In this article we will discuss about:- 1. Meaning of Sprayers 2. Basic Components of Sprayer 3. Type of Spray 4. Types 5. Care and Maintenance 6. Pumps.
Meaning of Sprayers:
Sprayer is a machine to apply fluids in the form of droplets.
Sprayer is used for the following purposes:
1. Application of herbicides to remove weeds.
2. Application of fungicides to minimise fungus diseases.
3. Application of insecticides to control insect pests.
4. Application of micro nutrients on the plants.
The main functions of sprayer are:
1. To break the liquid into droplets of effective size.
2. To distribute them uniformly over the plants.
3. To regulate the amount of liquid to avoid excessive application.
Desirable Qualities of Sprayer:
1. The sprayer should produce a steady stream of spray materials in the desired fineness of the particles so that the plants to be treated may be covered uniformly.
2. It should deliver the liquid at sufficient pressure so that it reaches all the foliage and spreads entirely over the sprayed surface.
3. It should be light yet sufficiently strong, easily workable and repairable.
Basic Components of Sprayer:
Components of a sprayer are as follows:
1. Nozzle Body:
It is the main component on which other components of a nozzle fit.
2. Swirl Plate:
It is the part of a cone nozzle which imparts rotation to the liquid passing through it.
3. Filter:
It is a component to remove suspended matter larger than a predetermined size from fluid.
4. Over-Flow Pipe:
It is a conduit through which excess fluid from a pump is by-passed by the action of a relief valve or pressure regulator.
5. Relief Valve:
It is an automatic device which opens when the pressure of the fluid or gas reaches a predetermined value.
6. Pressure Regulator:
It is an automatic device to control the pressure of fluid or gas within a range of settings.
7. Cut-Off Valve:
It is a mechanism between the pump and the nozzle to control the flow of liquid from the sprayer. This is operated by hand.
8. Spray Boom:
It is a spray lance with spray nozzles fitted to a head, mounted at right angles to the lance.
9. Nozzle Boss:
It is a lug on spray boom or spray lance to which a nozzle body or cap is screwed.
10. Nozzle Disc:
It is a component containing the final orifice of a nozzle usually a cone nozzle.
11. Nozzle Cap:
It is a component which retains the assembled parts in or on a nozzle body. The nozzle disc or tip may be integral with the cap.
12. Nozzle Tip:
It is a component containing the final orifice of a nozzle usually a fan nozzle.
13. Spray Lance:
A hand-held pipe through which the liquid reaches the nozzle mounted at the free end.
14. Spray Gun:
It is a lance from which the spray is readily adjustable during the operation.
Type of Spray Used in Sprayer:
Sprays can be of following types:
1. High volume spray (more than 400 litres spray/ha)
2. Low volume spray (5 to 400 litres, per hectare)
3. Ultra low volume (ULV) spray (Less than 5 litres spray/ha)
The selection of technique depends on type of vegetation, kind of pests and approach to the field.
1. High Volume Spray:
The dilute liquids are applied by hydraulic machines. It consumes more time and labour.
2. Low Volume Spray:
It uses air stream from a fan as a pesticide carrier with small quantities of liquid. There is saving of material and labour.
3. Ultra-Low Volume Spray:
ULV spraying can be defined as plant protection operation in which total volume of liquid applied amount to a few milliliters per acre. It is mainly used in air craft spraying.
Foam Spraying:
In this system a foaming agent (chemical additive) is added to the spraying solution. The spray is passed through a special nozzle. This system is economical.
Ultra – Low Volume Sprayer:
The sprayer has a motor powered by 6 or 12 volt battery. Tb the motor is attached a spinning disc, having grooves or teeth and rotates at a very high revolution per minute (4000-9000). The spinning disc receives the concentrated chemical from a plastic container having a capacity of 1 litre (approx.) Average droplet size varies between 35-100 microns. It is used for application of weedicide and for spraying small trees and crops.
Types of Sprayer:
I. Power Sprayer:
Power sprayers are operated usually with internal combustion engines. The prime mover capacity varies from 1 to 5 hp. The pressure pump is operated by a small power unit ensuring a constant steady pressure. They are operated at pressure from 20 to 55 kg/cm2. These machines are usually portable type. Sometimes, power sprayers are operated by the power take-off (pto) shaft of the tractor besides being pulled by it. Some sprayers are tractor mounted and pto operated also.
A power sprayer essentially consists of:
1. Prime mover
2. Tank
3. Agitator
4. Air chamber
5. Pressure gauge
6. Pressure regulator
7. Strainer
8. Boom
9. Nozzles
1. Prime Mover:
Prime mover is needed to supply power to the power sprayer. It is usually internal combustion engine. The power generally varies from 1 to 5 hp.
2. Tank:
Steel tank is widely used to prevent corrosion. Plastic tanks are also getting popular due to freedom from corrosion and ease of moulding into smooth shapes. A covered opening, fitted with a removable strainer is provided for easy filling, inspection and cleaning. A drain plug is there at the bottom of the tank for draining the liquid.
3. Agitator:
Agitators are needed to agitate the liquid of the tank. Propeller or paddle type mechanical agitators are provided for agitating the liquid. Horizontal shaft may be used with flat blades rotating at about 100 to 200 rev/min. Paddle tip speeds in excess of 2.5 m/sec may cause foaming.
4. Air Chamber:
An air chamber is provided on the discharge line of the pump to level out the pulsations of the pump, thereby providing a constant nozzle pressure.
5. Pressure Gauge:
The pressure gauge is provided on the discharge line to guide the operator regarding spray pressure. The spray pressure should be under specified limit.
6. Pressure Regulator:
It is meant for adjusting the pressure of the sprayer according to the requirement of the crops in the field.
7. Strainer:
A strainer is included in the suction line between the tank and the pump to remove dust, dirt and other foreign materials.
8. Boom:
Field sprayer to be driven by a tractor has a long boom in a horizontal place on which nozzles are fixed at specified spacing. The boom can be adjusted vertically to suit the height of plants in different fields.
9. Nozzle:
It is used to break the liquid into the desired spray and deliver it to plants.
A nozzle consists of:
(a) Body
(b) Screw Cap
(c) Disc
(d) Washer
(e) Vortex Plate
(f) Strainer
The body of the nozzle and the screw cap hold all the other parts in place. The disc has a number of holes including one hole in the centre and they are usually numbered from one to ten to denote the diameter of the hole. Each number usually denotes about 0.4 mm. The disc needs replacement, when the holes get enlarged due to constant use. The washer under the disc is provided to present leakage of the liquid.
Care of Power Sprayer:
Preparation for operation of power sprayer:
(a) Pour mobil oil into the crankcase up to the desired level.
(b) Put grease in all the grease points.
(c) Tighten the suction hose overflow hose and spray hose.
(d) Make sure that there is no break or clogging in the strainer at the end of the suction hose.
(e) Check the ‘V’ belts for damage and tightness.
Actual Operation of Power Sprayer:
(a) Set the pressure regulator to zero and start the prime mover.
(b) Make sure that the chemical comes back to the tank through the overflow hose.
(c) Warm up the sprayer with no load for a few minutes.
(d) Adjust the pressure regulator up to required pressure.
(e) Open the stop cocks to spray the chemicals.
Care after Use of Power Sprayer:
(a) After spraying, dip the suction hose into fresh water and run the sprayer for a few minutes to clean it. Then lift out the suction hose and run the machine for another few minutes to exhaust the water.
(b) Before stopping the prime mover, turn the pressure regulator to make the pressure zero.
(c) After spraying, check the machines to see that no screws are loose.
II. Hydraulic Sprayers:
Hydraulic sprayer may be:
1. Boom type field sprayer or
2. High pressure general purpose or orchard sprayers
Tractor mounting is popular for sprayers for small tanks whereas large units are of two wheeled trailed type.
Basic component consists of:
i. Tank
ii. Agitator paddle
iii. Screen
iv. By-pass line
v. Strainer
vi. Pump and
vii. Pressure gauge
Working:
Hydraulic field sprayers have horizontal booms for working in the field, the drop pipes are used between the two spraying of tall crops. Nozzles may be connected to the boom through drop nose.
III. Commercial Sprayer:
Commercial sprayers are of three types:
1. Manually Operated
2. Engine Operated
3. Airplane Sprayers.
1. Manually Operated:
Manually operated sprayers are classified as:
(a) Hand Atomizer Type
(b) Stirrup Pump Type
(c) Knapsack Type
(d) Bucket Type
(e) Hand Compression Sprayer
(f) Rocker Sprayer and
(g) Foot Sprayer
(a) Hand Atomizer Type:
These sprayers are provided with single action or continuous action air compression pump. When the air is compressed, it is passed over the end of a suction tube which extends down into the spray material.
When the compressed air escapes through the nozzle, it carries the spray material along with it. The blast of air breaks the spray material in form of mist. A common type is Mysto hand sprayer and Flit gun. Such sprayers are commonly used for household work and kitchen gardens.
(b) Stirrup Pump Type:
This type of sprayer consists of a single or double acting pump which may be kept in a bucket or a barrel. A foot rest is also provided to hold the pump while working. Single acting pump delivers the spray material on the downward stroke only while the double acting pump ensures constant delivery of spray material. Such sprayers are mostly used for small fields.
(c) Knapsack Type:
It is a sprayer with the fluid container carried on the back of the operator. It is a compressed air type sprayer which has an air tight chamber. An air pump is mounted on the chamber. The container is filled 3/4th full so as to leave enough space to compress a good volume of air above the spray material.
A few strokes of the pump build up enough pressure in the air chamber. When the nozzle is opened the spray material is forced out through the nozzle by the compressed air. These sprayers are suited for small area only.
(d) Bucket Sprayer:
Bucket sprayer consists of a single acting or double acting pump which is placed into a bucket containing spraying liquid.
(e) Hand Compression Sprayer:
It is a sprayer from which fluid is expelled by means of compressed air contained in a spray tank. This consists of an air pump fitted in an air tight chamber. The chamber is filled with spraying liquid. The pressure is developed by pumping air into the tank and the spray is forced out under pressure.
(f) Rocker Sprayer:
It is a hand operated sprayer. It is used for low crops and tall trees, go-downs and factories. It develops high pressure.
(g) Foot Sprayer:
It is used for spraying tall trees, fruit, tea, citrus plants and gardens. It consists of a plunger which operates the sprayers by its upward and downward motion. It is operated by foot.
2. Engine Operated Sprayer:
Engine operated sprayer are classified as:
(a) Knapsack mist sprayer duster and
(b) Power sprayer.
3. Airplane Sprayers:
These are used for very large areas only.
Types of Nozzle:
There are three common types of nozzle:
1. Hollow Cone Nozzle
2. Solid Cone Nozzle
3. Fan Type Nozzle
1. Hollow Cone Nozzle:
The liquid is fed into a whirl chamber through a tangential entry or through a fixed spiral passage to give a rotating motion. The liquid comes out in the form of a hollow conical sheet which then breaks up into small drops.
2. Solid Cone Nozzle:
This nozzle covers the entire area at small range. The construction is similar to hollow cone nozzle with the addition of an internal jet which strikes the rotating liquid just within the orifice of discharge. The breaking of drop is mainly due to impact.
3. Fan Type Nozzle:
It is a nozzle which forms narrow elliptical spray pattern. In this type the liquid is forced to come out as a flat fan shaped sheet which is then broken into droplets. This nozzle is mostly used for low pressure spraying.
Usually the flow rate for a particular nozzle is proportional to the square root of the pressure and the discharge rate is proportional to the orifice area. Nozzles on field sprayers have spray angles of 60° to 90° but high pressure nozzles have smaller angles. Operating pressure below 1.5 kg/cm2 is undesirable because the nozzle does not work satisfactorily.
IV. Self-Propelled High Clearance Sprayers:
It is a four wheel riding type spraying machine which consists of the following main parts:
1. One diesel engine of about 20 hp,
2. Two rear steered wheels,
3. Two front lugged wheels,
4. Gear box,
5. Oil tank,
6. Hydraulic pump,
7. Boom fitted with nozzles,
8. Eighteen nozzles with a spacing of about 675 mm are fitted on three booms.
Important features are:
1. The ground clearance under the chassis is maintained at about 1 metre.
2. The height of the nozzles can be adjusted between 300 mm and 1600 mm.
3. The width of the coverage of the sprayer is about 13 m.
4. Average field capacity is 1.8 ha/h with 225 l/ha of application rate.
5. It saves 15-20% labour and operating time and 30% on cost of operation compared to conventional tractor operated sprayer.
6. 10% increase in yield is reported.
7. It is suitable for cotton and other tall crops.
Care and Maintenance of Sprayer:
Proper care and maintenance of sprayers prolongs the life of the machine and gives efficient service.
The following are a few important cares to be observed:
1. All washers and packing should be soaked in oil or water before use.
2. The ends of the nozzle should be unscrewed and cleaned before starting the work.
3. When spraying is over, the sprayer should be operated for sometimes with clean water to remove sediments from the pressure vessel and the discharge tube. To keep the sprayers serviceable they should be thoroughly cleaned.
4. In case of power sprayers, special attention has to be paid to the following:
(a) Lubricating oil of the engine should be changed every 100 working hours unless otherwise advised by the manufacturers.
(b) Do not disturb the packing until a leak is observed.
(c) The spray pump should not be worked at more than recommended pressure.
(d) Oil level in the pump of the engine should be checked and all grease points should be greased once in a day.
(e) Recommended oils and fuels should always be used in the engine.
(f) Nozzle should be thoroughly cleaned after use, either by blowing through it or by using fine bristle. Never try to use thick wires to clean the perforations.
Pumps for Spraying:
Mostly three types of pumps are used for spraying:
1. Piston or Plunger Pump
2. Rotary Pump
3. Centrifugal Pump
1. Piston Pump:
Piston or plunger pump is a positive displacement pump. It has got a spring loaded by-pass valve to control the pressure. It is well suited for high pressure spraying. The volumetric efficiency of this pump is as high as 90%.
2. Rotary Pump:
Rotary pump is commonly used for low pressure sprayers. It may be Vane type or Propeller type. Rollers may be made of nylon, steel or carbon. When the rollers are in operation, they are held against the case by centrifugal force. Rotary pumps are compact and cheap.
3. Centrifugal Pump:
It is a pump working on high speed having high volume discharge. It is not a positive displacement pump. The discharge rate varies as the square of the speed and the power varies as the cube of the speed. It is a very popular pump due to its simplicity and its ability to handle abrasive material also.
Pressure Loss in Spray Hose:
When the chemical travels through the rubber hose from the power sprayer, the pressure is lower at the end of the hose than at the discharge part of the power sprayer. Such pressure loss is mainly caused by the friction of the moving chemical against the wall of the hose. The larger the spraying volume or the smaller the inside diameter of the hose, the greater is the loss.