 Spray Nozzle Maintenance
Some spray nozzle problems are easy to detect. For example, quality control issues and increased maintenance time will become apparent quickly. But there are several less noticeable symptoms that indicate your nozzles are not performing optimally.
Symptoms of Spray Nozzle Problems
Flow Rate Change
- In all nozzles, the flow rate will increase as the surfaces of the orifice and/or internal vane or core begin to deteriorate.
- In applications using positive displacement pumps, which provide the same capacity regardless of pressure, the spraying pressure will decrease as the nozzle orifice enlarges. Lower spray velocities and spray impact will result.
- Increased flow rates or lower spraying pressures may also result in larger drop sizes.
Visual Inspection Doesn't Tell the Story
- Nozzle tips show little visible difference when worn. The first tip below is new. The same size tip shown below has worn to the point at which it sprays 30% over capacity. Visual inspection shows little evidence of wear.
- Orifice viewed through optical comparator shows evidence of internal wear. A closer inspection and an analysis of spray collection data reveal the difference between the two tips.
Deterioration of Spray Pattern Quality
 Hollow cone nozzles: As orifice wear occurs, the spray pattern uniformity is destroyed as streaks develop and the pattern becomes heavy or light in sections of the spray.- Full cone spray nozzles: The spray pattern distribution typically deteriorates as more liquid flows into the center of the pattern.
- Flat fan sprays: Streaks and heavier flows in the center of the pattern, accompanied by a decrease in the effective spray angle coverage typify deterioration.
- Spray patterns of both tips show little difference. Spray collection in tubes gives dramatic evidence of 30% increase in capacity.
Increase in Drop Size
- As nozzle orifices wear, the liquid flow increases or the spraying pressure drops, resulting in larger drop sizes. Larger drops result in less total liquid surface area.
Lowered Spray Impact
- Spray impact is lowered as worn nozzles operate at lower pressures.
- In applications with centrifugal-type pumps, impact may actually increase because of the increased flow through the nozzle.
- Use the following equation to calculate total theoretical spray impact:
- I = K x Q x √P where:
- I: Total theoretical spray impact
- K: Constant
- Q: Flow rate
- P: Liquid pressure
If you suspect you have a spray nozzle problem but can’t pinpoint it, call for help. We can conduct specialized testing in our labs if necessary to help determine the source of the problem. Leaving spray nozzle problems unresolved can be very expensive.
Examples:
Cost of nozzles spraying 10% over capacity due to wear: $USD 60,000
- Assumes cost of liquid sprayed is $USD 1.00 per gallon at a flow rate of 5 gpm (19 l/min)
Cost of three hours of manual labor per day to maintain spray nozzles: $USD 11,250
- Assumes hourly labor cost of $USD 15.00
Cost of 2.5 hours of lost production time per week and waste due to nozzle problems: $USD 33,750
- Assumes value of production time at $USD $100 per hour and a waste cost of $USD 100 per day.
(Assumes a spray system operating 8 hours per day, 250 days per year.)
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