2.2 Types of sprayer
According to (Fraser and burrill 1979) The
most important goal in the application of agricultural pesticides is to
get uniform distribution of the chemicals throughout the crop foliage.
Under-dozing may not give the desired coverage and control needed.
Over-dozing is expensive as it wastes pesticides and increase the
potential for ground water contamination.
Two general types of
sprayers are available for application of pesticide, hydraulic and low
volume. There are many variations of these that fit particular crops or
growing methods.
In the hydraulic sprayer, a pump supplies energy
that carries spray material to the target (plant foliage) water is the
carrier and the pump creates the pressure at 40 – 1000 psi. spray
materials is usually applied to “wet†or “drip†nozzles on the boom or
handheld gun break the spray into small droplets and direct it to the
foliage.
In a low volume (LV) sprayer, spraying materials in a
water or oil carrier is infected into a high speed air stream developed
by a fan, blower or compressor. In most LV sprayers a small pump is
used to inspect a concentrate pesticide solution into the air stream.
The speed of the air stream may be as high as 200mph. To get sufficient
coverage, the air within the foliage canopy must be replaced with air that contain the pesticide. As the droplet size is much smaller, good
coverage can be achieved with less chemical. (Fraser and Burrill
1979)
2.3 Sprayer Differences
One way to distinguish between a hydraulic sprayer and law volume sprayer is by droplets size. Hydraulic sprayers produce a spray with most droplets in the 200 – 400 micron diameter range (thickness of the human hair is about 100 microns) or fig (0.05 – 50 microns). Small droplets from a mist or fog applicator can result in more uniform coverage and greater likelihood of contact with the insect or disease in contrast to the hydraulic sprayer. Sprayer material is usually applied to “glisten†as it is difficult to see the individual droplets on the leaf.
One disadvantage to smaller droplets is that they evaporate quicker when the humidity is low and may not reach the target. Another is that the tiny droplet tend to bounce or skip on the leaf surface. This can be overcome somewhat by adding a spreader and sticker. (Fraser et al 1979)
2.3.1 Types of Hydraulic Sprayer
A Hydraulic sprayer contains the following components: Tank, pump with agitator, pressure gauge, regulating valve, relief value, control valve, pipe and nozzles. Power source and support frame.
Compressed air sprayer: The smallest sprayers are hand carried compressed air sprayers. They contain a 1 to 5 gallon tank with an air pump in the top and a wand with a nozzle for directing the spray. Their belt use is for spot treatment of small areas. In operation the tank has to be pumped up frequently to maintain pressure and the tank must be shaken to agitate the chemical.
Backpack Sprayer: The tank in the sprayer holds about four gallons of materials. A hand operated pump pressures the spray materials as the operator walks along and the wand with nozzle directs the sprayer to the target. Its use in small areas that can be reached from a walkway.
Skid-Mounted Sprayer : With a tank size up to 200 gallons. These sprayers will fit onto an ATV or electric cart. They can also be mounted on wheels and pulled by hand or with a compact tractor. A small electric or gas engine powers the pump. The unit way contains a hose reel and gun or a boom with nozzles.
Irrigation Boom Sprayer : With increasing production in plug and cell trays, the use of the boom sprayer has become an important tool for getting uniform watering by installing three way turrets with nozzles for irrigation, misting and pesticides application, one piece of equipment serves multipurpose. An alternate method is to aid a pesticide application boom to the same transport cart. An independent mixing tank, pump, filter and valves are needed.
Central Pesticide Application System: In gutter connected ranges, it is possible to install a piping system that will deliver pesticides to any part of the greenhouse. Pesticide preparation and filtration are done in a mixing area. A single pump and piping that will handle the pressure developed and required. A hose can be easily attached to one or more outlets in each bay to apply the pesticide. The disadvantage is that the entire system must be drained and cleaned before changing to a new chemical. (Fraser, et all 1979)
Types of Low Volume Sprayers
According to Fraser et al (1979) Types of sprayer are
Backpack mist blower: A small gas engine and integral fan creates an air stream with a velocity of 100 – 200 mph, concentrate spray injected into the air stream by a special nozzle is carried into the foliage by the air. The spraying techniques is more complicated than with a hydraulic sprayer. The nozzle should be directed into the plant canopy to get good penetration and coverage but it should be kept at least six feet away from the plant to avoid blast damage. The operator should visualize that all the air within the canopy must be replaced by air from the mist blower.
Rotary Disc Sprayer: The spinning disk is used to impact and break a stream of water into droplets that are 60 – 80 microns in diameter. A variety of series are available for green house use.
Thermal forger: This machine required a specially formulated carrier that is mixed with the pesticide to improve uniformity of droplets size and distribution of the spray material. The carrier also decreases molecular weight allowing the particles to float in the air for up to six hours, a disadvantage if you have to get into the greenhouse to care for the plants. In the operation of thermal forger, the pesticide is injected into an extremely hot, fast-moving air stream that vaporizes it into for pesticides. Moving from one end of a greenhouse to the other, a thermal forger can cover in as little as 15minutes. A circulation from an HAT system will give more uniform coverage. Temperature and humidity also affect the spray droplets. Because of the noise associated with the jet engine, hearing protection is recommended.
Mechanical Forger: Also called a cold fogger, this device uses a high pressure pump (1000 – 3,000 psi) and atomizing nozzles to produce fog size particles. Distribution of the spray material is through a hand-held gun or external fan unit. With the fan unit, the distance and amount of area that can be covered depends on the capacity of the fan. Multiple units of settings may be needed to cover large areas. (Fraser and burrill 1979)
