What is the required main drain size for risers that are 4 inches and larger?

The requirement for main drain sizes in sprinkler systems is determined by the size of the risers used in the system. For risers that are 4 inches and larger, the main drain size must be appropriately sized to ensure efficient drainage of water during system testing or maintenance.

When risers are 4 inches in diameter or larger, a 2-inch main drain is specified to ensure that the system can discharge water effectively without excessive back pressure or flow restrictions. The 2-inch drain size provides a balance between maintaining adequate flow rates and minimizing potential obstruction within the drainage system.

It’s important to adhere to these specifications to ensure that the sprinkler system functions correctly and complies with safety regulations. A larger main drain, such as 3 inches or 4 inches, could lead to unnecessary costs and may not be required for effective drainage, while a smaller main drain would not be sufficient for the demand created by larger risers.