Abstract: The invention relates to a shut-off valve equipped with two pilot-valves and a main control-piston, the said valve connecting in inlet with an outlet when an upper switching pressure is reached and breaking this connection again when the pressure drops to a lower switching pressure. In order to reduce leakage and to improve the switching process, the pilot-valve (12), which determines the lower switching pressure, is in the form of a seat-valve held open by spring-force, the said pilot-valve closing off a control-line when the lower switching pressure is exceeded, and a second flow-path (21) being provided which is interrupted both by the main control-piston (3), in the shut-off phase, and by the pilot-valve (13) which determines the upper switching pressure, at least when, and shortly after, the shut-off (see drawing).