April 15, 2010
By Dr. Jason S.T. Deveau
OMAFRA application technology specialist

Did you know that your sprayer can lie to you? Even when you think you’ve done everything right, faulty pressure gauges and nozzles can result in run-off and drift, resulting in the need for more frequent applications to compensate for reduced protection. Nothing beats a solid routine of cleaning, calibrating and adjusting your sprayer to achieve the best results. But in a pinch, there are two things you can do to make a big difference.

Replace pressure gauge

Replacing old or suspect pressure gauges will considerably improve spray quality. In a recent survey of airblast sprayers in Ohio, some were out by more than 140 kilopascals (20 pounds per square inch). When you consider that airblast sprayers can operate anywhere from 40 to 120 psi, that means some of those sprayers were out by as much as 50 per cent! Here’s how you can prevent this from happening to you:
  1. Check your pressure gauge by connecting a new oil-filled gauge in parallel to compare readings. If they are appreciably different, swap to the new gauge and discard the old one.
  2. Now check the lines and boom pressure by temporarily installing reliable pressure gauges behind the last nozzle on each end of the boom. This works for airblast as well as boom sprayers. If the readings are appreciably different, release the in-line pressure and check for blockage throughout the lines. Clean and flush the lines, replace any suspect parts and check the pressure again to confirm all pressure gauges correspond.

Replace the nozzles

Gauges are available as either liquid-filled or dry. A liquid-filled gauge is best, because it dampens pressure pulsations and vibration. This results in a steadier reading, but it is slower to respond to changes in pressure. The maximum pressure indicated on the gauge should be approximately twice the intended operating pressure to enable an accurate pressure reading. A new gauge costs less than $20.

An often neglected area is monitoring nozzle performance. Tip damage has a direct impact on product effectiveness and cost. This arises from plugged nozzles that limit the volume being sprayed, or gaps in the spray pattern, creating unsprayed areas, or even over-spraying from worn nozzles.

Don’t rely on your tank being empty to indicate if your nozzles are worn – one plugged nozzle cancels out a worn one. You must check them individually. Inevitably, all nozzles wear out, even ceramics. Nozzle performance should be at minimum, tested before and mid-way through the season. Testing is simple, and depending on the size of the boom, does not take long:
  1. Temporarily install a pressure gauge on the boom behind the nozzle being tested.
  2. If the pressure at the nozzle is different from the intended operating pressure, adjust the regulator to compensate and accurately set nozzle pressure.
  3. Use a length of hose to direct nozzle output into a graduated container and measure the discharge of clean water over a one minute interval.
  4. Compare the rate to the manufacturer’s rate, and the flow rate from the used tip to the flow rate of a new tip of the same size and shape.
  5. Repeat the sequence on each nozzle.

“Replacing old or suspect pressure gauges will considerably improve spray quality.”

If a nozzle’s flow rate is five per cent or less than the ideal rate, remove, clean and retest the nozzle. If the rate is still five per cent or less, replace the nozzle. If two or more nozzles have a flow rate five per cent or more than the ideal rate, replace all the nozzles, not just the ones that appear damaged.

We use five per cent because it is just outside the nozzle manufacturer’s margin of error, and because you can clearly see five per cent when you test nozzle output. Some specialists recommend ten per cent, but would you rather lose five per cent of your annual spray bill or ten per cent?

You could follow all these steps, or you could consider buying the slightly cheaper stainless steel or polyacetal tips and habitually replace them each year. The cost of renewing an entire set of nozzles is generally a fraction of the potential cost of time, product wastage and potential crop damage.

Calibrate often

So, to prolong the life of your spray equipment and improve results, maintain and clean it according to the manufacturer’s recommendations. Calibrate frequently and consider the relatively minor investment of replacing your pressure gauges and regularly renewing your nozzles.

Note: It is important that all necessary protective safety clothing is used for calibrating, maintaining, adjusting and cleaning spray equipment.
Readers may contact Dr. Jason S.T. Deveau at jason.deveau@ontario.ca.