This SAE Recommended Practice applies to S-CAM, Wedge, and Disc air brake actuators where the stroke can be measured without disassembly from the brake.
Field inspections to determine if air brakes on commercial vehicles are in an out-of-service condition are excessively complicated. Current method requires measurement of the air brake actuator diameter to determine the air brake actuator size. A standard rated stroke for the air brake actuator size is then assumed unless a marking is found on the air brake actuator or ID tag that indicates a different rated stroke. Using the determined rated stroke and chamber size, a chart is referenced to provide the brake adjustment limit. The inspector then confirms through measurement that the air brake actuator stroke is less than the determined brake adjustment limit.
This method has many potential sources for error. A given actuator size may have several rated stroke options available. Charts converting air brake actuator diameters are not accurately maintained. Air brake actuator diameters are not accurately measured. Air brake actuator manufacturers do not have standardized ID tag nomenclature making it difficult to read the rated stroke. Air brake actuators can be covered in paint or road debris hiding rated stroke information. Stroke rating clamp tags require clamps to mount to and must be located in a clamp clocking that is accessible to the inspector.
This process can be simplified because the brake adjustment limit is a function of the rated stroke only. By putting a standardized rated stroke marking on the air brake actuator in a known location, the only conversion required is between the rated stroke marking to the brake adjustment limit. This document provides this recommended practice, reducing the likelihood of an inspector passing a vehicle that should be out of service or putting a vehicle out of service that is within acceptable operating conditions.
This new recommended practice also provides air brake actuator outside diameters developed from manufacturer's data for reference to support air brake actuators manufactured prior to this recommended practice. The SAE Truck and Bus Brake Actuator Committee have the largest representation of air brake actuator manufacturers making it the ideal source for such information.
If this document gets adopted, SAE J1817 will be revised to identify long stroke air brake actuator markings only to avoid overlap.