Average face velocity can hide local high-velocity zones caused by inlet momentum, upstream maldistribution, fouling, segment resistance, or vessel geometry. Local gas velocity often controls re-entrainment and separator stability more strongly than the calculated average velocity.

Increasing mist eliminator pressure drop can indicate fouling, liquid holdup, drainage problems, or hydraulic overload. Unexpectedly low pressure drop may indicate bypass or separator damage. Trend analysis under comparable operating conditions is more useful than a single reading.

High mist eliminator collection efficiency does not guarantee low vessel outlet carryover. Bypass, re-entrainment, gas maldistribution, excessive inlet liquid loading, incorrect droplet-size assumptions, installation problems, and downstream condensation can all reduce real system performance.

Poor drainage can cause liquid holdup, pressure-drop increase, re-entrainment, fouling, and separator flooding. Drainage capacity depends on separator geometry, orientation, liquid loading, supports, fouling condition, and cleaning arrangement.

Demister bypass, re-entrainment, and excessive upstream entrainment can all cause downstream liquid carryover. Their load behavior, pressure-drop pattern, installation condition, and process history help distinguish one mechanism from another.