Air Brake Manual

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Google Translate is a third-party tool, and is not owned or administered by SGI. SGI is not responsible for any errors or omissions as a result of the translation. In case of a difference in interpretation between the translated version and the laws and regulations governing Saskatchewan drivers and vehicles, the laws and regulations prevail.
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Section 2 summary

  1. The final factor that moves a vehicle is the amount of traction its tires have on the road surface.
  2. The final factor that stops a vehicle is the traction between tires and road surface.
  3. Heat generated is dissipated through the brake drums.
  4. If one or two wheels had brakes that were not properly adjusted, the other wheels would have to do more than their share of the braking, and that might be more than their brakes were constructed to stand. Excessive use of the brakes would then result in a build-up of heat greater than the brake drums could absorb and dissipate. Too much heat would result in brake damage and possible failure.
  5. Friction is the force which resists movement between two surfaces in contact with each other. To stop a vehicle, brake shoe linings are forced against the machined surfaces of the brake drums, creating friction. This friction produces heat.
  6. If weight is doubled, stopping power must be doubled to stop in the same distance.
  7. If speed is doubled, stopping power must be increased four times to stop in the same distance.
  8. When weight and speed are both doubled, stopping power must be increased eight times to stop in the same distance.
  9. Air that is compressed into a much smaller space than it normally occupies.
  10. PSI stands for “Pounds per square inch”.
  11. The total force exerted on the diaphragm would be 1,200 lbs. (40 x 30)
  12. Reaction Time: The time it takes from the moment a hazard is recognized to the time the brake pedal is applied, approximately 3/4 of a second to 1 1/2 seconds.

    Brake Lag: The time air takes to travel through a properly maintained air brake system, about 4/10 of a second.

    Braking Distance: The actual distance a vehicle travels after the brake is applied until the vehicle stops. This distance depends on the ability of the lining to produce friction, the brake drums to dissipate heat and the tires to grip the road.

    Stopping Distance: Stopping distance consists of three factors: Driver’s reaction time + Brake lag + Braking distance.

Section 3 and 4 summary

  1. An air pressure gauge is installed in the dash (plumbed in after the service reservoir) so you will know the amount of air pressure available for braking.
  2. If the low air warning system activates, you must stop and determine the cause.
  3. The purpose of a quick-release valve is to allow faster release of the brakes.
  4. The purpose of a relay valve is to provide faster application pressure to the brake chambers reducing lag time.
  5. The reservoir is protected from being over-pressurized by a safety valve.
  6. The low-pressure warning device activates when air pressure drops below 60psi (414 kPa).
  7. Brake lag to the rear wheels is minimized through a relay valve installed near the rear brake chambers.

Section 5 summary

  1. The basic principle is if there is an air loss in either circuit, the other circuit will continue to operate independently to prevent total brake failure.
  2. The valve used to protect the primary circuit from the secondary circuit is a two-way check valve.
  3. Yes. If there is an air loss in either circuit, the other circuit will continue to operate independently. Unless air is lost in both circuits, the vehicle will continue to have braking ability.
  4. Compounding the brakes happens when a service brake application is made with the park brake still applied. This can result in damaged brake components and possibly brake failure.
  5. Because they are held on by spring pressure and require no air.
  6. Parking brakes are held in the released position with air pressure of 70 psi or greater.
  7. To prevent compounding of the brakes.
  8. Parking-brakes are under extreme pressure, disassembling may result in serious injury. All discarded spring-brake chambers must be disassembled and disposed of by a trained professional.
  9. Two functions of the spring brakes are a service brake and emergency/parking brake.
  10. If a failure occurs in the primary circuit and a brake application is made, control air from the secondary side of the foot valve is directed to a spring-brake modulator.
  11. Blended air is taken from the primary and secondary circuits through a two-way check valve.

Section 6 summary

  1. The two-way check valve allows control of the trailer brake by use of the hand valve or foot valve. This valve will permit air to flow from the source that is supplying the higher application pressure.
  2. Gladhands should be protected to prevent water and dirt from entering the couplers and lines.
  3. The trailer brakes are controlled independently with the hand valve.
  4. 1. Closing supply valve on the tractor.

    2. Disconnecting the supply line between the tractor and trailer with the supply valve in the open position.
  5. No, trailer brakes must not be used to hold a parked vehicle that is left unattended. Loss of pressure may result in loss of brakes.
  6. To prevent air loss from the tractor when not hooked to a trailer or if a trailer breaks away.
  7. 1. It controls the tractor protection valve. The tractor protection valve will not operate if the trailer-supply valve is closed.

    2. It serves as a link between the tractor and the trailer parking-brake systems by supplying air to the trailer reservoirs, through the supply line.
  8. 1. The relay part of the valve relays air from the trailer reservoir to the trailer-brake chambers during a brake application. This part of the valve operates like the relay valve previously discussed. It also provides a quick release of the trailer brakes.

    2. The emergency part of the valve directs trailer reservoir pressure to the trailer brakes causing an emergency application sometimes referred to as dynamiting. This action occurs automatically in the event of a ruptured or parted supply line between tractor and trailer, or loss of air from the main reservoir system. The driver may operate the cab- mounted trailer-supply valve to cause an emergency application of the trailer brakes.

    3. The relay emergency valve has a one-way check valve that stops air in the reservoir from going back to the source of the supply. The driver has opened the trailer-supply valve to allow main-reservoir air pressure to be directed through the tractor protection valve to the trailer. Air pressure passes through the relay emergency valve to the trailer reservoir. Pressure builds up in the trailer reservoir to the same pressure as the main reservoirs on the tractor. This is known as charging the trailer system. The trailer-supply valve remains in the open position when pressure has built up to between 20 and 60 psi (138 and 413 kPa), depending on the make.
  9. The supply line (also called the emergency line) carries air to fill the trailers tanks.
  10. The service line carries air controlled by the foot brake or the hand brake.
  11. Rupture of the supply line (or an uncoupling of the supply line gladhands) results in a pressure drop in the supply line between the trailer-supply valve and relay emergency valve. This triggers the emergency action of the relay emergency valve, placing the trailer brakes into emergency application.
  12. If the service line is ruptured or disconnected, no action will take place until a brake application is made.
  13. Application air is directed to the control line through the tractor protection valve. Rupture of the service line will result in the escape of air pressure, if the brake application is held long enough to cause enough loss of pressure in the tractor system. This pressure drop causes the tractor protection system to close off, exhausting the supply line to the trailer. This will cause the trailer brakes to go into an emergency application.
  14. Yes. The two-way check valve allows control of the trailer brake by use of the hand valve or foot valve. This valve will permit air to flow from the source that is supplying the higher application pressure. Two-way check valves can permit a higher brake application to the trailer than the truck.

Section 7 summary

  1. Less than 2 minutes from 85 to 100 psi running the engine between 600 and 800 rpm.
  2. Single unit: maximum air loss after initial application must not exceed one psi in one minute.

    Combination unit: maximum air loss after initial application is four psi (28 kPa) in one minute.
  3. With trailer emergency brakes applied and truck park brakes released, try to gently pull ahead to test emergency application of trailer brakes.
  4. Yes. All drivers should be trained to make brake adjustments. The driver must be always aware of the condition of the vehicle’s braking system. You should be able to notice any defects developing in the braking system and be aware that service or adjustments are required. The extent of the driver’s responsibility to make repairs will depend on factors such as the maintenance policy of the company and the driver’s mechanical experience.
  5. Move the vehicle slowly ahead and make foot-brake application.
  6. Manual slack adjuster: 1/2 in. (12.7mm) to 3/4 in. (19mm) of push rod travel when manually (by hand) extended to place the shoes in contact with the drum.

    Automatic slack adjuster: Less than one inch (25.4 mm) when manually pulled and less than two inches (50.8 mm) when the brake is applied.

Air brake manual summary

  1. 1. Compressor

    2. Reservoirs

    3. Foot Valve

    4. Brake Chambers

    5. Brake shoes and drums or brake rotors and pads
  2. The 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 there is air pressure in the reservoir.
  3. The most common cause of loss of braking is poor brake adjustment.
  4. The reservoirs still need to be drained daily when in use.
  5. A driver must stop the vehicle and determine the cause.
  6. 100 psi
  7. If a safety valve blows off excess pressure, this indicates a problem with the governor.
  8. The purpose of a relay valve is to provide faster application pressure to the brake chambers reducing lag time.
  9. Spring brakes are held in the released position with air pressure of 70 psi or greater.
  10. Parking brake.
  11. Slack adjusters are used to (manually or automatically) maintain proper brake chamber stroke and lining-to-drum clearance during normal operation.
  12. To avoid compounding of the brakes.
  13. 4 psi in 1 minute for combination units

    1 psi in 1 minute for single units
  14. Drum thickness determines the amount of heat that can be absorbed and dissipated.
  15. Move slowly ahead and make foot-brake application.

Disclaimer

Google Translate is a third-party tool, and is not owned or administered by SGI. SGI is not responsible for any errors or omissions as a result of the translation. In case of a difference in interpretation between the translated version and the laws and regulations governing Saskatchewan drivers and vehicles, the laws and regulations prevail. 
Rev: 2024