What pressure will the safety valve on the supply tank vent at?

Answer: C — 150 psi

The safety valve on the supply tank is designed to vent at a specific pressure to prevent excessive pressure buildup that can potentially cause damage. In the context of air brake systems, the safety valve typically vents at 150 psi. This pressure point is crucial because it provides a balance between operating efficiency and safety. If the pressure exceeds this limit, the safety valve opens to release air, thereby preventing any dangerous conditions that could arise from over-pressurization. The choice of 150 psi as the venting pressure is standardized in many air brake systems, ensuring reliability across different vehicles and applications. Maintaining this pressure standard is key to ensuring the safety and functionality of the air brake system.