When selecting air lines for a tractor/trailer, the experts at Phillips Industries say it is recommended—and is sometimes required by law—to choose them with the following features:
• Airline assemblies that display the appropriate markings, which signify compliance with DOT regulations (required by law).
• Swivel fittings on the tractor end to avoid corkscrewing during installation.
• Spring guards to protect the hose or tubing from a sharp bend at or near the fitting.
• Added handle grips at the trailer end to provide protection from kinking of air lines during gladhand connection and disconnection.
• Coiled assemblies that extend to their maximum expected service length and return to their retracted position without sag.
However, the biggest factor is that proper overall working length should be used. In all cases, the length of the assembly must be adequate enough to ensure that the airlines are not stretched beyond a safe degree at their maximum expected service length, but must also be short enough to be protected from abrasion, snagging or tangling when in a relaxed state. To ensure that these standards are met, you must determine the proper length of the air assembly based on a number of factors.
These factors include the lead length, whether straight air lines or coiled assemblies are being used, the type of airline suspension method, and the positioning of the tractor/trailer when taking measurements.
According to SAE J702, the tractor connections on newer vehicles must be mounted low to allow easier access. This makes hook-ups more accessible but requires that the lines have a longer lead and some type of suspension system. Lead length is usually 12, 40, 48 or 72 in.; the most common is 48 in.
Lead length on the trailer side of the assembly should generally be between 6 and 12 in. Since the installation locations on trailers are usually very low, the use of leads that are longer than this will likely cause sagging of the lines.
After determining lead length, other factors need to be taken into consideration, although it should be noted that lead length does not necessarily always need to be determined first.
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