The sum of its parts – summer 2018 edition
This article follows on from the Practical feature in the summer edition of Pro Operator magazine on pages 18-23
A wide range of components go into building a self-propelled sprayer. Here we look at how these various assemblies, from the engine and transmission to the cab, operate together and interact to help influence application accuracy, efficacy and efficiency.
Most potential buyers will take a close look at the size, power and technology a self-propelled offers. Along with its reliability record and manufacturer’s reputation, these are the obvious points, but other aspects can have a big influence on performance.
At first glance the specifications of various ‘classes’ of self-propelled look much the same. Scratching below the surface, however, can reveal subtle differences with distinct technology and designs that will suit certain operators but are not what others want or need.
Here we take a tour of the latest Chafer Interceptor with the firm’s Joe Allen, explaining what lies behind the component choice and design. To find out more about the electronic controls we turn to Richard Reed from LH Agro.
Engine works with the transmission
Spraying operations need an engine with a flat torque curve, between about 1,200rpm to 1,800rpm, to maintain constant revs for climbing hills, with engine braking to hold the sprayer back when descending slopes. This happens naturally on mechanically-driven machines while more sophisticated hydrostatic transmissions use electronic control and even brakes in the wheel motors to deliver the same deceleration response.
A responsive transmission that seamlessly changes speed, preferably automatically, helps improve application efficacy, by maintaining the optimum speed at all times. This will ensure the nozzles always to work within their set limits and create correctly sized droplets. A constant pressure will also reduce the risk of drift.
Cab comfort enhances output
With operators spending longer and longer days behind the wheel, cab comfort is considered a top priority. A quiet, comfortable cab along with increasing levels of automation help operators to concentrate and, ultimately, do a better job.
Safety is also important with the Cat 4 classification offering the best protection against dust, aerosols and vapours with filters and by pressurising the cab
Suspension improves stability
Boom stability starts with the tyres and vehicle suspension, with wide flotation tyres, running at low pressures providing a much smoother ride than narrower, row crops.
The second line of defence is the suspension, which increasingly will be ‘active’ or load sensing. This not only protects the operator and booms from shocks, but also helps increase component life.
The vehicle’s suspension is the first line of defence for the boom, after that it’s down to the boom’s own system to ensure it remains stable in work.
Boom suspension ensures the nozzles remain at 50cm above the target, regardless of conditions. This helps to optimise coverage and cut drift, which research shows increases with height. A boom set at 1m creates ten times more drift than one set at the optimum 50cm.
High workloads and narrow application windows mean it’s vital to cut downtime to keep the sprayer out in the field working, not on the headland rinsing out or stood in a yard filling.
While many self-propelled sprayers are still supplied with manual, usually rotary suction and pressure valves, electronically controlled filling is now increasingly popular. These systems are not only simpler to use, they also speed up operations and reduce the risk of making mistakes.
All under control
Electronic control has probably brought the biggest impact, in terms of efficiency and accuracy, to spray applications. As well as being more powerful, the latest systems are adept at multi-tasking, with one terminal able to operate a wide range of functions.
Today, auto-section control is becoming almost standard on self-propelleds, providing the ability to shut down sections to prevent overlaps, often delivering savings of 3%-4% and, at the same time, saving money and protecting the environment. Single nozzle control, which offers even greater precision, is also becoming more common.
Keep on course
An important consideration is do you want the system to also auto-steer? This may determine the type of antenna and receiver that’s required. Accuracy is also important, while the basic EGNOS GPS correction signal is fine for steering in tramlines, it’s not good enough for some row crops.
Some systems, like the Topcon X35 terminal, can also be set to steer around the headlands as well. Once the field boundary has been recorded, it detects when it enters the headland zone and turns into the next tramline. Operators then don’t have to touch the steering wheel until they leave the field,” he says.