Class 5 Boiler Practice Exam

Vacuum relief valves are used to prevent which of the following?

1. Overpressure conditions

2. Vacuum conditions

3. Temperature fluctuations

4. Water hammer

The correct answer is: Vacuum conditions

Vacuum relief valves are specifically designed to prevent vacuum conditions within a vessel or system. When the pressure inside a boiler or storage tank drops below the atmospheric pressure, a vacuum is created, which can lead to potential structural damage. This can occur if the system cools rapidly, causing the steam or vapor to condense and thereby reducing the pressure. The proper functioning of vacuum relief valves allows for ambient air to enter the system, thereby equalizing the pressure. This prevents implosion or deformation of the vessel's structure due to the negative pressure. Thus, the purpose of vacuum relief valves aligns perfectly with the need to maintain appropriate pressure levels inside a system, affirming the validity of the answer provided. The other options relate to different types of safety concerns: overpressure conditions pertain to excess pressure situations, temperature fluctuations deal with variations in thermal energy, and water hammer refers to pressure surges caused by sudden changes in fluid flow. Each of these has distinct preventative measures that differ from the role of a vacuum relief valve.