Check valves should not be used to subdivide the dry valve system unless installed in which type of enclosure?

Check valves in a dry valve system are crucial for preventing backflow and maintaining the integrity of the system. They are typically used to control water flow and ensure that water does not return to sections of the system that are not meant to be filled. However, when subdividing a dry valve system, the use of check valves requires special considerations related to temperature.

Installing check valves in a heated enclosure is essential because it helps prevent the water within the pipes from freezing. In a dry pipe system, the presence of water in any section can lead to potential freeze damage if temperatures drop. Heated enclosures provide the necessary warmth to keep the water in a non-freezing state, ensuring the system operates effectively without the risk of ice forming, which could block water flow or cause pipe breaks.

In contrast, other types of enclosures may not provide adequate protection against freezing temperatures, which is critical for a dry valve system. Therefore, for check valves to function correctly and perform their intended purpose in a dry valve system, they must be installed within a heated enclosure.