A unit of pressure equal to the pressure exerted by a column of liquid water 1" high at standard conditions (70°F. at sea level); 27.7" of water equals 1 psi; usually expressed as inches water gauge (W.G.) or inches water column (W.C.).

A measurement of vacuum or pressure that is used to measure the airflow restriction. ( 070)

Units used to measure small pressure differentials across filter components for both vacuum and pressure applications. One inch of water column equals 1.868 torr (or 1 PSI = 27.7” H2O).