Module 11 AIR BRAKES Purpose Hydraulic vs air

Module 11 AIR BRAKES

Purpose Hydraulic vs. air brakes Air brake system functions Use air brake system safely Single and combination units Couple and uncouple How to monitor Test the system

To operate a vehicle with Air Brakes “A” endorsement Written Practical

How do Brakes Stop a Vehicle Heat Friction Momentum

How do Brakes Stop a Vehicle Driver Perception/Reaction Brake Lag Stopping/Braking Distance

Stopping Trucks Verses Cars Large vehicles take longer to stop than small passenger vehicles. Need more space and time to accomplish manoeuvres in larger vehicles. Mastering the relationship between speed and braking requirements is how to have a successful driving career.

Stopping Trucks Verses Cars If you double the weight? If you double the speed? If you double both weight and speed?

How Power is Obtained Mechanically Leverage Fulcrum Use of Air Compressed PSI

Leverage and Air Pressure Diaphragm

Review How is heat generated by the brakes dissipated?

Review - Answer Passed off into the atmosphere

Review If the weight of the vehicle is doubled, how many times must the stopping power be increased?

Review - Answer 2 Times

Review If the vehicle speed is doubled how many times must the stopping power be increased?

Review - Answer 4 Times

Review If the vehicle speed and weight is doubled how many times must the stopping power be increased?

Review - Answer 8 Times

Why Air Brakes? Air brakes provide several advantages: Generates greater power. Tolerant to small leaks. Pump more air pressure. Easier coupling of multiple combinations.

Air Brake Components Compressor Reservoirs Foot Valve Brake Chambers Brake Shoes and Drums

Air Compressor The function of the air compressor is to build up and maintain air pressure. Air compressors are either gear driven or belt driven. All compressors run continuously while the engine is running, but air compression is controlled and limited by a governor which “loads” or “unloads” the compressor. Traditional standard for measuring pressure has been pounds per square inch (PSI).

Air Compressor Conversions are outlined below: 1 PSI = 6. 895 k. Pa 1 PSI = 0. 0689 bar 1 k. Pa = 0. 01 bar 1 k. Pa = 0. 145 PSI 1 atmosphere = 14. 5 PSI 1 bar= 1 atmosphere = 100 k. Pa 1 bar = 14. 5 PSI 1 atmosphere = 1 bar = 100 k. Pa

Reservoirs are pressure-rated tanks that hold a supply of compressed air until required for braking or operating auxiliary air systems. Maximum air pressure available for brake applications depends on how much air is in the reservoir. A driver is not able to make a higher pressure brake application than the amount of air pressure in the reservoir. Each reservoir is equipped with a draincock valve that when fully open, the draincock allows reservoirs to be drained of moisture and other contaminants that build up in the system.

Reservoirs All reservoirs must be completely drained once a day.

Foot Valve Foot valve or Treadle valve Applies air to operate the brakes. How it works The amount of air delivered to the brakes is regulated by the driver. Styles you may see Made in overhead styles with a foot pedal hanging down, or a floor-mounted version with a foot treadle.

Brake Chambers Brake chambers or brake pots Convert compressed air pressure energy into a mechanical force and movement, which apply the vehicles brakes. Disc brakes (rotors and pads) Disc brakes can be either nonadjustable sealed units or adjustable.

Brake Shoes and Drums S-Cam Is rotated so the high points have acted against the cam rollers and forced the brake shoes against the drum. Drum thickness Determines the amount of heat that can be absorbed and dissipated to the atmosphere. Wear and malfunctions Thin or distorted drums, weak return springs, improper linings, poor adjustment, grease or dirt on the lining. Will all result in erratic, unpredictable and potentially dangerous brake performance.

Why Learn about Air Brakes? What jurisdictions require air endorsements? Who is responsible for the performance of their air brake system?

Why Learn about Air Brakes? Every jurisdiction in Canada, except Nunavut, requires drivers of air brake equipped vehicles to have an air brake endorsement. Air brakes are different, the pedals feel different and the vehicles reaction is different. There are more gauges and controls and they require more driver involvement to make sure the system is operating properly and safely.

Why Learn about Air Brakes? Who is responsible for the performance of their Air brake system? Drivers are ALWAYS responsible for the performance of their brake systems. They must understand how the brake system works. Perform effective vehicle inspections. Ensure the brakes are correctly adjusted. Use the brakes properly. Know how the vehicle reacts during various circuit failures.

System Operation Air is pumped by the compressor to the reservoir. Air pressure reaches 120 psi to 145 psi the governor places the compressor into its unloaded stage. At this stage the air system is fully charged. When the brakes are applied, air is delivered through the foot valve to the service-brake chambers against each service-brake diaphragm causing the push rod to move the slack adjuster.

System Operation The slack adjuster rotates the brake cam, which forces the shoes against the brake drum. When the driver releases the foot valve, air in the brake chambers is exhausted through the foot valve, which releases the brakes. When reservoir air pressure drops, the governor puts the compressor back into the pumping stage to keep adequate air pressure available for future brake applications.

System Operation

Air Tanks Supply reservoir or wet tank The reservoir closest to the compressor Service reservoir The second reservoir - air is drawn from this reservoir to operate the brakes. Service tank The supply tank will receive the air from the compressor and distribute it

Air Tanks Drain Valves or lanyard Available under all air pressure tanks. Can be opened with a manual tap or with a lanyard pull cable. How and when to drain them Lanyard should be pulled often during the day, during pre-trips, on-route inspections, and fueling. If moisture is accumulating, drain the tanks completely at the end of the shift. Tanks do not drain properly until after the air pressure is depleted and the contamination settles down and starts to drip from the tank.

Safety Valve The safety valve protects the supply reservoir from being over-pressurized and bursting. This valve is set at 150 psi and will blow off excess pressure. If the safety valve blows off excess pressure, this indicates a problem with the governor.

Safety Valve Safety valves are located in the supply circuit so components downstream are protected. Some are external. Some have the pressure spring and seat in the tank. Most air brake equipped vehicles have safety valves in both the air dryer and the supply tank.

Air Dryers Air dryers remove contamination from the air pressure being delivered by the compressor. Modern dryers use desiccant which adsorbs moisture as it passes by. Air Dryer Integrated System (AD-IS) The air dryer integrates system combines the governor, air dryer, safety valve and supply tank into one system. Inline Alcohol Injector Methyl-alcohol with a lubricant added to prevent rubber components in the valves from drying out.

Service Circuits The service circuits components include: Air tank protected by a check valve. Air pressure gauge and low air pressure warning device. Brake chambers, control valve and quick release or service relay valves. Power units have two service circuits; One for the steering axle, and one for the drive axles. Each trailer axle group will have its own independent service circuit.

Service Circuits The service tank holds the pressurized air used for service brake applications. The air tank stores air pressure for the simplified service circuit and is sized according to the air volume required for the brake chambers. The tanks are hydrostatically tested to handle at least five times the compressor cut-out pressure or 500 PSI (3, 448 k. Pa) whichever is greater. Air tank volume capacity must be capable of providing for a minimum of 12 full service brake applications for power units and 8 full service applications for trailers.

One-way Check Valve In case the air compressor fails or a leak develops in the supply reservoir, a one-way check valve is installed between the supply and service reservoirs to keep the air from bleeding back. The valve is spring loaded. Air passes through the valve when pressure at the outlet becomes greater than at the inlet. The one-way check valve seals, preventing air from flowing back through the valve.

One-way Check Valve Check valves protect the service tanks from air supply failure. Every service tank on every axle group is equipped with one. Is it different in air dryer integrated systems? AD-IS (Air Dryer Integrated Solution) systems use pressure protection valves built into the AD-IS module.

Air Pressure Gauge The pressure gauges’ measure air pressure in the two tractor service tanks Low pressure warning device Warns of a low air pressure and applies at a minimum of 60 psi (414 k. Pa). The Commercial Vehicle Safety Alliance (CVSA) out-of-service standard is a minimum of 55 PSI (310 k. Pa) or half of the governor cut-out pressure, whichever is less.

Brake Chambers Brake chambers convert air pressure into mechanical force. The two factors that affect this air-to-mechanical- force conversion are the brake chamber size and air pressure applied by the driver. Air pressure is a measurement of force over a surface area. Brake chambers are sized by the Original Equipment Manufacturer (OEM), but air pressure is controlled by the driver. Long stroke chambers have more total stroke before the push plate bottoms in the chamber.

Control Valve Control valves manage the air pressure flow from the tank through to the chambers. All control valves work the same regardless of how they are activated. Activation can occur by a linkage from the drivers’ foot or hand, by air or electric signal. Control valves manage pressure flow with the help of two internal valves: an inlet valve and an exhaust valve. When the brake is released, the inlet is closed, holding the air in the tank and the exhaust open. This leaves the chambers open. When the control valve is in the hold/balance position, both the inlet and exhaust are closed.

Quick Release Valve Allows a more rapid exhaust of air from the brake chambers when the brakes are released. The valve is mounted under the front cross member area or incorporated into the ABS system. Brakes apply normally through the foot valve. When the brake application is released, air pressure in the brake chambers exhausts through the quick release valve allowing the brakes to release more rapidly.

Relay Valve A relay valve is installed near the rear brake chambers to minimize brake lag. Crack pressure is the amount of control air pressure from the foot valve that must be initially delivered to the top of the relay before the valve starts to open to deliver air pressure from the service tank to the brake chambers. Service line booster relays are often found on converters. When service brakes are released, the air pressure in the chambers exhausts directly from under the relay and the smaller volume in the longer control line exhausts back out of the foot valve.

Bobtail Proportioning Relay Valve Some truck tractors are equipped with a bobtail proportioning relay valve, which is a combination of two individual valves in a single housing. During bobtail operation, this valve reduces stopping distances and gives the driver greater control over the vehicle. The driver will note that the brake pedal will have to be pushed farther to apply sufficient air to stop.

Review The Safety Valve is pre-set at ___ PSI and will blow off excess pressure. This indicates a problem with what?

Review - Answer 150 PSI The Governor

Review What is the function of the quick release valve?

Review - Answer Rapidly exhaust air from the controlled device

Review How is brake lag reduced?

Review - Answer Relay Valve

Brake Circuits Independent service systems apply in a straight truck. Primary (green) is for the drive axle(s) and secondary (red) for the steering axle.

Brake Circuits Cont.

Park Brake Circuit The park component rides on the back of the service chamber to apply the regular foundation brake components with mechanical force rather than air pressure. A spring mechanically applies the park brake. Air pressure from the service tank is used to release the park brake this begins to release the brake drag at 60 psi (414 k. Pa).

Park Brake Circuit Low 80 psi (550 k. Pa) to completely release the brake. This becomes important when adjusting the brakes. Spring brakes are dangerous. Springs released from chambers can lead to serious injury or death.

Park Brake Control Valve Controls air pressure to the park brakes. Air pressure is released when the valve is pulled. The park control valve (yellow button) is the driver’s control for the park circuit.

Park Brake Control Valve When air pressure drops off, the spring under the spool overcomes the air pressure holding the spool in and pops the spool and button out. This typically happens between 20 - 45 PSI (138 - 310 k. Pa). A vehicle must be placed out-ofservice if the park control does not default back to the park position when the air pressure is depleted.

Air Pressure Failure Application 82 - 84 PSI The park springs begin to expand. 55 - 60 PSI The brake lining starts to drag on the drums. 45 - 50 PSI The park springs are applied firmly. Spring park brakes begin to apply if system air pressure drops below 60 psi (414 k. Pa). Provides minimum reaction time and can reduce vehicle control.

Air Pressure Failure Application Control Valve Allows air pressure to flow to the pressure plate of the park diaphragm. It compresses the park spring to release the spring park brakes. Foot Valve Service brake applied with the foot valve use the service circuit and functions independently of the park circuit to provide normal braking. The park brake would remain released.

Manually Releasing the park spring Spring brakes can be manually released (caged) with a release bolt. Found in a side pocket on the chamber. Caging bolts (release tools) are used to pull the park spring off the application so the vehicle can be towed or repaired. NEVER TAKE THE PARK CHAMBER APART!

Caging the Park Brake Vehicles with no air pressure and caged park springs will have no service or park brakes. Ensure chock blocks are used Caging park springs is used for towing and repairs Do not operate vehicles with reduced braking capabilities.

Dual Air Supply Air pressure for the park circuit is delivered from the higher pressure Primary or secondary tank. Keeps the spring park brake released. Allows the driver to make a safe and controlled stop.

Trailer Air Brake Circuits Service and park brakes Air tank, relay valve and brake chambers

Glad Hand Couplers

Glad Hand Couplers Supply or emergency line

Glad Hand Couplers Service/control line

Trailer Air Supply Valve Tractor’s protection system If it does not work properly, the vehicle will be placed out-ofservice. Component #1 - the trailer supply valve Controls the supply line Component #2 - the tractor protection valve. Opens the service line

Trailer Air Supply Valve Red button Supply air pressure to the trailer Button will pop out at 20 psi or greater Yellow button This is the master button pulling it will also pop out the trailer supply valve (red button) will activate all the vehicle’s spring park brakes.

Foot Valve Application Applies the tractor and trailer brakes. Supplied by primary and secondary circuits. Trailer service application will occur should a primary or secondary circuit fail.

Trailer Control Valve Hand valve controls only the trailer service brakes Not to be used for parking This system is still used on most converter dollies and on some specialized equipment for heavy hauling. 1976 – CMVSS - requires spring park brakes on trailers. The trailer’s air system communications are the same as modern spring brake trailers

Park/Emergency Circuit When air to trailer is disconnected Emergency relay opens Very powerful emergency brake Increased risk of brake lockup The problem with air pressure park brakes They do not stay on Different operating procedures Trailers must be chocked Trailers must be charged with air pressure and the trailer service or park brakes applied before coupling.

Supply Circuit Failures Causes Plugged or collapsed line to a ruptured supply tank Recognized by the air pressure gauges What will happen? All brakes will work properly Limited by the amount of air pressure available in the service

Primary Service Circuit Failure Tractor spring park brake valve Failure occurs in the primary circuit Remain released with air pressure from the secondary circuit Service application will apply the steering axle and trailer brakes Sometimes called an inversion valve

Primary Service Circuit Failure What does it do? Will release a controlled amount of air pressure Park brake springs to apply the drive axle foundation brakes in a controlled manner. What should I do? A steady brake application

Secondary Service Circuit Failure What does it do? Park brakes remain released with air pressure from the primary circuit. The steering axle brakes will not apply What should I do? Hold a steady application to apply the brakes normally.

Park/Emergency Circuit Failure Causes both service circuits to lose air pressure Park brake applications are only half as strong as a full service application

Trailer Service Line Failure Dangers of this Braking distances will be dramatically increased. Continually down shift What to do? What can happen?

Trailer Supply Line Failure Control of the trailer Emergency line ruptures Tractor’s protection system should activate Proper air line security VERY important during coupling, pretrip and en-route Dangers

Crossed Trailer Air Lines Polarized Cannot be reversed How to know if they are reversed? Will not release spring brake What can happen if they are? There will be no service or park

Trailer Air Tank Failure How to recognize it What will happen What to do

Emergency Braking Monitor pressure gauges Avoid jackknifing Hold steady

Foundation Brakes Mechanical components at the axle ends If they aren’t working Will not be able to stop the vehicle

S-Cam Drum Brake Converted Type 20 Brake Type 30 Brake

S-Cam Brake Shaft

Slack Adjuster Converts push rod force Self Adjusters 5 -7 Inch

Brake Linings ¼ inch (7 mm) minimum thickness Must be replaced

Brake Drums Dissipates heat Condition is critical Correct and incorrect adjustments Dangers and procedures for being under the truck

Free Stroke Method ½ inch (13 mm) ¾ inch (19 mm) 2 inch (50. 8 mm) reserved Common cause of brake loss

Automatic or Self-Adjusting Slack Adjusters Maintain the brakes Must be checked daily Up to 12 applications at 100 psi

Manual Slack Adjuster Check-preferred method

Brake Adjustment Preferred method Raise the wheel to be adjusted off the ground so it rotates freely. Turn the slack adjustment mechanism until the wheel stops. Back off the adjustment until the wheel turns freely. This would be about one-quarter to one-half of a turn. Check push rod travel after

Brake Adjustment Alternate method Adjust the slack mechanism so there is 3/4 in. (19 mm) or less push rod travel when manually (by hand) extended to place the shoes in contact with the drum. Check for brake contact by gently striking the brake drum with a metal hammer A dull sound indicates brake drag and that re-adjustment is required until drag is eliminated. Check push rod travel after adjustment

Service Tests

Adjusting Manual Slack Adjusters

Adjusting Manual Slack Cont.

Automatic Slack Adjusters Installed on all trucks, tractors, trailers and busses since 1996. Are designed to continuously and automatically maintain the brakes in proper adjustment. Checked Daily. May take up to 12 brake applications of 100 psi to adjust them. When to take to a mechanic.

Disk Brakes How they work How to inspect them Adjustments and Repairs

How to Brake Safely Controlled When to ease off and why Safe speed and following distance

Tractor Bobtailing What are the dangers Less traction Loss of vehicle stability How to safely operate a bobtail tractor Avoid excessive acceleration and heavy brake applications. Reduce vehicle speed. Avoid using auxiliary retarders at their powerful settings. Leave an appropriate following distance. Use more caution when bobtailing.

Auxiliary Retarders What do they do? Different types? Hydraulic vs electric? When to use them? When not to use them?

Review Most brake linings operate best around what temperature? And should not exceed what temperature?

Review - Answer 250 C 425 C

Review What is the basic principle of the dual-circuit system?

Review - Answer Prevents total brake failure

Review What is meant by compounding the brakes?

Review - Answer Making a service brake application when the parking brake is applied

Review How many psi is required when making a brake application to adjust the automatic slack adjusters?

Review - Answer 100 psi

Review When should you manually release (cage) a spring park brake?

Review - Answer Being towed and repairs

Travelling on Down Grades Mountain grades Rural areas Urban areas Unfamiliar areas If speed increases

Runaway Lanes What are they? When to use them? What to remember?

Water on Roadways What are the dangers? How to adjust your driving? How to reduce water entering drums and shoes?

Combination Unit Braking Challenges Load distribution Trailer slide and swing

Brake Management Systems How to use them? When to service them? How do they help?

Antilock Brake Systems (ABS) ABS have been mandatory on all air brake trucks, buses, and trailers since April 1, 2000 What it does? Prevents wheel lockup and skids caused by over-braking and travelling too fast How to use them properly Apply firm, steady pressure to the brake pedal. How to tell if the trailer has ABS? ABS warning light located at the rear of the left side

Automatic Traction Control Variation of ABS Automatic traction control (ATC) Reduces driveline power Additional warning light When to repair

Stability Control Systems More advanced. Monitor rollover and yaw (jackknife). Greater ability to handle the multiple, programmed situations. Takes over if the vehicle does not react correctly. Requires vehicle inspections to ensure system is in safe operating