Which of the following statements about plumbing regulations is true?

In plumbing systems, water hammer is a common issue that occurs when a fluid in motion is forced to stop or change direction suddenly, creating a shock wave within the pipes. This can lead to loud banging noises and potential damage to the plumbing system. To mitigate this, water hammer arrestors are installed, which act as a cushion to absorb these shock waves.

The requirement for water hammer arrestors to be placed near quick-acting valves is critical because these types of valves can rapidly open or close, leading to sudden changes in water pressure and flow. By installing the arrestors in close proximity to these valves, the shock caused by their operation can be effectively dampened, preventing noise and reducing the risk of damage to the piping system.

This understanding reflects the importance of adhering to plumbing regulations regarding the appropriate installation and placement of devices designed to protect the integrity and functionality of plumbing systems. In contrast, the other options present statements that do not align with accepted plumbing practices or code requirements. For instance, low-hazard systems do still require inspections to ensure safety and compliance, drain sizes can vary based on specific applications, and pressure-reducing valves often are mandatory in systems that exceed certain pressure thresholds.