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.

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

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

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.

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.

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.

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.

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.

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.

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 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).

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.

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

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.

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.

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.

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.

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.

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.

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.