NS Air Brake Test key terms

The main air line running the length of the train that supplies air to each car and transmits the pressure change signal that tells cars to apply or release their brakes.

The chamber on each car where air pressure pushes a piston to force brake shoes against the wheels; the amount of pressure there determines braking force.

A storage tank on each car that is charged from the brake pipe and holds the air used to apply that car's brakes when brake pipe pressure drops.

The car-mounted valve that senses brake pipe pressure changes and directs air between the auxiliary reservoir, brake cylinder, and atmosphere to apply, hold, or release the brakes.

A second storage tank on each car that provides extra air volume during an emergency application, producing higher brake cylinder pressure than a service application can achieve.

The regulating device on the locomotive that maintains brake pipe pressure at the specified setting, such as 90 psi, by admitting air from the main reservoir as needed.

The large tank on the locomotive that stores compressed air from the compressor and supplies the brake pipe, air horns, and other pneumatic devices.

The air pressure maintained in the train line, expressed in psi; its level and rate of change signal cars to charge, apply, or release brakes.

The air pressure measured in a car's brake cylinder after an application, used to confirm the brake applies and to compare against required minimums.

The distance the brake cylinder piston moves when the brakes apply; excessive travel means the brakes must be adjusted before the car is safe to move.

The remaining thickness of the friction material on a brake shoe; worn below the minimum it must be replaced before the car can be moved.

A complete brake test performed at the point where a train is assembled or receives its initial charge, verifying that brakes apply and release on every car.

The most thorough brake test, required at initial terminals and after certain changes, checking brake pipe leakage, brake application and release on each car, and piston travel.

A less extensive test performed when cars are added or removed or the train is rearranged, confirming that the brake pipe is charged and brakes apply and release on the affected cars.

A limited test, often called a set-and-release check, used when a train has been standing or minor changes occurred, verifying that brakes set and release without full leakage testing.

A measurement of how much air escapes from the brake pipe over a set period, compared against an allowable limit to confirm the train's air system is sound.

The maximum allowable brake pipe pressure loss, commonly 5 psi per minute for a train, above which the leak must be found and corrected before departure.

A check confirming that a car holds its brake cylinder pressure after the brake pipe is reduced, detecting leaks in the brake cylinder or control valve.

The process of filling the brake pipe and auxiliary reservoirs to working pressure before a brake test or movement, allowing enough time for full charge.

A controlled brake application made by gradually reducing brake pipe pressure, producing smooth braking without triggering emergency action.

The smallest brake pipe pressure reduction, typically about 6 to 8 psi, that reliably sets the brakes without wasting air or causing rough handling.

A rapid, large reduction of brake pipe pressure that applies brakes at maximum force on all cars, used only to prevent an accident or stop immediately.

Restoring brake pipe pressure so control valves exhaust brake cylinder air and the brakes come off, allowing the train to move freely again.

A car or component found defective and unsafe to move until repaired, tagged and set out according to the railroad's bad order procedures.

A quick functional check in which the brakes are applied and then released to confirm they respond, often used for the limited Class III test.

The locomotive machine that produces compressed air to keep the main reservoir charged so the brake pipe and auxiliary reservoirs stay at working pressure.

A shutoff valve at each end of a car's brake pipe that controls air flow between cars and is closed to isolate a defective car or during switching.

The flexible coupling between cars that carries brake pipe air; a damaged or leaking hose must be replaced before the car can be moved.

A manually set valve that holds some brake cylinder pressure after release, used on grades to keep brakes applied while the brake pipe is recharged.

Techniques for controlling speed and slack on descending grades using planned brake applications and releases rather than continuous light braking.

The in-train movement between couplers as cars bunch or stretch; rough brake handling amplifies it and can damage lading or derail cars.

Recognizing conditions such as leaks, hot wheels, or dragging equipment that threaten safe operation, and reporting or correcting them promptly.

The process of inspecting brakes, wheels, and air lines to find faults such as leaks, worn shoes, or stuck brakes before they cause failure.

The actions taken when a brake emergency occurs, such as applying emergency brakes, protecting the train, and notifying the dispatcher immediately.

Following the published air brake and train handling rules exactly, including test requirements, pressure limits, and reporting duties, without shortcuts.