Regarding air filter velocity for dirt removal, which statement is correct?

• A. A typical value for best filtration is 50 feet per minute.
• B. Both statements are correct.
• C. Neither statement is correct.
• D. Velocity should be kept as low as possible.

Answer: (D)

Slower air flow through a filter gives particles more time to encounter and adhere to the filter fibers, improving dirt removal. Lower face velocity also reduces turbulence and the chance of captured particles being re-entrained, and it lowers the pressure drop across the filter, which helps the system run more efficiently and extends filter life. Because of these benefits, the best practical guidance is to keep the velocity as low as possible while still achieving the required airflow. A fixed value like 50 feet per minute isn’t universally correct because the optimal velocity depends on the specific filter media and system design; there isn’t a one-size-fits-all number.