ND CDL Air Brakes flashcards

31 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 stops the compressor from building more air, typically about 125 psi on most heavy-duty air brake systems.

Governor cut-in pressure

The pressure at which the governor restarts the compressor after cut-out, typically about 100 psi, keeping the system within its operating range.

Safety valve setting

A spring-loaded valve on the air tank that opens at about 150 psi to release excess pressure if the governor fails to cut out the compressor.

Supply (wet) tank

The first tank to receive air from the compressor; it collects moisture and oil and feeds the primary and secondary circuits through check valves.

One-way check valve

A valve that allows air to flow in only one direction, preventing a leak or failure in one brake circuit from draining air from the other circuits.

Foot (treadle) valve

The pedal-operated valve that meters air pressure to the brake chambers in proportion to how far the pedal is pushed, allowing partial braking.

Slack adjuster

The linkage that converts pushrod stroke into rotation of the brake camshaft; excessive travel means the brakes are out of adjustment and braking force is reduced.

Spring brake operation

Spring brakes are held off by air pressure and apply by spring force when pressure is released, so a loss of air causes them to apply automatically.

Low pressure warning threshold

The warning light and buzzer must activate before system pressure drops below 60 psi, alerting the driver that spring brakes will soon apply.

Static leak test limits

With the engine off and brakes released, pressure loss must not exceed 2 psi per minute for a single vehicle or 3 psi per minute for a combination vehicle.

Applied leak test limits

With the engine off and the service brake fully applied, pressure loss must not exceed 3 psi per minute for a single vehicle or 4 psi per minute for a combination vehicle.

Spring brake apply test

After the low pressure warning activates, continue pumping the pedal; the spring brakes must fully apply by the time pressure falls to about 20-45 psi.

Air build-up test

At fast idle, pressure should rise from 85 to 100 psi within about 45 seconds; slower build-up indicates a weak compressor, leaks, or a restriction.

Slack adjuster inspection

With the brakes released, pull each slack adjuster by hand; if the pushrod stroke exceeds the limit or the adjuster moves loosely, adjustment or repair is needed.

Tank draining

Drain air tanks daily to remove moisture and oil; on systems with automatic drains, verify they work, because water in tanks can freeze and block air flow.

Pre-trip pressure check

Before moving, build full pressure to governor cut-out, confirm the low pressure warning works, and verify the spring brakes apply and release properly.

Brake lag

The delay between pedal movement and brake application in air brake systems; steady, progressive pedal pressure is used instead of pumping or stabbing.

Downgrade braking technique

Select a low gear before the descent, use engine braking, and apply light steady service brake pressure rather than riding the brakes continuously.

Brake fade cause

Overheated drums and linings reduce friction and braking force; the response is to slow down, downshift, and let the brakes cool, not to press harder.

Minimum operating pressure

Normal driving should keep system pressure at or above about 100 psi; watch the gauge on grades and at stops because repeated applications use air.

Parking procedure

Set the parking (spring) brakes, place the transmission in a low gear or park, and chock the wheels on a grade when required.

Slippery surface braking

Apply the brakes gently and early in slippery conditions; abrupt applications can lock wheels and cause a skid, especially with lightly loaded axles.

Parking brake release check

Release the parking brake only after pressure is up, then verify the spring brakes have released by confirming the vehicle rolls freely.

Low pressure warning response

If the warning sounds while driving, stop as soon as it is safe; continued driving will cause the spring brakes to apply automatically at about 20-45 psi.

Loss of air pressure

If pressure is lost and the spring brakes apply, the vehicle stops; they cannot be released without air pressure, so do not try to drive through them.

Circuit failure response

If a chamber or line fails and air escapes, check valves isolate the failed circuit; the remaining circuit still brakes, so brake firmly and stop.

Service brake failure

If the service brakes fail but pressure remains, use the parking (spring) brake gradually to slow and stop; a full application can lock the rear wheels.

Compressor failure

If the compressor fails or its belt breaks, pressure will not build; stop and do not continue, because the spring brakes will eventually apply on their own.

Dragging brake response

If a brake is dragging or smoking, stop and let it cool; do not pour water on hot drums, because warping or cracking can result.

Skid recovery

If the vehicle begins to skid under braking, release the brake pedal to regain steering control, then reapply with less pressure.

Post-emergency stop rule

After any emergency stop caused by an air system fault, do not resume driving until the fault is found and corrected and full pressure is restored.