KS CDL Air Brakes flashcards

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

Governor cut-out pressure

The pressure at which the governor unloads the compressor, typically around 120 to 125 psi, stopping further pressure buildup.

Governor cut-in pressure

The pressure at which the governor reloads the compressor to rebuild pressure, commonly around 85 to 100 psi.

Air dryer function

Removes moisture and oil vapor from compressed air downstream of the compressor, cycling its purge valve each time the compressor unloads.

Wet tank

The first reservoir to receive compressor air; it collects moisture and oil before air passes to the dry tanks.

Safety valve setting

A spring-loaded relief valve on the supply reservoir that vents air if pressure exceeds about 150 psi, protecting the system.

Relay valve purpose

A valve mounted near brake chambers that uses a small control signal to deliver a large volume of air quickly, reducing brake lag.

Slack adjuster

The linkage that converts brake chamber pushrod stroke into rotation of the brake shoe; excessive free play reduces braking force.

Dual circuit design

Two independent service brake circuits, usually front axle and rear axle, so one failure still leaves partial braking capability.

Check valve role

A one-way valve that isolates the two brake circuits so a leak in one does not drain pressure from the other.

Low pressure warning threshold

An audible and visual warning must activate before system pressure falls below 60 psi, alerting the driver to impending brake loss.

Spring brake operation

Heavy springs apply the parking brake when air pressure is released; air pressure must be supplied to compress the springs and release the brake.

Tractor protection valve

A valve that closes the trailer supply line when pressure drops, preventing loss of tractor air through a broken trailer connection.

Trailer supply line color

The red coupler line charges the trailer air system; the blue service line carries brake application signals.

Parking brake knob

The yellow diamond control that releases air to apply spring brakes and supplies air to release them for driving.

Service brake leak test

With engine off and full pressure, hold the service brake; loss must not exceed 3 psi per minute single or 4 psi combination.

Spring brake leak test

With parking brake applied and engine off, pressure loss must not exceed 3 psi per minute single or 4 psi combination.

Warning device test

With engine off, pump the brake pedal until the low pressure warning sounds and lights, which must occur before pressure drops below 60 psi.

Spring brake pop-out test

Continue pumping the pedal with engine off; the parking brake knob must pop out between 20 and 45 psi.

Pressure buildup test

With system charged and engine at operating rpm, pressure must rise from 85 to 100 psi within 45 seconds.

Reservoir draining

Drain all air tanks daily to remove moisture and oil that can damage valves and cause freeze-ups in cold weather.

Brake chamber pushrod travel

The measured stroke of the chamber pushrod; travel beyond the adjustment limit indicates the slack adjuster needs service.

Progressive braking technique

Apply steady, light pedal pressure to meter air pressure smoothly; air brakes respond to pressure, not pedal force alone.

Air brake lag

The delay between pedal application and brake force at the wheels; it increases stopping distance compared with hydraulic brakes.

Downgrade braking rule

Select a gear that holds safe speed and use short firm brake applications; do not ride or fan the brakes continuously.

Pressure gauge monitoring

Watch the air pressure gauge continuously while driving; pressure should stay in the normal range and never fall below the warning threshold.

Low pressure response

If the warning activates while driving, stop as soon as safely possible before spring brakes apply automatically.

Service brake failure response

Downshift progressively, use engine braking, and apply the parking brake gradually to avoid locking the wheels.

Runaway ramp use

If brakes cannot control speed on a grade, steer for an escape ramp rather than continuing downhill with reduced braking.

Brake fade response

If brakes overheat and fade, stop and let them cool; do not continue downhill with reduced braking capability.

Skid recovery

If a wheel locks and skids, release brake pressure momentarily to regain steering control, then reapply with less force.

Alcohol evaporator

A device that introduces alcohol vapor into the air system to prevent moisture from freezing in lines and valves in cold weather.

Air dryer desiccant

The cartridge that absorbs moisture; a saturated cartridge passes water downstream and causes freeze-ups, so it needs periodic replacement.