When shutting down the relay, what should each driver/operator do first?

The correct procedure for shutting down the relay involves first decreasing the throttle and then opening the dump line valve. This approach is essential for ensuring the smooth and safe operation of equipment. By decreasing the throttle gradually, the driver/operator reduces the engine's power output, which helps prevent sudden disruptions that could lead to equipment damage or safety hazards.

Opening the dump line valve while the throttle is decreased allows for a controlled release of any accumulated pressure in the hydraulic system. This step is crucial as it prepares the system for shutdown by preventing pressure build-up, which could otherwise lead to malfunctions or hazardous conditions. Properly managing pressure is a key component of operating heavy machinery safely and effectively.

In contrast, the other options involve either increasing the throttle or closing the dump line valve, which could create potential instability and lead to dangerous situations if not handled correctly. Hence, the correct sequence of actions emphasizes safety through controlled power reduction and systematic pressure management.