Calibrating air-blast sprayers

WG-EQ-MR-1-Calibrating 1by Sanne Kure-Jensen
UNH Extension Field Specialist George Hamilton discussed the importance of and best techniques to calibrate air blast sprayers. Hamilton spoke to a room full of farmers at the USDA FSA headquarters in Warwick, RI.
Like every pesticide label, Hamilton recommends calibrating your sprayer before use. This will ensure effective, efficient, economical and legal spraying. Poor spray coverage is usually the cause of poor spray efficacy. Overuse of some sprays can lead to fines or unhealthy residues.
Hamilton recommends calibrating equipment at least twice a year — at the beginning and middle of every growing season. Another calibration is recommended when changing nozzles, operating pressure or wheels. New tractor tires can change the speed (and tachometer) as much as 10-20 percent.
Select the appropriate accessories. Gauges are most accurate at the middle of their range. If you work at 100 psi, get a gauge with a range to 200 psi. They should be oil-packed. Hamilton recommended against skimping on a cheap gauge.
Nozzles wear fastest when used with wettable powders, flowables or dispersible granules, especially at high nozzle pressures. Hamilton recommended using hard, wear-resistant tips and cores on the sprayer. Abrasion resistant nozzle components cost more up front, but are cost effective in longer effectiveness and applying the right amounts of spray.
Regular equipment maintenance will ensure a clean, residue-free sprayer in ready-to-use condition.
Benefits of Calibrating
When operators calibrate equipment before use, they can:
1. Determine the precise rate of material applied/acre
2. Verify proper placement of material
3. Ensure all nozzle tips operating at manufacturer’s specification/delivering proper output
4. Compensate for equipment changes, crop staging and environmental conditions.
Calibration Factors Affecting Application Rate
Steady speed is crucial for consistent spray application. The spray application per acre is inversely related to the sprayer’s ground speed. When ground speed is doubled, application rates drop by half. When ground speed drops by half, the application rate doubles.
The nozzle flow rate varies with the tip size, the pressure applied and the condition of the tip. If material is clogging the tip, spray rates will drop. If gaskets or tips are worn or damaged, spray rates will increase, patterns may be unpredictable.
Output requirements change dependant on plant spacing, crop and pest stage. Farmers must calculate each application separately, following the product labels. This is more critical today than five to 10 years ago. The smaller amounts of chemicals mixed in most tanks can lead to greater risk of errors with “casual” measuring or poor calibration.
Do not change hose diameter. This can cause a vast, unpredictable change in pressure and spray delivery.
Pre-Calibration
Before calibrating an air blast sprayer, Hamilton recommends:
1. Triple rinse tank, manifolds, piping and nozzles
2.  Use caution with pressure washers. Water may be forced into sealed bearings. Use a push broom or stiff brush to scrub air blast sprayer tank. Be sure to clean both sides of nozzles and pumps.
3. Clean tank filters, suction filters, final filters and every screen behind nozzles
4. Keep record of nozzle orifice and whirl disc sizes
5. Flush pressure gauge line; verify gauge is working
6. Check condition of all valves, diaphragms and O-rings
7. Be sure all manifolds match within 5 percent
8. Check pressure on all tires — sprayer and tractor
9. Verify tractor tachometer is working by timing a 264 ft. drive in your field (not a paved road); take the average time after three to six trials. Calculate the actual speed. Hamilton said an average of 40 percent of equipment is used at improper speeds. Speeds off by as little as .2 mph can cause 10 extra gallons spray/acre.
10. Fill sprayer half full of clean water.
11. Have operators and mechanics that work on sprayer/tractor combination on hand for sprayer calibration
12. Have sprayer operators manual handy
Sprayer Maintenance
Hamilton recommended this routine maintenance to prolong the life of your air sprayers
1. Remove nozzles and strainers; flush with clean water regularly
2. Keep a can of compressed air in the tractor to clean clogged nozzles; never use your mouth to blow out clogged nozzles. If you must use something hard, use a toothpick, not a nail or dental pick.
3. Change all nozzles annually. If you work more than 40 acres, skimping will cost you in spraying too much product with poor results and lower crop quality and yields.
4. Never clean nozzles or sprayer tips with any metal objects. Use a soft brush or can of compressed air (sold to cleaning computer keyboards).
5. Never apply corrosive fertilizer solutions through an air blast sprayer.
6. Remove and clean strainers after daily use or when products change on sequential applications, whichever comes first.
7. Check and change diaphragms and valves annually (Check owner’s manual for recommended frequency).
Calibration Notes
Hamilton advised all growers to keep records on sprayer calibration calculations. Make sure your staff keeps records as well to protect you. Use them to compare sprayer results over time and note potential changes to equipment due to wear. Records will also be helpful each time you check calibration and are essential, should you ever be challenged with product residue, pesticide drift or other spray complaints.
Hamilton shared the Sprayer Calibration Worksheet he uses. Fill in one form for each piece of equipment (tractor and sprayer) each time you calibrate. View the interactive worksheet and instructions for Air Blast Sprayers adjustment at http://extension.psu.edu/fruit-production/files/air-blast-sprayer-worksheet
For more information, email George Hamilton at george.hamilton@unh.edu or call 603-641-6060.

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