(1) "Air brake hose" means any flexible hose used as an integral part of a service or auxiliary (emergency stopping) air brake system, where flexibility in a connection is mandatory due to vehicle design and includes the service and emergency air hoses between vehicles in a combination of vehicles.

(2) "Air brake reservoir" means a storage container for compressed air.

(3) "Air compressor" means a device which compresses air used for actuation of the brakes and/or other components of the vehicle.

(4) "Air gauge" means a gauge usually mounted on the instrument panel which indicates the air pressure in the air reservoir tanks, brake application pressure, or other air system pressures.

(5) "Air governor" means a regulator which controls the supply of air pressure for the brake system, generally by controlling the air compressor cut-in and cut-out pressure within a preset range.

(6) "Air over hydraulic brake system" means a hydraulic type brake system actuated by an air-powered master cylinder.

(7) "Air pressure protection valve" means a unit through which air flow is prevented except when a preselected input pressure is exceeded.

(8) "Brake" means an energy conversion mechanism used to retard, stop, or hold a vehicle.

(9) "Brake assembly" means an assembly of brake parts, the components of which are determined according to the type or design of the brake system.

(10) "Brake cam" means a cam mounted on the camshaft and located between the ends of the brakeshoes. When rotated by the brake camshaft, the cam expands the brake-shoes against the brakedrum.

(11) "Brake camshaft" means the camshaft which is held to the vehicle axle housing or backing plate by bosses containing bronze or nylon bushings. Air pressure is converted into mechanical force by the brake chamber which is attached by a push rod to the slack adjuster. The slack adjuster multiplies the force by the lever principle and applies the force to the brakeshoes.

(12) "Brake chamber or actuator" means a unit in which a diaphragm converts pressure to mechanical force for actuation of the brakes.

(13) "Brake cylinder" means a unit in which a piston converts pressure to mechanical force for actuation of the brakes.

(14) "Brake master cylinder" means the primary unit for displacing hydraulic fluid under pressure in the brake system.

(15) "Brake pedal" means a foot-operated lever which, when actuated, causes the brake(s) to be applied.

(16) "Brakeshoe" means a rigid half-moon shaped device with friction material affixed to the outer surface. The brakeshoes are generally mounted on a backing plate and are located inside the brakedrum. When expanded by the brake mechanism, the brakeshoes press the brake lining against the brakedrum, which creates friction to stop the rotation of the wheels, which in turn stops the vehicle.

(17) "Brakeshoe anchor pin" means a pin which holds the brakeshoe in its proper place within the brakedrum and serves as a pivot for the brakeshoes. One end of each brakeshoe is generally connected to the backing plate or spider by anchor pins.

(18) "Brake system" means a combination of one or more brakes and the related means of operation and control.

(19) "Brake wheel cylinder" means a unit for converting hydraulic fluid pressure to mechanical force for actuation of a brake.

(20) "Contamination" means any grease, oil, or brake fluid on the brake lining, pad friction surface, or braking surface of the brake drum or rotor.

(21) "Diaphragm" means a rubber partition placed between the two halves of the brake chamber. When air pressure is introduced into the chamber on one side of the diaphragm, the pressure flexes the diaphragm and exerts force on the pushplate attached to the push rod. The pushplate is held up against the diaphragm by a light duty return spring.

(22) "Disc brake" means a brake in which the friction forces act on the faces of a disc.

(23) "Disc brake caliper assembly" means the nonrotational components of a disc brake, including its actuating mechanism for development of friction forces at the disc.

(24) "Disc (rotor)" means the parallel-faced circular rotational member of a disc brake assembly acted upon by the friction material.

(25) "Drum" means the cylindrical rotational member of a drum brake assembly acted upon by the friction material.

(26) "Drum brake" means a brake in which the friction forces act on the cylindrical surfaces of the drum.

(27) "Foot valve" means a brake application and release valve located on the floor or firewall of the motor vehicle between the throttle and the clutch. It may be either a treadle or a pedal and is operated by foot pressure applied by the driver to apply air pressure to the service brake system. The valve may be either attached to the treadle or may be remotely mounted under the floor and connected to the pedal by means of a rod. This valve generally applies air pressure to all braking axles on all vehicles in the combination.

(28) "Hydraulic brake system" means a brake system in which brake operation and control utilizes hydraulic brake fluid.

(29) "Pedal reserve" means the amount of total pedal travel left in reserve when the brake pedal is depressed to the "brake applied" position.

(30) "Push rod" means the sliding rod projecting from a brake chamber and connected to the slack adjuster by which the force of compressed air in the brake chamber is transmitted to the brakeshoes through connecting linkage during a brake application.

(31) "Safety valve" means a pressure release unit used to protect the air system against excessive pressure.

(32) "Service brake system" means the primary brake system used for slowing and stopping a vehicle.

(33) "Slack" means the sum of all clearances in the braking system and total system elasticity.

(34) "Slack adjuster" means a lever attached to the brake camshaft and connected to the brake chamber push rod. The slack adjuster provides a means of adjusting the brakes to compensate for brake lining wear.

(35) "Straight air brake system" means a mechanical type brake system actuated by air pressure in brake cylinders or brake chambers.

(36) "Supply air" means the air that is under pressure in the air supply system of a vehicle. It consists of those lines or tanks, except protected air tanks, which are under pressure when the system is fully charged and when all valves are in the normal position with the brakes unapplied.

(37) "Vacuum assisted hydraulic brake system" means a hydraulic type brake system which utilizes vacuum to assist the driver's effort to apply the brakes.

(38) "Vacuum brake reservoir" means a storage container for vacuum.

(39) "Wedge brake" means a wheel brake which uses air or hydraulic pressure to force wedges instead of cams between the brakeshoes to apply the shoes against the brakedrums. In air applied wedge brake systems, the brake actuator axis is parallel to the axle and pushes directly on the wedge in this direction instead of being mounted at right angles to push a slack adjuster and rotate a cam as in the conventional type of air brake system.