Pressure relief valve intended to be installed between an upstream pipe and a downstream pipe for the flow of a fluid, comprising: a body comprising a central portion in which there is formed a chamber having, along a first axis, a bottom and, between this bottom and an opening, a peripheral side wall and comprising opposite upstream and downstream connection end fittings (8, 9) having, along a second axis, upstream and downstream cylindrical orifices (17, 18) opening into the chamber through the side wall of the latter; a sleeve installed in the chamber, comprising a separation wall whose periphery is adjacent to or in contact with a peripheral region of the peripheral side wall of the chamber and extending between the upstream and downstream orifices (17, 18), the sleeve having a communication passage passing through the separation wall and able to establish communication between the upstream and downstream orifices (17, 18); and a piston borne in a sliding manner by the said sleeve and comprising an actuating portion subjected to the downstream pressure against the action of a return spring and a closure portion able to close the said communication passage when the downstream pressure reaches a maximum limit pressure (Pmax); the separation wall being arranged obliquely with respect to the said first axis of the peripheral side wall of the chamber; characterized in that the peripheral side wall of the chamber comprises an axisymmetric frustoconical portion along the said first axis, which is open on the side where the opening of the said chamber is located and has the said peripheral region adjacent to or in contact with the periphery of the separation wall of the sleeve, the said upstream and downstream cylindrical orifices (17, 18) open into the chamber through the said axisymmetric frustoconical portion and the periphery of the separation wall is provided with an annular seal bearing against the said axisymmetric frustoconical portion, the sleeve comprises a radial wall situated on the side where the opening of the chamber is located with respect to the upstream and downstream orifices (17, 18) and whose periphery is adjacent to or in contact with a cylindrical portion of the chamber, and the peripheries and of the radial wall and of the oblique separation wall join up in a region situated on the side where the downstream orifice or the upstream orifice is located. a body comprising a central portion in which there is formed a chamber having, along a first axis, a bottom and, between this bottom and an opening, a peripheral side wall and comprising opposite upstream and downstream connection end fittings (8, 9) having, along a second axis, upstream and downstream cylindrical orifices (17, 18) opening into the chamber through the side wall of the latter; a sleeve installed in the chamber, comprising a separation wall whose periphery is adjacent to or in contact with a peripheral region of the peripheral side wall of the chamber and extending between the upstream and downstream orifices (17, 18), the sleeve having a communication passage passing through the separation wall and able to establish communication between the upstream and downstream orifices (17, 18); and a piston borne in a sliding manner by the said sleeve and comprising an actuating portion subjected to the downstream pressure against the action of a return spring and a closure portion able to close the said communication passage when the downstream pressure reaches a maximum limit pressure (Pmax); the separation wall being arranged obliquely with respect to the said first axis of the peripheral side wall of the chamber; characterized in that the peripheral side wall of the chamber comprises an axisymmetric frustoconical portion along the said first axis, which is open on the side where the opening of the said chamber is located and has the said peripheral region adjacent to or in contact with the periphery of the separation wall of the sleeve, the said upstream and downstream cylindrical orifices (17, 18) open into the chamber through the said axisymmetric frustoconical portion and the periphery of the separation wall is provided with an annular seal bearing against the said axisymmetric frustoconical portion, the sleeve comprises a radial wall situated on the side where the opening of the chamber is located with respect to the upstream and downstream orifices (17, 18) and whose periphery is adjacent to or in contact with a cylindrical portion of the chamber, and the peripheries and of the radial wall and of the oblique separation wall join up in a region situated on the side where the downstream orifice or the upstream orifice is located.