When checking the push-pull valve, what is the allowable leakage at the body and cover plate?

The correct response is that there should be no leakage from the push-pull valve, which is critical for ensuring the proper functioning of the air brake system in a school bus. A push-pull valve directs air to activate the brakes, and any leakage can lead to reduced braking efficiency or failure, posing significant safety risks.

In brake systems, even the smallest amount of leakage can compromise the system's integrity and performance. A complete absence of leakage guarantees that the air pressure maintained is sufficient to engage the brakes when needed. This ensures that the vehicle can stop safely and effectively, which is especially vital in the case of large vehicles like school buses that transport children.

While other options suggest varying degrees of acceptable leakage, any amount of leakage is not permissible in this context, as a fully operational push-pull valve is essential for maintaining control and safety while driving.