When is it appropriate to close all drains and valves in the priming process?

Closing all drains and valves during the priming process is important to create a vacuum and allow the pump to effectively draw water into the system. When all drains and valves are properly closed, it ensures that there are no leaks or air pockets that could impede the flow of water into the pump. This controlled environment is crucial to achieving a successful prime, which allows the pump to build the necessary suction.

During priming, the goal is to eliminate air from the system, and having all openings sealed helps maintain consistent pressure and enhances the pump's efficiency. If drains or valves were left open during this process, it could lead to reduced suction and difficulty in priming.

The other scenarios do not align with correct practices during the priming process. Closing all valves and drains before starting the engine or when the tank is empty would not be effective because the system needs to be prepared for pumping water into the pump immediately after the engine is running. Keeping all drains and valves closed at all times is impractical as it would not allow normal operation or adjustments when necessary.