The safety relief valve in an air brake system releases air if necessary to prevent pressure in the system from becoming too high. If the valve starts releasing air, there is something wrong. Have a mechanic fix the problem.

All air tanks on air-braked vehicles must have one-way check valves located between the air compressor and the first reservoir. This prevents air from flowing out in the event of a leak.

In an air brake system, the air storage tanks are equipped with drains to allow water and compressor oil to be removed. The water and oil can damage the brakes if left to accumulate in the system.

Never push down the brake pedal while the spring brakes are activated. The combined force of springs and air pressure could damage the brakes.

All trucks, truck tractors, and buses must be equipped with emergency brakes and parking brakes. These brakes must be held by mechanical force.

If brakes are overused, they may overheat and stop working. This is referred to as brake fade.

Any vehicle with air brakes must be equipped with a low air pressure warning signal.

The purpose of an Anti-Lock Braking System (ABS) is to prevent wheel lockup while brakes are being applied.

Vehicles with Anti-Lock Braking Systems (ABS) have yellow malfunction lamps.

If the low pressure warning signal activates while you are driving, it is important that you safely exit the roadway as soon as possible and park your vehicle. If the air pressure gets too low, the brakes will no longer work well enough for you to stop safely.

Brakes can get out of adjustment quickly, especially if they are used to the point of overheating. Brake adjustment should be checked frequently.

Because air pressure can eventually leak away, the emergency brakes in an air brake system must be held on by mechanical force.

On a long or steep downgrade, brakes should only be used to supplement the braking effect of the engine. Apply the brakes just enough to feel a definite slowing down, then release them once you are about 5 mph below your target "safe" speed. Once your vehicle reaches its safe speed again, repeat this process.

The majority of heavy-duty vehicles are equipped with dual air brake systems.

There are two air brake systems in a dual air brake system. The systems share a set of brake controls, but each system has its own tanks, hoses, and lines.

Most newer heavy-duty vehicles use dual air brake systems. A dual air brake system has two separate air brake systems which use a single set of brake controls.

The air storage tanks in an air brake system store compressed air to be used for braking. They hold enough air for the brakes to still be used several times if the compressor stops working.

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.

A dual air brake system is made up of two separate air brake systems. The systems share a single set of brake controls, but each has its own air tanks, hoses, and lines.

Parking brakes should not be used in very wet weather when temperatures are below freezing. The brakes could become frozen in place, making it impossible to move the vehicle.

If you need to make an emergency stop, you can use either the controlled braking method or the stab braking method. It's important to brake in a way that keeps your vehicle in a straight line but will still allow you to turn if necessary.

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.

If brakes are used too much, they will overheat and become less effective. This is referred to as brake fade.

Brakes are particularly prone to getting out out adjustment if they are hot. Use proper braking techniques to avoid letting your brakes overheat.

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.