KS CDL Air Brakes key terms

Engine-driven pump that draws in outside air and forces it into the storage tanks, building and maintaining the pressure needed to operate the brakes and other air-powered devices.

Valve that monitors system pressure and signals the compressor to stop pumping at the cut-out pressure and to resume pumping at the cut-in pressure, preventing overpressurization.

The upper pressure setting, commonly around 120 to 130 psi, at which the governor unloads the compressor so it stops building pressure in the system.

The lower pressure setting, usually about 20 to 25 psi below cut-out, at which the governor lets the compressor pump again to restore system pressure.

Device placed between the compressor and the first tank that removes moisture and oil vapor from compressed air, helping prevent corrosion and freeze-ups in the brake system.

The wet tank that receives air directly from the compressor or dryer and stores it before it is distributed to the other tanks and brake circuits.

Storage tank in a dual system that holds air for one service brake circuit, typically the rear brakes, and is protected by its own check valve and low pressure indicator.

Storage tank in a dual system that holds air for the other service brake circuit, usually the front brakes, so a failure in one circuit does not disable the other.

Brake arrangement with two separate air circuits fed from a shared supply, designed so a loss of pressure in one circuit still leaves partial braking capability.

One-way valve that allows air to flow into a reservoir but prevents it from flowing back out, keeping each circuit's stored pressure from bleeding into another circuit.

Valve that closes off a failed or leaking circuit so the remaining air in the good circuit is conserved and can still operate its brakes.

Valve that shuts off air to non-safety accessories such as horns or seats when system pressure drops below a set level, preserving remaining air for braking.

The treadle valve operated by the brake pedal; it meters air pressure from the reservoirs to the brake chambers in proportion to how far the pedal is pushed.

Valve mounted near the brakes that uses a small control signal from the foot valve to send a large volume of air quickly to the brake chambers, speeding up application and release.

Valve that exhausts air from a brake chamber close to the wheel rather than back through the long supply line, giving faster brake release and reducing lag.

Cylinder containing a diaphragm that converts air pressure into mechanical force, pushing a pushrod that applies the foundation brake at the wheel.

Linkage between the brake chamber pushrod and the brake shoe that transmits force and provides a means of adjusting free play as linings wear.

The distance the brake chamber pushrod extends when the brakes are applied; excessive travel means the brakes are out of adjustment and stopping power is reduced.

Combination chamber containing both a service diaphragm and a heavy spring held off by air pressure; when air is lost the spring applies the brakes automatically.

System that mechanically locks the brakes applied, usually by exhausting air from spring brake chambers, so the vehicle stays put when parked or when air pressure is lost.

Dash-mounted push-pull valve, often the yellow diamond knob, that releases air to set or release the spring brakes for parking and emergency use.

Device that prevents service brake air pressure and spring brake force from being applied to the same chamber at once, avoiding damage from combined forces.

Buzzer and light that activate when system pressure falls below about 60 psi, alerting the driver that braking capability is being lost.

Dashboard gauge showing pressure in the brake circuits; the driver watches it to confirm normal operating range and to detect leaks or compressor problems.

Gauge that shows how much air pressure the driver is applying to the brakes, helping judge braking effort and detect problems such as dragging brakes.

Check performed with the engine off and brakes applied and released, watching the gauges to confirm pressure loss stays within the allowed limit over a set time.

Leak check made with the brake pedal held down firmly for a period while watching the gauges, to confirm the applied system does not lose pressure too fast.

The amount of pressure, in psi per minute, that a brake system loses while charged; excessive loss indicates a leak that must be repaired before driving.

Check that with the engine running at operating speed and air drained down, the compressor raises pressure from about 85 to 100 psi within a specified time, showing adequate pumping capacity.

The time the system takes to reach normal pressure from a low starting point; a long build-up time points to a weak compressor, a leak, or a slipping drive belt.

Inspection step in which the driver drains air and confirms the low pressure buzzer and light come on before pressure drops below about 60 psi.

Check that with pressure below about 45 psi the spring brakes have fully applied and the parking brake knob pops out, confirming automatic emergency braking works.

The delay between pushing the pedal and the brakes actually applying, caused by the time air takes to travel through lines and valves; it lengthens stopping distance.

Loss of braking power caused by heat from repeated or prolonged use, which reduces friction at the linings and drums and can require a lower gear and slower speed.

Technique of braking firmly to slow well below the safe speed, then releasing to let brakes cool, repeated on long downgrades instead of riding the brakes continuously.

Auxiliary braking device such as an engine brake or exhaust brake that slows the vehicle without using the service brakes, helping control speed on downgrades and reducing fade.

Controlled response to a sudden hazard or air loss: apply the service brakes firmly, downshift, use the parking brake if needed, and steer to a safe stop.

Loss of normal braking ability from air loss, a broken line, or a mechanical fault; the driver should downshift, use spring or parking brakes, and find a safe place to stop.

Device that feeds alcohol vapor into the air system to lower the freezing point of moisture, helping prevent ice blocking valves and lines in cold weather.

Condition in which moisture in the air system turns to ice in cold weather, blocking lines or valves and causing brakes to stick or fail to apply.

Cock or petcock at the bottom of each reservoir used to blow off accumulated water and oil; tanks should be drained daily to keep moisture out of the system.

Setting the slack adjusters so pushrod travel stays within the manufacturer's limit, keeping the brakes responsive and legally compliant.