Last week I hooked up my red air line and the shunt valve on the trailer didn’t automatically pop back up. This has never happened to me before in my few years of driving so I don’t ever check that is has sprung back up.
However, after a few miles, and speeds no greater than 50mph (I did have 20 tons on) I pulled over suspecting air problems. What astonished me when I looked under the trailer was [u]this[/u] and [u]this[/u].
So, make sure your shunt valve does pop back up.
be carefull. i know its the craze to have lights underneath a car at the mo but a trailer ■■. bit far fetced in it ■■ 
Thing is, there was an overwhelming desire to actually see it go up in flames. 20 tons of paper too. Give me a proper trailer fire and I’m an entertained man. Know what I mean?
is that a new defonition on cab microwaves or to cook rd kill as you drive along
you can usually tell when this happens as when you take you foot off the gas when moveing the truck will feel like is breaking and will not free wheel
Pretty in pink eh?
Did you have blue lights in the cab to go with it?
Ken.
alix776:
you can usually tell when this happens as when you take you foot off the gas when moveing the truck will feel like is breaking and will not free wheel
Thing is, I was doing that, but they must have been on ever so slightly as I did not feel any resistence. Which is what was puzzling me, and why I went on for so long just assuming my truck was underpowered.
if it felt that the truck was underpowered then that for me would be a warning sign that something was wrong
ezydriver:
Last week I hooked up my red air line and the shunt valve on the trailer didn’t automatically pop back up. This has never happened to me before in my few years of driving so I don’t ever check that is has sprung back up.However, after a few miles, and speeds no greater than 50mph (I did have 20 tons on) I pulled over suspecting air problems. What astonished me when I looked under the trailer was [u]this[/u] and [u]this[/u].
So, make sure your shunt valve does pop back up.
check your Trailerbrake 
left Front disc is still black
ezydriver:
alix776:
you can usually tell when this happens as when you take you foot off the gas when moveing the truck will feel like is breaking and will not free wheelThing is, I was doing that, but they must have been on ever so slightly as I did not feel any resistence. Which is what was puzzling me, and why I went on for so long just assuming my truck was underpowered.
some Trailers have a safety Valve you have to switch it that it opens the Brake.
but still not all wheels braked propperly
ezydriver:
Last week I hooked up my red air line and the shunt valve on the trailer didn’t automatically pop back up. This has never happened to me before in my few years of driving so I don’t ever check that is has sprung back up.However, after a few miles, and speeds no greater than 50mph (I did have 20 tons on) I pulled over suspecting air problems. What astonished me when I looked under the trailer was [u]this[/u] and [u]this[/u].
So, make sure your shunt valve does pop back up.
Can someone explain to me how/what’s actually happened here then? Surely if the shunt valve is in then the brakes are released on the trailer which in turn overrides any air line connections from the cab to the trailer and therefore would mean that pressing the foot brake in the unit would only activate the unit brakes and not the ones on the trailer… which is why I don’t understand why the trailer brakes are glowing?
Mick Bracewell:
ezydriver:
Last week I hooked up my red air line and the shunt valve on the trailer didn’t automatically pop back up. This has never happened to me before in my few years of driving so I don’t ever check that is has sprung back up.However, after a few miles, and speeds no greater than 50mph (I did have 20 tons on) I pulled over suspecting air problems. What astonished me when I looked under the trailer was [u]this[/u] and [u]this[/u].
So, make sure your shunt valve does pop back up.
Can someone explain to me how/what’s actually happened here then? Surely if the shunt valve is in then the brakes are released on the trailer which in turn overrides any air line connections from the cab to the trailer and therefore would mean that pressing the foot brake in the unit would only activate the unit brakes and not the ones on the trailer… which is why I don’t understand why the trailer brakes are glowing?
That was my thought too. Maybe the blue and red plugs/switches/knobs whatever you want to call them where put on the wrong plungers. I have seen that before, it was only if you looked at the writing behind the switch that you could see the ‘shunt valve’ was acually red and the ‘trailer brake’ was blue?
Mike-C:
Mick Bracewell:
ezydriver:
Last week I hooked up my red air line and the shunt valve on the trailer didn’t automatically pop back up. This has never happened to me before in my few years of driving so I don’t ever check that is has sprung back up.However, after a few miles, and speeds no greater than 50mph (I did have 20 tons on) I pulled over suspecting air problems. What astonished me when I looked under the trailer was [u]this[/u] and [u]this[/u].
So, make sure your shunt valve does pop back up.
Can someone explain to me how/what’s actually happened here then? Surely if the shunt valve is in then the brakes are released on the trailer which in turn overrides any air line connections from the cab to the trailer and therefore would mean that pressing the foot brake in the unit would only activate the unit brakes and not the ones on the trailer… which is why I don’t understand why the trailer brakes are glowing?
That was my thought too. Maybe the blue and red plugs/switches/knobs whatever you want to call them where put on the wrong plungers. I have seen that before, it was only if you looked at the writing behind the switch that you could see the ‘shunt valve’ was acually red and the ‘trailer brake’ was blue?
Would that make any difference if the air lines were connected though? It’s my understanding that if the system is pressurized ie. with the red line connected, that this automatically pushes the shunt button out. In my opinion this is further confirmed by the heavy resistance one receives when trying to push the shunt button in when the red line is connected, which won’t stay in and springs back out as soon as you let it go.
In this scenario I fail to see how a possible mix up of the trailer brake and shunt buttons would make any difference, ie. for the trailer brakes to be glowing a few miles down the road.
The only other possible explanation I can come up with is that the driver set off with an extremely low air pressure level which would explain why - initially - the shunt valve did not pop out. The low air pressure would mean that the system did not have enough air it in for the brakes to be properly released and hence create a heavy resistance for any forward or backward movement as well as making the trailer brakes glow like pictured as they are partly “stuck” on.
However, the driver stated that no resistance was felt so this possible explanation appears redundant. Also factor in that unless there’s a serious air leak in the system, after driving 100 yards down the road the air pressure would be within normal tolerance levels by that stage anyway.
I had it happen on one of our trailers I moved it on the shunt button but later picked the trailer up. as turned the shunt button was not coming out all the way wand the brakes were binding as a result. the button valve thingy was changed and its been fine since
Hi
I am New and i was told there is no silly questions so here goes,
what does the shunt valve do and what should i check, are we talking about the red and black/blue knobs on the trailer, i have wondered how do i applie a trailer brake when the airlines are off.
Stevie bee:
Hi
I am New and i was told there is no silly questions so here goes,what does the shunt valve do and what should i check, are we talking about the red and black/blue knobs on the trailer, i have wondered how do i applie a trailer brake when the airlines are off.
Welcome to TNUK. 
The shunt button allows you to move a trailer for a short distance without having to use the air lines. It is usually blue or black in colour, and located close to the park brake.
I personally never use them because if the air in the trailer drops below a certain level you will probably stop dead in your tracks!
Also, it is easy to forget to pull the button back out again. I would rather just hop on the catwalk and connect the lines. It isn’t that much of a chore.
Ah the fog has cleared thanks, am i also right that when you drop a trailer you are supposed to operate the red button as i see alot of Old Hands not bothering as they say that when the air is of the brakes are on anyway. or should i always press in the red park brake?
Stevie bee:
Ah the fog has cleared thanks, am i also right that when you drop a trailer you are supposed to operate the red button as i see alot of Old Hands not bothering as they say that when the air is of the brakes are on anyway. or should i always press in the red park brake?
This has been discussed a number of times before, but…
In theory, I think that some level of braking is applied brakes automatically when the red line is disconnected. It certainly seems to apply the brakes to some extent, but I don’t know enough about how trailer braking systems work to know exactly what it does and doesn’t do. However, IMHO, the park brake button must be there for a reason, otherwise they wouldn’t put it on.
Your training tells you to put the park brake on when leaving a trailer. If anything goes wrong, and someone gets squashed by the trailer running away, I doubt that any of those “old hands” would stand up beside you in court to defend your case of manslaughter. IMHO, it’s not worth the risk to save the couple of seconds it takes to pull the button.
If the shunters (or other staff) ask you to leave the park brakes off, then just ask them for that request in writing, on headed company paper 
.
Stevie, not a silly question.
There has been discussion recently in a certain Engineering magazine about the merits of using the Brake Valve prior to disconnecting the red air line. The discussion centred mainly (as I understood it) on the fact that operating the Brake Valve ‘dumps’ the air and applies the brakes ‘immediately’ (although I’ve found times when it hasn’t) as opposed to removing the Red line which allows the air to ‘exhaust’ through the associated pipework. The argument being that the mass of air having to travel along a 1/4" (or whatever it is since decimalisation) network of piping could result in a delay before the brakes are applied. Something which I can say I have never experienced.
Often it depends on the type of trailer. With a Fridge, it is always Park Brake first (and last).
If you want to learn more about it, go to the Pownall or the Knorr-Bremse sites, both of which are companies that make components for air braking systems. You may find some technical data of interest.
In the meantime, as others have said, do it the way you were trained.
![[u]this[/u]](http://img443.imageshack.us/img443/1811/dsc00477ef8.jpg){kind=link}
![[u]this[/u]](http://img340.imageshack.us/img340/8435/dsc00479ye2.jpg){kind=link}