NS Air Brake Test cheat sheet

The automatic brake valve controls brake pipe pressure: reduction applies brakes, restoration releases them. The independent brake valve controls locomotive unit brakes only, without affecting brake pipe pressure.

Brake pipe pressure reduction propagates as a pressure wave at roughly 900-1000 ft/s; the exhaust of air from the brake pipe at the controlling valve, not the air itself traveling the train, sets the brakes.

Auxiliary reservoir air charges through the control valve while brake pipe pressure exceeds auxiliary reservoir pressure; a brake pipe reduction reverses that differential and moves air into the brake cylinder.

Typical freight settings: brake pipe 90 psi, full service brake cylinder pressure about 50-64 psi depending on valve type and piston travel; graduated release is standard on passenger equipment only.

The equalizing reservoir is what the brake valve actually reduces; the brake pipe follows it through the relay valve or equalizing portion, which is why leakage between the two causes improper brake pipe pressure.

The control valve has four basic positions/conditions: release and charging, application, lap, and emergency. The quick service limiting valve and accelerated release functions modify application and release speed.

Emergency application is triggered by brake pipe rate of reduction, not just the amount of reduction; a service reduction too fast can cause an undesired emergency (UDE).

Two-way check valves on multiple-unit locomotives let the highest control pressure (brake pipe or independent) feed the locomotive brake cylinders, so independent release cannot override an automatic application.

Class I (initial terminal) brake test: a full test of the entire train's brake system performed at the point where the train is originally assembled, including inspection of brake rigging and piston travel.

Class II brake test: a test performed at a terminal or yard where the train is received in one piece; it verifies brake pipe leakage and application/release, but does not require the full 100% inspection of a Class I.

Class III brake test: a test performed after the train has stopped en route and only a portion of the brake system has been changed (e.g., cars set out or picked up); it verifies the brakes on the changed portion and the continuity of the brake pipe.

Class I requires that brake pipe leakage not exceed 5 psi per minute with the brake valve in lap and the feed valve cut out, and that the brake pipe pressure be restored before proceeding.

A Class I test requires a visual inspection of each car's brake rigging, piston travel within limits, and that all angle cocks are in the proper position and all retaining valves are in release.

Class II testing typically requires 100% of the train's brakes to apply and release; a Class III requires only the brakes on the added or changed cars to be tested, plus a check that the brake pipe is not obstructed.

Piston travel limits for freight cars are commonly 7 to 9 inches for 8-inch cylinders and 6 to 8 inches for 10-inch cylinders; out-of-limit travel is a defect that must be corrected before the test is complete.

A brake test is not complete until the brake pipe pressure is fully restored, the brakes are released, and the brake pipe leakage test has been passed; any car failing is bad-ordered and must be corrected or set out.

Leakage test procedure: charge the brake pipe to the prescribed pressure, cut out the feed valve, place the brake valve in lap, and observe the brake pipe gauge; leakage must not exceed 5 psi per minute on a freight train.

A leakage test is performed with the brake valve in lap, not in release; in release the feed valve masks leakage by replenishing the brake pipe.

Pressure retention test: after a brake application, the brake pipe is allowed to stabilize, then the brake valve is placed in lap and the brake pipe pressure must not drop more than 5 psi in 60 seconds, confirming the control valves hold.

If brake pipe leakage exceeds the limit, the source must be located (often a leaking angle cock, hose gasket, or control valve) and corrected before the train may proceed.

Leakage is measured on the brake pipe gauge at the head end; a large leakage rate can prevent the brake pipe from charging to full pressure at the rear of a long train.

The pressure retention test is sometimes called the brake pipe leakage and pressure retention test; both the leakage rate and the ability to hold pressure after application are checked.

A brake pipe that will not hold pressure in lap indicates a leak downstream of the brake valve; a brake pipe that holds but will not charge indicates a charging or feed valve problem upstream.

On a Class I test, the leakage test is performed after the brakes are fully charged and before the application/release portion is completed; results must be recorded per the railroad's rules.

Minimum reduction is typically 6-8 psi; a full service reduction is about 20-26 psi. Reductions beyond full service do not increase brake cylinder pressure further in a standard freight system.

To avoid a UDE, make brake pipe reductions at a controlled rate; rapid or large reductions, especially on a slack-stretched train, can trigger emergency application.

Release the brakes only after the brake pipe has had time to recharge; a release before the auxiliary reservoirs recharge leaves the train with reduced braking for the next application.

Use the independent brake to hold the locomotive while the automatic brake is applied; releasing the independent while the automatic is set can cause the locomotive to roll or the train to surge.

On grades, keep the brake pipe reduction steady and use dynamic braking to control speed where available; repeated small applications and releases can deplete auxiliary reservoir pressure.

When making a service application, bail off the independent brake to avoid locomotive wheel slide and to keep the locomotive's brake from fighting the train brakes.

A split reduction (reducing brake pipe pressure in stages) allows the brakes to set more evenly through the train and reduces slack action and UDE risk.

Before releasing brakes on a grade, confirm the train is fully stopped or controlled; releasing on a grade without sufficient dynamic or independent braking can allow the train to run away.

A car is bad-ordered when it has a defect that makes it unsafe to move or that violates the applicable inspection standards; it must be repaired or set out before the train proceeds.

Common brake defects include piston travel out of limits, a stuck or leaking control valve, a broken or missing brake shoe, a defective angle cock, and a leaking brake pipe hose or gasket.

Piston travel is measured with the brake applied and the car at rest; the measurement is taken from the face of the cylinder to the end of the piston rod or from the reference mark, per the railroad's standard.

Brake shoes are condemned when worn to the limits set by the car owner or the AAR; a shoe worn through the metal backing or with a broken key must be replaced.

A visual inspection includes brake rigging, slack adjusters, cutout cocks, retaining valves, and the condition of the brake pipe and hoses; any defect found is noted and corrected.

Bad order tags must be applied to cars that cannot be moved safely; the car must be set out and the defect reported to the car department or the appropriate authority.

A defective control valve or a car that will not apply or release must be cut out or set out; a cut-out car must have its brake pipe angle cock closed and its reservoir air bled off.

Defects found during a brake test must be corrected and the affected portion retested before the train is considered to have passed the test.

The brake test must be performed by a qualified employee and the results recorded as required by the railroad's rules and the applicable federal regulations.

A train may not depart until the required brake test is complete and the brake pipe leakage is within limits; the test must be repeated if the train is broken up or if the brake system is altered beyond the allowed limits.

The brake valve must be in the proper position for the test: release for charging, lap for leakage, and application for the application test; improper valve position invalidates the test.

When a train is picked up en route, a Class III test is required for the added cars and the brake pipe continuity must be verified before departure.

The air brake rules require that the brake pipe pressure be restored to the prescribed pressure before the train moves; a train may not be moved with the brake pipe below the required pressure.

Any employee who discovers a defect that affects safe operation must report it immediately to the proper authority and take action to prevent movement until it is corrected.

The rules require that the brake system be tested after any repair or replacement of a control valve, brake cylinder, or brake pipe; the affected car must be retested.

Compliance with the brake test rules is documented; the employee performing the test is responsible for the accuracy of the recorded results.

An emergency application is made by a rapid brake pipe reduction or by opening an emergency valve; it sets the brakes at maximum and must be followed by a full brake pipe recharge before movement resumes.

After an emergency application, the brake system must be inspected and the brake pipe recharged; the train may not move until the brakes are released and the brake pipe is restored to the required pressure.

A UDE is an undesired emergency application; it is investigated to determine the cause, which may be a rapid reduction, a defective valve, or a brake pipe obstruction.

When working around brake equipment, bleed off air pressure before disconnecting hoses or working on brake rigging; trapped air can cause sudden movement or injury.

Personal protective equipment, including gloves and eye protection, is required when working with brake pipe hoses and air lines; high-pressure air can cause serious injury.

In an emergency, the first priority is to stop the train safely; the emergency brake application is the primary means, followed by securing the train and protecting the area.

A runaway train or a train that will not hold on a grade requires immediate notification of the dispatcher and use of all available braking, including dynamic and independent brakes.

Hazard awareness includes recognizing that brake pipe pressure loss can cause unintended release or application; any abnormal brake behavior must be reported and investigated before the train proceeds.