A hydraulic damper for a motor vehicle hydraulic suspension damper, comprising: a tube filled with a working liquid, a main piston assembly disposed slidably inside a main section of said tube and attached to a piston rod led outside said damper, said main piston assembly dividing said tube into a rebound chamber and a compression chamber; said main piston assembly having a rebound valve assembly and a compression valve assembly to control a flow of said working liquid within said tube during a rebound stroke and a compression stroke of said damper, wherein at least one end of said tube is provided with a narrowed section (33, 34) having a diameter that is smaller than a diameter of said main section; said damper further comprising at least one additional piston assembly, displaceable along with said main piston assembly and adapted to be slidably introduced into said narrowed section (33, 34) of said tube to generate an additional damping force; said additional piston assembly comprising a compression valve assembly comprising at least one deflective disc (823, 824); a rebound valve assembly comprising at least one deflective disc (833, 834); and a sealing ring assembly disposed between said compression valve assembly and said rebound valve assembly; characterised in that said sealing ring assembly comprises a first annular member provided with a plurality of spaced axial channels covered at a rebound side by said at least one deflective disc (823, 824) of said compression valve assembly; a second annular member provided with a plurality of spaced axial channels, covered at the compression side by said at least one deflective disc (833, 834) of said rebound valve assembly; an axial projection disposed between said first annular member and said second annular member at the radially internal side of said axial channels of said first annular member and said axial channels of said second annular member; and a sealing ring (843a, 843b, 843e) displaceable axially between said first annular member and said second annular member and radially over said axial projection and adapted to cooperate with said narrowed section (33, 34) of said tube. a tube filled with a working liquid, a main piston assembly disposed slidably inside a main section of said tube and attached to a piston rod led outside said damper, said main piston assembly dividing said tube into a rebound chamber and a compression chamber; said main piston assembly having a rebound valve assembly and a compression valve assembly to control a flow of said working liquid within said tube during a rebound stroke and a compression stroke of said damper, wherein at least one end of said tube is provided with a narrowed section (33, 34) having a diameter that is smaller than a diameter of said main section; said damper further comprising at least one additional piston assembly, displaceable along with said main piston assembly and adapted to be slidably introduced into said narrowed section (33, 34) of said tube to generate an additional damping force; said additional piston assembly comprising a compression valve assembly comprising at least one deflective disc (823, 824); a rebound valve assembly comprising at least one deflective disc (833, 834); and a sealing ring assembly disposed between said compression valve assembly and said rebound valve assembly; characterised in that said sealing ring assembly comprises a first annular member provided with a plurality of spaced axial channels covered at a rebound side by said at least one deflective disc (823, 824) of said compression valve assembly; a second annular member provided with a plurality of spaced axial channels, covered at the compression side by said at least one deflective disc (833, 834) of said rebound valve assembly; an axial projection disposed between said first annular member and said second annular member at the radially internal side of said axial channels of said first annular member and said axial channels of said second annular member; and a sealing ring (843a, 843b, 843e) displaceable axially between said first annular member and said second annular member and radially over said axial projection and adapted to cooperate with said narrowed section (33, 34) of said tube.