Start the bus and let the air pressure build to at least 90 psi. Step on the brake pedal and put the bus into gear. Slowly take your foot off the brake and gently press the accelerator. The bus should not move.
How do air brakes work on a bus?
Air brakes work using compressed air instead of hydraulic fluid. The air compressor then pumps the air into the air storage tanks, which store the compressed air until it’s needed. Air pressure is used to apply the service brakes and release the parking brake. There are multiple air circuits in the system.
How do you release air brakes?
Press the yellow button labeled “Parking” while your foot is on the brake pedal. This will release the truck air brakes. Press in the red button labeled “Trailer” if a trailer is attached. This will release the trailer brakes.
Why do school buses have air brakes?
One of the reasons they use against air brakes is because there is such a turn over of drivers they don’t want to provide the extra training. Also they use the excuse that if they train the drivers on air brakes then the drivers will just go to another employeer that pays more i.e. public transit and trucks.
Why do buses use air brakes?
Since trucks and busses are heavy, they require a large force to stop. With a hydraulic system, the driver has to exert more effort on the brake pedal to stop the truck or bus, which is next to impossible. Air brakes use compressed air because of its high potential energy.
How do you drive with air brakes?
To apply the air brakes during normal stops, push the brake pedal down. Control the pressure so the vehicle comes to a smooth, safe stop. If you have a manual transmission, do not push the clutch in until the engine RPM is down close to idle. When stopped, select a starting gear.
Can you release air brakes manually?
In certain emergency situations, like when an air brake system failure has occurred and you need to move your truck to a safe position, you may need to manually release the brakes to enable the vehicle to be moved.
What happens when air brakes run out of air?
What happens when air brakes fail? When the air brake system is not pressurized enough, a low-air pressure alarm will sound. In these cases, semi-trucks and trailers, airplanes, buses, trains, and large trucks (such as fire engines) are equipped with a back-up emergency braking system for use when air brakes fail.
What happens when air brakes cam over?
Cammed over brakes will cause the brakes to lock up and you won’t be able to move the trailer. When the s-cam cams over, it rotates past the rollers on the brake and wedges the brakes against the drum.
What are the different types of brakes used on school buses?
Wedge brakes are rarely used on school buses. Disc brakes are still another variation in that the air chamber mechanically operates a caliper that is used to clamp “pads” against a “disc” that rotates with the wheels. In summary, service air is applied to the brake chambers, converting air pressure to mechanical force.
What happens if the air brake fails on a bus?
In either of the above cases, the low-air warning systems will be activated due to low air pressure in the failed system; however, the bus can be safely pulled to the side of the road and stopped. Do’s and don’ts With spring-type parking brakes, air brakes are considered fail-safe.
How often should you drain a school bus air dryer?
This reservoir should be drained daily, assuring these byproducts are kept out of the air system components downstream. Air dryers and automatic drain valves are found on many newer school buses; however, daily manual draining ensures no contaminates migrate into critical components, such as brake valves and chambers.
What happens if air is lost in the rear brakes?
In dual systems, should air be lost in the front system, the rear braking system will stop the bus. Conversely, should the rear brake air supply be lost, through special valving, the rear spring brakes’ release air will be bled off in direct proportion to the front brake application air pressure, thus stopping the bus normally.
