For a 4" sprinkler riser, what is the required width of the main drain?

The required width of the main drain for a 4" sprinkler riser is 2 inches. This is determined by NFPA (National Fire Protection Association) standards, which provide guidance on the sizing of system components for fire protection systems.

In the context of a 4" riser, a 2-inch main drain is adequately sized to safely discharge the required flow for testing and maintenance of the system. It allows for the efficient removal of water from the system during the testing process without risking excessive pressure buildup or flow imbalance within the sprinkler system. Proper sizing of the main drain is critical to ensuring that the system can function correctly and can be inspected thoroughly.

Understanding the sizing requirements of components like the main drain is essential for proper fire protection system design and compliance with relevant fire codes. It ensures that water can be drained effectively without impacting the overall performance of the system during operation or maintenance activities.