Although knapsacks are a good way of applying pesticides, they have had some bad press. Problems such as splashback when filling, leaks and drips down the back, plus fatigue from carrying and operating the sprayer, mean many people have a love/hate relationship with the knapsack. It is worth taking time to choose the right sprayer.
Sum of the parts
The main components of a knapsack sprayer are the tank, pump, filters, lever, straps, hand lance, hose and nozzle. All should be strong and fit together with seals in a way that means there is no leakage, yet should be easy to dismantle for cleaning, maintenance and replacement when necessary. The sprayer should meet the requirements of British/European standards.
The tank needs to be non-corrosive and should exhibit a good level of impact resistance to take the knocks and bangs of being dropped and bounced around inside a van. It needs a flat bottom for stability when filling and should have a degree of moulding so that it comfortably fits the user’s back. There must be no openings below the liquid level and it should be easy to clean and rinse.
Check the diameter of the filler hole for ease of filling and inspect the basket filter or strainer inside. A deep filter, one with mesh at the base and the sides, will help reduce splashback during filling.
Using a knapsack sprayer can be exhausting. Not only are you carrying the sprayer, which can weigh four or five kilograms, but you start out with 15, 18, 20 or even 22 litres of solution, depending on the tank capacity. Then there is the pumping action.
Most knapsack sprayers are diaphragm or piston-pump sprayers operated by a hand lever, so it’s “up, down, up, down, up, down” until your arm is aching. Meanwhile, the arm holding the lance at a steady distance from the ground is going numb through inactivity.
The best solution, and a must for those using knapsack sprayers for hours at a time, will be a model where the lever can be swapped from right-handed pumping to left-handed pumping. It needs to be a simple task to encourage the user to switch positions so the pumping arm gets a rest and the spraying arm gets some exercise. Motorised knapsack sprayers eliminate the need to pump. The extra weight of the petrol-engine is partly offset by a reduction in tank capacity.
Straps need to be wide and padded for comfort — it’s best if they are adjustable and have a quick-release mechanism — and must be made of non-absorbent materials. A grasp-carrying handle fitted to the tank is useful for moving the sprayer.
Check that the hand lance is of a suitable length for the height of the operators so they do not stoop. The trigger should be easy to use and there should be a range of nozzles. Select the most suitable type and size of nozzle to ensure minimal drift and correct application rate. Find out about spares and accessories: a hood or shield may be fitted to the lance to confine a pesticide to its target area. Operator contamination is a concern and attention must be paid to the provision and use of appropriate personal protective equipment.
Finally, think how the sprayer will be stored. Some models have excellent ways to stow the pumping lever and the hand lance in a tidy and safe manner.
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