How does moving the brake valve from left to right through the service zone affect pressure?

Moving the brake valve from left to right through the service zone has the effect of gradually reducing both the equalizing reservoir pressure and the brake pipe pressure. The service zone is designed to initiate a controlled reduction in air pressure, which in turn activates the brakes in a smooth and gradual manner rather than abruptly.

The reduction in brake pipe pressure is crucial for achieving a gradual application of brakes, allowing for better handling of the train and preventing sudden stops that could lead to derailments or other safety issues. At the same time, the equalizing reservoir, which balances the pressures in the brake system, also experiences a corresponding drop in pressure as part of this process. This coordinated reduction in pressure ensures that the braking force is applied uniformly across all cars in the train.

Gradual reductions help maintain control over the train's speed and stopping distances, thus enhancing safety and efficiency. Other options might suggest no change or immediate actions that don’t accurately represent the function of the brake system during this maneuver.