Warning

[depablo]

Just read this on the IRTE forum, it is a new post and due to it’s nature I have posted it here (minus the original posters details).

Has anyone heard or experienced this? As this is a drivers forum I will post a link to this site so people can view your experiences.

I feel I must draw attention to an inherent design defect with some trailer brake systems which will allow the trailer to move even though the park brake is applied. This defect manifests itself during the coupling process particularly if the “split coupling” method is used and results in free movement of the trailer with potentially fatal results.

My attention to this problem was first drawn whilst investigating a trailer, maintained by my company, which had fallen off the tractor during coupling damaging its landing gear. The experienced and competent driver was using the “split coupling procedure”. He reported that he had carried out the first part of the procedure, with the trailer park brake applied, the tractor under the trailer and the landing gear raised. As he connected the red suzie, the trailer moved backwards off the tractor and onto its nose.

On initial investigation everything seemed OK with the brake system. However, when replicating the circumstances of the mishap I found that brakes were released for a period of time of approx 3-4 seconds when the red suzie was connected.

The trailer was fitted with spring park brakes which were not fitted with quick release valves. In order for the spring brakes to apply the whole quantity of air in the system had to exhaust through the park brake control valve mounted at the front of the trailer, typically taking around 20 seconds to fully apply.

When the trailer is disconnected from its tractor the driver first applies the park brake, exhausting the spring brakes. When the red line is subsequently disconnected the emergency system is activated supplying air to the diaphragms and, via the anti-compound valve, supplying air to push the spring brakes off; the trailer is now parked using the service system. When the trailer is reconnected the process is reversed - the red line is connected and the emergency brake releases, exhausting the service diaphragms. Simultaneously, via the anti-compound valve, the spring brakes are exhausted, re-applying the spring brakes. However, as the spring brakes have to exhaust through the park valve there is a delay of around 3-4 seconds when neither brake is applied allowing the trailer to move.

The simple answer to this problem is to fit quick release valves to the park brake system which allows an almost instantaneous transition from one system to the other.

I have since checked a number of trailers, from a variety of manufacturers, (one less than a month old) for this problem and have found that approx 30% of the trailers I checked have this problem.

I am in discussion with the technical & safety departments at VOSA and have alerted several manufacturers to the problem.

I urge all that are responsible for the operation of these vehicles to check their fleets and, until an engineering solution is implemented, to stop the procedure of “split-coupling” of these trailers.

A simple test can be carried out to see if your trailer is at risk:

1. Starting with a coupled tractor/trailer apply the trailer park brake;
2. Start the tractor, release the tractor park brake, engage a low gear;
3. Firmly apply the footbrake and wait around 10 seconds to allow the trailer system to settle;
4. Release the footbrake and immediately attempt to pull away - if the combination moves you have a suspect trailer! (My best - or worst- trailer allowed me to drive around 20 m before the brakes re-applied)

This, I am sure you will agree, is a most serious situation which demands immediate attention.

[spardo]

Well, well, well, why am I not surprised? I have never trusted split coupling, even when everything works properly the slightest distraction can produce a mishap or a tragedy. There are ways of coupling safely without too much bother and if ever I roll again I will continue to use them .

Now I’ll sit back and wait for the flack.

[silver_surfer]

Don’t wind up the legs till the pin is engaged with split coupling!!! Raise the rear of the tractor a bit so the legs are just off the ground for the bite.

[rob_k]

Silver_Surfer:
Don’t wind up the legs till the pin is engaged with split coupling!!! Raise the rear of the tractor a bit so the legs are just off the ground for the bite.

You shouldn’t be winding the legs up before the pin’s engaged anyway!

The original post is interesting and something I shall bear in mind for future split couples but it won’t stop me coupling/uncoupling that way. With the work I do I’ve probably used the major of modern day trailer makes out there and can’t say I’ve had a problem as described above with any of them, but that’s not to say I don’t believe it could occur at some point.

Like everything in life, if one applies a bit of noggins when it’s needed then these things should not become problems. I’m always particularly careful if I’m split coupling on a down hill gradient as I have no desire to be crushed by the trailer, oddly enough. I always raise the units suspension as high as it will go to help level the trailer so that should something go wrong it won’t have as much of a gradient to run down. I also wait 3 or 4 seconds after connecting the red line to see if any movement occurs before connecting the other lines. Obviously if movement does start to occur then the red line comes straight back off again and the problem is investigated.

[ralliesport]

Its very reasonable though.

They have found a fault, and rarther than stopping all drivers from doing a split coupling they are rectifying the fault.

Maybee H&S is starting to take a small step back from banning everything.

[marcustandy]

Make sure the legs are down . . . . . and use chocks as well as the trailer park brake??

Some of the combinations I have driven simply couldn’t be coupled without split-coupling!! And ain’t that fat!!

[simon]

Rob K:
I’m always particularly careful if I’m split coupling on a down hill gradient as I have no desire to be crushed by the trailer, oddly enough. I always raise the units suspension as high as it will go to help level the trailer so that should something go wrong it won’t have as much of a gradient to run down…

Unfortunately that will have next to no effect Rob. Although the trailer body might be level, its wheels will be on the slope and that is what will cause the trailer to roll, what ever angle the trailer itself is at.
You will have a bigger space to drop down into, between cat-walk and trailer bed, if it should roll forward. If your quick enough.

[rob_k]

Simon:

Rob K:
I’m always particularly careful if I’m split coupling on a down hill gradient as I have no desire to be crushed by the trailer, oddly enough. I always raise the units suspension as high as it will go to help level the trailer so that should something go wrong it won’t have as much of a gradient to run down…

Unfortunately that will have next to no effect Rob. Although the trailer body might be level, its wheels will be on the slope and that is what will cause the trailer to roll, what ever angle the trailer itself is at.
You will have a bigger space to drop down into, between cat-walk and trailer bed, if it should roll forward. If your quick enough.

Hmm. I’m not sure of the physics of that Simon . I see where you’re coming from and agree to an extent but technically if the trailer did move it’s pushing the front of it up hill if the unit suspension is raised. I think it would depend greatly on the gradient. I’m not saying that the trailer would definitely not move, but by raising the suspension to max you are greatly reducing the potential.

[depablo]

You know the problem?

It’s the industry that employs us and the folk who lead it. Why ask someone to squeeze in between a tractor and trailer in the first place? Split coupling or any type of coupling procedure has its inherent dangers, human error plays a big part in any accident and the folk at the top have a responsibility to do something about it.

For years there’s been fridges that have been mounted under the trailer, probably not the best location due to the damage caused by road salt / debris etc. So why are they mounted at the front next to the bunk and where it makes it nearly impossible to couple up without the dangers of a close coupling procedure? The likely reason is cost, there will be other reasons which are valid but cost will rank high on the agenda.

Then you have the construction and use regulations that could be modified to make everyones life easier and safer, unfortunately again politics rules and we are all put at risk. Remember folks, do it right and you are fine, make one mistake and it could injure you or even worse, kill you stone dead!

[longwayround]

Sliding 5th wheel should be standard equipment.

[coffeeholic]

As long as you have raised the suspension so the fifth wheel plate is against the underside of the trailer it won’t matter too much if the trailer does roll forward when you attach the red line, the pin will catch. Yes it gives you a ‘moment’, and I speak from experience there, but it won’t crush you. You’ll just have the same amount of space as if you weren’t split coupling.

[depablo]

Coffeeholic

Too much left to chance, plus some combinations you can hardly get in between truck and trailer. So if you split couple then it rolls forward you could end up with sore ribs, anyway you use the tools provided by industry and take your chance.

[coffeeholic]

depablo:
Coffeeholic

Too much left to chance,

That is true with any type of coupling if it isn’t done correctly.

depablo:
plus some combinations you can hardly get in between truck and trailer.

So how are you going to couple it then? Split coupling or not you have the same amount of room with the pin engaged.

depablo:
So if you split couple then it rolls forward you could end up with sore ribs.

Yeah you could, but you could also end up with sore bits squeezing into a small gap while not split coupling so not much difference.

Any type of coupling or uncoupling procedure is dangerous if you don’t do it properly, if you do the chances of anything going wrong is greatly reduced. People have been hurt or killed while coupling up using the non split coupling method because they forgot to apply the unit park brake for instance. I don’t think one method is any safer or more dangerous than another, if done correctly

[depablo]

Coffeeholic:
So how are you going to couple it then? Split coupling or not you have the same amount of room with the pin engaged.

Point I was trying to make was if it is difficult to get in between the cab and trailer, you would probably lean over and couple the suzies.

If you have split coupled and are standing on the catwalk when it rolls forward and couples to the pin, you end up in a space where you would not have went in the first place.

Plus you have the chance it might jump the pin and not couple and you end up in the bunk.

Agree it is all down to the individual, but you should be able to couple from the seat, connecting air lines and electrical supplies automatically without going in between the unit and trailer.

[coffeeholic]

depablo:
Point I was trying to make was if it is difficult to get in between the cab and trailer, you would probably lean over and couple the suzies.

If the space is that small there wouldn’t be enough room to lean over and couple the lines.

depablo:
Plus you have the chance it might jump the pin and not couple and you end up in the bunk.

If you have raised the suspension so the plate is tight against the underside of the trailer it won’t jump over.

[depablo]

Coffeeholic
it won’t jump over.

Now thats commitment

[gav]

there i one easy solution to rid the dangers of split coupling, make it law that all new trailers must be fitted with one of them sliding things that sainsburys have got,slide it to the side,connect your lines while standing at te side of the wagon,then slide it back over,easy

[marcustandy]

gav:
one of them sliding things that sainsburys have got, ,easy

I’ve used one of those and I didn’t find it easy. Same as ‘leaning over’, you are to a greater or lesser extent, twisting your back & spine and then forcing your arms forward (i.e. pushing against the suzies air pressure etc) and this is a recipie for (back injury) disaster!

The only safe way for your back is to be able to place yourself square-on to to the connections. If this means split-coupling, then like Neil said, as long as it is done safely, it is the best option.

[rob_k]

marcustandy:

gav:
one of them sliding things that sainsburys have got, ,easy

I’ve used one of those and I didn’t find it easy. Same as ‘leaning over’, you are to a greater or lesser extent, twisting your back & spine and then forcing your arms forward (i.e. pushing against the suzies air pressure etc) and this is a recipie for (back injury) disaster!

The only safe way for your back is to be able to place yourself square-on to to the connections. If this means split-coupling, then like Neil said, as long as it is done safely, it is the best option.

Pushing the shunt button in and jacking the cab at 20 degrees or so to the trailer solves the “twisted back” problem Martin. Only thing you’ve got to remember is to make sure the ends of the lines are over that side already, otherwise you’ll still have to get up on the gantry to fish them out.

[marcustandy]

Rob K:
Pushing the shunt button in and jacking the cab at 20 degrees or so to the trailer solves the “twisted back” problem Martin.

True, if there’s room. Most of the time though, the trailers I am picking up have been parked in a ‘shunter-special-stylee’ with at least 2" between them!!