Coalescing

Canonical Definition

A water separation mechanism in which fine, emulsified water droplets in fuel or hydraulic fluid contact hydrophilic filter media fibres and merge (coalesce) into progressively larger droplets. The larger droplets, now heavy enough to overcome the fluid drag and surface tension forces that kept them emulsified, migrate to the outer surface of the coalescing element and drain by gravity to a sump for removal. Coalescing is distinct from absorption (retaining water within the media) — it removes free and emulsified water while allowing the bulk fluid to pass. Coalescing efficiency decreases with high surfactant concentration in fuel, which stabilises emulsions.

Engineering Context

Coalescing water-separation filters are the primary active water removal technology for fuel systems. HYDROCORE coalescing elements are rated for the required water separation performance of the approved application. The settled water must be drained from the filter bowl regularly — typically every 100–250 hours or when the water drain indicator activates — to prevent water re-entrainment in high-flow conditions.

Applicable Standards

Protection Systems

Knowledge Center Articles

Related Terms