Air Brakes

Inspecting Air brake components

- Foundation Brake components - Brake lining to drum contact - Brake lining conditions - Brake-lining contamination - Brake-lining Thickness Components that are damaged, missing or malfunctioning. Cracked, loose, missing or contaminated brake linings. Improper drum contact. Linings that are less than the required thickness.

Vehicle Weight

- The stopping distance will increase in proportion to any increase in vehicle weight. - It is possible to exceed the capacity of a vehicle's braking system by loading more weight than it is rated to carry. - When a vehicle is overloaded, the brake system may not be able to safely stop it.

Service Brake Subsystem

- normal stopping (service brakes) - parking - emergency braking

One way check valve

- prevents leaks and air from returning

Normal Air brake system pressure?

100 to 120 psi (690 to 828 kPa)

The governor's cut out pressure must not be lower than 60 psi 120 psi 145 psi 150 psi

120

Normal Cut Out pressure?

20 to 25 psi (138 to 173 kPa) ABOVE cut-in pressure

Normal PSI to release spring breaks

60 PSI of air pressure must be supplied to the spring break chamber to compress/ cage the spring - If system pressure is below 60 psi (414 kPa), the spring brakes start applying because there is no longer enough pressure to keep them released.

In what order should air tanks be drained? a. Wet, primary, secondary b. Primary, secondary, wet c. Primary, wet, secondary d. All at the same time

A

What can indicate that an air tank or mounting bracket is not secure? a. Unusual movement b. An air leak c. A fluid leak d. A deflated airbag

A

What is a reliable method for inspecting your brake adjustment? a. Measuring the applied pushrod stroke b. Checking the slack adjustment c. Checking the condition of the brake drum d. Measuring the brake chamber size

A

When testing the air-loss rate of the brake system, the brake pedal must be fully applied. a. True b. False

A

When testing the compressor, if there is a trailer attached, the trailer supply valve must be closed. a. True b. False

A

When testing the tractor protection system, the trailer supply valve must close before the pressure drops below: a. 20 psi b. 55 psi c. 60 psi d. 100 psi

A

Where are air brake chambers located? a. At each wheel b. At the drive wheels only c. At the trailer wheels only d. At both the drive and trailer wheels

A

Disc Brakes

A disc-shaped rotor and a calliper containing brake pads. When you press the brake pedal, *the pads press toward each other, clamping against both sides of the rotor's surface*.

Three types of foundation brakes systems

- "S" Cam brakes - Disc Brakes - Wedge Brakes

Internal Parts of ""S" cam brakes

- A brake spider that serves as the main mounting base for the brake shoes. - Single or dual anchor pins to attach one end of the brake shoes. - Anchor springs to hold the brake shoes in position at the anchor end. - The head of the "S" camshaft. - Camshaft rollers that rotate with the camshaft while moving the brake shoes inward and outward. - A return spring to pull the brake shoes in to the released position and keep the camshaft rollers engaged with the camshaft head.

Vehicle Speed

- As vehicle speed increases, the stopping distance increases at a rate that is greater than the change in speed. For example, when speed is doubled, the stopping distance increases by four times. - Stopping distance can be calculated based on time and speed. A split-second delay in brake application and release ranging up to one-half second is present in all air brake systems. This delay must be taken into account when determining suitable following distances and appropriate action during vehicle stops. Note: If you double your vehicle weight and double your speed, your stopping distance increases by eight times.

The brake-shoe lining not contacting the brake drum is an example of: a. A foundation brake component defect b. An issue with the brake chamber c. An incorrectly measured pushrod d. None of the above

A

Drum Brakes

A drum with brake shoes and linings inside the drum. When you press the brake pedal, *the brake shoes press outward against the drum's surface.*

Spring brake (parking and emergency) control valves

A pull/push type value fitted with a yellow, four-sided knob located near the driver - Most spring brake control valves are pushed to supply air and release the spring brakes, then pulled to exhaust air and apply the spring brakes - Spring brake control valves are designed to respond to air brake system pressure dropping below a certain level (normally 60psi [414 kPa]) by exhausting the remaining air that is holding the spring brakes in the released position. This causes sudden automatic application of the spring brakes and an uncontrolled vehicle stop.

Wedge Brakes

A type of drum brake that includes brake drums and shoes with no exposed brake linkage. - Air brake chambers are mounted so that their pushrods face inward toward the brake shoes and drum. - The stroke of the brake chamber pushrod slides a wedge between the brake shoes, forcing them outward against the drum. Wedge air brakes are designed to be self-adjusting. brake drums, brake shoes and linings, spiders, dust shields and brake chambers.

Air Tanks

Air from the compressor is stored in air tanks - One, two, three or more tanks may be used, depending on the specific needs of the vehicle. - The air that is drawn in by the air compressor contains *moisture or humidity.* As the air is compressed and passed into the tanks, the moisture condenses or "drops out" of the air and settles to the bottom of the tank

Spring brakes for emergency braking and parking

All vehicles with air brakes must have a way of stopping if the service brake system fails. Most vehicle manufacturers combine this emergency braking system with a parking-brake system using spring brakes. Spring brakes are not air applied like service brakes. They apply when air pressure leaves the brake chamber and release when air pressure builds up in the chamber.

Anti-Lock Braking System (ABS)

Anti-lock braking systems (ABS) help maintain steering control during emergency braking. - anti-lock braking system prevents tire skid and the accompanying loss of steering control. This improves vehicle safety during heavy brake use or when braking with poor traction. - Anti-lock braking systems help to prevent wheel lock but do not shorten the vehicle stopping distance. Warning indicator lights are used with anti-lock braking systems to indicate system malfunctions.

Brake pedal operation

As the pedal is pressed downward, compressed air passes through a valve attached to the brake pedal and is delivered to the brakes at the wheels. As the brake pedal is pressed harder, the valve opens farther, delivering higher air pressure to the service brakes and increasing the braking force at the wheels. - Since most brake-system designs use dual circuits, air is drawn from both the primary and secondary tanks and is directedto specific wheels on the vehicle

A brake chamber that includes both service brake and spring brake sections is called a: a. Brake chamber b. Spring brake chamber c. DD3 brake chamber d. Service brake chamber

B

Actual cut-in pressure for the governor should never be less than 90 PSI? a. True b. False

B

Automatic slack adjusters, if working properly, require regular re-adjustment. a. True b. False

B

Failure of the spring brakes to hold the vehicle stationary indicates defective service brakes. a. True b. False

B

How can air brake chamber air leaks usually be detected? a. Visually b. Audibly c. By checking pushrod travel distance d. None of the above

B

On a straight truck, tractor, or bus air loss test, what is the acceptable amount of air loss allowed within one minute? a. 2 psi b. 3 psi c. 4 psi d. 6 psi

B

What is the maximum air loss allowed when testing the air-loss rate of the brake system on a tractor and trailer? a. 3 psi b. 4 psi c. 6 psi d. 10 psi

B

What is the size of an air brake chamber based on? a. The type of chamber b. The area of the chamber diaphragm in square inches c. The pushrod travel distance d. The make and model of the vehicle

B

What should the air pressure be when performing a brake adjustment inspection at each wheel? a. Between 80 - 90 psi b. Between 90 - 100 psi c. Between 100 - 110 psi d. At maximum pressure

B

When grease or oil is present on the brake lining: a. The brake lining is properly lubricated b. Abnormal brake behaviour will result c. The brake lining has been over-lubricated d. The driver can continue to drive the vehicle as it will not cause any issues with brake function

B

When testing the air-loss rate of the brake system, the brake application must be held for: a. 30 seconds b. One minute c. Two minutes d. Three minutes

B

Before driving

Before driving the vehicle, it is important to ensure that the air brake system has enough air pressure (normally 60 psi [414 kPa]) to keep the spring brakes from applying. - Due to the way most spring brake chambers are currently constructed, it is very difficult to unintentionally release the spring.

Actual cut-in pressure of the governor should never be less than: a. 55 psi b. 80 psi c. 100 psi d. 120 psi

C

At what pressure do the spring brakes normally start to apply because there is no longer enough pressure to keep them released? a. 20 psi b. 40 psi c. 60 psi d. 85 psi

C

If you double your vehicle weight and double your speed, what does your stopping distance increase by? a. Four times b. Six times c. Eight times d. Ten times

C

What can cause damage or deterioration to brake hoses and tubes? a. Wear and cuts b. Wear, cuts, and heat damage c. Wear, cuts, abrasions, and heat damage d. Abrasions and heat damage

C

What is the purpose of the safety valve? a. Starts building air pressure at 100 psi b. Stops building air pressure at 140 psi c. Protects the supply reservoir from becoming over-pressurized and bursting d. Ensures the trucks safety features are working correctly

C

When checking the buildup rate (compressor operation) the engine should be building air pressure from _____ psi to ____ psi within two minutes: a. 45 - 65 b. 65 - 85 c. 85 - 100 d. 100 - 125

C

The safety valve will open to allow excess air pressure to escape at a level no higher than? a. 140 psi b. 145 psi c. 150 psi d. 155 psi

C 150 psi

Service Brake Chamber

Contains a flexible rubber disc called a *diaphragm, a metal rod called a pushrod and a return spring*. When you press the brake pedal, compressed air fills the service brake chamber, causing the diaphragm to move and push out the pushrod to apply the brakes

At what level must the low pressure warning device activate? a. At or above 60 psi b. Between 40 - 50 psi c. At or above 85 psi d. At or above 55 psi

D

If the governor fails to signal the compressor to cut-out what allows the excess air pressure to escape? a. The air dryer b. A one way check valve c. The low pressure warning system d. A safety valve

D

What is the maximum air loss allowed in one minute on a tractor with two or more trailers? a. 3 psi b. 4 psi c. 5 psi d. 6 psi

D

Brake hoses and tubes

Deliver compressed air to all components of the air brake system These are made from a wide range of natural and synthetic materials in various colours, sizes and styles. - Each hose and tube must be the correct size and type - Manufacturers currently follow an industry colour code, but this is not the case with older vehicles.

Spring (Parking and Emergency) Brake Subsystem

Designed to work when you are parking your vehicle or in an emergency when your service brakes fail.

Air Tank Drain Valve

Drains the tanks - Should be drained daily - When draining the tanks, the supply tank should always be drained first to prevent accumulated moisture flowing into the next tank being drained.

Two major brake types

Drum Brakes Disc Brakes

If the compressor takes longer than two minutes to build air from 85 psi to 100 psi, it would be considered a major defect True Or Flase

False

Spring breaks use air to apply the brakes True or False

False

Problems with supply/wet tank

If the mixture of moisture and oil that collects in the supply tank passes into the rest of the air brake system, it can damage brake components and interfere with the operation of the system. 1) The collected moisture and oil mixture can form a sludge that can pass from the tank into other components of the air brake system, damaging seals and causing brake valves to stick. 2) The mixture of moisture and oil can become corrosive and damage the air tank and other system components. 3) Moisture in the brake system can freeze in cold temperatures and may cause brake failure. 4) Too much moisture and oil collecting in the air tanks can reduce the volume of air and may cause brake failure.

Foundation Brakes

Importance: function and appearance of the various types of foundation brake assemblies, and be able to inspect the components for safety defects. The brake-assembly components at the wheels of a vehicle are generally called the foundation components because they form the basis on which the rest of the system is built.

Measuring length of pushrod stroke?

In the most common brake designs, some of the brake linkage — the components linking the brake chamber to the brake assembly — is exposed. As a result, the length of pushrod stroke can be measured and compared to the prescribed adjustment limits for that size, type and style of brake chamber.

Vehicle Speed and Weight

Increasing how much weight your vehicle carries or how fast you drive increases the demand on your brake system. As it increases, the brakes must do more work. In an air brake system, this means greater brake application pressure will be needed to meet the higher demand. To achieve this, you must press the brake pedal farther.

Air Brake System

Large commercial vehicles as they can develop and transmit high mechanical forces over great distances using simple components and connections. - Uses *compressed air*, which is stored in tanks, to produce the force that applies the brakes at each wheel

Slack adjuster (Pushrod and a lever)

Link the brake chamber to the brake assembly (which contains the brake drum or disc). - When you press the brake pedal, the pushrod extends farther from the brake chamber, moving the slack adjuster forward. - The motion of the slack adjuster transfers to the brake assembly, *causing the brake shoes or pads to make contact with the brake drum or disc.*

Appearance of "S" cam brakes

Located in the wheel - Characteristic of the "S" cam brake design is the exposed pushrod. This allows easy access to the brake linkage to check adjustment. - The components within the wheel are difficult to see, particularly when a dust shield or backing plate is used to protect the components.

Air pressure gauge

Located on the vehicle's instrument panel, the air pressure gauges let you know how much air pressure is in the air brake system to ensure the system is operating normally. - Air pressure gauges indicate air pressure in the vehicle's dual service (primary and secondary) air tanks.

Air brake system pressure should never be lower/ higher than?

Lower than 100 psi (690 kPa) - Cut in pressure Higher than 145 psi (1000 kPa) - Cut out pressure

Hydraulic Brake System

Main braking system for almost all passenger vehicles and light trucks. - Uses *brake fluid* to transmit force when the brakes are applied. - Since brake fluid cannot be compressed, force is transmitted *immediately and directly at each wheel when you press the brake pedal.*

"S' cam brakes

Most common type with air brakes systems - Drum brake that uses air brake chambers and lkinkage to press the brakes shoes against the surface of the brake drum. - The stroke of the air brake chamber pushrod acts on the slack adjuster attached to the end of the camshaft. - Pushrod stroke causes the camshaft to rotate. - The "S" shape on one end of the camshaft forces the brake shoes apart and against the brake drum.

Safety Valve

Prevent over pressure of the system If the governor fails to signal the compressor to cut out and too much pressure builds up, the safety valves will open to allow the excess air pressure to escape. Safety valves normally open at 150 psi (1035 kPa). - Important: A safety valve that is venting air means there is too much pressure building in the system, requiring immediate repair.

Air Compressor

Produces air for the brake system Draws in air at normal pressure and forces it into a much smaller space, causing the pressure of the air to increase. Powered by the vehicle's engine or by using belts and pulleys, a form of stored energy. - Air compressors are mounted directly on the engine or by brackets and fasteners.

Air Dryer

Reduce the amount of moisture that passes into the air brake system - Located between the air compressor and supply tank - An air dryer removes moisture from the air brake system and expels it when the compressor reaches cut-out pressure.

Alcohol Evaporator

Reduces the risk of freezing water in air tanks - An alcohol evaporator adds alcohol vapour to the air brake system to help prevent moisture in the system from freezing.

Air brake chambers

Round metal containers, located at each wheel, where compressed air is converted into mechanical force to apply the brakes and stop the vehicle 1) Service brake chambers 2) Spring brake chambers

Factors for Brakes while driving

Speed and Weight of vehicle brake adjustment anti-lock braking system

Spring System Brake Chamber

Spring brakes use a different type of brake chamber from service brakes. - *Include both service brake and spring brakes* - Spring brake chambers apply the brakes by means of a large coil spring that provides enough force to hold the brakes in the applied position, instead of using air to apply the brakes.

Pushrod stroke

The action of the pushrod extending from the brake chamber - Stroke length is the distance that the pushrod travels out of the chamber. The pushrod stroke is dependent on the pressure of the compressed air that enters the brake chamber. For example, when application pressure increases from 10 psi (69 kPa) to 80 psi (552 kPa), the stroke increases noticeably.

Pushrod Stroke Limit (stroke-length capacity)

The brake linkage includes a device to adjust the position of the brake chamber in relation to the position of the brake shoes. As brakes wear, the linkage must be re-adjusted to ensure the pushrod stroke is always within its normal operating range. This type of brake re-adjustment is required at regular intervals. Since the drop in brake force can be significant when stroke exceeds the adjustment limits of a brake chamber, it is critical that brakes are correctly adjusted to ensure the function is retained. *Each brake-chamber style, type and size has a specific pushrod stroke-adjustment limit.

Stopping a moving vehicle

The brake shoes or pads exert pressure on the brake drums or rotors. The resulting heat produces heat that is absorbed and dissipated by the brakes and components. Too much heat can rest in brake fade, brake failure or even tire fire.

Supply / Wet Tank

The first tank that the compressed air enters is called the supply tank. Since it collects most of the moisture and oil that drops out of the air, it is also called a "wet" tank.

How is the normal range of an air brake system determined

The points where the air compressor is turned on (cut-in pressure) and turned off (cut-out pressure).

Brake Drums Overheating

They expand to the point where they may not even contact the shoe. When brakes overheat due to overuse or improper adjustment, it is advisable to *stop and allows them to cool before proceeding.* While stopped, the driver should check all the brakes and their current adjustments. Normal: 240-260 C Hot: 420-440 C Danger: 1100 C

Governor

To *prevent the compressor from producing too much compressed air and to reduce the load on the engine*, a governor is used in the air brake system. - When air pressure is high enough in the system, the *governor* causes the compressor to stop pumping air (cut-out). - When the air pressure drops to a certain point, the governor will cause the compressor to start pumping air again (cut-in).

Spring Brake operation

To accommodate the large coil spring, a section must be added to the service brake chamber that is clearly visible and adds significantly to its size. - The spring brake section is "piggy-backed" onto the service brake section and these two sections function as two separate chambers. - The portion nearest the pushrod end is the service brake section and it works in the same manner as a separately mounted service brake chamber. - The large coil spring inside a spring brake chamber is under high tension and can be hazardous.

Dual-service tanks (primary/secondary)

When air leaves the supply tank, it splits into two circuits, passing into primary and secondary air tanks called dual-service tanks. - Also called dry tanks/ collect less moisture - If one fails, the other circuit can provide enough brake function to stop the vehicle - The two circuits are referred to as the primary circuit and the secondary circuit.

Brakes adjusted correctly

When brake chamber pushrod stroke exceeds the adjustment limit, braking ability can be reduced so much that the brakes may not stop or hold the vehicle. Brakes must be kept properly adjusted to ensure each chamber pushrod stroke is within its adjustment limit. Remember: Proper brake adjustment ensures that the brake chamber always produces the necessary force. When a brake is out of adjustment — when pushrod stroke exceeds the adjustment limit — braking ability is reduced.

Air Brake inspection

When conducting an inspection, make sure the vehicle is parked on a level surface, in a secure manner and in a safe location. - Wheel chocks or blocks should be used to prevent vehicle movement during an inspection. - During an inspection, drivers must be cautious of moving vehicle parts and compressed air exhausting from the vehicle.

Air brake chambers inspection

When inspecting the air brake chambers, the driver must check for audible air leaks, cracks and non-manufactured holes. When inspecting the brake chambers on each side of a steering axle, the driver must check for mismatched slack adjusters and air brake chamber size.

Air Brake System cont

When you press the brake pedal, *compressed air must travel from one part of the system to another.* Special valves make sure that the air moves through the system as quickly as possible; however,* there is a split-second delay in brake reaction from the moment you apply or release the brake pedal* This split-second delay in brake reaction occurs in all air brake systems.

What is air pressure measured in?

kiloPascals (kPa) Pounds per square inch (psi)

Disc Brakes cont

uses both external and internal components, but there are fewer involved. All disc air brakes use callipers and rotors. - The brake rotor is only partially visible because the wheel, calliper and dust shields usually cover parts of it. - Disc brake designs use brake chambers that may have exposed linkage and a slack adjuster. - Brake chamber pushrod stroke presses the brake pads against the rotor. - rotors, calipers, brake pads, slack adjusters and brake chambers.

External Parts of ""S" cam brakes

• Brake chamber and mounting brackets. • Slack adjuster. • Pushrod. • The shaft portion of the "S" camshaft .• Support brackets and bushings for the camshaft. • Dust shields or backing plates. • Brake drums.