49 CFR 229.55 - Piston travel.
(a) Brake cylinder piston travel shall be sufficient to provide brake shoe clearance when the brakes are released.
(b) When the brakes are applied on a standing locomotive, the brake cylinder piston travel may not exceed 1 1/2 inches less than the total possible piston travel. The total possible piston travel for each locomotive shall be entered on Form FRA F 6180-49A.
(c) The minimum brake cylinder pressure shall be 30 pounds per square inch.