A pipe coupling comprising: a left side clamp which in use is tightened against a large diameter pipe, a right side clamp which in use is tightened against a small diameter pipe, and a cylindrical member that connects or bridges between the left side clamp and the right side clamp, the said cylindrical member comprises at its ends an inner abutment, wherein each of the said left and right side clamps comprises an annular clamp housing that has ends which are provided with two opposing clamp members and that comprises one or more tightening elements for tightening said clamp members towards each other in a direction transverse to an axial length of said annular clamp housing so as to apply a radially-inward clamping force on a pipe being clamped in said annular clamp housing; and wherein an annular seal mounted in a tightening chamber with borders defined by inner walls of said annular clamp housing and defined by said inner abutment, said tightening chamber having a single annular opening that faces radially inwards, wherein the pipe coupling is arranged such that upon sufficient tightening of said one or more tightening elements, said annular seal does not expand against the borders of said tightening chamber and only expands radially inwards through the single annular opening, and said annular seal extrudes outwards of said tightening chamber, and wherein the said inner abutment is arranged not perpendicular to a circumference of a pipe inserted in said clamp housing, the said inserted pipe extending along of said axial length of said annular clamp housing and said inner abutment is arranged slanted so that a radially inward area of said tightening chamber is smaller than a radially outward area of said tightening chamber, and so that the said tightening chamber has a radially inward length in the direction of said axial length of said annular clamp housing, and the said tightening chamber has a radially outward length in the direction of said axial length of said annular clamp housing, characterised in that the said radially inward length of said tightening chamber is smaller than the said radially outward length of said tightening chamber. a left side clamp which in use is tightened against a large diameter pipe, a right side clamp which in use is tightened against a small diameter pipe, and a cylindrical member that connects or bridges between the left side clamp and the right side clamp, the said cylindrical member comprises at its ends an inner abutment, wherein each of the said left and right side clamps comprises an annular clamp housing that has ends which are provided with two opposing clamp members and that comprises one or more tightening elements for tightening said clamp members towards each other in a direction transverse to an axial length of said annular clamp housing so as to apply a radially-inward clamping force on a pipe being clamped in said annular clamp housing; and wherein an annular seal mounted in a tightening chamber with borders defined by inner walls of said annular clamp housing and defined by said inner abutment, said tightening chamber having a single annular opening that faces radially inwards, wherein the pipe coupling is arranged such that upon sufficient tightening of said one or more tightening elements, said annular seal does not expand against the borders of said tightening chamber and only expands radially inwards through the single annular opening, and said annular seal extrudes outwards of said tightening chamber, and wherein the said inner abutment is arranged not perpendicular to a circumference of a pipe inserted in said clamp housing, the said inserted pipe extending along of said axial length of said annular clamp housing and said inner abutment is arranged slanted so that a radially inward area of said tightening chamber is smaller than a radially outward area of said tightening chamber, and so that the said tightening chamber has a radially inward length in the direction of said axial length of said annular clamp housing, and the said tightening chamber has a radially outward length in the direction of said axial length of said annular clamp housing, characterised in that the said radially inward length of said tightening chamber is smaller than the said radially outward length of said tightening chamber.