Install an accurate pressure test gauge in the secondary service reservoir.To check the trip pressure of the yellow parking brake control valve: That said, the FMCSA Commercial Driver’s License Manual includes a note in the air brake section that says the parking brake valve should close, or “pop out,” at approximately 40 psi - a specification that isn’t supported by regulation, and which can cause some confusion, Bendix says.
Parking brake “pop pressure” isn’t addressed in Federal Motor Carrier Safety Regulations (FMCSR) for in-use vehicles, the Federal Motor Vehicle Safety Standard (FMVSS) for newly manufactured vehicles, or the out-of-service criteria checked during inspections such as roadside checks by the Commercial Vehicle Safety Alliance (CVSA) although FMVSS 121 does require a single control for the park valves on a tractor-trailer and all the vehicles in a combination train. The parking brake control valve - the one with the yellow button - has no Federal Motor Carrier Safety Administration (FMCSA) regulations specifying the pressure at which it must automatically trip to apply the vehicle parking brakes. The good news is, it’s easily cleared up with a quick review of what these two dash valves do and how to test them.” (See diagram at end of the story.) “And while it’s not something we’re asked about every day, the confusion goes back a long way.
“We periodically get questions about straight trucks, tractors and buses being cited for dash control valves not automatically ‘tripping’ to the exhaust position at a predetermined system pressure,” says Brian Screeton, Bendix technical training supervisor. The tips focus on the red and yellow dash control valves for tractor protection and parking brakes. This edition of Bendix Tech Tips Series addresses regulations for dash valve trip pressures and how fleets and owner-operators stay compliant and safe.
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