For what is such an essential part of a well-maintained and safe vehicle, it is vital to get it right when keeping it safe in brake operations. Bob Woodward, Chief Engineer, Australian Trucking Association, reckons there can often be confusion around brake systems, especially when it comes to mixing brake airlines and park brake operations.
An issue the ATA’s Industry Technical Council (ITC) continues to be made aware of is instances where newly purchased and installed fittings or airlines have failed to seal correctly. Those experiencing the issues reported the installations leaking excessively while the vehicle was under test in the workshop. In these cases, the installations were replaced without further incident, but if they went undetected these leaks could cause a range of problems including the unintended activation of emergency braking systems.
But what causes these incidents in the first place?
Metric airlines and their fittings are available through a range of parts networks to support European truck models. However, the Australian market typically uses imperial sizes of airlines and fittings.
Confusion can arise given the similar, but not equivalent, sizes of these airlines. For example, the metric 12-millimetre line will appear to accept the imperial ½ inch olive, which has an equivalent to 12.7-millimetre outside diameter.
This means the mismatch of fittings and airlines will result in a loss of integrity of the assembly. Additionally, the metric line has a smaller inside diameter restricting airflow, which could potentially result in the vehicle not being compliant with Australian Design Rules.
To combat this issue, the ITC believes it essential that airlines and fittings use the same airline size and applicable standard, whether it be metric or imperial. It’s also recommended that workshop staff double-check the size printed on the airline before selecting matching fittings. Recommended follow up actions are to separate metric and imperial airlines and fittings, ensuring the stores are labelled correctly, and to educate staff about their differences.
Another operational braking issue that has been reported is incidents in which setting the park brake on a prime mover either applied its trailer’s brakes on air or did not apply the trailer brakes at all.
In Australia, the standard practice is that trailers are parked using the mechanical force of their spring brakes. Applying the park brake in the cab of a prime mover should apply these spring brakes on all connected trailers.
Under the Australian Design Rules, trucks and prime movers that meet the European brake standard are deemed to meet the Australian standard, as long as they also meet a performance specification. However, some of these units use park brakes that only apply service air to the brakes on connected trailers, rather than spring brakes.
This is a less safe practice, because the brakes would release if the air leaked out, or a driver mistakenly disconnected the airlines in the wrong order. If a trailer is parked on spring brakes, the brakes will remain engaged even if the air pressure is lost – the brakes fail to safe.
The European standard only requires the brakes to maintain pressure for 15 minutes, because drivers routinely fit wheel chocks. But because Australian operating practices don’t include the use of wheel chocks in these situations, there’s a real danger these braking systems could lead to a trailer rolling away, or damage of its landing legs.
To assist operators in finding out what kind of park brakes are installed in a vehicle, the ITC developed a Technical Advisory Procedure that provides essential checks that ensure park brakes on their trucks restrain the trailers safely.
The procedure recommends operators don’t park a combination on air, and that operators fit a door interlock system that sounds an alarm if the door is opened without the park brake being applied. It’s also recommended that drivers are trained to disconnect airlines and electrical cables before dropping landing legs and releasing the fifth wheel.
Established in 1994, The ATA’s Industry Technical Council (ITC) is the trucking industry’s brains trust that solves issues and saves lives. Bringing together operators, suppliers, engineers and industry specialists, the ITC benefits its members and the trucking industry by raising technology and maintenance standards and improving the operational safety of the heavy vehicle industry.
To view the Park Brake Operation Technical Advisory Procedures and others, head to the ITC website
