A brake cylinder device including a brake piston operable by a spring force to an application position and to a release position in response to an opposing fluid pressure force, and a fluid pressure operable locking device operable responsively to release pressure for locking the piston in the release position and for delaying such locking of the piston in the release position during normal operations to prevent untimely locking-up of the piston. The brake pressure cylinder is particularly concerned with a spring-actuated brake cylinder device of the type comprising a brake piston which is acted on one side thereof by a spring member for exerting a brake-applying force in one axial direction, and on the opposite side thereof, by service brake pressure prevailing in a release pressure control chamber for effecting a partial or total neutralization of the spring force, and wherein the improvement comprises a locking device including a locking element for axially locking the brake piston in a brake release position, when reduction of said service brake pressure occurs at a rate in excess of a certain rate, for actuating said locking element, said locking piston being subjected to the service brake pressure acting thereon in a direction in which the locking device is operated to an unlocked position against means exerting a lock-applying force thereon. Although the brake cylinder device embodying the invention is essentially intended to be used with pneumatic brake systems for railway vehicles, it can also be used with pneumatic brake systems for highway vehicles and with hydraulic brake systems for any type of vehicle. Certain brake cylinder devices are already known which comprise a spring-actuated piston capable of acting on a rod connected to a friction brake when the pressure decreases sufficiently in a release chamber.