Abstract: A spring-loaded brake cylinder has a piston therein one side of which is loaded by a spring and the other side of which is subjected to a pressure medium introduced into the cylinder. The cylinder is provided with an auxiliary release device comprising a screw coupling having a first coupling member which is rotatable but not axially displaceable and a second coupling member threadedly engaged with the first coupling member and acting upon the brake cylinder through an abutment coupling against the force of the load spring. The first coupling member is provided with a reversible thread and a second coupling means is provided to retain the second coupling member against rotation when the pressure acting upon the cylinder falls below a predetermined level.