is the microfoil boom.
When large areas are treated, it is often more efficient to meter the
herbicide into the suction side of the pump and eliminate the time spent filling and mixing
tanks. Water is drawn into the pump through "water boxes" built into the bottom
of the spray boat (Figure 10). Normally, one or more plastic tubes are tapped into the pump
suction
line. Each tube has a valve for opening and closing the lines. Tubes have an in-line orifice used
to
meter the correct amount of herbicide into the system. Figure 11 shows how a typical herbicide
withdrawal hose is constructed.
A number of suction hoses can be used so application can continue without interruption.
When the herbicide in the container being used is depleted, the applicator opens a valve in the
hose
in a second container and closes the valve of the empty one.
Other than not using a tank and having the previously described equipment on the suction side
of the pump, equipment used for spraying in this manner is very similar to tank-mix units.
Invert emulsions
An invert emulsion contains water droplets dispersed in a continuous oil
phase. This is contrasted to a normal emulsion, which is oil droplets dispersed in a continuous
water phase. Invert emulsions, which are a thick mayonnaise-like material, do
not
generate as many fine droplets as water-based sprays, and the emulsion adheres to the target
vegetation. Invert emulsions are often used as a carrier for herbicide sprays
when working in areas where spray drift would be especially detrimental.
Suction side metering equipment is usually used for invert emulsion applications but tank-mix
inverts can also be made. Various proportions of diesel fuel or xylene and an emulsifying agent
were
used in the past for making invert emulsions; special lighter oils are usually used now.
When mixing the invert in a tank, the ingredients are added to the tank and the vigorous
stirring of a good mechanical agitator causes the formation of the emulsion. If there is no tank, a
mixture of the oil and emulsifier is metered into the pump's suction line in the right proportion.
Water, oil, and emulsifier then pass through the pump and into a mixing unit that vigorously
agitates
the mixture and forms the invert emulsion. There are at least two types of mixing units. One is a
power-driven unit that does the mixing in a manner similar to household mixers. The other type
unit
has baffles similar to an exhaust muffler. Ingredients mix because of the turbulence caused by
changing directions as the liquid flows through the unit.
This description simplifies the procedures of using an invert system. Invert pumps and
systems are generally expensive, must be kept airtight and experience is required to set up,
operate
and maintain a trouble-free system. Expertise from a manufacturer or agency familiar with
inverting
systems should sought before setting up a system.
Applying sprays containing polymers.
Polymers are long-chain carbon molecules which, when united with
water, thicken the solution and increase the number of large droplets. They are often used
when spraying surface weeds with a handgun.
Applicators may find that the output from their sprayer will diminish greatly when spraying
with 1 to 2 percent polymer. The reason often given for the flow reduction is that the
water-polymer
mixture flows less readily, and the pump is unable to force the material through the nozzles,
however,
this is not the reason for the reduced flow.
Positive displacement pumps normally used in aquatic weed spraying have the capability to
force any amount of material that enters the pump out of the pump. If the engine speed (rpm) is
set
by a governor (as are most small gas engines that power sprayer pumps used in aquatic weed
spraying) the output will be the same for a viscous liquid as it would be for water, as long as the
same
amount entered the pump. The difference is that the pressure required to force the viscous liquid
through the discharge hose would have to be greater. More pressure means the engine has to
deliver
more horsepower.
Output reduces when using these high concentrations of polymer because the amount entering
the pump suction is reduced. Flow rates of water and water-polymer mixture through a given
nozzle
at a given pressure vary little. Most of the flow reduction is because the pump is starved on the
suction side. A system used to apply water-polymer mixtures should have
extra-large suction lines with a minimum of fittings between the tank and pump
inlet.
Granular Formulations
Granular herbicides are normally applied with a bow-mounted centrifugal or blower-type
spreader (Figure 12). Centrifugal spreaders can treat a wide swath when relatively large granules
are
used. The ability to treat a wide swath (30 to 40 ft) without requiring any type
of structure extending beyond the sides of the boat makes granular application attractive. The
disadvantage is the large quantity of material (20 to 400 lb/acre) that must be handled.
The rotor that slings the granules is driven by a 12-volt DC motor. Normally,
the
spreader is purchased as a complete unit except for the mounting system. Because boats used to
treat
aquatic weeds are normally used to apply both sprays and granular applications from the bow,
the
spreader is usually mounted so that it can be quickly removed.
Blower-type spreaders use air pressure generated by a low pressure high speed 2-cycle
blower, with a venturi discharge nozzle to propel the granules. An advantage of
blower type spreaders is that little dust is created as compared to that created when the
mechanical rotor of centrifugal spreaders strikes pellets or granules.
a. Spraytank. The herbicide and the diluent usually
water, are mixed in a tank, and the mixture is applied to the weeds.
The spraytank method is suitable for treating relatively small areas or when
mixing several herbicides. When large areas are treated, it may be more efficient to use the
direct metering method to reduce the time spent refilling the tank.
The boat-mounted tank, usually made of fiberglass, has
a capacity of 50 - 100 gallons. Usually the tank will have graduations on the side that indicate
the
volume at that level. The tank should have a large opening for easy filling and cleaning.
Figure 3. Typical boat-mounted tank mix sprayer for applying aquatic
herbicides.
Most spraytanks are equipped with some
type of agitation system. Good agitation is important for maintaining a uniform
spray mixture and for mixing of adjuvants such as inverting oil or polymers.
Figure 4 shows hydraulic and mechanical agitators. Some tanks are equipped with both types of
agitators.
Figure 4. Agitation systems for keeping aquatic herbicides and adjuvants in suspension.
The inner and outer layers of all hoses should be
resistant to the chemicals used. Check with the chemical and hose supplier if there is any doubt;
a
hose weakened by chemicals might leak or burst unexpectedly. Two materials widely used for
hoses
are ethylene vinyl acetate (EVA) and ethylene propylene dione monomer (EPDM).
Pump output (gpm) Suction Side Pressure SideHose size (in)
<_12 3/4 5/8
12-25 1 3/4
26-50 1-1/4 1
Figure 5. Pressure drop in hoses.
PUMP CHART GOES HERE
Figure 6. Basic plumbing for a roller pump system.
Figure 7. Basic plumbing for a piston pump system.
1. Handgun spraying of surface, emersed, and ditch bank species:
Handguns are
equipped with nozzles that provide a high flow rate (3 to 6 gal/minute), a straight
stream, and a large droplet size. This arrangement ensures thorough wetting of the
target vegetation with minimum spray drift.
Direct Metering into Pump
Figure 8. Hoses for herbicide injection just below the water surface.
Figure 9. Hoses for deep injection of aquatic herbicide.
Figure 10. Basic system for withdrawing herbicide directly from container and water
from boat bottom intakes.
Figure 11. Plumbing for herbicide withdrawal hose.
Figure 12. Blower type spreader for granular aquatic herbicide
formulations.
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