19 June 1998

Air induction nozzles tackle drift trouble

AIR induction nozzles have superseded low-drift versions of conventional spray tips as the best non-active method of controlling drift, believes Tom Robinson, Novartis applications specialist.

"They are brilliant at cutting drift and reasonably versatile in terms of the spraying situations in which they can be used," he says. "If you need a finer spray than that produced by an air induction nozzle, then go to a standard tip."

The Novartis Sprays & Sprayers event will see the debut of new designs from Spraying Systems (TeeJet), Tecnoma, Sprays International, Lechler and Lurmark challenging the established Air Bubble Jet from Billericay Farm Services.

All work on the same principle of metering fluid as it enters the nozzle, using the venturi effect to draw in air through small slots or holes, and then mixing air and liquid before discharging the mixture in a spray with few drift-prone fine droplets.

In that respect, and the fact that the larger droplets contain small bubbles, the nozzles are similar to active twin-fluid designs like the Cleanacres Airtec and Spraying Systems AirJet. But these designs give the operator control over the air/liquid mixture to produce sprays of different characteristics or qualities, and the compressed air propels the spray into the crop.

"The air induction nozzle is a low energy, low-tech design by comparison but with some of the advantages and characteristics of twin-fluid systems," says Mr Robinson. "For example, the fact that the larger droplets contain tiny air bubbles is believed to help them collapse on impact with leaves rather than bouncing or rolling off."

The relatively coarse spray can have adverse effects on ultimate spray efficacy. But in limited trials conducted jointly by Billericay Farm Services and Novartis, results have been good enough with fungicides, plant growth regulators and broad-leaved weed herbicides for the nozzles to be used with confidence. "But you would not want to use an air induction nozzle for blackgrass, for example, because you need a fine spray to ensure good target coverage and achieve the high level of control needed to have any effect on blackgrass populations," explains Mr Robinson. "Similarly, I wouldnt advise their use in standard form for blight control on potatoes – the big droplets tend to fall vertically because of their mass, with most of the fungicide ending up on the top leaves."

BFS has addressed this short-coming by designing a twin Air Bubble Jet nozzle that sets two of the companys air induction tips at forward and backward-facing angles. That produces a trajectory proven to improve penetration into dense canopy broad-leaved crops. This too will make its debut at the Sprays & Sprayers event.

Air induction nozzles have taken over from low-drift types as the best way to limit spray drift, says Novartis Tom Robinson.