Whether you are a tractor owner-operator or a truck and trailer manufacturer, it's important to know how the air brake system works. This is particularly true for combination vehicles, where there are a number of parts to control the trailer brakes.
A key part of the braking system is the tractor air brake valve. It helps prevent the air from being lost in a rupture of the air lines connecting the tractor to the trailer.
The Red Valve
The tractor Air Brake Valve (also known as the Red Valves) keeps the brake system of a tractor-trailer combination in good working order. Without these valves, if the air supply line from the tractor to the trailer ruptured due to a leak, the entire tractor would lose all of its air and the trailer would not have enough pressure to apply the spring brakes.
The merged outputs of the foot-valve and trailer-hand-valve are directed through this valve and onward via the blue service line. This prevents the spring brakes from automatically applying, thereby giving the driver more control and preventing the vehicle from grinding to a stop in an unsafe position.
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The Yellow Valve
The yellow knob on the dash is labeled the Parking Brake Valve and controls the application of and release of the truck's parking brakes. This will also apply the trailer's supply valve if you have an air brake equipped trailer attached to the vehicle.
The tractor's Air Brake System operates by applying pressure to the air lines from the driver's foot and then venting it back out through quick release valves located throughout the tractor's braking circuits. This process can take a while, depending on the amount of air required to travel back and forth between the service line's output and the driver's foot valve or relay valve.
If the tractor air system loses pressure, the red valve will pop open causing the tractor Air Brake Valve to close and simultaneously apply the trailer Spring Brakes. This is a very important safety feature and must be inspected and maintained regularly.
The Blue Valve
The tractor Air Brake Valve is an automatic shuttle valve on the towing vehicle that is designed to stop high volume air loss in the event of a severed or disconnected trailer air line or other trailer leak source.
It also prevents air loss out of the towing vehicle if there is no trailer attached. This valve is operated by the trailer supply valve and opens when a brake application is made on the towing vehicle.
During a brake application, air pressure from the red push/pull knob is directed to the service line port of the tractor protection valve. When the air pressure reaches 45 psi, the tractor protection valve opens and allows application air to travel down the service line to the trailer.
The Green Valve
The tractor Air Brake Valve, also called the trailer supply valve or emergency line on older trucks, shuts off air to the trailer in an emergency. This is to prevent the loss of air in the event that the trailer breaks loose, the hoses break or a part of the line loses pressure.
The Green Valve is an innovative control device which permits the recovery of part of the energy dissipated during the throttling process thanks to the inclusion of a water turbine inside the valve body. This technology can substitute existing control valves without the need to install further components on the pipeline or to change the systems operating conditions.
This technology is suitable for use in industrial plants and distribution networks in different fields (electricity production, water, oil & gas, etc.). The rotor, which can be made of metal, plastic or composite materials, is designed to rotate in a continuous manner under the flow.