Setting the Sprayer Flow Rate for Non-Water Solutions

Setting the Sprayer Flow Rate for Non-Water Solutions March 18, 2016

Table 1. Conversion Factors for Solutions other than Water at 60° F.
Weight of Solution (lbs/gal)Specific GravityConversion Factor
6.6 (kerosene) 0.79 0.89
7.0 0.84 0.92
8.0 0.96 0.98
8.34 (water) 1.00 1.00
9.0 1.08 1.04
10.0 1.20 1.10
10.65 (28-0-0) 1.28 1.13
11.00 (7-21-7) 1.32 1.15
11.06 (32-0-0) 1.32 1.15
11.4 (10-34-0) 1.37 1.17
11.5 (12-0-0-26) 1.38 1.17
11.6 (11-37-0) 1.39 1.18
12.0 1.44 1.20

The rate a fluid flows through a spray orifice varies with its density. Since product recommendations are based on spraying water, which weighs 8.34 lb per U.S. gallon, conversion factors must be used when spraying solutions which are heavier or lighter than water. To determine the proper size nozzle for the solution to be sprayed, multiply the desired GPM or GPA of solution by the water rate conversion factor. The conversion factors are the square root (√) of the fluid’s specific gravity. (See Table 1.)

Example 1. Nitrogen (28-0-0) Only

In this example, the specific gravity of 28% nitrogen (28-0-0), which weighs 10.65 lb/gal, is calculated:

10.65 (weight of 28-0-0/gal) = 1.28 specific gravity
8.34 (weight of water/gal)

The √1.28 is 1.13. Thus, the conversion factor for 28-0-0 fertilizer or 28% nitrogen is 1.13.

Here's how to use the conversoin factor to achieve the desired application rate of 20 GPA of 28% nitrogen.

GPA (solution) x Conversion factor = GPA (water)
20 GPA (28%) x 1.13 = 22.6 GPA (water)

A nozzle size should be selected that will supply 22.6 GPA of water at the desired pressure, speed, and nozzle spacing.

Example 2

Using another example, the following has been recommended for an ecofallow corn field:

75 lb of nitrogen from 28% UAN
Density of 28% N = 10.65 lb/gal
10.65 x 0.28 (UAN) = 2.982 lb N/gal

75 lb N
2.982 lb N/gal = 25.151 gal of 28% solution

Several ingredients will be added in much smaller amounts to the solution. Here's the process to see how the total mixture would spray out.

Example fertilizer-herbicide mixture
IngredientAmountGallons
28% Nitrogen 75 lb N 25.151
Balance Pro 2.0 oz 0.016
Fultime 2.25 qt 0.563
Gramoxone Extra 2 pt 0.250
Crop Oil Concentrate 1 qt 0.250
2,4-D 6 LVE ½ pt 0.063
Total 26.293 or 26.3 gal/acre

To determine how this will spray out and how many gallons of water are needed to get 26.3 gal/ac of this spray solution, three steps are required.

1. To determine specific gravity, weigh an equal amount of this spray solution and an equal amount of water.

 Spray solution = 13.08 lb
Water = 10.3 lb
Determine specific gravity weight of spray solution:

 13.08 lb (wt of spray solution) = 1.27 specific gravity
         10.3 lb (wt of water)

 (Since most of the spray solution is 28-0-0, the specific gravity is the same as 28-0-0.)

2. To determine conversion factor: √1.27 = 1.13

3. To determine the quantity of water to calibrate sprayer:

 Spray rate x Conversion factor = Water amount equivalent
26.3 gal/ac x 1.13 = 29.6 gal/ac
Now calibrate the equipment to apply 29.6 gal of water. For more information see Calibrating Your Sprayer for Effective Application.

 Remember, if you have a flow meter and it has been calibrated with water, it will read the same for a spray solution as with water. If connected to a rate controller, it will change the pressure to adjust the output.

Robert Klein
Extension Western Nebraska Crops Specialist