Manometer pressure drop reading guide

A clean intake-ceiling filter typically reads 0.1-0.3 inches of water column ("WC) at design airflow. As the filter loads, pressure drop increases, particulate accumulates, restricting flow. End-of-life threshold is typically 0.5-1.0" WC, varying by booth design and the manufacturer's specification. The HMI alarm (where present) fires near the upper end of that range.

Reading the manometer, most installations use a magnehelic gauge mounted on the booth's control panel. The needle reads in inches of water column. Some installations use digital readouts. The reading is steady when the booth is at operating airflow; transient spikes during fan startup are normal.

Interpreting the reading, single readings are less useful than trends. A reading of 0.4" WC tells you you're partway through the cycle; a reading that's risen from 0.3" to 0.4" over the past two weeks tells you about the loading rate. Track readings weekly (or after each significant volume event) and watch the trend.

Multiple manometers, installations with separate intake-ceiling, exhaust-pit, and AMU pre-filter monitoring have a manometer for each position. The HMI typically aggregates them for the alarm; the per-filter readings are visible separately on the gauge or display.

When the reading doesn't match the visible filter, if the manometer reads end-of-life but the filter looks clean, check the gauge calibration (zero offset can drift). If the filter looks loaded but the manometer reads low, check the gauge for damage or a clogged sense line. Professional service handles gauge calibration and sense-line repair.