Dew Point

Canonical Definition

The temperature at which water vapour in compressed air reaches saturation and begins to condense into liquid water, expressed at the system operating pressure (pressure dew point, PDP) or at atmospheric pressure (atmospheric dew point, ADP). ISO 8573-1 defines water quality classes by pressure dew point: Class 1 requires PDP ≤ −70°C; Class 2 ≤ −40°C; Class 3 ≤ −20°C; Class 4 ≤ +3°C; Class 6 (general industrial) ≤ +10°C. Dew point is measured by chilled-mirror hygrometers or capacitance-based sensors calibrated to NIST standards.

Engineering Context

Compressed air distribution systems must maintain dew point below the minimum ambient temperature to prevent condensation in pipes, actuators, pneumatic instruments, and process equipment. Condensed water causes pipeline corrosion, microbial growth, pneumatic valve freezing in sub-zero environments, and contamination of sensitive process streams. Refrigeration dryers achieve PDP of +2°C to +10°C for general industrial air; desiccant dryers achieve PDP of −40°C to −70°C for instrument and process air. DRYCORE compressed air filtration systems include coalescing pre-filters and particulate post-filters working in series with drying equipment.

Applicable Standards

Related Technologies

Related Terms