Sprayers
Introduction 
Dusters Sprayers Type of appliances Selection of appliance Selection of equipment Application Technique Target and application method Working principle of spray equipment Spray Volume Spray calibration Spray droplets Leaf Area Index (LAI) Selecting a spray nozzle Every sprayer should have Plant protection equipment classification Before spraying During spraying After spraying
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- No matter how well the sprayer is designed and equipped, even if it is new, all sprayers wear out and deteriorate.
- All parts should be inspected. Worn out, broken and damaged parts should be replaced.
- These costs are nominal, compared with the value of the chemicals to be used. The nozzle is the most neglected, precision component of sprayer.
- If nozzle is worn out and delivers a 10 % overdose, chemical wastage in a couple of hours would cover the cost of a new one.
- A detailed instruction book giving simple advice and illustrated drawing of component and assemblies are provided with each new sprayer.
- To avoid guess work and waste of time, it is necessary to specify correct name and code number of the part specified in the manual. Parts that are likely to be needed should be kept in stock.
- Extra time should be devoted to the sprayer at the end of the spraying season, before it is kept in the store.
- Sprayer should be cleaned thoroughly, since residual chemical if left over for several months will corrode parts of sprayer. Filters and Nozzles should also be cleaned thoroughly.
- Corroded parts should be painted. The pump should be greased and operating / moving parts should be well oiled.
TopHand Rotary Dusters
Rotary type dusters
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- Rotary dusters are provided with an agitator, which stirs the powder and releases it evenly through the discharge vent.
- The blower sucks the dust or powder from the hopper through the connecting pipe, and pushes it out forcefully to achieve efficient dispersal.
- The operator carries the duster by means of one or two shoulder straps, and holds the lance in his left hand cranking the handle with his right.
Plunger type duster
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Bellows type dusters
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Power operated dusters
Rotary type
- Here the air is sucked in by a motorized blower and discharged through the blower outlet.
Air Jet Type
- A jet air from the blower enters the hopper, which agitates the dust and blows it out simultaneously with a jet of air.
Manually operated sprayers
Foot operated sprayers
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Rocker type sprayers
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Pressure retaining knapsack sprayers
- Also known as the Battery Sprayer, this model permits the use of more than one tank depending upon the number of operators employed.
- A separate charge pump with an inlet and an outlet device is used to fill the tank with air and liquid. The tank is first pumped with air upto a pressure of 40 – 50 psi and then charged with liquid, boosting the pressure to 100 – 110 psi.
- As soon as the liquid is completely discharged from the tank, a check valve designed like a float seals the outlet vent, preventing the air from escaping.
Compression sprayers
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Knapsack sprayers
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- The tank is non-pressurised and made of brass, or galvanized steel. The pump may be fitted into or outside the tank, and sucks the liquid from the tank and expels it through the discharge line.
- A spray boom or rig may be attached when wider areas have to be covered. The knapsack sprayer develops 30 – 40 psi pressure.
Bucket sprayers
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Nursery sprayers
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ower Operated Sprayers
Hydraulic sprayers
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- Hydraulic sprayers may be engine or electric motor driven, and are available with single, double, and the triple piston pumps.
- The single piston pump develops a maximum pressure of 150 psi, whereas the double and triple piston type develops 300 – 400 psi. Only two discharge lines can be used with the single piston pump, whereas the double and triple piston pumps can accommodate 4 – 6 discharge lines.
- Operation is by means of 1 – 2 HP electric motor, or 2 – 3 HP petrol, petrol-kerosene or diesel engine.
- These sprayers can also be driven by a power tiller or tractor.
Motorised Knapsack Mistblower cum duster
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- This agitates the powder which is then thrust out by the velocity of the air coming out of the blower, through the pleated hose and out through the nozzle.
Tractor mount sprayers
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- The boom has a swivel arm to direct the spray correctly. The main frame allows the spray boom to be adjusted according to the height of the crops being sprayed.
Spinning disc sprayers
- Liquid is fed from the tank on to the spinning disc by the force of gravity. The spinning disc, which has 180 channels on the wall and 180 teeth on its periphery, operates at 4000 – 5000 rpm to stir the liquid and create very fine, even particles for low volume spraying.
- A smooth flow of liquid with highly controlled droplet (100 – 165 microns) application is thus achieved. The stainless steel disc is interchangeable.
Electrostatic spraying
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- In this process, a free charge flows to the plant in response to the presence of an electrical field, which is created by a charged cloud. The surface charge is of the opposite polarity to the charged cloud, and has a magnitude and distribution that maintains the plant at ground potential (Zero Volts) in the presence of the charged cloud.
- The most commonly used version of this new system is the hand-held Electrodyn Sprayer, which atomises and propels charged droplets, by means of electrical forces set up between a high voltage, positively charged nozzle, the droplets and the earthed crop.
- The formulation is fed by gravity to the ‘bozzle’ (bottle plus nozzle) where it picks up a high voltage charge.
- The formulation then forms a number of uniform ligaments, which in turn are broken up into electrically charged droplets.
- These droplets are of uniform size and mutually repellent and form a tenacious, even coating all over the crop, including stems and undersides of leaves.
- No mechanical energy is required at the nozzle to induce droplet formation; neither are compressors or centrifugal energy employed, so the whole system works without moving parts.
- Pesticides are available in various forms.
- Application Equipment are designed according to the types of formulations to be sprayed.
- Application Equipment are available in a variety of sizes ranging from small to big keeping in view the application capacity and the source of energy.
- These application equipment may be either manually or power operated.
- They can be further classified into moveable and protable appliances.
- By ‘Moveable’ is meant that which can be moved around on wheels or lifted by two or more persons.
- ‘Portable’ means equipment which can be carried by one person.
Nozzle
- The nozzle performs four basic functions
- Atomizes liquid into droplets.
- Disperses the droplets in a specific pattern.
- Meters liquid at a certain flow rate.
- Provides hydraulic momentum.
The Nozzle Tip is one of the most important and least expensive part of a spraying system.
Adjustable nozzle
- Most suitable for spraying targets which are not within the reach of a man.
- Gives a wide angle hollow cone to a straight solid stream that is, it gives a jet to a cone type of spray pattern.
- Difficult to calibrate as the flow and droplet sizes vary widely with the nozzle angle.
Double swirl spray nozzle
- Used for spraying in two different directions simultaneously.
- Nozzles can be fitted with different types of tips like hollow cone, solid cone or flat fan.
- Suitable for high volume applications
- The shape and size of Nozzle Tip orifice controls the spray angel, discharge rate and spray pattern. Spray angle influences the swath of a spray.
- And also:-Droplet size increases as orifice size increases (for any given pressure). Droplet size decreases with an increase in fan angle (for any given nozzle size and pressure). When it is desired to spray with more than one nozzle with the help of a spray rig or a spray boom, care should be taken in mounting to avoid overlapping or gapping.Overlap causes double dose Higher dose is harmful to crop Gap leaves untreated area Poor biological efficacy.
Purchase of pesticide appliance is a long term investment. One needs to keep in mind the type of job one wants to handle and check the appliance for the following;
- Suitability for the job
- Ease of operation and maintenance
- Good performance
- Good serviceability
- Easy availability of spare parts
- Reasonable cost
- The wise farmer will use the following check-list when selecting his sprayer or duster:
- Carefully check the quality of all the raw material used in the equipment.
- Check welded joints and seams, and examine moving parts for smoothness and finish.
- Make sure detachable parts fit securely and are easy to assemble and take apart.
- Do not be put off by higher price – it usually means superior quality. Ensure that you get the equipment most suitable for the job you wish to do.
- Select the Nozzle most suited for your purpose. Test the nozzle for discharge rate and degree of spray angle.
- Ask for the equipment to be demonstrated and make sure you understand completely how it works, before buying it.
- Check availability of parts and after-sales service. Always purchase genuine spare parts, preferably from the manufacturer’s authorized dealer or stockist.
- Spray Volume : Depending upon the volume of spray required per hectare the application is categorized
HV : High Volume = More than 150 l/ha.
- Suitable for insecticides, fungicides, herbicides.
- Can be done woth knapsack sprayers, tractor mounted sprayers.
LV : Low Volume = Approx. 10-150 l/ha.
- Suitable for insecticides, fungicides.
- Can be done with motorized knapsack sprayer, air craft, (in other countries) low r.p.m. Spinning Disc Appliances are also used.
- Various equipment and techniques being used in last three decades are shown diagrammatically alongside.
ULV : Ultra Low Volume = Approx. 1-5 l/ha.
- Suitable for insecticides.
- Can be done with High r.p.m. spinning disc appliances, motorized knapsack sprayer fited with special spinning disc with special spinning disc attachment and air craft.
- According to the volume of spray applied per unit area, pesticide spraying techniques are broadly classified as High Volume (HV) and Ultra Low Volume (ULV).
- These terms describe the volume of water used as a carrier. Initially high volume spraying technique was used for pesticides application but with the advent of equipment improvement in the technique of producing smaller droplets the trend is to use minimum amount of carrier or diluent liquid and this leads to the usuage of low volume and ultra low volume technique.
- Besides the most common classification of HV, LV and Ulv at times intermediate classifications like Medium Volume (MV) and Very Low Volume (VLV) is also adopted. MV is intermediate to Hv and LV whereas VLV is intermediate to LV and ULV.
- Whatever may be the volume of water HV, MV, LV, VLV or ULV, the quantity of pesticide per unit area remains the same.
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- A pesticide needs to be applied to a particular ‘Target’ area occupied by pests – and insect, disease or weed.
- If pesticides are to be used more efficiently, the actual target needs to be defined judiciously.
- Selection of the target requires knowledge of the biology of pests in order to determine at which stage it is most vulnerable to pesticides.
- The selected target may not be the most obvious site or the site where the damage is caused. The spray application method essentially requires
- Thorough knowledge of the target
- Where, when and what amount of pesticide to be applied
- Correct droplet size, density and distribution.
Foliar Application
Directed Application
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Band Soil Application
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Spot Treatment
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Working principle of spray equipment
- Conversion of spray liquid into droplets is achieved using some form of energies.
- Various forms of kinetic energies such as hydraulic, gaseous and centrifugal are utilized in this process.
- The type of sprayer and nozzles or atomizers can be classified according to the energy used.
Hydraulic Energy
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Gaseous energy
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Centrifugal energy
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- Theoretically speaking if ideal droplet diameter and the desirable droplet density are known, the minimum volume of pesticide spray per unit area can be calculated. Such a calculation of optimum droplet density is difficult because the effectiveness of the droplet is dependent on many other factors.
However, the following broad indications can serve a general guideline:
- 5-10 droplets/cm2 – for translocated herbicides.
- 20 droplets/cm2 – for most insecticides and systemic fungi-cides.
- 50-70 droplets/cm2 – for non systemic fungicides
- In case of insecticides, to achieve satisfactory biological efficacy atleast 20 droplets are required per square centimeter irrespective of their size.
- To achieve effifient deposition a narrower droplet spectrum is needed to minimize losses caused by the droplets which are larger than 300 microns and also which are smaller than 100 microns.
- Most wastage of pesticide is undoubtedly due to the largest droplets which have high terminal velocity and fall rapidly.
- Even if large droplets fall on target they are liable to bounce off.
- A 400 micron droplet will contain 1000 times the dose to a 40 micron droplet. If this is not retained on the target there will be considerable wastage.
- In actual practice, spray volume applied is always more than the value obtained from the theoretical calculation, the reasons being the loss of spray volume due to drip and drift, the deposition of spray on non-target areas and also due to erratic distribution of droplets on target surfaces.
Spraying efficiency can be represented as follows:
| Spraying efficiency (%) = | Minimum spray volume required |
X 100% |
Actual spray volume applied |
Spray Application Area
- The target infested by an insect, pest, disease or weed needs to be sprayed.
- Generally the spray application area differs from the land area except in the case where pre-sowing treatment is required on soil where land area equals the area to be sprayed.
- The area required to be sprayed varies with the distance between the rows of plants, distance between the plants in the same row and growth of the crop.
- This is being illustrated diagrammatically.
- In order to ensure uniform application of pesticide on crops, it is essential to carry out sprayer calibration exercise before undertaking actual spraying work. Required spray volume can also be marked out by sprayer calibration.
- The spray volume can be found out theoretically by using formula.
- However, practical method known as Area/Volume (Volume used on marked area) is easier for a normal farmer to follow.
| Application Rate in Litre per Acre or Hectare | = |
Plot Area |
X | Spray Volume used for marked area. |
Marked Area |
- Pesticides are mostly applied on the target in the form of spray droplets. Droplets produced by hydraulic nozzle are not uniform in size.
- Sprays contain both fine and coarse droplets. They are defined in term of their diameter and density on the target.
Coarse Droplets
- Narrow swath
- Less under leaf coverage
- More spray volume is required
- Particles coalesce and run off
- Poor penetration into the crop
- Less loss due to wind, thermal current.
- Poor biological efficacy
- Spray pattern like rain.
Fine Droplets
- Wider swath
- More under leaf coverage
- Less spray volume is required
- Particles do not coalesce and run off
- Good penetration into the crop
- More loss due to wind, thermal current
- Good biological efficacy
- Spray pattern like mist
- To understand how spray application equipment delivers pesticides to a target, it is necessary to know a little about the physical properties and behaviour of droplets.
- Droplet size and density (number of droplets per unit area of target) are two important factors for effective spraying.
- Knowledge of droplet diameter and density is important for efficient use of pesticides.
- The droplets diameter of a given spray can be measured as the median of either the volume or number of droplets.
The Volume Median Diameter
- The Volume Median Diameter (VMD) is defined as that droplet diameter which divides the volume of spray into two equal parts i.e. the volume of spray with droplets of a diameter less then VMD equals the volume of droplets with a diameter greater than the VMD.
The Number Median Diameter (NMD)
- The Number Median Diameter (NMD) is the droplet diameter where the number of droplets above the NMD is equal to the number of droplets below the NMD.
- The NMD is usually smaller than the VMD because most pesticide sprays usually contain a large number of very small droplets.
- The VMD is affected by relatively few large droplets whereas the NMD is more influenced by small droplets.
- The more uniform the size of droplets, the closer the ratio of VMD and NMD approaches.
- In a normal course, the spray droplets are in a spherical shape.
- To understand the mathematical logic and for simplicity in calculations the droplets may be considered in the shape of a cube and not a sphere.
- Imagine that the ideal spraying has been carried out which has produced all droplets of same size in cube shape having all sides of equal dimensions say 2 mm.
- The volume of a droplet is the sum arrived at after multiplication of length, breadth and height i.e. a cubic relation.
- If the droplet size is reduced from 2 mm to 1 mm, number of droplets produced will increase by 8 times from the same volume.
- The area occupied by the droplets is the sum arrived at after multiplying length and breadth i.e. a square relation.
- Similarly when the size of a droplet is reduced the contact area of droplets on the target increases.
- Thus by reducing the droplet size from 2 mm3 to 1 mm3, double contact area can be achieved from the same amount of spray volume.
- Conclusively, if the droplet size is reduced from 2 mm3 to 1 mm3 in other words by a factor of two, from the same volume of pesticide:
- Eight times more droplets can be produced. This means number of droplets increase by the cube of the factor of size reduction.
- Double contact area of droplets on targets can be achieved. This means the contact area increases by the same factor of size reduction.
- Spray droplets density will be eight, time more, in other words, it increases by the cube of the factor of size reduction.
Optimum Droplet Size
- Optimum droplet size for application of pesticide are generally specified within a range of droplet diameter.
- More precise definition of optimum droplet size in application of pesticide on Agricultural Pests may not be possible, due to biological complexity of target.
- Besides this, the fate of droplets from the time of their formation by a nozzle until their deposition onto a target is influenced by several factors such as:
- Velocity of droplet ejection
- Gravitational force
- Wind velocity
- Air Turbulence caused by thermal movement
- Volatility of the spray liquid and
- Characteristics of target surface
- Droplet size is most important for efficient application with minimum contamination of environment. A 500 micron droplet will contain 1000 times the Lethal dose of a 50 micron droplet. To reduce wastage, narrow range of droplet spectrum is essential.
- Coarse droplets are largely influenced by gravitational force and relatively unaffected by turbulence. Fine droplets will be influenced by wind and turbulence and have a tendency to drift.
Target |
Droplet sizes (Microns) |
|---|---|
| Flying Insects | 10-50 |
| Insects on foliage | 30-50 |
| Foliage | 40-100 |
| Soil application (avoidance to drift) | 250-500 |
- Different spraying techniques like High Volume (HV), Low Volume (LV) and Ultra Low Volume (ULV) are most commonly used.
- In these spraying techniques a range of droplets is produced as shown in the diagram.
- Droplet sizes more than 300 microns are lost by drip whereas the droplet sizes less than 100 microns are lost by drift.
- Loss of spray by drip and drift are more prominent in HV and ULV spraying technique respectively.
- The target leaf area requiring treatment may be much greater than the ground area. The Leaf Area Index (LAI) is the ratio of Leaf Area to Ground Area.
Leaf Area Index (LAI) = |
Leaf Area |
Ground Area |
- It will vary with different crops according to the plant growth.
- The LAI ratio seldom exceeds about 6 – 7 depending upon the crop.
- This is the reason why per acre requirement of water in a spray solution varies from crop to crop depending upon the total leaf area to be covered.
- The total leaf area required to be covered with droplets depends upon the actual pest i.e. whether it is the leaf of a weed, a highly mobile foliage insect or non-mobile fungus infection on the leaf and the mode of action of the pesticides.
Theoretical droplet density from 1 litre of pesticide sprayed over 1 hectare (assuming even distribution and no loss onto non-target surfaces)
| Droplet Diameter | Drople density per cm2 at LAI values 1-7* | ||||||
|---|---|---|---|---|---|---|---|
1 |
2 |
3 |
4 |
5 |
6 |
7 |
|
10 |
19,100 |
9,550 |
6,364 |
4,773 |
3,818 |
3,182 |
2,717 |
20 |
2,380 |
1,190 |
795 |
596 |
477 |
398 |
341 |
50 |
153 |
77 |
51 |
38 |
31 |
26 |
22 |
100 |
19 |
9.5 |
6 |
5 |
4 |
3.2 |
2.7 |
200 |
2.4 |
1.2 |
0.8 |
0.6 |
0.5 |
0.4 |
0.3 |
400 |
0.3 |
0.15 |
0.1 |
0.08 |
0.06 |
0.05 |
0.04 |
*If both upper and lower surfaces are considered, the droplet density per cm2 dhould be halved.
- To demonstrate the relationships between droplet diameter, droplet density, LAI and spray volume it is assumed that all droplets are of one size, distribution on the target is uniform and that no loss of pesticide occurs on non-target surface. In practice, of course, this is never achieved.
- The proper selection and use of spray nozzle is the most important part of pesticide application.
- The nozzle determines the amount of spray that is generated over a given area, the uniformity of the spray produced, the coverage obtained and the amount of drift that occurs.
- The nozzle selected must optimize coverage application rate and pressure and minimize loss through drift. For each kind of application, dependent upto the physical conditions prevailing, a different nozzle design is available.
- Nozzle tips are usually available in brass, stainless steel, and engineering plastic. Steel tips are most resistant to corrosion and abrasion.
- Brass tips are very commonly used, but ear out more easily and can be corroded by some chemicals. Engineering plastic is likely to become the most serviceable material for spray nozzles, being highly resistant to wear-and-tear and corrosion.
Hollow cone nozzles-Disc and core type
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Flat fan nozzles
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Floodjet nozzles
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Adjustable nozzles
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Single swivel nozzles
- Here the joint of the nozzle and extension rod is capable of swiveling without leakage, it can be locked for use at any angle between 0 – 180 degrees.
Double swivel nozzles
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Double fixed nozzles
- Double fixed nozzles are fixed on the ‘U’ bend, which is, in turn, coupled with the end of a straight extension rod.
- NOTE: Single swivel, double swivel and double fixed nozzles come in both cones-spray and flat fan varieties.
Spray boom
- This design consists of several nozzles mounted on a rod, ideally suited to row crops, and can be operated with foot / rocker / knapsack / power operated sprayers.
Spray guns
- Spray guns consist of cut-of-value extension rod and nozzle and can be trigger or hand-operated.
- The spray pattern is adjustable from solid jet to hollow cone, and are most widely used for tall trees.
Cut-off Valves
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- A discharge Line consisting of a delivery hose with couplings and a spray lance.
Every Spray Lance must have;
- A cut-off valve
- An extension rod-straight or goose-neck
- An appropriate nozzle
Extension Rod
- Comes in varying lengths, according to customer requirements but lengths longer than 90 cms are difficult to handle.
- For tree spraying, bamboo lances i.e. brass tubes inserted into a hollow bamboo are recommended.
- The larger diameter of the bamboo helps to off-set the length of the lance (up to 2.5 meters, making it easier to handle).
Plant protection equipment classification
Plant Protection equipment falls into two major categories;
- Dusting equipment, which is used for the dispersal of insecticide in powder form.
- Spraying equipment, which is used for the dispersal of insecticide in liquid form.
- Both dusters and sprayers are available in manually operated and power operated varieties.
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