20 November 1998

Fail safe trailer braking system beats legislation

By Andy Collings

NEW Euro legislation concerning trailer braking – which could be introduced next year – will require 40kph rated trailers with a gross laden weight of between 3.5t and 25t to be fitted with fail safe systems.

Proposals currently being considered state that these trailers must have parking brakes which can only be released when the service brakes are returned to full operational status. It adds that continuous or semi-continuous service brakes with one hydraulic line or two pneumatic lines should be employed.

Automatic brakes must also be fitted with an optical or acoustic warning if line pressure drops below stated pressures – 90 bar for hydraulic systems and 5 bar for pneumatic systems.

All of which, if instigated, could see some changes, both in actual braking systems employed, and the cavalier attitude many operators undoubtedly have when it comes to the question of trailer brake maintenance.

When it is known that a recent survey by one company involved in brake technology revealed that over 50% of farmers admitted they had experienced an unplanned parting of loaded trailer and tractor, such changes are perhaps to be welcomed.

And some, more safety conscious operators, might consider taking advantage of new innovations in trailer braking systems before mandatory rules apply.

GES Hydraulics, for example, based at Crowland, near Peterborough, has developed an automatic fail safe braking system which is now being adopted by several major trailer manufacturers.

Designated the Euro Safe, the system provides automatic application of trailer brakes in the event of the trailer becoming detached from the tractor and also allows the operator to apply full parking brakes without having to leave the cab.

Designed to be used with all tractor/trailer combinations using hydraulic braking, its key component is an accumulator, which, once charged from the tractors hydraulic braking system, retains a pressure reservoir to activate the trailers brakes in the event of a separation.

Plumbed in to the hydraulic brake line, the accumulator comprises two parts – a section pre-pressurised to 100 bar with nitrogen at the top end and, with a diaphragm between, a lower end which holds hydraulic brake oil at the same pressure. The accumulator, when pressurised from the tractors brake circuit, holds 0.7 litres of oil, sufficient volume for the majority of trailers used in agriculture but should larger trailers with greater braking demands be used, two or perhaps three accumulators can be employed collectively.

When the trailer and tractor are properly coupled (hydraulic brake supply and electrical drawbar plug socket), two electrically activated solenoid valves are employed – one retains the pressure in the accumulator (shut) and the other allows oil to flow from the tractors braking system to the trailers brakes (open). In the event of a separation, the electrical power cut-off, as the tractor and trailer depart company, causes the pressure retainer solenoid to open – releasing stored pressure to activate the brakes, and the other to shut – preventing any flow back to what is likely to be a broken feed pipe.

While full pressure is designed to be retained in the accumulator for the duration of the journey -and for some considerable time afterwards – any undue loss of pressure activates a high-pitched buzzing noise and a flashing light to warn the operator.

Cab-mounted controls

More sophistication is to be found in the cab-mounted control system. Wired into the tractors electrics – either permanently or as a temporary hook-up – the trailers brakes will be applied fully if the on/off switch is switched to off or, as previously described, the electrical supply to the accumulator is broken. Both, in effect, do the same thing.

At start up, if the buzzer and light warnings are activated, accumulator pressure iis restored by pressing the tractors brake pedal.

Recognising it is not always in everyones interest to have a trailer, say, with a full load of sugar beet stuck across the road with its brakes on, GES has built in an override system. Pressing and holding a button on the side of the control box discharges the accumulator and, as a result, releases the brakes.

While few could disagree that the Euro Safe system has a useful part to play in helping reduce accidents with trailers – its £400 price tag is comparatively small – there remains the problem of brake maintenance. There is, after all, little point having automated braking if, at the end of the line, there are no brakes to apply. &#42

Euro Safe system, with GES technical director Tony Thompson, provides automatic application of trailer brakes if the tractor and trailer become detached.

Fail safe braking systems could soon be a legal requirement for 40kph trailers with a gross laden weight of 3.5t-25t.