Coalescing Filters

A coalescing filter is a highly efficient filtration device designed to remove submicron-sized liquid aerosols and solid particulates from gas or compressed air streams. It works through a multi-layered media that causes fine liquid droplets to collide and merge (or "coalesce") into larger droplets. These are then heavy enough to drop out of the airflow by gravity and are drained away from the filter housing. 

Coalescing filters are typically installed after an air compressor and air dryer to remove oil carryover and water aerosols. This prevents contamination of downstream tools, instruments, and final products

Coalescing filters typically use depth media, such as borosilicate microfibres, to ensure fine contaminant removal down to 0.01 microns.

Coalescing filters are specifically designed to remove:

• Oil aerosols (common in compressed air systems)
• Water vapour and moisture droplets
• Fine solid particulates such as rust, scale, and carbon

These filters are essential in any compressor system where compressed air or gas purity is critical. Common industries include:

• Food & Beverage (protecting packaging and filling lines)
• Pharmaceuticals (sterile air supply, tablet coating)
• Oil & Gas (instrument air and gas dehydration)
• Automotive (paint spraying, pneumatic tools)
• Electronics (semiconductor cleanroom environments)

Particulate filters remove only solid contaminants. Coalescing filters are engineered to remove both solid particles and liquid aerosols.

The key difference lies in media structure: coalescing filters have a much finer and denser media structure designed to trap submicron droplets, merge them, and allow liquid drainage. Coalescers typically follow a pre-filter (particulate) in a multi-stage filtration setup.

High-performance coalescing filters can achieve up to 99.9999% removal efficiency for particles as small as 0.01 microns. For compressed air applications, this aligns with ISO 8573-1 Class 1 or 2 requirements for oil and particulate removal.

Elements should generally be replaced every 6–12 months, depending on:

• Contaminant load
• Operating pressure and temperature
• Pressure drop monitoring (usually recommended change-out at 0.6–0.8 bar differential) Neglecting replacement can reduce system efficiency, risk oil carryover, and damage downstream equipment.

Yes. Industrial-grade coalescing filters are available for high-pressure environments, with housings rated up to 1500 psi (103 bar) or more. These are commonly used in gas processing plants, breathing air systems, and hydraulic controls.

See our full range of Compressed Gas & Vent Filters HERE and our Gas Filter Housings HERE. 

The filtration media is typically made of borosilicate glass microfibres.

Higher temperatures reduce coalescence efficiency, as smaller droplets evaporate or pass through the media more easily. Filters should be selected based on the system’s maximum operating temperature. For compressed air systems, most coalescing filters operate efficiently up to 65–120°C depending on materials.

Yes. Filters come in various grades based on pore size and efficiency:

• General-purpose (1 micron, 99.9%)
• High-efficiency (0.01 micron, 99.999%)
• Ultra-high efficiency (sub-0.01 micron) Grades may also be denoted by colour-coded elements (e.g. blue for general, red for high-efficiency, white for sterile)

Maintenance includes:

• Monitoring pressure differential
• Draining the housing condensate (automatic or manual drain recommended)
• Cleaning housing interior during cartridge replacement
• Regularly checking seals and gaskets for degradation

Mechanical coalescing relies on fibre density and media layering to trap droplets. Electrostatic coalescing uses electrical fields to attract and combine droplets. The latter is often used in high-flow, low-viscosity oil-water separation systems. For compressed air and gas, mechanical coalescing is standard.