Brake Pipe Leakage and Pressure Retention Tests
Brake pipe leakage test
Charge the brake pipe to 90 psi, cut out the automatic brake valve, and observe the brake pipe gauge for 60 seconds. Leakage must not exceed 5 psi per minute on a freight train. If it does, find and correct the leak - hoses, couplings, angle cocks, dirt collectors, or a defective control valve - and retest.
Pressure retention test
With the brakes applied, commonly a 20 psi brake pipe reduction, allow the system to stabilize, cut out the automatic brake valve, and observe for 60 seconds. Brake pipe leakage must remain within 5 psi per minute, and brake cylinder pressure must not drop more than 5 psi in 60 seconds. A brake cylinder that bleeds off indicates a leaking cylinder, piston packing, or control valve.
Worked example
Brake pipe is 90 psi. After cut-out, it reads 86 psi at 60 seconds: 4 psi loss, pass. A second test reads 83 psi: 7 psi loss, fail. The crew inspects the trainline, finds a partially open angle cock, closes it, recharges, and retests.
Traps that cost marks
Testing before the train is fully charged. Leaving the automatic brake valve cut in. Reading the gauge at 30 seconds instead of 60. Confusing brake pipe leakage with brake cylinder leakage. Not allowing auxiliary reservoirs to recharge between tests. Assuming a passing leakage test proves the brakes apply - it does not.