It is widely assumed that trailer spring brakes are applied simply by disconnecting the red (emergency) line and that the park button does nothing more than this. Not only is this assumption about the so-called fail safe nature of trailer brakes technically inaccurate, it could prove positively dangerous at the time a trailer is re-coupled.
The risks involved in failing to apply park brakes properly on motive units and trailers have been evident for some time, most starkly illustrated by fatal accidents.*
It is taken from POWNALL’s site which is well worth a look.
Front page here. pownall.co.uk/tspv1.htm
Trailer Safety Park Valve - Accident Scenario’s here.
My C1 instructor taught me to reverse upto the trl, then get out and walk round it to check for damage and ALSO to check TB was on, before going under…
Regardless of the micky taking and shouting from the shunters I STILL get out to check the TB… Most (sare I say all) of the others don’t, and just hitch straight up… everytime without incident, but I still do it my way…
As far as un-hitchin is concerned, I usually jam the plate in the back of the front mud-gaurd, so I walk past the TB before I do anything else… It’d be silly NOT to put it on… even then, the next step is the legs, which are right next to it… Shunters I can forgive, but drivers…
Having looked around the website I have to say I think they do some very good devices.
And the pictures of roll aways on the parking brake alarm page make the point of why such a system is worth the money.
Ragtop:
My C1 instructor taught me to reverse upto the trl,
C1 = Lorries between 3500kg and 7500kg.
Did you do this test with a trailer??
All (well, 99%) our students miss out C1 and go straight to C. There’s virtually no difference in cost. Having said that, if they were >18 to <21 they wouldn’t have that option.
Ragtop:
My C1 instructor taught me to reverse upto the trl,
C1 = Lorries between 3500kg and 7500kg.
Did you do this test with a trailer??
All (well, 99%) our students miss out C1 and go straight to C. There’s virtually no difference in cost. Having said that, if they were >18 to <21 they wouldn’t have that option.
I think Chrissie means C1 = Class 1 - and not the actual C1 category
Daxi, that’s useful bit of information you have found but, without wishing to disagree (which, actually, I am) the origin of the concern points to an article in 1996 and reading further, appears to suggest that the fault lies with an early version of ABS which (I presume) required an electrical signal to a ‘check valve’ to unload the Spring Brake chamber.
On the Knorr-Bremse site detailing the operation of the Relay Emergency valve it states,
In the event of a loss of pressure in the trailer Supply (Red) line, for example from an intentional or accidental de-coupling, the emergency feature of the valve will automatically apply the trailer service brakes using the trailer reservoir stored air.
Whilst I can accept that there may still be a very small number of trailers in use which are subject to the deficiency described by Pownall, and what they recommend is certainly ‘Good Practice’, I cannot visualise that the Industry has failed to rectify a simple ‘design fault’ in the ensuing 9 years. I think there is some ‘creative marketing’ apparent in their site.
However it is still a valuable site for some of the thought provoking tales of vehicles rolling off out of control, and I like the sound of their Parking Brake alarm that activates when the driver’s door is opened, and remains active until the brake is set.
loading at immingham docks, there’s a big sign saying take care cos brakes may not be applied.
nice bike roll-poles behind the wheels to stop a run-away but still, always the risk. not worth it.
I get out to make sure my truck will go under it, and to check the basics (why bother coupling up if the trailer’s not roadworthy? just more hassle later then aint it!) - and so I too check the trailer brake regardless.
came up against something new to me though on the docks… I learned with pneumatic and air applied TBs only, so when I couldn’t find the sodding button after 3 walk-rounds I was about to go and ask for help - then spotted a little winder like a mini version of the leg-jack handle… gave it a twiddle each way, saw the cable tightening and made the assumption it was the TB. Hope I was right! put it on, coupled up, took it off.
or was I probably modifying some other feature?
el gordo 78:
came up against something new to me though on the docks… I learned with pneumatic and air applied TBs only, so when I couldn’t find the sodding button after 3 walk-rounds I was about to go and ask for help - then spotted a little winder like a mini version of the leg-jack handle… gave it a twiddle each way, saw the cable tightening and made the assumption it was the TB. Hope I was right! put it on, coupled up, took it off.
or was I probably modifying some other feature?
Yes, that was probably the brake.
The trailer I used for my C+E test had a cable-operated brake. It was a ratched handle under the body just forward of the wheels. You ratchet the cable up until it’s tight; that puts the brake on, and to release it, you just push it hard the opposite way. Two things to remember - when you disconnect the suzies, the cable slackens off, and you have to retighten it; and when you release the ratchet it sometimes releases a lot more cable than is necessary, and it dangles down, so you have to take up the excess slack with the ratchet.
put it on, coupled up, took it off.