A long time ago, I read that the red and yellow buttons go to one unit. The article recommended that the driver pull the yellow button and let the red button pop out. Then, if the driver wants to release the trailer brakes he will push the red button. Supposedly, this will prolong the life of the valve.

that's how I do it, but for a different reason.. if you hold the red button in and you dont have your hand just right, it pops out and bends your little finger back THAT HURTS

That's why I always used my thumb to hold the red in. Or put the palm of my hand on the red valve and pulled the yellow one.

the red knob is also know as the 'tractor protection valve" it will pop out to if there's a sudden loss of back line pressure---example: you forget to set it and then disconnect the supply line to trailer....the valve is suppose to pop before the tractor loses all air pressure.

Another thing to remember during the colder months, you shouldn't set your trailer brakes overnight. They may freeze. You are safer setting the tractor brakes because the spring pressure will open them. Spring pressure in the trailer will close them. You have a better chance of unsticking your tractor brakes, if they are frozen than you are your trailer brakes.

I was corrected on this once, so I am passing the info along. The tractor protection valve is another valve usually located at the rear of the cab. The red button is connected to the trailer supply valve. Perhaps, a mechanic will help us out here.

Yes...correct...the actual valve itself is not up there behind the dash...but the Trailer Air Supply...is also know as the "tractor protection valve control" sorry for leaving off the 'control' term.

by several dot:
http://www.lowestpricetrafficschool....oks/cdl/en/6/5

Test Tractor Protection Valve. Charge the trailer air brake system. (That is, build up normal air pressure and push the "air supply" knob in.) Shut the engine off. Step on and off the brake pedal several times to reduce the air pressure in the tanks. The trailer air supply control (also called the tractor protection valve control) should pop out (or go from "normal" to "emergency" position) when the air pressure falls into the pressure range specified by the manufacturer. (Usually within the range of 20 to 45 psi.)
If the tractor protection valve doesn't work right, an air hose or trailer brake leak could drain all the air from the tractor. This would cause the emergency brakes to come on, with possible loss of control.
Test Trailer Emergency Brakes. Charge the trailer air brake system and check that the trailer rolls freely. Then stop and pull out the trailer air supply control (also called tractor protection valve control or trailer emergency valve), or place it in the "emergency" position. Pull gently on the trailer with the tractor to check that the trailer emergency brakes are on.
Test Trailer Service Brakes. Check for normal air pressure, release the parking brakes, move the vehicle forward slowly, and apply trailer brakes with the hand control (trolley valve

Actually, Bendix, a manufacturer of the Two Button Modular Dash Control Valve (MV-3) recommend that you DO NOT do this. It can damage the the dash valves and may impact its ability to function automatically during parking brake applications.. I have one in my classroom that I am sure was damaged by the previous owner because he held the yellow one in, while he pulled the Red one out.

The proper sequence for setting your brakes is, pull the Yellow dash valve, Red should follow.

If you need to keep the trailer released for some reason, pull the yellow and let both dynamite, then push in the Red which will release the trailer.

Also, why it says "Not for Parking" is because if you are hooked to an older trailer that has only service brakes on it, once the air leaks out of the tanks, the brakes will release. You would need to block the wheels of this type of trailer BEFORE you unhooked and drove away.

If you have springs on the trailer then it will work as a parking brake once you have unhooked the trailer from the tractor, but ONLY if the brakes are set up properly.

Always remember, Spring Brakes only work as well as the adjustment of the service brakes. If the service brakes are out of adjustment, so will the parking brakes be out of adjustment.

So true......So true
And imagine what would happen if you left the tractor/trailer connected--landing dollies up--and only set the "not for parking" knob...and had no maxi spring brakes....so many 'run-a-ways'