A non-return insert valve for a fluid circuit, in particular of a vehicle, this valve being configured to be inserted into a pipe and comprising: - a tubular body having a main axis A and comprising an external cylindrical surface configured to be surrounded by an internal cylindrical surface (24b1) of the pipe, this body comprising an internal annular rim and an internal annular seat, - a ring mounted at least partly in or on said body and comprising guides extending in a radial direction with respect to said axis A, - a piston mounted in said body and comprising a head carrying a first annular seal configured to come to be supported on said seat, the piston comprising a first side, the piston further comprising a second opposite side, and - an elastically deformable member mounted between the head and the ring and configured to bias the seal in axial support against said seat, said piston being axially movable from a closed position of the valve in which the first seal is in axial support on said seat, to an open position of the valve in which the first seal is at an axial distance from said seat, this displacement being intended to be caused by a fluid which is intended to apply a force on said second side which is greater than an elastic return force imposed by said member, the vane being characterized in that the piston comprises tabs extending axially from the first side and configured to slidingly cooperate with said guides, the piston further comprising fingers extending axially from the second side and configured to slidably cooperate with an internal periphery of said rim, and in that the head comprises at its external periphery lugs which extend in a radial direction with respect to said axis and which are configured to be supported axially against an internal cylindrical shoulder of said body, when the piston is in said first position, in order to precisely define this first position, the fluid being intended to flow between these lugs when the piston is in said second position. - a tubular body having a main axis A and comprising an external cylindrical surface configured to be surrounded by an internal cylindrical surface (24b1) of the pipe, this body comprising an internal annular rim and an internal annular seat, - a ring mounted at least partly in or on said body and comprising guides extending in a radial direction with respect to said axis A, - a piston mounted in said body and comprising a head carrying a first annular seal configured to come to be supported on said seat, the piston comprising a first side, the piston further comprising a second opposite side, and - an elastically deformable member mounted between the head and the ring and configured to bias the seal in axial support against said seat, said piston being axially movable from a closed position of the valve in which the first seal is in axial support on said seat, to an open position of the valve in which the first seal is at an axial distance from said seat, this displacement being intended to be caused by a fluid which is intended to apply a force on said second side which is greater than an elastic return force imposed by said member, the vane being characterized in that the piston comprises tabs extending axially from the first side and configured to slidingly cooperate with said guides, the piston further comprising fingers extending axially from the second side and configured to slidably cooperate with an internal periphery of said rim, and in that the head comprises at its external periphery lugs which extend in a radial direction with respect to said axis and which are configured to be supported axially against an internal cylindrical shoulder of said body, when the piston is in said first position, in order to precisely define this first position, the fluid being intended to flow between these lugs when the piston is in said second position.