Knapsack Sprayer: Types, Uses, Maintenance and More

Introduction to Knapsack Sprayer

A knapsack sprayer is a small, portable backpack container made of either plastic, brass, or stainless, and is used for spraying herbicides, insecticides, cleaning agents, and fungicides.

The sprayer is commonly used by small-scale farmers and commercial farmers where mechanized sprayers are not available, and where cost is to be minimized

The tool consists of a tank, nozzle, pressure device, pressure regulator, valves, air chamber, agitator, and more, which are usually mounted inside the spraying tank.

The sprayer contains a tank where water and other solutions are poured as well as a hand and two belts for lifting and mounting at the back.

The sprayer is equipped with a long handle in the shape of an ‘L’ that can be pulled up and down to increase the pressure of the knapsack as well as the nozzle which is used for spraying the solution.

The sprayer comes in various sizes and shapes. However the 16-liter sprayer is considered the best because it is durable, has efficient pumping fittings, is gender-friendly, has affordable replacement parts, easy to maintain, and requires little technical know-how.

Three types of knapsack sprayers exist which can be motorized backpacks knapsack, motorized knapsack dusters, and hand-carried knapsack sprayers with various capacities and volumes.

The sprayer is commonly used for fumigating, spraying liquid fertilizers, insecticides, fungicides, herbicides, and control of fire outbreaks.

While the sprayers have been used for many decades, they are still being used in many parts of the world, particularly in the hands of subsistence farmers or small-scale farmers.

In developing countries, the sprayer is the only instrument used for spraying herbicide, insecticide, and fungicide.

while in developed nations, the backpack sprayer has been replaced by mechanized and sophisticated implements such as air tractors and helicopters.

Types of knapsack sprayers

There are three types of knapsack sprayers, they are;

Hand-operated knapsack sprayers

The hand-operated knapsack is usually carried on the back of the operator and it is operated by the hand as the name sounds. The knapsack is usually about 10 -16 little capacity sprayer.

It has a flat base and resembles the shape of a gallon. The sprayer has a hydraulic pump mounted inside the tank, two filters, a horse, a lace (spray gun) nozzle, and a trigger for flow control.

the knapsack is made of plastic and metal of various categories. this type of sprayer is most popular in the hands of small-scale farmers.

The handle of the knapsack is pulled up and down to increase the pressure of the knapsack while the right hand is used to press the trigger (flow control lever) and control the direction of the spray.

Advantages of the hand-operated knapsack.

The usefulness of this sprayer are:

It is simple to maintain
It does not require skill to operate
Does not require special skills and technical knowledge for servicing and repairs.
It is very economical to purchase
It is Light in weight and easy to carry on the back of the operator unlike the motorized sprayer
A large area can be sprayed without fatigue
The parts are affordable
It is durable if it is well maintained.
It is economical to spray without wasting chemicals

Disadvantages of the Knapsack Sprayer

The demerits of the sprayer are:

The nozzle can easily be blocked by the sand and dry leaves
A weak pressure chamber may lead to the leaking of pressure.
The part of the Knapsack can easily rust and corrode if not properly stored or maintained.
If left outside high temperatures or sunlight may weaken the rubber tank leading to breakage.

Motorized Knapsack Sprayer

The motorized Knapsack sprayer is a backpack sprayer that is powered by an engine. It is an improvement over the hand-operated Knapsack. The sprayer is made of plastic, metal, and brass.

The motorized Knapsack has a powerful petrol engine with a spark plug and a liter fuel tank that can hold up to one liter of fuel mixed with light oil. The tanks of the sprayer can be 12 liters, 16 liters, and 20 liters, however, the 20-liter is considered too heavy to be mounted on the back.

The engine capacity of the sprayer is about 1.2- 3.0 hose power and consists of a tank, hose, fleeted air hose, flow regulator knob, and a plastic atomizer grate.

The sprayer can be used for various agricultural activities such as spraying herbicides, fertilizers, fumigation, insecticides, and fungicides.

To operate the Motorized Knapsack sprayer simply pull the small short rope to ignite the engine. Once the engine is on, the blower releases high-velocity air mixed with the chemical solution, which is then sprayed in the form of mist or dew.

Advantages of the Motorized Knapsack Sprayer

the merits of the motorized Knapsack sprayer are:

a large area of land can be spread within a short time
it requires little effort to operate compared to a hand-operated sprayer
it is less drudgery
it is less economical compared to other machined sprayers such as trailer sprayers

Disadvantage of the Motorized Sprayer

the demerits of the motorized sprayer in agriculture are:

it is capital intensive as extra income is spent on fuel and light oil.
it requires skills to operate
it is difficult to maintain the sprayer, compared to a hand-operated Knapsack.
it requires high technical knowledge to repair and service the Knapsack
it is too heavy to carry on the back, especially the 20-liter Knapsack.
it may lead to the wastage of chemicals if the sprayer does not equate the moving rate of the operator.

Motorized Knapsack Duster.

The motorized Knapsack duster has the same working principle as the motorized Knapsack sprayers. The producer of the sprayer package along with the sprayer duster accessories, can be interchanged when the need arises.

This can be achieved by replacing the liquid hose with a bigger diameter hose and air distributor located on the bottom of the tank, which helps to mix and keep the solution in suspension.

The bigger diameter hose helps to convey the powdery solution from the tank into the air stream, and the blower releases a high velocity of air when the sprayer is on.

knapsack Sprayers Diagram

The Capacity of the Knapsack Sprayers.

The sprayer is designed to hold various capacities or volumes of water. However, the choice of the sprayer to be used depends on the manufacturer and farmers.

The backpack sprayers are available in various designs such as 5-liter sprayers, 16-liter sprayers, 20-liter sprayers,

Uses of the Knapsack Sprayers

The following are the uses of the sprayers

Fumigation of the Environment: The sprayer is a veritable tool for fumigation of the environment. it can be particularly useful in a residential area where mosquitoes, tsetse flies, sand flies and other insects are a nuisance. Insecticides can be mixed in the required quantity in water and used to control dangerous insects in the environment with the use of a sprayer.
Spraying of Insecticides: a sprayer is a useful tool for managing the high incidence of insect pests on the farm. Insect pests such as grasshoppers, aphids, white flies, and more that inhabit the leaves and stems of plants can be effectively controlled using the Backpack sprayer. Spraying a mixture of insecticide solution onto the leaves of the affected plants can effectively control the incidence of insect pests on the farm.
Spraying of Fungicides: Various types of fungicides can be dissolved in water and sprayed onto affected crops with the aid of the hand-operated Sprayer. The Sprayer can be checked and adjusted to suit different types of spraying solutions.
Spraying of Liquid Fertilizers: the sprayer can be used to spray liquid fertilizers on the farm. The fertilizers are dissolved in water and poured into the sprayer containers for application.
Spraying Herbicide: the backpack sprayer is a highly used tool for spraying herbicide on the farm. It has become one of the most vital instruments in the hands of small-scale farmers due to its low budget and ease of operation. The hand-operated sprayer has replaced the mechanized sprayer such as the tractor and helicopter sprayer on the farm, and requires little technical know-how to operate.
Control of fire Outbreaks: If there incidence of fire outbreaks in the farm or farmstead, the sprayer can effectively be used to control fire in the farm in the absence of a fire control instrument.
Light Watering in the Nursery: the sprayer is effective for watering seedlings in the nursery when they are in the seedbed or tray. the sprayer can be effectively used in the watering of seedlings in the nursery by adjusting the sprayer to prevent the rate of dropping from affecting young plants’ growth. This ensures that the pour-down does not damage plants in any way.
Irrigation purpose: during the dry season or drought, the knapsack sprayer can be used to irrigate crops effectively. The sprayer is very effective in irrigating plantation crops during the dry season. On the other hand, the sprayer is a cost-effective method compared to the irrigation facilities
Spraying Disinfectants on Livestock Houses: The sprayer is used for spraying disinfectants in and around the livestock houses. Disinfectants are sprayed around the livestock pen or structure to prevent the spread of pests and diseases, and the knapsack is crucial for the spraying of this disinfectant in the pen.
Spraying pesticides on the farm: The sprayer can be used to spray pesticides on the farm

Parts of Knapsack Sprayer and Their Functions

Tank: The tank is made of plastic material designed to house all the components of the backpack sprayer. The tank is made up of high-quality rubber that is resistant to rusting and corrosion. The tank is the major component of the sprayer and it is used for storing water or carrying mixed solution of herbicide, fungicide, and insecticide water for spraying. The tank is made of various capacities, but the most popular knapsack is the 16-liter sprayer due to its convenience and ease of carrying.
Filters: the backpack sprayer consists of two types of filters. The first filter is located close to the tank cover while the other is a long narrow filter located close to the trigger. These two filters are used to prevent dirt, or any other materials from blocking the nozzle.
Spraying Nozzles: the sprayer nozzle could be 30 ^o C, twin spray, fan spray, and four-hole spray nozzle. The nozzle consists of a plastic washer that prevents the water pressure from coming directly into the crops. This ensures that the water is released in the form of dew or mist which is very suitable for crops.
Pump: the pressure pump is one of the most important components of the knapsack sprayer. It acts as a hydraulic sprayer, equipped with special devices that help to gather pressure that can help covey or move water from one area to another. The backpack devices work by mechanical action that helps to discharge liquid line the capacity of the pumps. The capacity of the pump is directly proportional to the speed. The pump is protected by a pressure relief valve that helps to protect the pump from damage.
Pressure regulator: The pressure regulator is located close to the pump and is used for adjusting the pressure of the knapsacks when spraying. The pressure regulator is responsible for maintaining the required pressure for any spraying job within the pressure range of the pump. It is a safety device that redirects the excess pressure from the pump back to the tank.
Valves: These consist of the cut-off valve and bypass valves. It is used to regulate the flow of liquid or gas from the pump and flow from the pump to the tank.
Air chamber: an air chamber is a portion where the air temporarily stored provides a constant nozzle pressure for the pump.
Agitator: this device is used to stir the solution in the tank and keep the contents thoroughly mixed. The agitator helps to mix various types of materials in the tank such as powdery, fungicides, water paints, or other spray materials, and allows a thorough mixture of substances.
Pump handle: this is also called the Lever’s arm, It is a long L-shaped fixed with the pump cylinder which is pulled up and down to increase the pressure of the knapsack.
Strap buckles: this is where the knapsack belt is fixed which enables the knapsack to be carried from one place to another.
Hose: the hose is a long, hollow tube that is used to carry the solution from the tank to the nozzle for spraying.
Trigger: This is used to release the solution from the tanks to the nozzle to commence spraying. Whenever the trigger is pressed down the desired flow rate is achieved. The trigger contains a small button that is used to lock or open when necessary.

How to Use the Knapsack Sprayer

Half-filled the sprayer to the required volume.
Measure out the required quantity of herbicide, insecticide, and fungicide. For example, Pour 240ml of herbicide into the 16-liter sprayer. This can be used to control weeds on the farm.
After pouring the required quantity of herbicide, insecticide, and fungicide into the tanks refill the sprayer to the maximum level to ensure a thorough mixture of the solution.
Ensure that the desired level is not exceeded as this will lead to the spilling of herbicide, and insecticide on the body, and lead to the death of the plant.
Operate the arm lever or the pump handle up and down to draw liquid into the pump pressure chamber and to create the required spraying pressure.
To commence spraying press down the trigger to release the mixed solution into the nozzle for desired spraying flow. The trigger contains a hand lock level that is used for opening and locking the nozzle when busy or needs to perform different activities.
Continue operating the pump handle and the trigger in a steady motion while spraying.
Adjust the nozzle jet by twisting it to achieve a mist (in the form of a dew) spraying.
always spray in the direction of the wind, this will carry the solution of the chemical around the material to be sprayed. Don’t spray against the wind as this will lead to contamination of the operator.

Maintenance/Precautionary measure of the knapsack sprayer

The following maintenance or Precautionary measures should be observed when using the backpack sprayer.

Use the knapsack sprayer, particularly for the purpose it is designed for. Such as the application of agricultural chemicals, disinfectants, cleaning agents, etc.
Do not use the spray for spraying corrosive substances.
Spraying should be done at 6-11 am and 4-6 pm. This is because, during a hot day, the intensity of the sun may prevent plants from observing the chemical residue.
Thoroughly wash inside the tank of the sprayer with clean water after use.
Wear protective equipment such as a cover-all, Google, hand glove rain boat, and other useful materials while spraying.
Wash, clean, and service all the components of the sprayer regularly.
Cover the food, drinking water, and more before spraying to ensure that the solution of herbicide or insecticides doesn’t drop on the food which is harmful if consumed.
Don’t intentionally spray toxic subsistence towards people, animals, or food.
Do not leave the sprayer on the farm as this may expose the knapsack to risk of fire incidences or theft
Don’t leave the sprayer outside or on the farm as strong sunlight may weaken the plastic tank and this will lead to the destruction of the tank.
Always Lubricate movable parts with light oil.
Store the Knapsack Sprayer in a well-ventilated area as the wet area will lead to rusting the pole
Store the knapsack sprayer out of the reach of children, rodents, and animals.
Do not use or spray on a rainy day.
Do not eat, drink, or smoke whilst using the sprayer.
Wash hands, legs, and face after use.
After thoroughly cleaning your body take one tin of milk or drink two glasses of water to detoxicate your system.

What to do if my knapsack nozzles are blocked?

If your nozzle is blocked, you don’t need to worry and get frightened over it. It is a normal thing to have a block nozzle. Just do the following If the nozzle becomes blocked or fails to spray precisely.

Firstly; unscrew the spray head Sealing ring at the tip of the nozzle, and reduce any dirt, sandy particles, and pieces of grass that would have blocked the nozzle from spraying. Rinse all the components in water to ensure that they are thoroughly clean and free of dirt.
Secondly; unscrew the hose, spray Lever, check the filter, remove all the instruments blocking the nozzle from proper function, and rinse in clean water.

What are the components of a nozzle of a sprayer?

The components of the nozzle of a sprayer are the Hose, spraying lever spraying lance, the nozzle of sprayer Split sleeve, spindle o-ring, spray head sealing ring, and the nozzle (which could be 30^o c, two hole Sprayer, Fan Sprayer, and Four Hole Sprayer Nozzle.

What is the procedure before using the knapsack sprayer?

The following are the steps to follow before using the sprayer

Before using the knapsack sprayer, check the sprayer’s shoulder straps ensure that the belts are correctly fitted, and adjust if necessary, so that the sprayer can be balanced on the back.
Unscrew to open the tank cap, check the filter, and remove dirt and any foreign materials on the tank.
Check the handle of the sprayer to ensure normal functioning.
Pour one or two liters of water into the sprayer.
Operate the pump handle to draw liquid into the pump pressure chamber to check the working pressure of the sprayer.
Oil the felt sealing washer to help ensure the smooth operation of the air pump.
If the pressure is low, the knapsack can be serviced for normal working.

How much is 16L knapsack sprayer in Nigeria?

Currently, the prices of the 16L knapsack sprayer in Nigeria are #16,000 to #25,000 (that is $10 to $16) the price is subject to change due to inflation and the dollar rate.

The best knapsack sprayer

The best knapsack sprayer is the 16 litter sprayer, it is considered the best because it is durable, has efficient pumping fittings, is gender friendly, components are affordable when destroyed or broken, it requires little technical know-how and it is self-servicing.

Reference

Draper Tools Limited (2024) 12L knapsack Pressure Sprayer, Draper publisher, Hampshire. United Kingdom.
Faithfull Tools (2024) Knapsack Sprayer 16 Liters, Faithfull Tools publisher Norwich, Norfolk.
Oypla garden tool (2024) Knapsack Sprayer user manual. Oypla Publisher com LLP, Uxbridge.
West Africa Examination Council (2015) Practical agricultural past question on Knapsack Sprayer. Retrieved from Waeconline.org
Course, H. (2019) Parts and Functions of A Sprayer Knapsack. Retrieved from course hero. com
GBPS Lecture Note (2024) Sprayers And Their Functions, Classification, Manually Operated Sprayers, Power Sprayers – Dusters, Types And Uses Sprayers. Retrieved from GBPS Lecture Note

Knapsack Sprayer: Types, Uses, Maintenance and More.