Which type of valve prevents water from entering a dry standpipe system until a fire is detected?

The pre-action valve is specifically designed for automatic fire suppression systems, particularly in dry standpipe systems. This type of valve achieves two primary functions: it prevents water from entering the system until a fire is detected and, simultaneously, it ensures that the system remains dry until it is necessary to activate it.

When a fire is detected through a connected fire alarm system or by heat-sensitive devices, the pre-action valve opens, allowing water to flow into the standpipe system. This staged approach minimizes the risk of accidental water damage in areas where a fire has not occurred, as the system remains dry under normal conditions.

In contrast, the other types of valves serve different purposes within fire protection systems. Control valves are more general in function, allowing manual or automatic control of water supply but do not prevent water entry based on fire detection. Quick opening devices facilitate the rapid flow of water during an activation but do not control when water enters a dry system based on detection. Reducing valves help manage water pressure within the system but again do not interact with fire detection mechanisms. Thus, the pre-action valve is uniquely suited for controlling water entry in response to fire detection, which is why it is the correct choice.