Agitation Effectiveness

Introduction

The objective of this research project was to devise a standard test that can be used to determine the effectiveness of agitation in field sprayers. Requirements for an effective agitator are low toxicity and time efficient.

Test Parameters

Pesticide formulations
There are three different formulations typically used in field sprayers. These are:

1. Solutions (water soluble or liquid),
2. Emulsifiable Concentrates,
3. Suspensions (wettable powders and dry and liquid flowable).

1. Initial Agitation - This is where the desired formulation is introduced to the system by the specified method. The speed the formulation disperses at its uniformity indicate initial agitation effectiveness.

2. Re-agitation - This is where a previously introduced uniformly distributed solution formulation is allowed to settle for a specified time in the spray tank. Then, the agitation system is operated and the speed the formulation disperses and its uniformity indicate re-agitation effectiveness.

3. Maintenance Agitation - This is the agitation available while the sprayer is actually spraying. How uniform the dispersed formation remains indicates maintenance agitation effectiveness.

Specific to individual sprayer -
1. Agitator Type - hydraulic, mechanical, sparge
2. Agitator Orientation - horizontal, vertical
3. Agitator Location - top, bottom, left, right
4. Number of Agitators

Variables within a sprayer -
1. Orifice Size (hydraulic agitators)
2. Agitator Flow - depends on nozzle flow, pump condition, etc.
3. Induction Method - top fill, easy fill, etc.

To test all chemicals in each agitation mode and for all sprayer configurations is impossible given time constraints. So, the first step is to narrow down the field of chemicals to a single representative of each formulation type (solution, emulsion or suspension). Further reduction to a single formation is not suggested as correlation of agitation effectiveness between formulation types is not immediately obvious.

Solutions
Water soluble formulation remains in a solution after being initially dispersed. Thus for these formulations, re-agitation and maintenance agitation are not applicable. Thus only initial agitation effectiveness can be measured.

Tests were carried out using a water soluble formulation (Fastgreen FCX) (see Appendix I). Four different orifice sizes were used as well as two different induction methods; c/o CONC vs. time, profiles were established for each configurations. The results show measurable differences in the effectiveness of each configuration. The absolute times to reach "uniformity" were not large (≈1 - 2 mm) as the solution dispersed readily.

Consequently, extension of results to practical application where formulations are much harder to disperse run the risk of presumption. Therefore, without correlation work, the results are not very practical. The advantages of this method are that it is quick (1.5 hr/run), easy (concentration measured with spectrophotometer) and non-toxic.

Emulsions
An emulsion is a colloidal suspension of one liquid in another. An emulsion in water can run from high rates of settling to being suspended indefinitely. For stable emulsions, only initial agitation can be tested.

Limited testing (experimenting) was done with an emulsifiable concentrate, namely, Heliose 10C. Heliose 10C forms a stable emulsion in water and dispenses readily. Essentially, it appeared to behave similar to the Fast Green FCF solution. Consequently, actual agitation tests were not performed.

The disadvantages to using this type of emulsion are as follows -

• Heloise 10C is flammable and precaution must be taken.
• Heliose 10C is slightly toxic [ORAL LD_{SO (rats)} ≈ 4000 mg/kg]
• Slightly toxic to fish thus cannot dispose of through sewer system.

Two types of suspension could be used in testing -
1. Wettable Powder Blank
2. Cupravit [ISO 5682/2 - 1986 (E)]

Cupravit (if available) would give results that may be compared to others don by this same standard.

What Needs To Be Done

Pursue suspension formulation testing.

Formulation -

1. Wettable Powder - order wettable powder blank (Murray-March)
2. Cupravit - investigate ISO standard further (Rick-March/April)

Testing -
1. When - July (Murray)
2. Where - Lab
3. Equipment - write of test equipment needed (Murray-June)
4. Procedure - devise test procedure (Murray-June)
5. Sample Measurement - Methods, ASTM etc. (Murray-April); equipment (Murray-June)
6. Report

Wettable to powder - gravimetric test
1.Scope
1.1 This method covers determination of the mass concentration of suspended solids at different times during the re-agitation of a wettable powder solution in an agricultural field sprayer tank.
1.2 This method adopts procedure for measuring the sample particulate matter concentrations from the proposed ASTM test method titled: Proposed Test Method For Particulate Matter in Water. (See Appendix I)

2. Applicable documents

3. Summary of method
3.1 Sprayer to be tested should be set-up and outfitted with the following equipment:

-pressure gauge to monitor pump output pressure
-pressure gauge to monitor agitator pressure
-sample take-off valve.

4. Significance

5. Interferences

7. Apparatus
7.1 Analytic Balance - capable of weighing to 0.1 mg.
7.2 Dessicator - use activated silica gel (indicating type) or equivalent.
7.3 Drying Oven.
7.4 Filtration Apparatus.
7.4.1 Filter holder - Gooch Crucible and adapter.
7.4.2 Gooch Crucible - 30 ml (20).
7.4.3 Suction Flash - 500 ml (2).
7.4.4 Suction Pump - 1 atm.
7.5 Glass Fiber Filter Disk, Prefilter size (Whatman type GF/D), 47 mm^ø. (This may need to be trimmed.)
7.6 Glass Fiber filter Disk, Final filter (Whatman type 934-AH) 32 mm^ø.
7.7 Crucible tongs.

8. Reagents
8.1 Purity of water.
8.1.1 Spray tank water is tap water.
8.1.2 Distilled water used for gravimetric procedure.

9. Sampling

10. Preparation of apparatus
10.1 Sprayer.
10.1.1 Predetermine operation parameters (agitator pressure).
10.1.2 Close off regulator valve (may not affect results).
10.1.3 Set-up sprayer monitors.
10.1.3.1 Monitor of dump output pressure.
10.1.3.2 Monitor of agitator pressure.
10.1.3.3Sample take of valve (pressure side of pump not with pump outlet and boom valves).
Note: Zero-flow portion should be as short as practical.
10.1.4 Use graduated cylinders to collect samples from same take-off valve.
10.1.5 Sprayer should be set up level.
10.2 Gravimetric test (as per Appendix I, Section 10).

11. Procedure
11.1 Collecting Samples.
11.1.1 Bring spray pump to op. temp. (Hyd models) by pumping at cut-off pressure (no agitation).
11.1.2 Open agitator and simultaneously start time.
11.1.3 Open sampling valve to desired flow.
11.1.4 Collect samples at desired time interval in graduated cylinders (100 ml; 80-90 ml samples).
Note: Sampling valve may be closed b/w long sample interval but should be opened a few seconds before sample time in order to obtain a representative sample.
11.1.5 After collecting all mixing samples, leave agitator running and mechanically mix (w/paddle) to ensure complete mixing. Then take a control sample in same fashion as other.
11.1.6 Shut off pump and agitator valve and allow tank contents to sit a prerequisite amount of time before resampling.
11.2 Gravimetric Analysis (as per Appendix I, Section 11, Omit 11.1).

Test procedure - other
1.Wettable powder blank: needs to be ordered in the spring (during plant production runs).
2.Time required for Tare Crucibles to reach constant weight - use two hours. (See Appendix III)
3.For Crucible with sample dry approximately 24 hours.
4.Double set of Crucibles are needed for a one day cycle.