July 15, 2009
By Dr. Jason S.T. Deveau
OMAFRA application technology specialist

You have the best sprayer on the market. You know everything there is to know about how the weather affects spraying. You scouted your crop and today is a perfect time for spraying. You spent a LOT of money on your product. So, why did you get crummy coverage and poor control?

Did you check your nozzles?

All of that work, planning and money comes together when the spray leaves the nozzle, so it’s surprising that the most critical part of the sprayer, the nozzles, are so often neglected. Monitoring nozzle performance pays financial dividends because tip damage has a direct impact on product effectiveness and cost (see chart). If the application is seriously compromised, the operator might have to re-spray, which incurs additional labour, time, fuel, and wear-and-tear on equipment.

The solution lies in proper maintenance and early detection. Tip orifices have delicate edges, so clean them with a soft-bristled brush, or use a can of compressed air. Even a wooden toothpick can distort some plastics, so imagine what a wire does. Better still, carry spare nozzles for quick field replacements and clean them later in the workshop where they won’t get lost. Be sure to clean nozzle screens with a brush, as well, because flushing does not dislodge buildup. Nozzle performance should be tested during each calibration (before and midway through the season at minimum), or whenever damage is suspected. Testing is simple, quick and inexpensive.

Temporarily install a pressure gauge on the boom behind the nozzle (commercial or home-made). Installing quick-connects along the line is a handy strategy to make this easier. If the pressure at the nozzle is different from your intended operating pressure, adjust the regulator to compensate and accurately set nozzle pressure.

Use a graduated container or commercial tip tester to measure the discharge of clean water over a one-minute interval. Compare the rate to the manufacturer’s rate, or compare the flow rate from the used tip to the flow rate of a new tip of the same size and shape.
Detach the gauge and repeat the sequence on each nozzle.

If the flow rate is 10 per cent (or even five per cent) more than the ideal rate, replace all nozzles, not just the ones that appear damaged. Replace them once a year or at the first signs of deterioration, whichever is first. The cost of renewing an entire set of nozzles is a fraction of the potential cost of wastage and potential crop damage. As an example, an airblast sprayer with 16 nozzles sprays a product that costs $150/hectare (~$60/acre). Nozzle tips are worn by an average 10 per cent, which sprays an additional $15/hectare ($6/acre). Sixteen new ceramic hollow cone tips and gaskets cost $80 at $5 each. The nozzles pay for themselves in 5.3 hectares (13.3 acres), and you get better coverage and protection.

The rate of tip wear depends on spray pressure, product sprayed, and the material of which the nozzle is made. Upgrading to a harder, more durable tip can reduce maintenance costs. Never mix nozzle materials on a boom.  From softest to hardest: brass, stainless steel,  today’s new plastics, hardened stainless steel, ceramic.

Inevitably, all nozzles wear out, so include regular nozzle maintenance and replacement in every spray program.

The potential impact of damaged nozzles

Nozzle damage Result Possible causes Potential impact
Worn nozzle Over application Regular use (particularly with wettable powders) Higher product cost / Phytotoxicity (particularly on heat-or moisture stressed plants) / Unacceptable residue level
Plugged orifice Under application Debris / Dirty carrier water / Product build-up Inadequate protection / Increased risk of resistance / Increased risk of resistance
Distorted orifice Uneven application Regular use / Improper cleaning All of the above