Main control valves for sprinkler systems must be of which type?

The main control valves for sprinkler systems must be of the indicating type because these valves provide visual confirmation of whether the valve is open or closed. This is critical for firefighting operations, as firefighters need to quickly assess the status of the valve without needing to physically inspect it.

Indicating valves typically feature a visual indicator or a position indicator that shows the valve's status, making it easy for emergency responders to determine if the water supply to the sprinkler system is available. This feature enhances operational efficiency and safety during a fire response, ensuring that firefighters can effectively utilize the sprinkler system as part of their overall firefighting strategy.

The other types of valves do not provide the same level of clarity and safety. Automatic valves could operate without human intervention, but they may not provide immediate status visibility. Manual valves require physical operation and inspection, which can delay critical decision-making in emergencies. Closed type valves imply that they are designed to shut off flow, which may not be suitable for ensuring instant visibility on system status.