Patent ID: 8505981

Claim:
A double-walled vent pipe section, comprising: a first cylindrical structure having: a first outer wall, a first inner wall coaxially disposed within the first outer wall having an outer cylindrical surface defined by a diameter extending along the first inner wall a first length from an end of the first inner wall toward an opposing end of the first inner wall, and said first outer wall having a first coupling feature on a first end of the first cylindrical structure and a second coupling feature on a second end of the first cylindrical structure, a second cylindrical structure having: a second outer wall, a second inner wall coaxially disposed within the second outer wall, the second inner wall having an inner cylindrical surface having a diameter extending a second length from an end of the second inner wall toward an opposing end of the second inner wall, the diameter of the inner cylindrical surface allowing the first inner wall to be inserted into the second inner wall so that at least the first and second lengths substantially overlap, and a first annular region separating the first outer wall from the first inner wall, and a second annular region separating the second outer wall from the second inner wall; said second outer wall having a first coupling feature on a first end of the second cylindrical structure and a second coupling feature on a second end of the second cylindrical structure; said first coupling feature of the first cylindrical structure adapted to mate with the second coupling feature on the second end of the second cylindrical structure, and said first inner wall having an annular ridge formed therein at a spaced distance apart from said end of the first inner wall, the annular ridge having a height above the outer cylindrical surface and extending into the first annular region, wherein the first end of the first cylindrical structure including the annular ridge is inserted into the second cylindrical structure so that the outer cylindrical surface mates with the inner cylindrical surface along the first and second lengths and the annular ridge engages with the inner cylindrical surface at a spaced distance apart from the end of the second inner wall within the second length.