Compared to Australian brake systems, European systems appear to be complex and potentially dangerous.
We hava a tractor protection valve, which controls air supply to the trailer. Application of the prime mover parking brake automatically turns off the air supply to the trailer.
The supply line (red) has a female fitting with a sealing valve that stops the air when disconnected.
The signal line (blue) has a male fitting. The female trailer fitting is free flowing, lacking the check valve.
Trailers are fitted with maxi brakes, a two chamber actuator. One chamber operates the service brake, the other operates the parking brake, automatically applied when the supply line is disconnected. It is impossible to push the trailer back when hooking up as the brake cannot be released until the supply line is connected.*
Our system makes hooking upsafer and easier. The trailer cannot unexpectedly move and the air line is always connected with no pressure resisting connection.
The exception to this is when the trailer has been fitted with a shunt button, that supplies air from small, dedicated air tank to supply to release the brakes for a yard movement.
ALMOST? Yes!
With enough attempts, even âfoolproofâ systems will eventually find a fool!
At the moment, and I can`t imagine any change coming soon, the basic UK and EU regs are the same. There are some country variations but the underlying systems meet the same standard.
We seem to have the same system in the trailer?
Two air lines. one to feed it, (red) one to give signals. (yellow here). Both are âCâ type coupling in the UK, female on unit red line.
Disconnect the red and the trailer brakes come on and the parking brake button on the trailer chassis pops out.
There is a shunt button to enable (unbraked) movement of the trailer in a yard.
After reconnecting the red line the brakes remain on until the Park Button is pushed in.
That sounds all the same?
We donât have the isolator valve in the cab.
On my DAFs the park brake in the cab put full line pressure on the yellow service line, so reconnecting the lines there was full line pressure in both air lines. It does take a fair old shove.
I believe some on here are shunters so do they connect all lines all the time? What sort of state are their wrists in?
As a question? Do you have any trailer stability systems fitted?
If it senses the trailer might go over it applies differential braking to even out the roll and keep it on the deck.
It wonât stop an enthusiastic fool, but is an interesting thing.
Iâve had one kick in and it was quite a surprise.
Driving on a swooping twisting dry road with a few heavy pallets right up the front, so there was very little weight on the trailer axles. The trailer presumably sensed that the wheels were lifting so dragged the trailer brakes on for a second or so.
Strange feeling.
Makes me sound like I was about to chuck it on itâs side? Well, I accept I was going quick, but not in imminent danger. No complaints really if it kicks in slightly earlier than I might have liked. Better safe etc.
Edit⌠we are missing out secondary and emergency barking systems, and the various flavours of antilock, but this a post not a book!
Two line or the old three line system all have/had valves to isolate the air supply when running without a trailer.
Trailers have had load sensing valves for decades.
While as I always told new drivers there is redundancy in the air brake supply side but there is only one set of shoes and drums and when they are too hot they are gone no matter how many different ways you can try apply them.
Obviously the more axles that can be braked for parking braking the better.
Yeah, trailer stability is a thing here, but as yet not part of the ADRs, (Australian Design Rules), so only fitted occasionally by the likes of fuel companies.
Do even vintage trucks have blue line systems now?
Taps are a no-no.
Yes. They started as mechanical systems which relying on deflection of springs to regulate the air allowed through.
You only realised they were useful when they stopped working, and you had no trailer brakes at all, or left black lines and clouds of smoke from an empty trailer.
Not a patch on the sophisticated electric systems of today.
NIce to agree.
When the friction materials get too hot? You;re goosed.
Agreed again!
Very apparent in snow when only the drive axle is braked. Stupid idea.
Helps stop tankers slopping about too.
I added the âalmostâ caveat to the title, knowing that with enough effort, a dedicated moron can circumvent any safety system.
I once had such a dedicated moron in my employ a few years hence. Wherever Russel went, disaster was one step behind.
The day I sacked him, he was given instructions to pick up a preloaded trailer and deliver the load. The trailer was parked up on a slope, in a yard we share rented with a number of other businesses, including Volvo who used to store trucks, direct from the wharf, awaiting pre-delivery.
Russel backed under the trailer, forgetting to apply the brake. Easy done, Iâve done it myself, no major problem. Trailer hooked up, legs wound up, Russell climes up to connect the suzzies. As soon as the trailer gets air, itâs off, with Russell still behind the cab. Still no major problem, just disconnect the air and the whole show will come to an abrupt halt.
But no, not disaster on legsâ reaction; he decides to jump off the left side of the truck, run around in front of the driverless truck, open the door, climb in and apply the brake. Russellâs reflexes are slower than those of a dead cat. He almost got run over and never made it to th door.
The casualty list was extensive. Our six month old truck needed a new cab, as did four brand new, less than delivery kilometers, Volvos, one Volvo was repaired.
I sacked him, not for forgetting to apply the brake, but for the stupidity of putting himselfand any innocence bystanders in danger.
Franglais, shunters wrists are fine. Lets assume here that we are talking about a dedicated shunt motor (Terberg) and not someone using a road unit; Iâve not used nor seen a shunt motor that didnât have taps on the airlines which means zero back pressure on the lines. Also the locating â â â â â â â on the airline collar are invariably ground off to save locating the collar before releasing the airlines.
When I started we had the 3 air lines and cable handbrakes on the trailers.
For newer drivers.
On older trailer systems dropping the redline would apply the trailer brakes fully. But it was air pressure holding the brakes on, not a mechanical spring, so when the air drained out the trailer would only have the cable handbrake stopping it. IF that was applied.
Drivers were killed through misuse of what should have been a safe system.
On one occasion 1970âs a driver dropped a trailer in OCL compound Soton, (A trailer park with them dropped back to back). he didn`t apply the cable hand brake. The trailer was collected a few days later and that driver didnât check the handbrake.
Banged it under and crushed a driver fixing lenses to the trailer behind it.
Awful.
Then we had the introduction of spring brakes. They come on and stay on irrespective of air in/out of the trailer.
But they would come off exactly as SDU has described. Connect redline and sheâs away! No button to push.
No where near as much damage but in one yard we parked the trailers two or maybe three deep on a gentle slope. Our own âRussellâ starts out with the same mistakes. No trailer brake and unit brake left off. On catwalk connects redline and she moves off. He jumps down and is halfway in the door when the unit grazes the adjacent parked trailer. He was extremely lucky he wasnât chopped in half bu the door. Didnât stop him complaining when a mate climbed over him to back it up and release him!
Yeah thems the ones I guess the taps just simplify things really. Ours werenât road legal so there was never an issue with that. When as a shunter youâre busy I guess that seconds matter. Itâs not commonly known that a red airline will actually stretch across four standard bays before finally letting go! Allegedly
Ours work exactly the same in this respect and have for decades. No red line attached no movey trailer. Insufficient air pressure in system no movey trailer.
I guess the taps just simplify things really. Ours werenât road legal so there was never an issue with that. When as a shunter youâre busy I guess that seconds matter. Itâs not commonly known that a red airline will actually stretch across four standard bays before finally letting go! Allegedly