If the locomotive recalibrating valve is set at 90 PSI, what pressure is required on the rear car during a Class 111 air brake test?

In a Class 111 air brake test, the goal is to ensure that the brake system is functioning correctly and effectively. The recalibrating valve on the locomotive plays a crucial role in this process by helping to maintain appropriate pressure levels.

When the locomotive recalibrating valve is set at 90 PSI, the necessary pressure on the rear car should be lower than the valve setting to allow for a functional brake test. According to the standards set forth in the GCOR, a standard practice is to have the rear car maintain a pressure that is approximately 5 PSI lower than the set pressure of the locomotive valve. Therefore, if the locomotive's recalibrating valve is at 90 PSI, the ideal pressure on the rear car would be set at 85 PSI.

However, the values provided in the options indicate a slight adjustment in this typical scenario, and 75 PSI is a commonly recognized standard threshold for ensuring safety and performance during brake testing, allowing for variances in system performance and ensuring effective braking with a balance of operational pressure levels.

Therefore, setting the rear car to 75 PSI aligns with the protocols ensuring the system's reliability and functionality during air brake testing on freight and passenger services. This level is in place to ensure that the brakes engage