What is the appropriate piston travel for truck-mounted brake cylinders when brakes are applied?

The appropriate piston travel for truck-mounted brake cylinders when brakes are applied should be within the limits of the travel indicator. This is crucial because the travel indicator provides a visual means to ensure that the brake system is functioning properly and that the brake cylinders are operating within their designed specifications. Proper piston travel ensures effective braking performance and helps prevent brake failure. If the piston travel is beyond the specified limits, it may indicate wear or malfunction within the brake system, potentially leading to safety issues.

While other options might suggest specific measurements or requirements, such as having clearance or extending a certain length, they do not effectively encompass the full range of proper operation as defined by the travel indicator, which considers factors like brake wear and system pressure. Thus, adhering to the travel indicator helps train operators to maintain the brakes in optimal conditions, ensuring safety and reliability in braking performance.