What must be installed on a pneumatic water system?

A relief valve is essential in a pneumatic water system because it serves as a safety device that prevents excessive pressure buildup within the system. Pneumatic systems often rely on compressed air to maintain pressure and operate effectively. If the pressure exceeds the system's safe operating limits, the relief valve actuates to release the excess pressure, thereby protecting the system components from failure or damage. Additionally, this mechanism contributes to the overall safety of the installation, preventing potential hazards associated with over-pressurization, such as pipes bursting or equipment malfunctioning.

In the context of the other options, while pressure regulators can help maintain a consistent pressure, they do not specifically address the need for pressure relief in case of an overpressure situation. Flow restrictors are used to control the flow rate but do not provide safety against excess pressure. Backflow preventers are critical for preventing contamination of the potable water supply and are not primarily designed to manage pressure issues in pneumatic systems. Therefore, the relief valve's role is crucial for maintaining the integrity and safety of a pneumatic water system.