According to standards, what must the check valve do in reference to the feed-pipe?

The function of a check valve in a feed-pipe system is critically important for ensuring that water flows in only one direction. Specifically, it must prevent water from flowing back to the source. When a boiler is being fed with water, the check valve ensures that once the water has entered the system, it cannot flow backward into the feed water source, which could lead to potential contamination or a loss of water supply.

This one-way flow is essential for maintaining pressure and functionality within the boiler system. If the water were allowed to flow back, it could disrupt the boiler's operation, potentially causing safety hazards or equipment malfunction. Therefore, the primary role of the check valve is indeed to safeguard against reverse flow, thereby protecting the integrity of the system.

The other options mentioned do not align with the primary function of the check valve. For example, while pressure relief is important within a boiler, it is usually managed by specific pressure relief valves; check valves do not directly relate to pressure relief processes. Similarly, measurement tools for water levels and temperature control are handled by other types of equipment and not by a check valve.