The Courier & Advertiser (Fife Edition)
Trailer brakes and worker welfare
Trailer braking performance brought to the fore after farm worker’s death following crash
The issue of trailer braking performance has been brought to the fore with the prosecution of a farming business for inadequate brake maintenance after a young farm worker died following a tractor crash.
It comes as a timely reminder to farmers and contractors that silage and grain trailers standing idle for much of the year will soon be pressed into service again, travelling along farm tracks and on public roads carrying heavy loads of grass and grain.
There are worker and public welfare issues, the public image of farming and machinery maintenance and repair costs at stake here, yet making sure the braking performance of trailed farm equipment need not be an expensive or time-consuming affair.
Only regular inspection and adjustment to compensate for brake shoe wear, as well as formal testing of older trailers to see if they can adequately cope with current farm transport expectations, will ensure that trailer brakes are up to scratch.
But what does “up to scratch” mean in this context?
According to agricultural engineering consultant Andy Scarlett, it means achieving a balanced braking effort from a tractor and trailer combination, with both the tractor and the trailer
contributing the same braking effort relative to their weight.
“If the trailer doesn’t make its due contribution, the tractor brakes have to work harder to slow the outfit,” he said.
“At best, that will result in additional wear and higher servicing costs and at its worst an outfit that is less stable and could be prone to jack-knifing under heavy braking.”
Regular inspection and occasional performance testing can help avoid such issues.
“In many cases, it will just be a case of adjusting the set-up to achieve optimum performance,” said Dr Scarlett.
“In others, it may require upgraded components that, at most, would cost about £400 per tandem axle trailer, which is a minuscule proportion of the trailer’s value to the farm business.”
As an illustration of “balanced braking” performance, he cites the example of a typical 16-tonne tandem axle trailer with suspension, flotation tyres and a roll-over sheet weighing in at about six tonnes empty.
With a full load on board, the trailer shares about three tonnes of its gross weight with the tractor via the drawbar, which leaves 19 tonnes on the axles.
“The accepted norm for any vehicle capable of 40kph or more is that it should achieve 45-50% braking efficiency,” said Dr Scarlett .
“So, the trailer’s brakes need to achieve a braking force equivalent to 45-50% of the weight on its axles to deliver braking performance that matches the tractor’s capabilities.”
While new and other trailers just a few years old should be equipped to achieve that standard, older units may not or may have been modified in a way that diminishes their braking performance.
“In some instances, older trailers will not have brake actuators – the component that translates hydraulic or air pressure into movement at the brake shoes – of sufficient size,” said Dr Scarlett.
“Some will also lack a load-sensing mechanism to prevent wheels locking up by moderating the braking effort when the trailer is running empty or partially laden.”
He also highlights the negative effect on braking of replacing original tyres with taller ones to achieve increased flotation and/or greater ground clearance.
“A taller tyre generates more rotational torque, which can only be compensated to maintain braking performance by adjusting the actuating mechanism,” he added.
Establishing for sure whether trailer brakes are, indeed, “up to scratch” requires a properly structured dynamic braking test – merely driving along a flat surface and slamming on the brakes with the trailer empty will simply not do.
Machinery dealers throughout the country can carry out such a test to measure the capabilities of both service and parking brakes on tractors and trailers, as well as other heavy trailed equipment such as manure spreaders, slurry tankers and big seed drills and cultivators.
They use the agricultural version of BrakeSafe, a device produced by Turnkey Instruments that was developed in association with BAGMA, the dealer trade organisation, the Department for Transport and the Health & Safety Executive (HSE).
This kit provides an informed measure of whether brake mechanisms need to be adjusted or upgraded by recording various parameters during a dynamic test.
Once positioned securely in the tractor cab, the BrakeSafe unit uses an accelerometer to measure peak and mean deceleration, while also recording the test speed, stopping distance and time taken to stop from the point the brakes are applied.
A pedal force transducer or switching unit connection to the tractor’s hydraulic or air-brake system records the brake pedal force applied and any slope in the test course can be taken into account to ensure a “true” result.
A built-in printer provides an instant hard copy of the results, which can also be transferred to a computer for the farm records.
BAGMA provides training of experienced agricultural technicians in the use of the system, including refresher training, which is considered advisable every five years.
Dealers can have their BrakeSafe recalibrated annually to ensure it consistently delivers accurate results.
There is no standard charge for such a test but BAGMA’s Keith Christian indicates that dealers are unlikely to charge more than £100 per trailer; and some will do it for less.