This is what we teach in the school, and what ICBC (Insurance Corporation of British Columbia, they run the whole show up here) does at the Road Tests for class 1's.

With the truck shut off, and the lines still connected, pump the brakes down to where the RED dash valve (tractor protection supply valve) pops out. It must be no lower than 20 PSI and should be in the 20 to 45 range, although it can be higher.

Once the red dash valve has popped out (dynamited) you get out of the truck and break the red line (supply) and listen for leaks. With the red line still disconnected, you break the blue line (service) and then make a brake application. There should be no leak from either line. If there is, then your tractor protection valve is leaking and it will probably be an OTS (out of service).

There is NO requirement that your yellow dash valve has to dynamite when doing a tractor protection test.

There is NO requirement that your yellow dash valve has to pop out anytime, ever, for any reason. Even when they are brand new at the factory.

The guy who gave you the ticket and made you repair the truck did not know what he was talking about. As long as he was putting you out of service for the Yellow Dash valve. It might have been for something else. Maybe you had an air leak in the TPV.

Except that is the way they USE to do it. He obviously has not be taught the new regulations.

I know this to be true, as I got the info from a Commercial Vehicle Inspector who works for the Dept of Motor Vehicles in BC. All of our pretrips and courses have been designed with their help to make sure we teach the law, not what the law enforcers would like the law to be.

 

The trouble is, there are different standards...there is the FMVSS 121, then there is state law, then there is state law interpreted by the people who write the DMV study guide, then there is what they teach in school, and there is what the truck and equipment manufacturers say, and there is what old time truckers say, and of course what the DOT cop says, etc, etc.

Anyway as a mechanic and driver I agree with what was said above...the yellow knob does not HAVE to pop at all although most of them do at some point but that is highly variable in my experience.

Also FWIW the red knobs often have an orfice that the trailer supply air flows through, such that if the red line gets disconnected or blown the red knob will pop immediately rather than waiting until tractor air is depleted to such a level as to pop the red knob. This retains much more air in the tractor to try and keep things under control as long as possible.

Birken

 

Yes my RED knob does pop out between 20 and 45 psi, but my yellow when pushed in alone pops out just b4 0 psi, b4 i had TPV replaced it didnt pop out at all. and i was shut down for it not popping out, ive heard all types of answers as far as if the yellow is suppose to pop out, dont want to ask DOT this week here in NC(I drive local) because they are working hard all week in the scales here in NC, if you drive through here this week you know what im talking about :lol:

 

You guys are talking about two separate tests adn calling both of them Tractor Protector Valve.

If you pump your brakes until both valves pop, that is NOT a tractor protector valve check, that is a low air pressure valve test and yes, both valves must pop to pass the inspection. This sets the tractor brakes in the event of a major air loss in the MAIN or PRIMARY system

If you take the red line off, push in both red and yellow valves, your red valve should pop out when the pressure in the secondary air system reaches 20-40 lbs. The Yellow should NOT pop out due to a line leaking on the trailer. Your Primary system should loose little if any pressure due to a broken trailer line.

 

quote="thebaldeagle655"]You guys are talking about two separate tests adn calling both of them Tractor Protector Valve.

If you pump your brakes until both valves pop, that is NOT a tractor protector valve check, that is a low air pressure valve test and yes, both valves must pop to pass the inspection. This sets the tractor brakes in the event of a major air loss in the MAIN or PRIMARY system

i bet that if you go to your truck right now... press in the yellow and red buttons (trailer attached)... and then drain your primary reservoir to zero..... .....neither the yellow, nor the red button will pop out

If you take the red line off, push in both red and yellow valves, your red valve should pop out when the pressure in the secondary air system reaches 20-40 lbs.

we've already verified (many times over) that the red pops between 20 and 45 psi...

when you pull the red curly line off..... .....does ONLY secondary reservoir pressure drop???

The Yellow should NOT pop out due to a line leaking on the trailer. Your Primary system should loose little if any pressure due to a broken trailer line.[/quote]

you're sure???

 

What Bob is saying is that the push/pull dash valves, and the trailer air system, do not differentiate between tractor primary (rear) and secondary (front) air. When both reservoirs are at equal pressure (which is the normal case) then the trailer air system and the tractor spring brake system use air from both reservoirs pretty much equally. (Yes, I realize that some of the newest valves are slightly biased to primary)

If you drain either reservoir on your tractor to zero the other one will still supply pressure to the tractor spring release and the trailer supply systems.

What I think thebaldeagle655 was referring to was the fact that many trailer supply (red knob) valves have an internal restriction in their supply line. If the red hose to the trailer was to get broken or disconnected (wide open) the amount of air flowing would be extreme and the pressure downstream of the restriction in the trailer supply valve would drop below the valve's trip point and the valve would pop. This way the tractor air would be protected without having to wait for both the primary and secondary tractor reservoirs to drop all the way to 45 psi or whatever the trip point of the valve is, leaving the driver precious little to control the truck with. Instead the driver would have almost full system pressure in the tractor still.

Birken

 

This is not a comment at anyone in particular, it is just a statement in general.

It always amazes me how little so many drivers of Air Brake equipped vehicles know about how the air brake system works especially taking into account that their lives depend on it.

It is absolutely clear to me that many many drivers need to re-take an air brakes course. Not just a two or four hour one either. In BC the air brakes course has to be 20 hours minimum. And I find I can barely fit into that amount of time what is necessary.

 

You have to remember, some of us didn't have the privilege of a "course" to learn to drive. We learned by getting in and driving. Then Uncle Sam decided they needed rules and regulations that basically prove that the people that make those rules and regulations have no idea at all what we do for a living! Course on Air Brakes? From Who? No course required to renew a CDL, just go pay the money, no test except the eye test.

I learned what I know about the air brake system over 30 years ago and from the experience I've had. In that time there have been more than a few improvements. (and maybe a few that weren't exactly "improvements".)

I've seen a few of these graduates that had no more business opening a truck door and starting the engine to head out on the open road than I would tying to fly a 747! BUT the school makes them experts (if you don't believe it just ask them!)

 

I was not talking about a course in driving, I was talking about a classroom course in Air Brakes.

It would be the same as trying to learn how to use a computer without first leaning how to type, or use a keyboard properly.

Typing is a fundamental that without being able to do it, makes the user of the computer at a significant disadvantage to someone who knows how to use a keyboard.

Of course, the real difference is no one every killed anyone because they could not touch type.

I am not aware of a single thing that has been done in the dual air system that is not an improvement over the single circut type. Blended air, two way check valves, spring brake modulator valve, dual air foot valve, larger tanks, etc, etc.

And the moment that someone thinks they have no more to learn, or that they cannot learn by reviewing, it is time to find something else to do.

Every single student that takes air brakes with me and then come back one or two months later for the course again say that they understand it significantly more the second time than the first. And it is exactly the same course I teach each and every time.

Complacency kills a lot of people.

 

That, and overconfidence in their equipment.