Ministry of Agriculture
Pesticide Application Equipment
Essential components of any chemical spraying equipment are the power source, pump, tank and nozzles. Others which must be considered are agitators, screens, filters, valves, pressure regulators, booms, hoses, gauges and hand-guns.
The power-sprayer is normally driven by the PTO (power take-off) of the tractor or by an auxiliary engine. The power rating of these should be double the theoretical power required by the pump.
A pump creates the pressure required for atomization and penetration of the spray on almost all types of sprayers.
Choose a pump that: has enough capacity for your spraying needs, can produce the desired operating pressure at the capacity you need, can handle the pesticide formulations you need without wearing or corroding too much, can be repaired economically and quickly, and can be used with your power source.
Common pumps include:
- roller pumpexcessive wear can occur with wettable powders
- piston pump
- diaphragm pump
For spraying insecticides or fungicides, sprayers require
either diaphragm or piston pumps to develop the higher pressures
needed (700 kPa or 100 psi) to get thorough plant coverage.
Determine the capacity of the pump by the highest rate of
application the sprayer is expected to deliver, an adequate
volume for agitation and an additional 25% volume to account for
the pumps wear. During operation there should always be flow in
the bypass line indicating the pump has enough capacity to
send some excess to the tank. Note the maximum rpm allowed for
the pump and always operate the tractor throttle so that the
maximum is not exceeded. Be aware that increasing the pumps rpm
will also increase its output, therefore, the tractors throttle
setting must not change during calibration and sprayer operation.
Operating at too low an rpm may decrease the pumps output below
that required for the sprayer.
The size of the spray tank depends on the intended application rate and the mounting space available. The tank should be equipped with a large screened opening for easy filling and cleaning. Tanks may be constructed of steel, stainless steel, epoxy-coated steel, fiberglass, polyethylene or aluminum. Fiberglass, stainless steel and polyethylene tanks are preferred because of their rust and corrosion resistance.
The herbicide Roundup and liquid nitrogen fertilizers must not be put in galvanized steel tanks, as a hazardous chemical reaction can result.
The rusting of steel tanks can be reduced by proper draining, cleaning and airing of the tank after use and by the use of rustproofing compounds.
|Fiberglass tank||A screen is needed in the tank opening|
The tank must have either hydraulic bypass or mechanical agitation. If hydraulic agitation is used in the spray tank, additional pump capacity is required.
Mechanical agitation with paddles gives the best mixing for wettable powder formulations. If hydraulic agitation is used, 1/10 to 1/20 of the tank capacity should be recirculated per minute. This flow should be supplied from a separate pressure line, not from the relief valve bypass.
Tanks should be equipped with drains in the lowest part of the tank to allow complete emptying of the tank. Drains should be easy to operate to encourage operators to drain the tank at the end of each day.
For proper mixing of pesticide dilutions it is important to
know the volume capacity of the spray tank.
Suction hoses (from the tank) should be reinforced so they will not collapse, be resistant to chemicals and oils, and be of the same diameter as the pump inlet hole. The same type of hose can be used for the bypass line.
Hoses on the pressure side of the pump must be able to handle
pressures higher than the intended use and preferably as high as
the maximum pressure the pump can develop. To avoid excessive
pressures on the hose the relief or unloading valve should be
released before flow to the boom is shut off.
The size of droplet produced by various nozzles depends upon operating pressures and nozzle design. The droplet size decreases with a higher pressure and with a smaller nozzle tip opening. Droplets that are too big give poor coverage and droplets that are too small drift easily.
Types of Nozzles:
Nozzles help control the amount of spray applied, the size of spray droplets, the specific pattern, and the uniformity of the application. Often, several types and sizes of nozzles are needed, Select the best pattern and size of nozzle for your spraying needs. The main nozzle types used for chemical application are:
- Flat spray nozzles (Also called fan type or TeeJets):
These are used for low-pressure spraying such as the application of herbicides and insecticide drenches. They produce a fan-type pattern with less material applied along the edges of the spray pattern. By properly overlapping the spray, a uniform application is produced across the spray boom. Offset flat spray nozzles at an angle of 10 degrees to the boom to prevent interference of the overlapping spray patterns. Nozzle spacing on the boom and the height of the boom above the target are critical to obtain a uniform application. Sprayer equipment suppliers and nozzle manufacturers catalogues can advise growers as to the correct height of the boom at different nozzle spacings and for different nozzle spray angles. Do not operate these nozzles above 400 kPa (60 psi) to prevent excessive wear and fine spray droplets. Refer to manufacturers specifications for recommended nozzle pressures.
- Even spray nozzle tips:
These produce an even spray pattern across the entire fan width. These nozzles are used in band spraying of herbicides where there is no overlap from other nozzles. Align even spray nozzles with the spray boom. These nozzles are designed to operate at low pressures (less than 400 kPa or 60 psi). Refer to manufacturers specifications for recommended nozzle pressures.
- Cone nozzle tips:
These are used for medium to high-pressure spraying (mostly fungicides and insecticides). These nozzles produce a good swirling mist so the spray material can reach the undersides of leaves. Nozzle spacing should allow the adjacent spray patterns to cover the entire target otherwise skips may occur. An example of skips would be when the nozzles (and boom) are too close to plants - the plants close to the boom and between the nozzles will be missed. Cone nozzles are available as either hollow cone or solid cone types both produce the same swirling mist but the solid cone nozzles are used when larger volumes are required. Cone nozzles are used in both boom and most air-blast sprayers.
- Air-shear nozzles:
These use a high-speed air stream to break up the liquid into droplets, so this nozzle is limited to air-blast sprayers with a high-velocity air discharge (at least 250 km/h or 150 mph). Air shear nozzles operate at low pressures and have large openings which minimizes plugging. Air-blast sprayers using regular cone nozzles normally operate at air-velocities of 160 km/h (100 mph) and air-velocity is not critical for droplet formation.
Various sizes of flat, even and cone nozzle tips may be used to obtain the volume of water desired. Consult with your sprayer equipment supplier for information on nozzle outputs for the various nozzle sizes. Ask for a catalogue with nozzle outputs in litres per minute.
Nozzle Tip Materials
Nozzle tips are made from a variety of materials. Choice of material depends upon the abrasiveness of the spray mixture. Wettable powders are more abrasive than emulsions. Brass tips are cheap but the metal is softer and the tips wear faster. In increasing order of durability the following materials are used: plastic, brass, stainless steel, hardened stainless steel, ceramic and tungsten carbide. By making flat and even spray tips out of colored plastic with a small amount of stainless steel or ceramic in the center with the spray orifice, the more durable tips can be made at a very reasonable cost. These nozzles are more cost-effective than nozzles made entirely of brass.
|Cone nozzles - nozzle discs and cores|
|Nozzle screens and strainers|
As nozzle tips wear out, the rate of application increases. Tests have shown that some wettable powders wear nozzle tips sufficiently to increase the rate as much as 12% after spraying only 20 ha. For this reason, frequent calibration of equipment is necessary. Also, very worn nozzles should be replaced because their spray pattern is distorted and uneven application will result.
Screens prevent foreign material from entering the system, clogging the nozzles and wearing out the sprayer.
|Different mesh sizes of screens for line strainers||Clean line strainers regularly|
Suction strainers, line strainers and nozzles should all be equipped with 50 mesh or coarser screens when wettable powders are to be used. Some pesticides may require coarser suction strainers. It may be necessary to have more than one suction strainer for the sprayer. Screens finer than 50 mesh (100 mesh, for example) may plug with some wettable powders.
Screens are generally used in fine nozzles, but slotted strainers can be used in those that have a larger opening. Consult the nozzle manufacturers catalogue for recommendations on specific screen mesh sizes for specific nozzles. Generally for flat spray nozzles with small holes (TeeJet 80015 or smaller) a 100 mesh nozzle is recommended. Generally larger nozzles (TeeJet 8002 to 8008) should use a 50 mesh screen. Disc-core cone nozzles should normally be used with a slotted strainer equivalent to a 16 mesh screen (any Spraying Systems D3 or larger disc and No. 25 and larger core). A slotted strainer equivalent to a 25 mesh screen should be used with D2 discs.
Clean screens and strainers are essential to the efficient operation of the spray system. They should be cleaned often and checked for breaks in the screen. If the nozzle screens are plugging too often, check to make certain the chemicals are properly mixed, the spray tank and plumbing system are properly rinsed and cleaned between sprays, and that the suction and tank screens are in place when filling and using the sprayer. If the plugging problem persists, consider changing to an alternative pesticide formulation. Also check to see if a larger nozzle that has a larger recommended screen size can be used. Do not operate the sprayer without the recommended nozzle screens.
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