A passive backflow prevention apparatus includes a tubular base that has a non-planar end defining an opening. The passive backflow prevention apparatus also includes a flap assembly that includes a non-planar flap. The passive backflow prevention apparatus further includes a hinge that pivotably couples together the tubular base and the flap assembly such that the flap assembly is pivotable from an open position, in which the non-planar flap of the flap assembly is disengaged with the non-planar end to enable a fluid, flowing in a first direction, through the opening, to a closed position, in which the non-planar flap of the flap assembly is engaged with the non-planar end to prevent a fluid, flowing in a second direction, through the opening.

An intake pipe for intake gas of an internal combustion engine has an intake pipe channel and a flap unit with a flap shaft and a flap fixedly arranged on the flap shaft. The flap unit alternatingly opens or closes the intake pipe channel. A hollow insert body is disposed in the intake pipe channel, wherein the flap unit is arranged in the insert body and the flap is positioned in a hollow interior of the insert body. The insert body has opposite end faces and the opposite end faces are open. The flap shaft extends through opposite walls of the insert body in a radial direction relative to an insert body axis of the insert body. The insert body is rotatable on the flap shaft. A radial inner circumferential side of the insert body widens toward at least one of the open end faces.

Provided is a foamable filling device that includes a foamable material and is disposed within a hollow structural member. The foamable filling device includes a carrier member and an opening/closing member. The carrier member includes a through hole and a mounting portion to which the foamable material is mounted. The opening/closing member includes a cover portion formed in a size capable of blocking the through hole; and a biasing portion that biases the cover portion, and the opening/closing member is fittable to the carrier member. The opening/closing member is configured such that, when the opening/closing member is fitted to the carrier member, the biasing portion is elastically deformed and biases the cover portion to thereby bring the cover portion into contact with a seat portion provided at an end of the through hole of the carrier member.