At what pressure will the main reservoir be if the park brakes are applied?

The main reservoir pressure when the park brakes are applied will be less than 350 kPa because activating the park brake system typically results in a release of pressure in the main reservoir. The air is redirected and held in the brake cylinders to hold the vehicle stationary, which can reduce the overall pressure in the reservoir as pressure is utilized for the braking mechanism.

When the park brake is applied, the system creates an imbalance between the reservoir and the brake cylinders, leading to a drop in the remaining pressure within the reservoir itself. This pressure drop must be considered when evaluating the pressure in the main reservoir; therefore, it is expected to be below the threshold of 350 kPa.

Higher pressure options are not correct in this context, as they would suggest that the reservoir maintains its pressure while the brakes are actively applying force, which is not operationally consistent with how pneumatic brake systems function during engagement.