The connection between the towing vehicle and towed vehicle is subjected to significant strength demands.
Whilst coupling functionality is reliant on appropriate maintenance and operation, more importantly the last line of defence, being a visual inspection to ensure – that the coupling is correct and primary and secondary locks are engaged.
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Typically, in larger combinations this may include a mix of mechanical coupling types, fifth wheel/s and automatic pin couplings. Other combinations, semi-trailer or truck and dog trailer may only include one type of mechanical coupling, a fifth wheel or an automatic pin coupling.
The increasing number of new combinations has come with new challenges. Many drivers have advanced to A-doubles from B-doubles with little or no exposure to Automatic Pin Couplings. You don’t know what you don’t know!
This is why a comprehensive introduction and training to all new equipment is important. If in doubt, ask!
Couplings
Heavy vehicle couplings are designed and manufactured to standards to perform engineering functions reliably.
However, like all things mechanical and structural, they must be maintained and operated in accordance with the manufacturer’s specifications, with due attention to the operating environment.
ADR 62/02 requires that fifth wheels/kingpins and automatic pin couplings comply with Australian Standards. In brief, couplings shall be designed to provide automatic coupling of the towing vehicle to the trailer and automatic locking to prevent the possibility of partial engagement.
Locking shall only occur upon complete engagement. The coupling shall incorporate a secondary mechanism for automatically retaining the locking mechanism in the locked position, and the operation of this mechanism shall be visually verifiable by a person when in a position to operate the locking release handle.
Locking mechanisms
‘Quick Release Couplings’ must incorporate a positive locking mechanism together with a separate means of automatically retaining this mechanism in the locked position. This locking must be readily verifiable by visual examination.
Events of heavy vehicle coupling disconnections in-service (on the road) have been reported both in Australia and New Zealand. In coupling disconnection, the reference is to the fifth wheel and kingpin or pin coupling and tow eye.
These would seem to be the result of not confirming positive coupling and locking; or, ancillary systems resulting in an uncommanded release of the coupling, not actual equipment component failure.
Whilst many operators provide fixed lighting for inspection of the fifth wheel/kingpin engagement and locking, few if any provide the same aid for pin couplings.
Coupling hazards
A fifth wheel set for ‘coupling’ is generally not a hazard for personal injury, as the ‘trigger’ for coupling connection is activated by the kingpin and requires significant force.
Whereas, an automatic pin coupling set for coupling (often referred to as ‘loaded’) has potential for personal injury hazard. Accordingly an automatic pin coupling should never be left ‘loaded’, except in preparation for when coupling to a drawbar is planned in the short term (assembling combinations).
Automatic pin couplings have a lower bush where the nominal diameter is around 35mm to receive the pin, but the bush reduces in diameter to less than 20mm to provide a landing for the pin.
Herein lies potential for problems with debris accumulation. If the coupling is left ‘loaded’ (set for coupling) then the lower bush is exposed to road grime (gravel) and product (especially from tippers).
The reduced diameter may result in debris being compacted, thus preventing the pin to ‘land’ and therefore neither the primary or secondary lock will engage – hence the importance of visual validation of locking indicators.
Therefore, except when in the process of coupling vehicle units, automatic pin couplings should not be left ‘loaded’. This will also reduce the potential for debris ingress.
Hands and fingers should NEVER be placed in the ‘line of fire’ of any vehicle coupling or other mechanical vehicle.
NAIM and remote release couplings
No air in motion, or NAIM, is a safety function that prevents a vehicle from moving when it shouldn’t, like during loading or unloading, by removing air pressure from interlocks like gates and hose reels and other air operated ancillaries.
NAIM systems are used in trailer brake interlock safety systems to prevent drive-away incidents; with variations of NAIM to manage air operated ancillary functions. E.g., an interlock to prevent operation unless the parking brake is applied.
There are many ‘air operated ancillaries’ on modern transport equipment. Roll-back bodies, dangerous goods valving, air operated uncoupling. Air to all ancillaries must be supplied via a protected circuit – the last system to lose air supply/pressure being the braking system, as is required by the Australian Design Rules.
Where a remote-control device is employed, there shall also be a remote indication device which shall at least indicate the open condition of the coupling; and, there shall be a dedicated switch (i.e. master switch, lever or valve) to enable the coupling to be opened or closed by means of the remote-control device.
If this master switch is not located in the driving cab it shall not be in a position where it is freely accessible to unauthorised persons or it shall be lockable.
The operation of the coupling from the driving cab may only be possible when inadvertent operation has been precluded, for example by an operation requiring the use of two hands or NAIM interlock.
It shall be possible to ascertain whether opening of the coupling under remote control has been completed or not. Visually check all couplings prior to each departure.
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