A Comparative Study of the Integrity of Joints Between Multilayer Fuel Line Constructions and Different Connector ‘Barb’ Designs - Part 2

Last year, McKechnie Vehicle Components established (Paper 2000-01-1098) that there were two factors influencing joint integrity between a multilayer fuel tube and the barb design of a plastic quick connector:

• The relationship between barb O.D. and tube I.D.
• The type of lining material of the tube and the overall hoop stress the tube applies to the joint after assembly.

It was recommended that future work should address the following points if a full understanding of the fuel tube material to barb type is to be achieved:

• Assess the sealability of different materials onto a common barb type
• Assess a range of different barb designs to depict the optimum

This year the authors have attempted to address the above points. Two conductive liquid fuel tubes of different commercial sizes (American and European) were manufactured in commercial multilayer structures. These had different material inner layers (PA12 and PBT). The tubes were joined to commercial conductive quick connectors (7.89mm SAE J2044 stub size specification) of 3 barb designs. The first barb design is used in Europe, Asia and South America on 8×6mm tube. The second barb design is used in USA on 8.35×6.35mm tube. The third barb design contains an ‘O’ ring and is used globally on 8×6mm tube.

The burst strength of the tubes was measured to give an indication of the hoop stress applied by the tube on the barb. Comparative room temperature ‘pull off’ and leakage test data was obtained on both unconditioned and conditioned joints.

Explanations were made based on the observed differences in materials, tube dimensions and barb design.