# Anyone know about semi trucks and those blue and red brake hose thingies?



## 54706 (Dec 19, 2011)

I'm writing a scene where a person is doing a daredevil move, going from the top of a semi tractor trailer to the space between the trailer and the cab, landing on the 5th wheel ... all in an attempt to make her way to the driver's side door while the truck is in motion.

My question is this:  If she grabs the blue air brakeline hose and pulls it out, will the emergency brake red hose thingy still work?

And if yes, how does one apply the emergency brake from inside the cab?

Thank you in advance to any truckers out there willing to share.


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## DarkScribe (Aug 30, 2012)

ellecasey said:


> I'm writing a scene where a person is doing a daredevil move, going from the top of a semi tractor trailer to the space between the trailer and the cab, landing on the 5th wheel ... all in an attempt to make her way to the driver's side door while the truck is in motion.
> 
> My question is this: If she grabs the blue air brakeline hose and pulls it out, will the emergency brake red hose thingy still work?
> 
> ...


Do you have any idea how much strength would be required to pull apart a high pressure hydraulic line? More than any human, male or female is ever likely to possess. Maybe she should have some cutting tools.


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## Guest (Mar 18, 2013)

DarkScribe said:


> Do you have any idea how much strength would be required to pull apart a high pressure hydraulic line? More than any human, male or female is ever likely to possess. Maybe she should have some cutting tools.


How do you know her character isn't of a type similar to mine?


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## Mathew Reuther (Jan 14, 2013)

glutton said:


> How do you know her character isn't of a type similar to mine?


Two posts to make it about Rosy.


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## Guest (Mar 18, 2013)

Mathew Reuther said:


> Two posts to make it about Rosy.


She isn't the only character of that type of mine you know. Far from the only one. 

As long as the physicality level is consistent and fits the story it should be fine. Daredevil from Marvel comics rips a mailbox out of the street and uses it to knock out a superstrong character and he's only supposed to be an 'unaugmented human' in strength.

If the character is shown having trouble lifting a TV and then pulls off a feat of superhuman strength though, it's probably not fine...


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## Greer (Sep 24, 2011)

ellecasey said:


> I'm writing a scene where a person is doing a daredevil move, going from the top of a semi tractor trailer to the space between the trailer and the cab, landing on the 5th wheel ... all in an attempt to make her way to the driver's side door while the truck is in motion.


When there's a trailer attached to the tractor, isn't the fifth wheel covered? I don't know if it is, or if that has any bearing on your story, but I just wanted to put it out there, just in case...


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## 54706 (Dec 19, 2011)

DarkScribe said:


> Do you have any idea how much strength would be required to pull apart a high pressure hydraulic line? More than any human, male or female is ever likely to possess. Maybe she should have some cutting tools.


I've done some reading, and it says they are removed manually whenever a trailer is changed. So that tells me they can be pulled apart. And there are safety mechanisms in place in case they do come off, so that also tells me it's possible. But anyone out there with real-world experience is more than welcome to teach me otherwise.



Shayne said:


> When there's a trailer attached to the tractor, isn't the fifth wheel covered? I don't know if it is, or if that has any bearing on your story, but I just wanted to put it out there, just in case...


I think it's still partially showing. At least, it appears that way in the photos I've seen. I don't have any real semi's available to me right now out here in the middle of southern France where the roads are too small for them.


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## Greer (Sep 24, 2011)

ellecasey said:


> I've done some reading, and it says they are removed manually whenever a trailer is changed.


When they say 'manually', might they mean with hand tools?


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## Guest (Mar 18, 2013)

ellecasey said:


> I've done some reading, and it says they are removed manually whenever a trailer is changed. So that tells me they can be pulled apart. And there are safety mechanisms in place in case they do come off, so that also tells me it's possible. But anyone out there with real-world experience is more than welcome to teach me otherwise.


Is she supposed to be incredibly strong? I don't have experience with this, but if she isn't and Darkscribe is having doubts...


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## 54706 (Dec 19, 2011)

Shayne said:


> When they say 'manually', might they mean with hand tools?


Here's what wikipedia says: "Glad-hand" connectors (also known as "palm couplings,") are air hose connectors, each of which has a flat engaging face and retaining tabs. The faces are placed together, and the units are rotated so that the tabs engage each other to hold the connectors together. This arrangement provides a secure connection, but allows the couplers to break away without damaging the equipment if they are pulled, as may happen when the tractor and trailer are separated without first uncoupling the air lines.

And in this scene, she's going to grab onto it to keep herself from falling. So she'll have full body weight on it.


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## Mathew Reuther (Jan 14, 2013)

To me that sounds as if full body weight (while in motion) will be sufficient to yank them free.

Not sure what the immediate effects are though.


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## 54706 (Dec 19, 2011)

Mathew Reuther said:


> To me that sounds as if full body weight (while in motion) will be sufficient to yank them free.
> 
> Not sure what the immediate effects are though.


My expert wikipedia says it will cause the truck to go into an immediate stop. Like emergency stop. But I don't want to just assume that's correct without hearing from a real live trucker. I'm sure someone on this board must know one! Come on KBoards! Don't let me down! lol


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## DarkScribe (Aug 30, 2012)

ellecasey said:


> I've done some reading, and it says they are removed manually whenever a trailer is changed. So that tells me they can be pulled apart. And there are safety mechanisms in place in case they do come off, so that also tells me it's possible. But anyone out there with real-world experience is more than welcome to teach me otherwise.
> 
> I think it's still partially showing. At least, it appears that way in the photos I've seen. I don't have any real semi's available to me right now out here in the middle of southern France where the roads are too small for them.


Yes, they are manually removed - but with the pressure off and using tools. There could be little more dangerous than a hydraulic brake line that came apart easily. Those lines can contain hydraulic pressure that reaches thousands of pound per square inch. They are steel braided and they are very strong. If they break - or are cut - some vehicles will apply the brakes on the prime mover only. Most will simply lose braking all ability as once the ability to deliver hydraulic pressure to the drums or discs is lost there is no way to activate them.


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## 54706 (Dec 19, 2011)

DarkScribe said:


> Yes, they are manually removed - but with the pressure off and using tools. There could be little more dangerous than a hydraulic brake line that came apart easily. Those lines can contain hydraulic pressure that reaches thousands of pound per square inch. They are steel braided and they are very strong. If they break - or are cut - some vehicles will apply the brakes on the prime mover only. Most will simply lose braking all ability as once the ability to deliver hydraulic pressure to the drums or discs is lost there is no way to activate them.


Okay, but if the blue one comes loose, the red one is supposed to immediately apply the emergency brake, right? Mr. Wiki Pedia says that.


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## Betsy the Quilter (Oct 27, 2008)

Elle,

my hubby, who was a transporation major and worked for the American Trucking Associations for awhile (and is a lifelong gearhead) says:

The fifth wheel is covered by the trailer, so she couldn't land on that, though she could probably land on the chassis.  If she pulled on the airhose and separated the couplers, the brakes would be applied; the air pressure in the hose keeps the brakes off, not on.

He suggests you contact a local trucking company or the ICC perhaps, and I found a number of truckers' forums by Googling.

He thinks it is doubtful that there is anything on the back of the cab that could be grabbed to keep from falling off....on the side of the cab there are handles....

For what it's worth...his thoughts when I read your post.  (It has been a long time since he worked for ATA.)  But ATA's safety or engineering department might also be good sources.

Betsy


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## 54706 (Dec 19, 2011)

Betsy the Quilter said:


> Elle,
> 
> my hubby, who was a transporation major and worked for the American Trucking Associations for awhile (and is a lifelong gearhead) says:
> 
> ...


Yes!!! Thank you!!! This is what I needed. I"m going to have her grab the hose to keep from falling off, have the truck go into an immediate braking, and since it wasn't going that fast to start with, have it come to rest without jack-knifing.


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## DarkScribe (Aug 30, 2012)

ellecasey said:


> Okay, but if the blue one comes loose, the red one is supposed to immediately apply the emergency brake, right? Mr. Wiki Pedia says that.


If you are only talking about vehicles with air brakes the same thing applies. They can be disconnected by hand, but only when they have no air pressure as you have to compress the coupling in order to turn and uncouple it. You can't do this when they are under pressure. If you want to activate the spring brakes - which are NOT very efficient - you will need to cut the line - it will not just pull apart.


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## Guest (Mar 18, 2013)

DarkScribe said:


> If you are only talking about vehicles with air brakes the same thing applies. They can be disconnected by hand, but only when they have no air pressure as you have to compress the coupling in order to turn and uncouple it. You can't do this when they are under pressure. If you want to activate the spring brakes - which are NOT very efficient - you will need to cut the line - it will not just pull apart.


Just curious - about how much force would it take to pull them apart with pressure?


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## Betsy the Quilter (Oct 27, 2008)

ellecasey said:


> Yes!!! Thank you!!! This is what I needed. I"m going to have her grab the hose to keep from falling off, have the truck go into an immediate braking, and since it wasn't going that fast to start with, have it come to rest without jack-knifing.


He was kind of dubious about whether it would actually be possible to grab anything...

Betsy


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## 54706 (Dec 19, 2011)

Betsy the Quilter said:


> He was kind of dubious about whether it would actually be possible to grab anything...
> 
> Betsy


Looking at pictures, I think it's within the realm of possibility, especially when faced with do it or die. I'll just have to use a little artistic license.


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## DarkScribe (Aug 30, 2012)

glutton said:


> Just curious - about how much force would it take to pull them apart with pressure?


I have no idea as to the exact pressure, but in one of the mining camps in 2010 I saw a prime mover that was uncoupled from the trailer but still had its lines connected started and driven. The airlines tore the mounting brackets loose from both ends before breaking. The mounting brackets were made from steel that was close to a centimeter thick. When you go to uncouple them the air pressure gauge in the prime mover has to drop from 120/150 psi to zero before you can release the coupling.


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## Guest (Mar 18, 2013)

DarkScribe said:


> The airlines tore the mounting brackets loose from both ends before breaking. The mounting brackets were made from steel that was close to a centimeter thick.


Sounds like OP's character better be Daredevil-esque.


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## 54706 (Dec 19, 2011)

glutton said:


> Sounds like OP's character better be Daredevil-esque.


She's a krav maga expert and as fit as a human can be, pretty much.


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## CEMartin2 (May 26, 2012)

I hate to be a nitpicker, but... if the line is full of air, it's pneumatic, not hydraulic. Hydraulic means it's full of fluid. 


/nitpick


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## Guest (Mar 18, 2013)

ellecasey said:


> She's a krav maga expert and as fit as a human can be, pretty much.


Going by that and assuming it's a story with pulp-esque action it sounds like it might be fine... without knowing that it was unclear.


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## 54706 (Dec 19, 2011)

glutton said:


> Going by that and assuming it's a story with pulp-esque action it sounds like it might be fine... without knowing that it was unclear.


I'm not sure that it's pulp-esque. But it's a post-apocalyptic world with only teens in it, and these trucks have been sitting for at least 6 months and of course will only last as long as the diesel they have in them. So you could assume all kinds of things, like the kids didn't put the lines on very well, they've gotten less secure after sitting, the full body weight of a person swinging from one with additional force of swerve-induced force could cause them to loosen.... I think I'm good enough that I won't get 1-starred for being a total dumbass. lol


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## WG McCabe (Oct 13, 2012)

Elle, sorry I missed this thread. I drive for a living. There are all kinds of things on the back of a tractor to grab onto.










When connecting the glad hands they push down to lock, meaning to disconnect them you have to grab the air hose by the glad hand and pull it up and out. The One hose removal applies the trailer spring breaks but has no effect on the tractor. If they both come disconnected they emergency breaks will pop on both the tractor and trailer. The blue hose is the service line, which is basically connected to to the brake pedal. The red hose is the emergency line which both fills the trailer's air tanks and activates the spring brakes in case of a problem.










The yellow knob is for the tractor, the red for the trailer. You can drag a trailer with the break engaged. BUT if the air hose comes free the air pressure level will eventually fall below 60 PSI and engage the tractor's parking break (the yellow knob). Depending on the pressure built up in the tanks (normal operating pressure is between 60 and 120 PSI) it could drop below that level in one to 10 seconds.

So, if the truck is not going very fast (as you said) I would have the heroine disengage both sets of glad hands.


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