A valve for the hydraulic braking of work machines comprises an outer casing provided with a longitudinal seat and with at least one-to-third connection port, a slider slideable along the seat and provided with a contoured portion to control passage of the fluid through the connecting ports, and a reaction surface which is connected to the third connecting port, and an actuation for actuating sliding of the slider in the seat, which comprises first elastic element, interposed between the casing and the slider to contrast pressurized fluid thrust against the reaction surface, second elastic element interposed between a first abutment element of the slider and a second abutment element arranged inside the casing, which are adapted to contrast thrust of the first elastic element, and a manual actuation for actuating loading/unloading of the second elastic element.