3rd Class Power Engineering (3B1) Practice Exam 2025 - Free 3rd Class Power Engineering Practice Questions and Study Guide

Non-return stop valves, also known as check valves, are strategically utilized in boiler systems to prevent backflow of water and steam. The correct context for their use is when multiple boilers are connected to the same header. This configuration presents a risk where one boiler could potentially backflow into another boiler, especially if they operate at different pressures or temperatures. By employing non-return stop valves, you ensure that steam or water flows in one direction only, maintaining system integrity and efficiency.

When installed in a system with multiple boilers on the same header, these valves safeguard against issues such as pressure fluctuations and water hammer, which can occur if backflow happens. The setup ensures that even if one boiler shuts down while others are in operation, the non-return valve will keep the remaining boilers functioning without interference from the deactivated boiler.

Using non-return stop valves is not typically necessary for a single boiler system, as there is no risk of backflow from other boilers. Additionally, the application of these valves is unrelated to low-pressure conditions, as their primary function focuses on preventing backflow regardless of the pressure levels in the system. Thus, the use of non-return stop valves is crucial in maintaining the operational reliability and safety of multi-boiler systems connected to the same header.