With a fully-charged air system, turn off the engine, release the parking brake, and time the air pressure drop. The loss rate should be less than two psi in one minute for single vehicle brakes released, and three with the brakes applied.

Drivers behind you must be warned when you put your brakes on. The air brake system does this with an electric switch that works by air pressure. The switch turns on the brake lights when you put on the air brakes.

With a fully-charged air system, turn off the engine, release the parking brake, and time the air pressure drop. The loss rate should be less than two psi in one minute for single vehicle brakes released, and three with the brakes applied.

All vehicles with air brakes have a pressure gauge connected to the air tank. If the vehicle has a dual air brake system, there will be a gauge for each half of the system.

Park on level ground and chock the wheels to prevent the vehicle from moving, release the parking brakes so you can move the slack adjusters, using gloves and pull hard on each slack adjuster that you can reach, and if a slack adjuster moves more than about one inch where the push rod attaches to it then adjustments are needed.

Shut the engine off when you have enough air pressure so that the low-pressure warning signal is not on. Turn the electrical power on and step on and off the brake pedal to reduce air tank pressure. The low air pressure warning signal must come on before the pressure drops to less than 60 psi in the air tank.

A low air pressure warning signal is required on vehicles with air brakes.

Snub braking method is used for steep downhill grades, in this method apply the brakes just hard enough to feel a definite slowdown. When your speed has been reduced to approximately five mph below your "safe" speed, release the brakes. When your speed has increased to your "safe" speed, repeat.

To check slack adjusters on S-cam Brakes. Park on level ground and chock the wheels to prevent the vehicle from moving and apply the parking brake.

The use of brakes on a long and/or steep downgrade is only a supplement to the braking effect of the engine. Once the vehicle is in the proper low gear you should only have to apply the brakes just hard enough to feel a definite slowdown.

A parking brake control in the cab allows the driver to let the air out of the spring brakes. This lets the springs put the brakes on.

Slack adjusters are an important part of your air brake system that allows you to adjust the brakes to ensure that they are safe. They are located in different places, depending on the type of brakes that you have.

Air brakes are really three different braking systems: service brake, parking brake, and emergency brake.

With air brakes there is an added delay called Brake Lag. This is the time required for the brakes to work after the brake pedal is pushed.

Any time you park use the parking brakes. Pull the parking brake control knob out to apply the parking brakes, push it in to release.

You put on the brakes by pushing down the brake pedal. Pushing the pedal down harder applies more air pressure. Letting up on the brake pedal reduces the air pressure and releases the brakes.

Even if the low-pressure alarm is for the secondary system you need to stop at a safe location, park, and get the issue fixed. It is unsafe for the vehicle to remain in motion with a low air alarm.

The tractor protection valve keeps air in the tractor or truck brake system should the trailer break away or develop a bad leak, and it will close automatically if air pressure is low (typically 20-45 psi).

If the low air pressure warning comes on, stop and safely park your vehicle as soon as possible.

Never leave your vehicle unattended without applying the parking brakes or chocking the wheels. Your vehicle might roll away and cause injury and damage. Exceptions are when the brakes are very hot, or wet and it is very cold outside. In this case use wheel chocks.

All vehicles with air brakes have a pressure gauge connected to the air tank, and it tells you how much pressure is in the air tanks.

Drum brakes are on each of your vehicle's axles and contain about 10 different parts, including the axle, slack adjuster, and brake drum itself. While a safety valve is part of the air brake system, it is not part of the drum brake.

A safety relief valve is installed in the first tank the air compressor pumps air to. The safety valve protects the tank and the rest of the system from too much pressure. The valve is usually set to open at 150 psi. If the safety valve releases air, something is wrong. Have the fault fixed by a mechanic.

Stab braking means that you: apply your brakes all the way, and release brakes when wheels lock up. As soon as the wheels start rolling, apply the brakes fully again.

When driving, powerful springs are held back by air pressure. If the air pressure is removed, the springs put on the brakes. A leak in the air brake system, which causes all the air to be lost, will also cause the springs to put on the brakes.