Auxiliary drains are required for each section of trapped pipe in which types of fire protection systems?

• A. Wet Pipe and Dry Pipe Systems
• B. Dry Pipe and Pre-Action Systems
• C. Wet Pipe and Deluge Systems
• D. Deluge and Pre-Action Systems

Answer: (B)

Auxiliary drains are used to vent and drain sections of piping that can trap air in certain fire protection systems. In a dry pipe system, the piping is charged with air under pressure to keep water out; when a sprinkler is triggered, water enters and air must be vented from the section to prevent air locks and to ensure proper water flow. An auxiliary drain provides a dedicated outlet to discharge that trapped air and to drain the section for maintenance or hydrostatic testing. In a pre-action system, portions of the piping may also be dry or partially charged until the triggering event occurs, so draining each section after testing or maintenance helps verify that the line is clear and leak-free. Wet pipe and deluge systems are normally filled with water, so there isn’t trapped air in the sections that would require an auxiliary drain for routine operation, making the per-section auxiliary drain requirement specific to dry pipe and pre-action systems.