A Fresh Look at 3 Tier Systems

"To avoid having to even think about Spray Quality transition pressures on the job, I am suggesting that we take a different approach to the set-up and configuration of the 3TS; simply put..."

A three tier system (3TS) is one that essentially provides three different nozzle configurations using two “rows” of nozzles.

1. Tier one, the first row, is typically 015 (green) nozzles;
2. Tier two, the second row, is typically 02 (yellow) nozzles; and
3. Tier three, rows one and two operate together with a combined output of a virtual 035 nozzle.

When I refer to “rows” of nozzles, this may in fact be two individual boom lines of 50 cm spacing, offset by 25cm or as technology has been advancing, a single boom line, with alternating nozzles being individually controlled to achieve the same three tiers with less weight of plumbing.

There are many variations on this theme, but that generally describes what’s going on.

The average 3TS allows you to commence spraying on tier 1, as speed increases the system will transition over to tier 2, then when maximum speed is attained, then depending on required rate of litres per hectare, then tier one may kick back in to provide the third “all on” situation.

One would think that is simple enough, as the system is designed for you to “just drive” or at least monitor things while your sprayer is driving itself, while the spray controller and the three tiers automatically do all the rest.

The problem that presents with this apparently ideal scenario though, is your label requirements in terms of Spray Quality and the various Spray Quality transition pressures for your nozzles which have to be made to synchronise with speed related tier transitions.

This is further complicated in that different size nozzles will transition at different pressure, (or not at all), so maintaining an M or C Spray Quality will require compromises and/or limitations in speed or volume in order to remain within a label specified Spray Quality. Isn’t that what automated systems are supposed to save you from?

An important thing to remember here, is that the Spray Quality requirement for your tank mix must be according to the Coarsest chemical in it.  If your tank mix contains two products, one requiring M, and the other requiring C, then your legal obligation is to make your nozzle selection according to C for the whole mix.

To avoid having to even think about Spray Quality transition pressures on the job, I am suggesting that we take a different approach to the set-up and configuration of the 3TS; simply put, using nozzles that will deliver the label required Spray Quality across your full range of operating speeds and/or volumes, and not change somewhere in between.

It is a very simple matter to go through each of your intended chemical products and write down their various Spray Qualities, group them into your various tank mixed and note which is the coarsest required in that mix.  That will determine the nozzle selection for that day’s spraying regardless of speed and volume. Given that almost every product you use will be C or M, the issue is even further simplified.

So, compared to the typical 3TS set-up described above, my suggested preferred system works like this. Let’s say we have desired rates from 50 lit/ha to 100 lit/ha with a travelling speed in both cases of between 15 and 25 km/h.

MEDIUM Spray Job

50 to 100 lit/ha @ 15 to 25 km/h

1. Tier one, 015 (green) Air Induction Nozzle - C
2. Tier two 025 (purple) Pre-Orifice Nozzle – M
3. Both, equivalent to 04 (red) C/M combination (Note #2 below)

Although our 015 AI nozzle is officially a C, it is compliant with a chemical labels M rating and will still contain a relatively higher percentage volume of medium droplets, than say an 02.

The use of the 025 Pre-Orifice, will deliver a formal M Spray Quality on tier 2. The 025 is chosen instead of the 02 to remain within its pressure constraints across the maximum range of speeds and volumes.

COARSE Spray Job

50 to 100 lit/ha – 15 to 25 km/h

1. Tier one, 015 (green) Air Induction Nozzle – C
2. Tier two, 02 (yellow) Air Induction Nozzle - C
3. Both, equivalent to 035 - All C

All of your options will be achieved with 3 sets of nozzles; a set of 015’s permanently on one row, and a switchable 025 Pre-Orifice/02 Air-Induction on a multi nozzle body on the other.

#Note that the Air Induction 015 nozzle would need to be of a type that remains a C for the full operating range of 3 to 7 BAR, of which there are many available brand choices.

The benefits are many and include avoiding the need for multiple volume/pressure transition configurations in your controller, eliminating speed and volume compromises, increasing your potential to get the best results possible against small targets where M is the compliant Spray Quality and eliminating the risk of inadvertently transitioning to a finer spray quality than is legal for the products in your tank at higher speeds and/or volumes!

Inadvertently Spraying MEDIUM, when your tank mix demands COARSE, can easily occur with low pressure Air Induction nozzles, some of which may transition from COARSE to MEDIUM when exceeding 3 or 4 BAR. Presets' for COARSE application with transition pressures this low may limit your speed and rate options.

It's a good idea to check your transition presets and compare them against the Spray Quality for your nozzle set to be sure you are in compliance with your labels, particularly at higher rates and speeds.

Setting Optimum Transition Pressures (derived from volume)

It is not enough to simply look at the minimum operating pressure of the next nozzle up. Those values represent the absolute limits according to the manufacturer, not the the optimum performance range which is generally towards the mid to upper part of the range, especially with many air induction nozzles.

Setting the step up volume too low (by calculated the total volume output of all the nozzles on the row at the desired transition pressure), results in a not very elegant pressure drop and quite possibly a disruption of your fan angle at transition.

We should aim to calculate the step up pressures to engage the next tier as close as possible to it’s mid range, and not its minimum within the maximum limits of the preceding nozzle. This is another reason why not having to consider Spray Quality transitions, makes this process a lot easier.

Let’s go back to our two M and C scenario’s

MEDIUM - 3TS nozzle set-up

1. Tier one, 015 (green) Air Induction
   1. Calculate the total volume for transition to tier 2 at 0.9 lit/min/nozzle, resulting in the switch over and the 025 kicking in nicely at 2.8 BAR.
2. Tier two 025 (purple) Pre-Orifice
   1. Calculate the total volume for transition to tier 3 at 1.3 lit/min/nozzle, resulting in both activating together at 2 BAR with the objective to continue your speed increase to be working around between 2.5 and 5 BAR for this combination.

COARSE - 3TS nozzle set-up

1. Tier one, 015 (green) Air Induction Nozzle
   1. Calculate the total volume for transition to tier 2 at 0.9 lit/min/nozzle, resulting in the 02 kicking in at 4 BAR.
2. Tier two, 02 (yellow) Air Induction Nozzle
   1. Calculate the total volume for transition to tier 3 at 1.3 lit/min/nozzle, resulting in both activating together at a smidgen under 3 BAR with the objective to continue your speed increase to be working between 4 and 7 BAR for this combination.

As you will see from the examples above, both work on the same preset transitions.  In any set of circumstances though, engaging both lines (tier 3) will result in a significant pressure drop and ought to be seen a step up on your way to a higher speed to bring your operating pressure into the mid to high pressure range.

Summary

The important take home points I've outlined above are these;

• A three tier system (3TS) is one that essentially provides three different nozzle configurations using two “rows” of nozzles.
• Label requirements in terms of Spray Quality make it difficult to calculate transition volume/pressure settings.
• Select nozzles that deliver the label required Spray Quality across your full speed/rate range.
• Calculate the step up pressures to engage mid pressure range of the next tier.
• Aim to continue to increase speed through your transitions to operate in the mid-high side of the nozzles next tier's pressure range.
• Be sure you are able to select a COARSE Spray Quality for your full range of rates and speeds.
• Don’t forget that you can engage any tier you wish at any time, effectively putting three different sprayers at your disposal, each with it’s own specific capabilities.

Finally, this article is deliberately written as a thought provoking 3TS configuration option.

We have a host of 3TS solutions specifically for the various ARAG/ASJ Spray-Jet nozzles encompassing a broad range of rate options including;

• 30 - 60 lit/ha for Compact Fan Air
• 40 - 70 lit/ha for Compact Fan Air ULTRA
• 45 - 100 lit/ha for Compact Fan Air TILT - Stubble Jet
• 50 - 100 lit/ha for Compact Fan Air
• 70 - 110 lit/ha for Compact Fan Air ULTRA
• 70 - 140 lit/ha for Compact Fan Air
• 70 - 150 lit/ha for Compact Fan Air TILT
• 50 - 150 lit/ha for Low Drift Ceramicand of course,
• 50 - 100 lit/ha for the CFA/LDC combination described above.

Contact Dave Young anytime on 08 6102 5886 and receive a copy of nozzle pairs and presets for any or all of the above 3TS combinations.

Article authored and posted by David Young,

05 September 2017.

IMPORTANT TO NOTE

#1. Pressure Volume & Spray Quality values in these examples have been derived from ARAG/ASJ Spray-Jet Compact Fan Air 110015, Compact Fan Air 11002 and Low Drift Ceramic (pre-orifice) 110025 for any 3TS system. Other brands and or/nozzle sizes will require re-calculation.

#2. In our combined C/M configuration, given that we have an independent row of M nozzles on the go, we have aimed for a distinct performance improvement over a conventional AI, AI (C+C=C) combination for Label Approved M products.

E&OE

Reference:

• Australian Pesticides and Veterinary Medicines Authority - Spray Drift Labeling

https://apvma.gov.au/node/958

Instructions for ground application—for COARSE droplet size or larger categories Mandatory instructions for ground applications

USE ONLY nozzles that the nozzles’ manufacturer has rated to deliver a COARSE, a VERY COARSE or an EXTREMELY COARSE droplet size category, as referenced in ASAE S572.1 or BCPC. Choose a nozzle that is specified to provide the droplet size category required in the label Spray Drift Restraints.

DO NOT use a higher spray system pressure than the maximum the manufacturer specifies for the selected nozzle to deliver the droplet size category required in the label Spray Drift Restraint.