Which of the following causes the air to spin in a pneumatic air filter?

• A. Deflector plate
• B. The oil residue
• C. The absence of a filter element
• D. The presence of a seal

Answer: (A)

The air spins because a deflector plate inside the filter housing redirects the incoming flow, forcing it to swirl as it passes through the separation chamber. This swirl creates centrifugal forces that fling heavier oil droplets toward the chamber walls, where they coalesce and drain away, leaving cleaner air. Oil residue, absence of a filter element, or a seal don’t impart the spinning motion themselves; they relate to contamination or filtration status rather than the mechanism that induces the swirl.