KY CDL Air Brakes flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Air compressor

Engine-driven pump that builds and maintains air pressure in the brake system; a slipping belt, restricted intake, or worn compressor causes slow pressure buildup or failure to reach governed pressure.

Governor

Valve that controls when the compressor loads and unloads, typically cutting out near 120-125 psi and cutting in near 100 psi, so system pressure stays within the safe operating range.

Air dryer

Device that removes moisture and oil vapor from compressed air before it enters the reservoirs; a saturated cartridge lets water into the system and can cause valve freeze-up in cold weather.

Supply (wet) tank

First reservoir to receive air from the compressor; it collects moisture and passes air on to the primary and secondary tanks through one-way check valves that prevent backflow.

Foot valve (brake valve)

Treadle-operated valve that meters air pressure to the brake chambers in proportion to pedal travel; releasing the pedal exhausts air and releases the brakes.

Spring brake chamber

Brake chamber containing a strong spring that applies the brakes when air pressure is lost; air pressure releases the spring, making the system fail-safe.

Slack adjuster

Lever that converts pushrod stroke into rotation of the brake camshaft; automatic types maintain clearance, but excessive pushrod stroke still signals needed repair.

Low-pressure warning

Light and audible buzzer that must activate before system pressure falls below 60 psi, alerting the driver to a pressure loss before spring brakes apply.

Dual air brake system

Two separate circuits with separate reservoirs, typically primary for rear brakes and secondary for front brakes, so a failure in one circuit does not deplete the other.

Tractor protection valve

Valve that closes automatically when tractor pressure falls to about 20-45 psi, preventing air loss through a broken trailer line and applying the trailer spring brakes.

One-way check valve

Valve at each reservoir inlet that allows air in but blocks backflow, preserving remaining pressure in a tank if the supply line or compressor fails.

Safety valve

Pressure relief device on the supply tank set to open around 150 psi, protecting the system if the governor fails and pressure rises above safe limits.

Parking brake control

Yellow diamond knob that releases air to apply the spring brakes; pulling it out applies the parking brakes, and it is not a substitute for service brakes when stopping.

Fail-safe design

System design in which loss of air pressure causes the spring brakes to apply automatically, so a pressure failure results in braking rather than loss of braking.

Compressor belt check

Inspection of the compressor drive belt for cracks, glazing, and correct tension, plus checks for oil or coolant leaks at the compressor that reduce pressure buildup.

Draining reservoirs

Daily procedure of opening drain cocks on all tanks until no water comes out, removing moisture and oil that can freeze or damage brake valves.

Pushrod stroke measurement

Check of pushrod travel with brakes fully applied at normal pressure; stroke beyond the vehicle specification means brakes are out of adjustment and the vehicle is out of service.

Leak check with soapy water

Method of applying soapy water to fittings and hoses and watching for bubbles, which reveal air leaks that a pressure gauge alone may not localize.

Brake chamber inspection

Check of chambers for dents, cracks, and loose or misaligned clamp rings, and of pushrods for bending or misalignment that requires repair before driving.

Brake lining inspection

Check through inspection holes for lining thickness, oil contamination, and drum cracks; contaminated or worn linings reduce stopping ability and cannot be fixed by adjustment.

Static leak test

With engine off, system charged, and brakes released, observe pressure for one minute; a loss greater than 2 psi or the manufacturer's limit indicates a leak.

Applied leak test

With engine off and brakes fully applied, hold for one minute; a loss greater than 3 psi or the manufacturer's limit indicates a leak in the applied brake system.

Low-pressure warning test

With the engine running, pump the brake pedal to reduce pressure and confirm the warning light and buzzer activate before pressure drops below 60 psi.

Governor cut-in and cut-out

Pressure points at which the compressor resumes pumping (cut-in, about 100 psi) and stops (cut-out, about 120-125 psi); both should match the vehicle specification.

Build-up rate test

With the engine at operating rpm, pressure should rise from about 85 to 100 psi within 45 seconds, per the vehicle specification, showing adequate compressor output.

Spring brake application test

With the system charged and engine off, fan off air pressure and confirm the spring brakes apply automatically when pressure drops into the 20-45 psi range.

Air brake lag

Delay between pedal movement and brake application as air travels to the chambers; apply the pedal smoothly and allow time for pressure to build before expecting full braking.

Progressive braking

Smooth, controlled application of the brake pedal proportional to needed stopping force; avoids fanning or pumping, which wastes air and lowers reservoir pressure.

Trailer hand valve

Control used to apply trailer brakes for testing only; using it for normal stopping while moving can cause a jackknife and is not the intended service brake.

Cold-weather moisture control

Draining tanks and maintaining the air dryer to keep water out of lines and valves, preventing freeze-up that can disable brakes in low temperatures.

Snub braking

Downgrade technique of applying brakes firmly to reduce speed about 5 mph, then releasing and letting engine braking hold speed, repeated as needed instead of continuous pressure.

Escape ramp

Runaway-vehicle arrest area, often gravel or sand, designed to stop a vehicle that has lost braking; steer into it rather than continuing down the grade.