Minnesota Boiler License Practice Exam

When two stop valves are used on a steam outlet line, it is good practice to have one valve:

1. Slow opening

2. Automatic non-return

3. Quick opening

4. Electric actuated

The correct answer is: Automatic non-return

Having one of the two stop valves in a steam outlet line designed as an automatic non-return valve is important for ensuring safety and system integrity. An automatic non-return valve, often referred to as a check valve, permits steam to flow in one direction while preventing backflow. This characteristic is particularly crucial in steam systems where the possibility of backpressure could lead to dangerous situations, such as reverse flow damaging equipment or creating hazards due to pressure fluctuations. In systems utilizing two stop valves, the non-return valve serves as a safeguard. It allows safe isolation and maintenance of equipment by mitigating risks associated with backflow when the primary valve is closed. This setup is especially beneficial in preventing water hammer—damage caused by the sudden change in water flow—and maintaining continuous pressure in the line, which is vital for the efficient operation of steam-using equipment. Other options such as slow opening and quick opening valves have specific operational characteristics that may be beneficial in certain contexts, but those functions do not address the critical need for preventing flow reversal in the same way that an automatic non-return feature does. Similarly, electric-actuated valves are more about convenience and control rather than the fundamental need for preventing backflow in this scenario.