|Iowa State University|
Venturi Nozzles for Drift
by Bob Hartzler
March 21, 2000 - Several new nozzle types have been introduced in recent years that are designed to minimize the formation of small droplets prone to move from the target site. One of the more popular designs is the venturi nozzle that consists of a flow-metering preorifice and an air inlet that results in mixing of the spray solution and air. Researchers at the University of Tennessee recently reported the results of research investigating the droplet spectra produced by several of these nozzles (Etheridge, R. E., A. R. Womac, and T. C. Mueller. 1999. Characterization of the spray droplet spectra and patterns of four venturi-type drift reduction nozzles. Weed Technology 13:765-770.)
The nozzles included in the study were: 1) Spraying Systems AI Teejet, 2) Lurmark Ultra Lo-Drift, 3) Greenleaf TurboDrop, 4) Delavan Raindrop Ultra, and 5) Spraying Systems XR Teejet. The first four nozzles are venturi types, whereas the XR Teejet is a standard flat fan nozzle included for comparison purposes.
Spraying Systems AI Teejet
Spraying Systems XR Teejet
Lurmark Ultra Lo-Drift
Delavan Raindrop Ultra
All nozzles had a 110 degree spray angle and were evaluated in sizes equivalent to a 110015, 11003 and 11004 nozzle. Nozzles were evaluated at pressures ranging from 15 to 90 PSI. In addition, the effect of three herbicides (Liberty, Roundup Ultra, and Gramoxone Extra) on nozzle performance was evaluated. Droplet size distribution was measured with a laser analyzer and pattern variability was determined with a Lurmark patternator table.
The effects of the different parameters studied are summarized in Table 1. The Volume Median Diameter (VMD) is the droplet size (microns) that half of the spray volume is in droplets larger than the VMD and half is in droplets below the VMD. Generally, the larger the VMD the less risk of drift. V205 is the percentage of spray volume in droplets less than 205 microns. Droplets less than 200 microns are considered to be susceptible to off-target movement. Drift potential increases as the V205 increases. Each nozzle type was tested using the three herbicides, three nozzle sizes and four pressures. The data presented are means of the listed factor over the different variables. Thus, the value for the AI TeeJet is the average performance of this nozzle used under several different conditions (three nozzle sizes, three herbicides and four spray pressures). Likewise, data for herbicides represent means of that herbicide applied with the different nozzles and spray pressures. In most situations the nozzles performed similarly under the different uses (i.e. as spray pressure increased, droplet size decreased for all nozzles). However, there were situations where unexpected interactions occurred and important ones will be discussed.
Table 1. Effect of several factors on droplet size distribution with venturi nozzles.
|Lurmark Ultra Lo-Drift||439||18.6|
|Delavan Raindrop Ultra||654||10.5|
All of the venturi nozzles increased the VMD and decreased the volume in droplets less than 205 microns compared to the Extended Range Flat Fan tip. For example, the VMD for the XR flat fan was 173 microns compared to 472 microns for the TeeJet AI nozzle. Averaged over the different application parameters, the Delavan Raindrop Ultra had the largest VMD and smallest percentage of drift-prone droplets. As would be expected, increasing spray pressure reduced the VMD while increasing the percentage of spray in small droplets. The herbicides significantly influenced droplet output by the nozzles. Liberty produced the greatest volume of small droplets, whereas Gramoxone Extra had the lowest. It should be noted that the differences in output due to the herbicides is relatively small compared to the differences resulting from nozzle type or spray pressure. Decreasing tip size tended to increase the volume in droplets prone to drift, however there was not a consistent response in VMD among the three nozzle sizes. Most nozzles produced larger droplets as nozzle size increased; however, the Delavan Raindrop Ultra droplet demonstrated the opposite trend.
The big increase in VMD provided by venturi nozzles may raise questions as to whether these nozzles will provide sufficient coverage of weeds to achieve effective control. The British Crop Protection Council recently set specifications for categorizing droplet sizes. According to these guidelines, a VMD between 354-464 microns is classified as coarse droplets. Generally, coarse droplets are adequate systemic postemergence herbicides under most situations. However, coarse droplets may compromise herbicide activity when using contact herbicides or in situations with dense weed infestations. All of the venturi nozzles fell within or near the coarse range except for the RainDrop Ultra. The large droplets produced by the RainDrop probably would be more appropriate for preemergence herbicides. The researchers who did this research also studied the effect of nozzle type on herbicide performance. Results of that research have not yet been published, but I will post the results when they are available.
The researchers also evaluated the uniformity of the pattern across the width of the boom with the different nozzle types. The boom was mounted 16 inches above the spray table and nozzle spacing was set at 20 inches. The sprayer was operated at 40 PSI and output was collected using a spray table. Uniformity across the boom width was expressed using the coefficient of variation (CV). The greater the CV, the more variability in output across the width of the boom. The relationship between output and CV can be seen in Figure 1 which plots the output of the XR Teejet tip and the GreenLeaf Turbo Drop nozzles. The output of the XR nozzle was much more uniform and had a CV of 12.1% compared to 24.2% for the TurboDrop nozzle.
Figure 1. Relative distribution of output across the spray boom with two nozzle types.
Adapted with author's permission from Etheridge et al. 1999. Weed Technol. 13:765-770.
The pattern produced by venturi nozzles generally was more variable than produced by the XR Flat Fan nozzles (Table 2). Uniformity of the spray pattern decreased with the smaller nozzle sizes in the TeeJet AI and Delavan Raindrop Ultra nozzle tips, whereas the TurboDrop nozzle was most variable with the 11004 nozzle. At 15 PSI several of the venturi nozzles produced narrow, irregular spray patterns (data not shown).
|Nozzle type||Nozzle size|
|Lurmark Ultra Lo-Drift||13.3||15.0||16.5|
|Delavan Raindrop Ultra||27.2||14.3||14.2|
|XR Flat Fan||12.3||13.3||12.1|
In summary, all of the venturi nozzles reduced the percentage of spray volume found in droplets prone to movement off the target site. However, the venturi nozzles generally produced a more variable pattern across the boom width than the XR flat fan tips. Uneven distribution can result in inconsistent product performance, thus checking variability across the boom is an important task when changing nozzle types. Bob Kline (University of Nebraska) has found that pattern uniformity can be increased by going to 100% overlap rather than 50% that traditionally has been recommended with flat fan nozzles. Thus, changing nozzle spacing might improve the consistency of the pattern across the boom width. While selecting nozzles that reduce the number of small droplets can help reduce problems with off-target movement, this new technology does not eliminate the need for good judgement on part of the operator to know when conditions are likely to lead to problems with drift.
For further information:
Greenleaf Technologies - http://www.greenleaftech.com/
Spraying Systems - http://www.teejet.com
Delavan - http://www.delavan.com/
Prepared by Bob Hartzler, extension weed management specialist, Department of Agronomy, Iowa State University
more information contact:
ISU Extension Agronomy
2104 Agronomy Hall
Ames, Iowa 50011-1010
Voice: (515) 294-1923
Fax: (515) 294-9985
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