Hi, I’m quite new on artics but was unsure about what the red airline actually does… Maybe simple answer for experienced drivers
I know from theory that yellow is service and red is emergency, but what does this actually mean?? Is it that yellow gets used by footbrake, so what does red do…■■
Answers appreciated
Just out of curiosity but do you actually have a licence 
No I don’t yet…
It releases the trailer brakes. One of the first things you’ll be taught when you or if you start training for your licence. Good luck btw if you do decide to join the driving fraternity. 
Sometimes the red emergency line is called the supply line. Trailers with spring brakes require the air pressure from the red line to release & hold the brakes off, while the yellow service line generally allows air through only when the brake pedal / foot valve is opened.
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The red line supplies all the air that operates the brakes and suspension on the trailer.It feeds via an emergency relay valve the tanks.When you couple the red line it feeds a quick release valve which supplies air to the spring brake chambers to release the brakes.When you pull the line off the QR valve then allows the air in the spring brakes to vent to atmosphere and the springs apply the brakes.
The yellow line only supplies a signal via the foot valve or hand brake to the modulator block which when activated allows air from the tank to the service side of the brake chambers to apply the foundation brakes.When you release the pedal the signal is exhuasted through the foot valve the modulator valves close and the exhaust port opens and the air is dumped releasing the foundation brakes.
Bit more to it than that but thats the basic idea.
Classic. Someone asks a question and gets ■■■■ taken.
TruckNet is a Trollsome place to be lately
One other bit thats a bit hard to get your head round is that when you take the hand brake off in the cab is that it supplies air to the tractor spring brakes to let them off but dumps air from the trailer chambers(service side)to get them to release.The trailer control valve does all this foolery for you.
The red line only affects the trailer spring brakes not the main brakes.
midlifetrucker:
Classic. Someone asks a question and gets ■■■■ taken.
Some people do that to hide there own inadequecy! It was a sensible question.
I could of asked, why has the trailer I had picked up last week, got 2 red airline connections on it, well I didn’t know, but I do know, with out the help of the know all gob ■■■■■■ on here.
Ignore the last comment if it doesn’t apply to you!
As I mentioned further up, people may talk about the Supply or Emergency line. The yellow may also be addressed as the Service or Control line, some trailers will have this marked.
This obviously goes with the advice already given above, especially as many newer lorries come fitted with two black air lines. In the UK we are about the only ones to use male and female couplings known as C Type. They are impossible to get the wrong way round, but I still prefer palm couplings for ease of use and keeping clean.
Anyone who remembers the third blue line would know that as the Auxiliary line and these had a larger coupling called a CA Type. We also had air taps too 
I always remember, when very first driving, guy said to me, if you hitch up and you forgot handbrake and she starts rolling PULL THE RED AIR LINE 
this was of course back in the day, with ratchet handbrakes on trailers that nobody ever used, hook and run days
Thanks for the replys people, some good knowledge taken
weeto:
midlifetrucker:
Classic. Someone asks a question and gets ■■■■ taken.Some people do that to hide there own inadequecy! It was a sensible question.
I could of asked, why has the trailer I had picked up last week, got 2 red airline connections on it, well I didn’t know, but I do know, with out the help of the know all gob [zb] on here.
Ignore the last comment if it doesn’t apply to you!
If that was aimed at me so be it! The man asked a question and I tried to give him a reasonable answer.
Bking:
If that was aimed at me so be it! The man asked a question and I tried to give him a reasonable answer.
Not only a reasonable answer - I thought your answers were both bloody good ones! Helped me get my head around what goes on when I connect those lines, press the pedal or pull that lever.
On the principle that “Every day is a school day” I thank you for providing today’s lesson 
Wheel Nut:
Anyone who remembers the third blue line would know that as the Auxiliary line and these had a larger coupling called a CA Type. We also had air taps too
Ah yes i remember the taps and blue line.
I always thought the taps were a good idea. My dad had them on his ‘G’ plate 113 when he first got it back in the early 90’s
As previously said the Read Line ( Emergency ) will always be charged with air (as long as the vehicle has air before someone says )…Generally you only have air in the yellow ( Service line ) when the footbrake or handbrake is applied…So if your yellow(Service line) failed for example ,as long as you don’t press the footbrake or pulled on the handbrake ,you could pull over or to a safe place as no air will be lost …The supply from the red (Emergency line) will keep the brakes released .If your red (Emergency line ) fails then the air from the brakes is exhausted and the trailer brakes will come one…Basically if you dropped your and snapped the red line the brakes on the trailer would come on and prevent it rolling away, though the chance of a trailer rolling away are zero after it nose dives and the legs dig in .
I remember the blue line ,was taught yellow =service blue = secondary red =emergency
The army use palm couplings ,they are better ,generally the O ring would fail but is only pennies to change
Must congratulate bking on his posts ,just wish he could be more like that and not so angry
norb:
Must congratulate bking on his posts
Hear Hear!!! Great explanation, well written & easy to understand. Well done Bking.