What do you call a sprinkler system that always has water in the pipe?

A sprinkler system that always has water in the pipe is referred to as a wet system. This type of system is constantly filled with water under pressure, allowing for immediate activation and response in the event of a fire. When a sprinkler head is activated due to heat from a fire, water immediately sprays from the head to extinguish or control the flames.

Wet systems are commonly used in areas where the temperature is maintained above freezing, as the presence of water in the pipes eliminates the risk of freezing and ensures rapid firefighting capability. Their straightforward design and quick response time make them an effective choice for many applications, especially in commercial and industrial settings.

In contrast, dry systems contain pressurized air instead of water in the pipes, allowing for operation in environments where freezing might occur. Pre-action systems require both heat detection and the activation of the sprinkler head to release water and are often used in areas with sensitive equipment. Deluge systems are designed to release large amounts of water through multiple sprinkler heads simultaneously and are typically used in high-hazard areas.