Massachusetts Plumbers Journeyman Practice Exam

According to sizing requirements, what should be the cross-sectional area at the valve seat of vacuum relief valves?

1. Equal to the cold water supply size

2. Two pipe sizes smaller than the cold water supply

3. One pipe size smaller than the cold water supply

4. Half the cold water supply size

The correct answer is: One pipe size smaller than the cold water supply

The correct answer is that the cross-sectional area at the valve seat of vacuum relief valves should be one pipe size smaller than the cold water supply. This sizing is critical because it allows for adequate airflow while maintaining enough pressure differential to function effectively. This configuration helps prevent potential damage due to vacuum conditions that can occur within piping systems, especially in heated water applications or when cooling occurs rapidly. Having the valve seat sized appropriately—not exceeding one pipe size smaller than the cold water supply—ensures that the valve can act rapidly to relieve any vacuum conditions without being excessively restrictive. This contributes to overall system efficiency and safety. Other choices suggest sizing that might be too small or too large for effective operation, which could compromise the functionality of the vacuum relief valve. Ensuring a proper size is essential to both the operational efficiency and the safety of plumbing systems.