Piping unit for transporting fuel

A piping unit arranged between an engine and a fuel tank for transporting a fuel, comprising:

• a resin tube as an essential element for the piping unit,
• a connector attached to an end portion of the resin tube for connecting the resin tube to a mating pipe, the connector having a connector body including a retainer holding portion on one end of the connector body along an axial direction and a tube connecting portion on the other end of the connector body along the axial direction for connecting to the resin tube, a retainer held in or on the retainer holding portion for engaging with the mating pipe to securely fix the connector body in an axial direction, and a sealing member contacting air tightly with an outer peripheral surface of the mating pipe to provide a seal between the connector body and the mating pipe,
• wherein the resin tube has a multilayered construction including an inner fuel barrier layer and an outer layer made of polyamide covered further with a protective layer on an outer peripheral surface of the outer layer, the resin tube inside the protective layer has a small outer diameter (od) up to 6 mm and a wall-thickness (t), a ratio of the outer diameter (od) of the resin tube/the wall thickness (t) of the resin tube is in a range of 4 to 8.