Final line filters for instrument air must be rated for at least what percentage efficiency and at what micron size?

• A. 100% @ .10
• B. 98% @ .01
• C. 100% @ .01
• D. 98% @ .10

Answer: (B)

Instrument air feeding delicate controls must be very clean, since tiny particulates can clog sensors, affect readings, or cause valves to stick. The final line filter is the last barrier before the air reaches the equipment, so its rating shows how well it protects that equipment.

A specification of 98% efficiency at 0.01 micron means the filter removes the vast majority of particles as small as 0.01 microns, passing only about 2% of those ultra-fine particles. That level of filtration helps keep instrumentation and pneumatic controls reliable without creating an excessive pressure drop or flow restriction.

The other options either imply unattainable perfect filtration or target larger particles, which would allow more submicron contaminants to slip through and potentially affect instrumentation.