Poorly maintained spray systems can "drain a lot of money from your operations," according to Jon Barber, specialist with the Industrial Service Machinery Team at Spraying Systems Co. "The cost of wasted water alone can approach $100,000 annually even in a system with relatively minor performance problems." This number rises sharply when the costs of excess chemicals, wasted energy, extra scrap, unplanned downtime, and additional labor are added in. (Illustrated above, good spray tip.)
The causes of spray nozzle deterioration include erosion/wear, corrosion, high temperatures, caking/bearding clogging, improper reassembly, and accidental damage. While such deterioration is "totally undetectable with the naked eye," notes Barber, certain signs can point to potential problems. These include quality control issues and increased scrap, increased maintenance time, flow rate change, decreased spray pattern quality, increased spray drop size, and reduced spray impact. (Illustrated above, worn spray tip.)
Barber''s maintenance checklist includes:
- Flow rate for centrifugal pumps -- monitor flow meter readings for increases
- Flow rate for positive displacement pumps -- monitor line pressure for decreases
- Spray pressure (in nozzle manifolds) for centrifugal pumps -- monitor for increases in liquid volume sprayed
- Spray pressure (in nozzle manifolds) for displacement pumps -- monitor pressure gauge for decreases in pressure and reduction in impact
- Spray pattern -- visual inspections with protractor
- Spray nozzle alignment -- check uniformity of spray coverage
- Quality -- check for uneven cleaning and drying, and for changes in temperature/dust content/humidity.
Nozzle life can be extended by taking some of the following steps, when possible:
- Decreasing spraying pressure -- slowing the liquid velocity rate can help reduce wear and corrosion.
- Reducing the quantity of abrasive particles, or the concentration of chemicals, also helps lower wear and corrosion rates.
- Adding line strainers or switching to nozzles with built-in strainers can alleviate orifice deterioration/clogging.
- Cleaning nozzles with care -- recommended tools include plastic bristle brushes, wooden or plastic probes. "Never use wire brushes, pocket knives, or welder''s tip cleaning rasp," Barber warns. For stubborn clogs try soaking the orifice in a noncorrosive cleaning chemical.