Air brake issue

If the yellow is supposed to pop first then there would be absolutely no reason to have a tractor protection system.

 

No. The tractor protection system exists.

Remember we did not have those before a certain date. Trucks are suppose to alarm and eventually throw the springs down when pressures fall enough. If you had a trailer on everything is going to stop. There is that red glad hand to think of.

IF the red gladhand is charged with air, connected to the trailer... then if your trailer is gone in say a breakaway, both buttons must pop. If you are just the tractor your red does not matter (Otherwise you would have drained the air.. the red will refuse your efforts to stay pushed in thanks to the protection valve)

My head hurts. (**Pours bottle of medicine....) I'll deal with this question this week. I know a friend who has a 18 wheeler around a time or two. We will settle this right quick.

In the old trucks with the blue trailer supply, you could just drain everything not pulling it. It will sit there and howl until the air is gone.

 

Of course it exists, which was my point. The Tractor protection system exist to attempt to stop the yellow button from popping and locking the tractor down. Say you lose your trailer, both air lines are ruptured. The red button has to pop out (Most will pop prior to that around 40-45 psi but below 20 is OOS ) which stops air flow to the now non existent trailer.The tractor protection valve also closed at some time during this pressure drop preventing any service air from leaving the tractor if you apply service brakes. Both of those events happen to try and prevent the yellow button from popping (During an inspection there is no requirement for it to pop or not pop). Additionally the yellow button is not required to pop, the red is. Bendix wrote a paper on this in 1998 stating the only reference to the yellow button popping is in the CDL manuals and the manuals are not consistent with the regulations. Its a pdf but if you want it here it is
www.bendixvrc.com/itemdisplay.asp?documentid=5194
Most manufactures build in the system (With the springs inside the dash valves) at least a 5 psi difference in pop pressures with the red (TSV) pop pressure higher than the yellow park brake button.

Another more likely event is a rupture of the supply line without trailer loss. Do you really want the tractor and trailer both locking down, especially empty on a wet road or would you rather the trailer dragging the tractor stopped.

Sorry but the TPV has nothing to do with the red button staying in. All the TPV does is stop service air from leaving the tractor (When you apply service brakes) when supply pressure is low enough for it to close, and allows service air out to the trailer when supply pressure is high enough to open the TPV. Behind the button is a spring. When air pressure is lower than spring pressure (Manufacturer decides the pressure rating of spring) spring pushes button out. When air pressure is higher than spring pressure, button stays in.

Don't remember a blue trailer air supply button, I do remember a blue, sometimes white and sometimes just a valve stem sticking out the dash for the DPC.

 

Ok Now I can see where it's at. This is what I call meat and potatos of airbraking in a 18 wheeler (OR any CDL Vehicle)

We aint never taught any of this minutae of detail information. The Manual we see in DMV does a disservice about that stupid yellow button.

Ive always thought Mr Pop will kick in whenever it felt like it. Provided you aint dropped below 30 yet. Which brings me to another thought you offered.

"Another more likely event is a rupture of the supply line without trailer loss. Do you really want the tractor and trailer both locking down, especially empty on a wet road or would you rather the trailer dragging the tractor stopped. "

I would PREFER the entire rig to lock down. Call me a blockhead but Ive stunted 18 wheelers enough so that the associated physics and control does not bother me. She's going to lock down at some point, in my mind Im already picking out where to set her down as the air falls below 40 PSI. MR Pop should show up at some point at 30 or less. Sometimes more.

In some cases the trailer alone locking up is UNWELCOME. If it's gone in a breakaway I want the #### thing to lock up so maybe it does not kill people. It's gone. The tractor Protection Valve would be my main thinking plus where to stick it as the trailer falls down somewhere back there. If I am on say Cabbage or Seven Mountains (US 322 in PA) and the trailer brakes lock up on me without breakaway? On those curves? It's going to get people hurt or killed. I already know what I am planning on doing if Mr Pop did show up on the entire tractor trailer. Been there done that.

I really appreciated you taking the time to write. This is the stuff that we should all learn. But no one teaches anything like that in school or the DMV. It's a multipule choice test for license. Dumbed down. You follow me? (Not necessarily the prospective student graduate would possess a few brain cells....)

I really nerd out on this stuff. Evidence I can work with to support or defend a position taken from experience.

 

What’s that? I get my safety info from fmcsa

 

FMCSA doesn’t set OOS criteria, they and the inspectors get their out of service info from the CVSA North American Standard Out Of Service Criteria manual.

 

what does the dot require on your truck mattress

 

393.76 (e) Equipment. A sleeper berth must be properly equipped for sleeping. Its equipment must include:

(1) Adequate bedclothing and blankets; and

(2) Either:

(i) Springs and a mattress; or

(ii) An innerspring mattress; or

(iii) A cellular rubber or flexible foam mattress at least four inches thick; or

(iv) A mattress filled with a fluid and of sufficient thickness when filled to prevent “bottoming-out” when occupied while the vehicle is in motion

 

The service brake side would leak only when the pedal was pressed. The spring brake side can leak whenever the emergency brakes are released.

 

Years ago, I remember trucks that had the 3rd blue valve, and some were black. I think it just applied the tractor emergency brakes, without exhausting the trailer, or something. As far as the "Wigwag", we called them wigwags, the 1st heavy duty truck I drove ,a '63 IH R-190 tandem dump truck, had no emergency brakes, ( except the manual band brake, which would NEVER stop you in an emergency, for parking only)and had a wigwag. The leadman told me, if that ever drops while driving, head for a ditch and jump,,, and believe it or not, at the time for safety, this was the best they had!
Wig wag (truck braking systems) - Wikipedia