Section 5

5.1 Air compressor

-The air compressor is connected to the engine through gears or a belt. -The compressor may be air cooled or cooled by the engine cooling system. -could have oil, check oil.

5.2 Dual Air brake

-primary -secondary -let the air pressure rise above 100 psi cannot fall below 60-psi

Air brakes have

-service brake -parking brake -emergency brake

5.3 inspecting air brake system

-step 2- check Air Compressor Drive Belt -step 5 walk around inspecting check manual slack adjuster on s-cam brakes If a slack adjuster moves more than about one inch where the push rod attaches to it, it probably needs adjustment

5.1 wedge Brakes

-the brake chamber push rod pushes a wedge directly between the ends of two brake shoes. -the shoves them apart and against the inside of the brake drum -wedge brakes may have a single brake chamber or tow brake chamber, pushing wedges in at both ends of the brake shoes -can be self adjusting or manual adjuster

5.3 check brake drums

Brake drums (or discs) must not have cracks longer than one half the width of the friction area

5.3 hoses

Check the air hoses connected to the brake chambers to make sure they aren't cut or worn due to rubbing

5.3 check that the spring brakes come on automatically

Chock the wheels, release the parking brakes when you have enough air pressure to do it, and shut the engine off. Step on and off the brake pedal to reduce the air tank pressure. The "parking brake" knob should pop out when the air pressure falls to the manufacturer's specification (usually in a range between 20-40 psi). This causes the spring brakes to come on.

5.1 low air pressure warning

Light comes on if the pressure falls below 60

5.3 check linings

Linings (friction material) must not be loose or soaked with oil or grease. They must not be dangerously thin.

5.4 using air brakes

Perception Distance + Reaction Distance + Brake Lag Distance + Effective Braking Distance = Total Stopping Distance The air brake lag distance at 55 mph on dry pavement adds about 32 feet. So at 55 mph for an average driver under good traction and brake conditions, the total stopping distance is over 300 feet. This is longer than a football field.

5.3 test low pressure warning signal

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 (or tank with the lowest air pressure, in dual air systems).

5.4 brake fading

The other brakes can then overheat and fade and there will not be sufficient braking available to control the vehicle(s). Brakes can get out of adjustment quickly, especially when they are hot. Therefore, brake adjustment must be checked frequently.

5.3 check rate of air pressure buildup

When the engine is at operating rpm, 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. Check the manufacturer's specifications.) In single air systems (pre-1975), typical requirements are pressure buildup from 50 to 90 psi within three minutes with the engine at an idle speed of 600-900 rpm

5.1 Air compressor governor

Will pump air into the air storage tanks. -stops when it reaches 125 pounds -starts when it falls below 100

5.3 Check Air Compressor Governor Cut-in and Cut-out Pressures.

With the engine idling, step on and off the brake to reduce the air tank pressure. The compressor should cut-in at about the manufacturer's specified cut-in pressure. The pressure should begin to rise

5.1modulating control valves

a control handle on the dash that applies the spring brake.

Wig Wag

a mechanical arm if it drops below 60

5.1 disc brakes

air pressure acts on a brake chamber and slack adjuster...like scam brakes -instead of the scam, a power screw is used -the pressure of the brake chamber on the slack adjuster turns the power screw -the power screw clamps the disc or rotor between the brake lining pads of a caliper, similar to a large c-clamp. -wedge brake and disc brakes are less common than scam

5.1 supply pressure gauuges

all air vehicles have a pressure guage connected to the air tank. -if the vehicle has a dual air brake system, there will be aguage for each half of the system -or a single gauge with tow needles -dual system show how much pressure is in the tanks.

5.1 dual parking control valves

allows you move the spring brakes.

5.1 stop light switch

an electric switch that works by air pressure.

Service brake

applies and releases the brakes when you use the brake pedal during normal driving.

5.1 Brakes Drums

are located on each end of the vehicle's axles. -wheels are bolted to the drums -the breaking mechanism is inside the drum -to stop, the shoes and linings are pushed against the inside of the drum. -too much heat can cause the brakes to stop working

5.1 parking brakes controls

diamon shaped, yellow, push-pull control know -never comine air brakes

5.1 Alcohol Evaporator

helps reduce the risk of ice in air brakes

5.1 Air tank drain

may be left with water -manual drain -or automatic drains that have a heater device.

5.1 Front brake limiting valve

normal and slippery slippery cuts the air pressure in half to the front brakes -actually reduced the stopping power

5.1 Safety Valve

opens up at 150 psi

5.1 The brake Pedal

pressing the brake pedal on a constant bases can release more air than the compressor can produce. Causing the brakes not to work.

5.1 Foundation Brakes

s-cam brakes are the more common ones.

5.1 application pressure gauge

shows how much pressure you are applying to the brakes.

5.3 test air leakage rate

step 7 final air brake check With a fully-charged air system (typically 125 psi), turn off the engine, release the service brake, and time the air pressure drop. The loss rate should be less than two psi in one minute for single vehicles and less than three psi in one minute for combination vehicles.

5.1 air storage tanks

store air

parking brake

system applied and releases the parking brake when you use the parking brake control.

Emergency brake

system uses parts of the service and parking brake systems to stop the vehicle in the even of a brake system failure.

5.1 s-cam

when you push the pedal, air is let into the chamber. -air pressure pushes the rod out -moving the slack adjuster -twisting the brake cam shaft -scam forces the brake shoes away from one another and presses them against the inside brake drum. -when you release the brake pedal, the cam rotates and pulls the shoes away from the drum.

5.1 spring brakes

will come on if the air pressure drops 20 to 45 psi