Which of the following is used to prevent water from leaking out of the pump volute?

The correct choice highlights the importance of sealing components within a pump system. Packing and mechanical seals are specifically designed to prevent leaks from the pump volute, which is crucial for maintaining efficiency and preventing water loss.

Packing refers to a series of materials that create a seal around the shaft. When properly tightened, it compresses to fill any gaps, thus minimizing leakage. Mechanical seals take this a step further by employing precise engineering; they consist of two flat surfaces that face each other and are kept together under pressure, which effectively prevents fluids from escaping the pump.

Other components mentioned have different functions: O-rings are used as seals but are typically found in static applications and smaller gaps rather than in the context of the pump volute. Safety valves are used to prevent overpressure situations, while check valves prevent backflow in a system, but none of these are designed specifically to stop water from leaking out of the pump's hydraulic area. Therefore, packing and mechanical seals play a vital role in ensuring the pump operates efficiently and effectively, making them the correct answer.