Calibrating Turfgrass Chemical Application Equipment

Bulletin 817-00

Calibrating Liquid Application Equipment:
Manual Hand Pump and Backpack Sprayers

Manual sprayers – hand pumps, hand cans and back packs (Fig. 8) – are designed for spot treatment and for spraying other areas not suitable for power sprayers. Most of these sprayers do not have pressure gauges or pressure controls. The pressure drops continuously as you spray. Therefore, you need to repressurize the tank at frequent intervals. When spraying, either hold the nozzle steady at a constant height and walk back and forth, or swing the nozzle in a steady, sweeping, overlapping motion. Maintaining a uniform walking speed is essential to keeping the application rate relatively uniform throughout the spraying operation. Here is how you can calibrate manual sprayers.

Fig. 8. Backpack sprayer.

Step 1. Measure and mark off an area equal to 1,000 sq ft (such as 20 ft x 50 ft).

Step 2. Add a measured amount of water to the tank, spray the area and then measure the amount of water remaining in the tank. The difference between the amount in the tank before and after spraying is the amount used per 1,000 sq ft.

Step 3. Compare the measured rate with the intended or recommended rate, make necessary adjustments and recalibrate the sprayer.

An alternative method is to record the time required to spray 1,000 sq ft and later catch and measure the spray from the nozzle (or nozzles) used for the same time period.

Hints for Improving the Uniformity of Application

Here are some hints for obtaining a more uniform application when using manual sprayers:

• Tie a weighted cord or chain to the wand near the nozzle. This can serve as a height gauge to maintain a set distance from the nozzle to the turf.
  
  
• Walk a known space that should be covered by the sprayer. Practice until you can consistently spray this area with the correct amount of material. A ticking stop watch or timer will improve your pacing.
  
  
• For hand pump sprayers, attach a pressure gauge to the spray wand and check how fast the pressure drops. Count the number of seconds needed for the pressure to drop 10 psi. Count the number of pumps needed to return the pressure to the proper level.
  
  
• For backpack sprayers, attach a gauge to the spray wand and determine how fast you need to pump to keep the gauge pressure constant while spraying.