How long should listed indicating valves take to close when operated at maximum speed from full open position?

The correct answer is based on the requirements set forth by NFPA 13 regarding the operational characteristics of listed indicating valves. These valves should close within a specified timeframe to ensure effective system performance and safety. The standard stipulates that when operated at maximum speed from a fully open position, listed indicating valves must close within 5 seconds.

This requirement is significant because a rapid closure helps in minimizing the water hammer effect and potential damage to the piping system, which could occur if the valve closes too slowly. Additionally, maintaining a prompt response helps in effectively controlling the water flow in the event of an emergency, ensuring that the fire protection system can function as intended.

The higher time frames of 10 seconds or 15 seconds would not meet the guidelines set forth by the standard and could lead to inefficiencies or compromised safety in a system designed to protect lives and property in the event of a fire.