Air Brake Manual


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Glossary

  • Air brakes - A braking system where the brakes are applied by air pressure.
  • Air over hydraulic brakes - A braking system where the brakes are applied hydraulically but application is made by air pressure.
  • Air dryer - A filter that removes most liquid and water vapour from the air before it reaches the reservoirs.
  • Air pressure gauge - A dash-mounted gauge telling the driver how much air pressure is in the primary and secondary reservoirs
  • Application pressure gauge - A dash-mounted gauge which tells the driver the amount of air pressure being delivered when brakes are applied.
  • Blended air - Air taken from the primary and secondary circuits.
  • Brake fade - Loss of braking efficiency due to overheating the brakes.
  • Brake lag - The time required for air to flow through the system when brakes are applied.
  • Brake pads - Steel plates with lining which squeeze against the rotor (disc).
  • Brake pots - A term sometimes used to describe the brake chambers
  • Brake drums - Large cast-iron drums located behind each wheel on vehicles equipped with drum brakes. The brake shoes are forced against them when the brakes are applied creating friction which stops the vehicle. Brake drums also dissipate heat.
  • Brake rotor - A steel disc located behind each wheel on vehicles equipped with disc brakes. The pads squeeze against it when the brakes are applied.
  • Brake shoes - Curved steel plates with an outer lining which press against the brake drums when the brakes are applied.
  • Breakaway - When the trailer becomes disconnected from the tractor.
  • Caging - The manual release of the spring brake chamber using the wind-off bolt.
  • Compounding - Making a service brake application when the parking brake is applied.
  • Compressor - A pump operated from the engine which builds and maintains air pressure.
  • Cut-in - The point at which the governor allows the compressor to resume pumping.
  • Cut-out - The point at which the pressure in the system has reached maximum capacity and the governor stops the compressor from pumping.
  • Diaphragm - A heavy rubber partition in the brake chamber which activates the brakes when air is forced against it.
  • Draincocks - Drain valves mounted on each reservoir so they can be drained of moisture and other contaminants.
  • Dynamiting - A slang term for an emergency application of the brakes due to sudden air loss.
  • Emergency line - A term sometimes used to describe the supply line.
  • Firewall - The metal panel between the cab and the engine compartment.
  • Foot valve - A foot operated valve used to apply the brakes.
  • Front axle ratio valve - A valve which reduces application pressure to the front brakes.
  • Fulcrum - The point or support on which a lever pivots.
  • Glad hands - The coupling devices used to connect the air lines from the tractor to the trailer.
  • Hand valve - A hand-operated valve which applies only the trailer brakes.
  • Loading - A term used to describe cut-in.
  • Low warning device - A light, buzzer or wig-wag which warns the driver of low air pressure.
  • Low warning switch - A switch which activates the low warning device.
  • Parking brake valve - A yellow diamond-shaped valve mounted on the dash which activates the parking brakes.
  • Piggyback - A term sometimes used to describe the spring brake chamber.
  • Pop-off valve - A term sometimes used to describe the safety valve.
  • Primary reservoir - A tank that normally supplies air to the brakes on the rear axle(s).
  • Quick release valve - A valve which exhausts air quickly to reduce release time.
  • Relay emergency valve - A valve located on or near the trailer reservoir on a trailer without spring brakes.
  • Relay valve - A valve which reduces brake lag.
  • Reservoirs - Tanks where the air is stored.
  • Safety valve - A valve mounted on the reservoir to prevent over-pressurization.
  • S-cam - A rotating S-shaped cam which activates the brake shoes.
  • Secondary reservoir - A tank that normally supplies air to the brakes on the steering axle.
  • Service brake chamber - A chamber which converts air pressure to mechanical force when the brakes are applied.
  • Service line - The rubber hose connecting the tractor and trailer. Air flows through it when the brakes are applied.
  • Slack adjusters - Devices used to manually or automatically keep the brakes in proper adjustment.
  • Spike - A term sometimes used to describe the hand valve.
  • Spring brake chamber - A chamber housing a large powerful spring which applies the brakes if there is an air loss or as a parking brake.
  • Supply line - The rubber hose connecting the tractor and trailer. Air flows through it when the trailer supply valve is opened. Sometimes called the emergency line.
  • Supply reservoir - The first tank where air is stored when it comes from the compressor. It supplies clean, dry air to the rest of the system.
  • Tractor protection system - A series of two valves which prevent air loss from the tractor if a trailer breaks away.
  • Trailer-supply valve - A red octagonal valve mounted on the dash which supplies air to the trailer.
  • Two-way check valve - A valve which ensures a steady supply of air in the event of an air loss in one system.
  • μm - A unit of measurement. 2.5 μms = 2.5/1000 of a millimetre or the thickness of three sheets of paper.
  • Unloading - A term used to describe cut-out.
  • Wet tank - A term sometimes used to describe the supply reservoir.
  • Wig-wag - A warning sign which drops down from above the windshield to notify the driver the air pressure is too low.
  • Wind-off bolt - A device on the brake chamber used to manually release the spring brakes.

Disclaimer

Rev: 2018