If the length of pipe between the test header and the discharge side of the pump exceeds a certain length, what is the minimum nominal pipe size that must be used?

In fire protection systems, the length of pipe between the test header and the discharge side of the pump can significantly impact the performance of the system. When the length of the pipe exceeds a certain distance, it is crucial to ensure that the nominal pipe size allows for adequate flow rates and pressure levels to meet the system's operational requirements.

A nominal pipe size of 15 inches is often considered a standard for long runs, as larger diameters help minimize friction loss over extended distances. This helps maintain the necessary system pressure and flow, ensuring that the sprinkler system operates efficiently when activated.

Using appropriately sized pipe is critical in optimizing the hydraulic performance of fire sprinkler systems, as undersized pipes can result in inadequate water supply during an emergency, leading to ineffective fire suppression. Therefore, selecting a minimum nominal pipe size of 15 inches provides a reliable safety margin for the system's functionality when faced with long pipe runs.

This rationale explains why understanding the implications of pipe lengths and diameters is integral to designing effective fire protection systems.