Plastic barb-style connectors provide designers with a capability to accommodate the widest possible range of tubing properties and application conditions, including a multitude of configurations such as tees, wyes, elbows, and manifolds. Several barb designs are available — each with unique characteristics to tailor connection performance to specific needs — for handling assembly forces, tensile resistance and blow-off resistance without the need for clamps.
Barbs derive their holding capability by expanding tubing above its nominal inside diameter, creating some amount of interference for a secure seal and good mechanical retention. The tube expansion can vary dramatically, from lower profile, easier connections to much more aggressive interferences, depending on the pressure and tensile pull requirements.
The selection of the proper barb style is essential to the connector’s tube holding capability. The cylindrical surface behind the barb should allow the tubing to relax against the connector. In choosing a barb style, the barb chosen should be designed with a sharp peak, allowing it to “bite” into the tubing for optimal retention.
Many plastic connectors and almost all metal connectors use multi-barb surfaces, which usually produce an inferior tube connection and seal. Multi-barbs cannot create a sharp bite on the tube, which inhibits retention. Also, they do not allow the tube a chance to relax behind the barb, resulting in poor tensile pull strength. Multi-barbs are also relegated to a manufacturing process that leaves a parting line on the sealing surface, creating a potential leak path.
This is an inherent design flaw, yet all multi-barb connector designs, including metal connectors, display this liability. In fact, poor quality single-barb plastic connectors are also afflicted with a parting line, reducing the efficacy of the connector. A well designed and properly manufactured connector will incorporate a singular barb with no parting line, a sharp bite, and a clean sealing surface.