It is essential that your low pressure warning light function properly. After allowing the system to charge, you can test the warning signal by rapidly applying and releasing the brake pedal. This will release air from the braking system and the warning signal should come on when pressure drops to a dangerous level.

A modulating control valve allows a driver to gradually apply spring brakes. In equipped vehicles, the valve is controlled by a lever located on the dashboard.

A one-way check valve is required to be between an air compressor and the first main reservoir. This valve prevents air from escaping the system if the air compressor develops a leak.

In an air brake system, the air compressor pumps air into the air storage tanks. The air compressor is controlled by the air compressor governor.

On newer vehicles with air brakes, the parking brake is controlled by a yellow, diamond-shaped knob. The knob is pulled out to set the brakes, and pushed in to release them.

To make a normal stop in a vehicle that is equipped with air brakes, you should simply press the brake pedal down.

In newer vehicles with air brakes, the parking brake is controlled by a yellow, diamond-shaped knob. The driver should pull the knob outward to apply the parking brakes and push the knob inward to release them.

On long and/or steep downgrades, you should primarily use engine braking to control the speed of your vehicle. Use your brakes only as a supplement to this effect.

A vehicle that is equipped with air brakes must also be equipped with a supply pressure gauge. This gauge tells the driver how much air pressure is in each of the vehicle's air tanks.

Never apply the brake pedal if your spring breaks are activated. Brakes can be damaged if they are subject to both springs and air pressure.

Some pre-1975 vehicles have a front brake limiting valve, which has "normal" and "slippery" settings. The idea behind these valves was to limit the air pressure available to the front brakes when driving on slippery surfaces, and thereby reduce the danger of a front-wheel skid. Studies have found that this is not actually a concern, so if your vehicle has a front brake limiting valve, leave it in the "normal" position.

The controlled braking method for emergency stops involves applying the brakes as hard as you can without locking the wheels. Keep steering wheel movements small when braking in this way.

If used and maintained properly, air brakes are a safe and effective way to stop large, heavy vehicles.

If a vehicle is equipped, an application pressure gauge shows how much air pressure is being applied to the brakes. This gauge can help a driver identify if their brakes are beginning to fade.

In an air brake system, the application pressure gauge shows how much air pressure is being applied to the brakes. Not all vehicles with an air brake system have this gauge.

Air brakes consists of three separate braking systems: the service brake system, the parking brake system, and the emergency brake system. The service brake system applies and releases the brakes when you use the brake pedal while driving normally.

While driving, spring brakes are generally held in place by air pressure. If the air pressure gets low enough, the springs will activate the brakes.

Truck tractors with air brakes built on or after March 1, 1997, and other vehicles with air brakes built on or after March 1, 1998, must be equipped with anti-lock brakes.

In an air brake system with manually operated drains, the tanks should be drained at the end of each day of driving.

When performing a static leakage test on a single vehicle with air brakes, the leakage rate should be no more than 2 psi in a minute. If the air leaks from the air brake system at a quicker rate, the vehicle should not be driven because something likely needs to be repaired.

A wig wag is a type of low air pressure warning device in an air brake system. It drops a mechanical arm into the driver's view when the air pressure in the tanks falls below 60 psi.

Always apply the parking brake when leaving your vehicle unattended.

The method of controlled braking involves applying the brakes as hard as you can without locking the wheels. If you need to make large steering adjustments while using controlled braking, you should remove your foot from the brake pedal, steer, then reapply the brakes.

Some air brake systems contain an alcohol evaporator. This evaporator introduces alcohol into the system to help prevent ice from forming in cold weather.

In a vehicle with dual parking control valves, there is a separate air tank that can be used to temporarily release the spring brakes if they have been activated due to low air pressure. Pushing in the proper control will release the spring brakes for a short period of time, allowing the driver to move the vehicle in an emergency.