Air brakes Flashcards
Oil and water usually collect in compressed air tanks. If you do not have an automatic tank drain, when should you drain the air tanks?
After every working day.
If your vehicle does not have automatic air tank drains, drain your air tanks at the end of each working day to remove moisture and oil. Otherwise, the brakes could fail.
What is the S-cam used for?
To apply the brakes.
When you push the brake pedal, air is let into each brake chamber. Air pressure pushes the rod out, moving the slack adjuster, thus twisting the brake camshaft. This turns the s-cam forcing the brake shoes away from one another and presses them against the inside of the brake drum.
Which of the following makes the total stopping distance for air brakes longer than that for hydraulic brakes?
Brake lag distance.
With air brakes there is an added delay or Brake Lag. This is the time required for the brakes to work after the brake pedal is pushed. With hydraulic brake, the brakes work instantly. With air brakes it takes a little time, one half second or more, for the air to flow through the lines to the brakes.
The brake system that applies and releases the brakes when the driver uses the brake pedal is the:
Service brake system.
To make an emergency stop with air brakes, using the stab braking method, you should:
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.
Brake lag distance at 55 mph is _____ feet?
32.
If your vehicle has an alcohol evaporator, it is there to:
Reduce the risk of ice in air brake valves in cold weather.
Some air brake systems have an alcohol evaporator to put alcohol into the air system. This helps to reduce the risk of ice in air brake valves and other parts during cold weather. Daily air tank drainage is still needed to get rid of water and oil.
What can legally hold a parking or emergency brake in position for a truck, truck tractor or bus?
Spring pressure
All trucks, truck tractors, and buses must be equipped with emergency brakes and parking brakes. They must be held on by mechanical force because air pressure can eventually leak away. Spring brakes are usually used to meet these needs.
The braking power of the spring brakes:
Depends on the adjustment of the service brakes.
The braking power of spring brakes depends on the brakes being in adjustment. If the brakes are not adjusted properly, neither the regular brakes nor the emergency/parking brakes will work right.
If the air tanks are not drained,
your brakes may fail because of water freezing.
Compressed air usually has some water and some compressor oil in it, which is bad for the air brake system. For example, the water can freeze in cold weather and cause brake failure.
If your vehicle has a properly functioning dual air brake system and minimum-sized air tanks, the air pressure should build from 85 to 100 psi within ____ seconds.
45.
When the engine is at operating rpms, the pressure should build from 85 to 100 psi within 45 seconds in dual air systems. If the vehicle has larger than minimum air tanks, the buildup time can be longer and still be safe.
The air compressor will stop pumping air into the air tanks at ____ psi.
125.
The governor controls when the air compressor will pump air into the air storage tanks. When air tank pressure rises to the “cut-out” level around 125 psi, the governor stops the compressor from pumping air. When the tank pressure falls to the “cut-in” pressure around 100 psi, the governor allows the compressor to start pumping again.
Excessive use of the service brakes may result in overheating, which can lead to
Expansion of the brake drums.
Brake fade results from excessive heat causing chemical changes in the brake lining, which reduce friction, and also causing expansion of the brake drums.
During normal driving, spring brakes are usually held back by
Air pressure.
Parking or emergency brakes must be held on by mechanical force because air pressure can eventually leak away. Spring brakes are usually used to meet these needs. When driving, powerful springs are held back by air pressure.
To test the static air leakage rate, you should
turn off the engine, release the parking brake, and let the system settle.
With a fully-charged air system (typically 125 psi), turn off the engine, release the parking brake (push in); and time the air pressure drop.
When you press the brake pedal,
compressed air enters the brake chambers.
Air brake equipped vehicles must have:
A supply pressure gauge.
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.
If you must make an emergency stop, you should brake so that you:
Stay in a straight line and can steer.
You should brake in a way that will keep your vehicle in a straight line and allow you to turn if it becomes necessary. You can use the “controlled braking” method or the “stab braking” method.
The most common type of foundation brakes found on heavy vehicles is the:
s-cam brakes.
When driving down a long steep hill you should:
Release the brakes when you are 5 mph below your “safe” speed.
The modulating control valve is?
In some vehicles, a control handle on the dash board may be used to apply the spring brakes gradually. This is called a modulating valve. It is spring loaded, so you have a feel for the braking action. The more you move the control lever, the harder the spring brakes come on. They work this way, so you can control the spring brakes if the service brakes fail.
Spring brakes are
Spring brakes are an important backup system: powerful springs that automatically apply the brakes if they sense that air pressure has been lost for some reason, such as a leak. They will also apply the brakes if the psi gets too low, although ideally, you should take control of your brakes before that happens.
In the event of a brake system failure, the emergency brake system uses __________ to stop the vehicle.
parts of the service brakes and parking brakes.
Repeatedly pressing and releasing (fanning) the brake pedal may result in
a loss of brake air pressure.
Each time you release the brakes, some compressed air leaves the system and must be replenished by the air compressor. If you keep pressing and releasing the brake pedal, air may leave the system faster than the air compressor can replenish it, and the air pressure may drop to the point that the brakes won’t work.
