Abstract: This invention relates to a safety-valve for restricting the pressure within a fluid-containing enclosure. It comprises a flap firmly applied against the seal of such an enclosure by means of an adjustable spring, whereby there is generated in said enclosure an overpressure adapted to cause said flap to rise and, accordingly to cause fluid to be vented from said enclosure, in which said flap is provided with a nozzle adapted to be obturated by means of a needle firmly applied against said nozzle by a piston driven by a balancing spring, the force of which can be adjusted by means of a screw with the annular clearance between said needle and the body of said flap forming a calibrated orifice or port.