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 the trailer emergency valve or place it in with the tractor to check that the trailer emergency brakes are on.
No less than 30 psi
supplies air to the trailer brakes to allow the operator to release the brakes
Yellow for the tractor brake control valve, red for the trailer supply valve.
what does the service air line do
If you're not pulling a trailer (or a trailer which doesn't have air brakes), you only push in the yellow brake control valve. If you push the red trailer supply valve in, all you'll do it dump air out the emergency line.
They have their own air compressor which provides air to the system.
They are what's used to connect the trailer to the trailer supply air lines.
The Bendix OEM knobs for those valves are yellow and red. Yellow is for the brake control valve, which releases the brakes on the power unit. The red is for the trailer supply valve, which provides air to the trailer, both to release the trailer brakes, to inflate the air ride suspension, and to actuate the brakes when the brake pedal is depressed.
It is the metal connector at the end of the hoses that supply air to the trailer brakes from the tractor.
It's a trailer control valve.
The tractor air control valve? Stops air from flowing to trailer red air line. Safety switch incase trailer falls off truck all the air will not go out the broken hose and cause tractor spring brakes to lock up due to low air. It can be tested by disconnecting red air line while trailer brakes air released. Air should stop at about 30psi I think.