HEPA Filter Air Flow Velocity

PURPOSE: To determine the volume of air delivered through each HEPA filter and to calculate the average airflow, uniformity range and room air exchange rate, within the Cleanroom.

INSTRUMENTATION: Shortridge - Calibration documents for equipment used for testing will be included in the certification reports.

  • Unidirectional Air Flow Test: Divide the work zone entrance into a grid of 2' x 2' sections. Test with the anemometer / Shortridge 12" below filters.
  • Non-unidirectional Air Flow Test: Divide the filter into 2' x2' sections. Orient the anemometer perpendicular to the velocity flow vector being measured. The probe should be positioned at a distance of no more than 6" (15 cm) from the filter face.
  • Airflow volume test using anemometer / Shortridge: Measure and record the linear flow rate and average the result(s). Multiply the average velocity by the effective filter area to arrive at total cubic volume.
  • Airflow volume test when using a Balometer: The flow hood opening is placed completely over the filter or diffuser, seating the face of the hood against a flat surface to prevent air bypass and inaccurate readings. Measure and record the flow rate in cubic volume per minute for each filter or diffuser.
ACCEPTANCE: The average airflow velocity or the average or total airflow volume for the cleanroom of clean zone should be within ± of the value specified for the cleanroom or clean zone, or within other tolerance limits agreed upon by the buyer and seller.

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