What to look for in a sprayer
1 Tanks must be made of non-corrosive materials and have a filler opening of sufficient size that the operator has no difficulty pouring the chemical into the tank. Tank filling is potentially a high-risk area when it comes to operator contamination. Low-level induction hoppers or closed transfer systems — required on machines where the filler would normally be above 1m from the ground — reduce that risk.
2 Pumps must also be non-corrosive. With skid-mounted and trailed sprayers the pump is usually powered by an on-board motor. For tractor-mounted sprayers, the pump is driven by the tractor PTO. There is normally a pressure relief valve to control the output pressure.
3 Filters are essential for accurate application of chemical products. They are there to prevent solid material reaching and blocking the nozzles. Dirt can enter the system as soon as the filler is opened. Contaminants can also enter in the water used to mix chemical products. It is important that there is a filtering device, such as a basket, at the point of filling — but make sure it also has some way of letting air out as the tank fills, otherwise there could be serious belch-like splash-back. More filters are needed at the pump and nozzles.
4 Controls for large sprayers are increasingly sophisticated, with global positioning systems (GPS) now playing a part. Some systems may have sensors to help you maintain a consistent forward speed. With a basic system it is down to the operator to keep a steady speed in order to give uniform distribution of the product.
5 Clean water tanks and clothing lockers should be fitted.
6 Maintenance should be designed into the sprayer. Look for sensible drain-down points. Sprayers need to be easy to clean out — and that includes all the spray lines, nozzles and filters as well as the tank.
Choose the right nozzles
It’s the nozzles that actually force the liquid product into droplets ready for application. The main types are fan, cone and anvil. Generally, use a fan nozzle for applying product to large, flat areas. Fan nozzles are commonly associated with boom sprayers.
Choose cone nozzles for applying insecticides and fungicides, as this type of nozzle gives a good overall coverage of a plant’s surface due to the “swirling” spray produced.
Anvil nozzles are often used with knapsack sprayers as they operate at low pressure. They produce coarse droplets and are particularly suitable for herbicide application. Each type of nozzle is offered in a range of designs and pressure ratings.
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