6.3 Hydraulic (manual) sprayers and nozzles

Hydraulic nozzles remain the most widely used method of spraying chemical pesticides. They are fitted to a wide range of spraying systems, ranging from the very basic hand-held ‘trombone’ sprayers, side-lever knapsack sprayers, compression sprayers (originally designed for vector control, but used by some cocoa farmers) as shown below:

Three types of manual hydraulic sprayer used in cocoa

The two common forms of manual side-lever knapsack sprayer are illustrated:

(i) where the tank mixture is pumped using a diaphragm or
(ii) a piston mechanism; both require two valves.

‘Pulsation’ (variations in pressure with pumping) is minimized with a pressure chamber that is mounted either internally (often as part of the pump mechanism) or outside the main tank, and certain sprayers have a pressure control mechanism mounted either in the tank or on the spray lance (“wand”).

Filters beneath the tank lid are usually fairly coarse, so farmers should be careful to use clean water to avoid blockage of the finer filters next to the nozzle tips.

Compression sprayers are less than completely filled with water and added pesticide, then pumped-up to 600 kPa or more, before lifting on the back and spraying.

This has the advantage of leaving both hands free for operating the lance; however, unless a pressure regulating device is fitted, the pressure and flow at the nozzle gradually decreases until the sprayer is pumped up again.

In addition, especially in Asia, motorised hydraulic sprayers are becoming increasingly available: where the energy provided by manual side-lever action is replaced with an electric pump, or even a 2-stroke engine.

It is important not to confuse these motorised hydraulic sprayers with motorised mistblowers (below).

Whereas the latter can be used to reduce volume rates, motorised hydraulic sprayers are often fitted with very high flow rate or multiple nozzles, so there is a danger of increasing VAR in comparison with manual spraying.

When buying this sort of spray-equipment, it is important to check the flow rate range and validate with calibration.

Distribution of spray deposited with a lance depends very much on the skill of the operator in keeping a steady pumping and walking speed and directing the nozzle to the target areas (pods, foliage, branches, etc, depending on the pest).

The FAO has produced guidelines on minimum equipment standards [1] for manual sprayers that include various aspects relating to weight, durability, leakage, ease of cleaning and maintenance, instruction manuals, etc.

The guidelines specifically indicate the responsibility of sprayer manufacturer to comply with requirements for atomizers supplied including:

Nozzles supplied with or recommended for a sprayer should be manufactured to international standards (ISO) [2].
“The sprayer manufacturer should include in the sprayer manual, information on: nozzle flow rates, characteristic spray patterns and spray angles…”