The Frazier High Differential Pressure Air Permeability Tester was the 2nd model of the Frazier Air Permeability Instrument developed by Frazier Instrument Company for the United States Air Force.
This is an extend range version of the FAP-LP that has the same resolution and repeatability at the low end but extends to 21" of water pressure drop and to 5000 CFM / SF of airflow. This model is used for testing very open material with high airflows and also materials that have no readable airflow at 0 to 1" of differential water pressure.
For a more compact and mobile version of the FAP-HP, see the FAP-HPC and for a lower end version see the FAP-LP. For a computerized version see the FAP-F2.