The diagram below shows a cross section through a WAGNER powder injector:

The functional principle

Compressed air from the feed air connection is pushed through the injector nozzle (also known as the Venturi nozzle) into the collector nozzle. The small diameter of the nozzle ensures a high air velocity.	On its way through the injector the feed air passes across the powder suction tube where it sucks in powder due to the vacuum. The air and the powder now continue to flow at a high velocity through the collector nozzle into the powder hose and finally to the spray gun.

Good to know: The powder particles must be delivered at a speed of around 12 m/sec in order to achieve a uniform powder delivery and a soft cloud.

feed air low / dosage air high = small flow of powder

The sum of both air flows, i.e. the total air, and the powder velocity in the tube remain the same.

Wear

The abrasive effect of the powder/air mixture wears the collector nozzle over time. The powder speed decreases with increasing wear of the collector nozzle. The result is a reduction of the Venturi effect and consequently of the powder output.

New collector nozzle

Worn collector nozzle

In order to maintain the desired powder output the experienced powder coater increases the feed air at this point. Normally, this measure works until the collector nozzle is completely worn and must be replaced.

Typically, the life span of a collector nozzle lies between two weeks and one year (depending on the powder characteristics, the feed air quantity used etc.)


Tip: Don’t forget to reduce the feed air again, as soon as you start using the new collector nozzle. Otherwise, there will be a significant wear right from the beginning.