Coalescing filtration removes liquid and particulate contaminants from compressed air and other compressed gases, providing protection for critical equipment and components. Liquid contaminants removed include oil and water aerosols. Particulate contaminants removed include rust, pipescale and dust.
The basics of coalescing filtration
Coalescing filtration refers to a continuous process whereby oil and water aerosols and fine droplets run together to form larger, heavier droplets that are gravitationally drained away.
Coalescing filters should always flow from the inside of the filter element to the outside of the filter element. This allows for the oil and water droplets to collect on the fibers of the filter element, merge at crossover points to become larger droplets as they travel down the filter element, and naturally drain off the base of the element into the sump area of the filter housing. From there, the liquid releases into an automatic float drain where it is drained out of the system.
Methods for contaminant removal
Coalescing filters remove liquid contaminants by three methods:
- Direct Impact – typically 1 micron and larger size particles
- Interception – typically between 0.1 and 0.6 micron
- Diffusion – typically 0.1 micron and smaller size particles
Coalescing filters remove oil and water contaminants from compressed air and other gases. These contaminants originate from compressor lube oils, residual cutting oils, condensed moisture, carbonized oils, and solutions of dissimilar oils.
As a natural byproduct of their design, coalescing filters also offer high efficiency depth filter particle removal. Solid contaminants such as rust particles, dust, solder particles, welding flash, etc., will determine the useful life of the filter element because they become permanently trapped in the element, creating a barrier that restricts flow and increases differential pressure drop in the compressed air system. This can easily be measured using a differential pressure indicator, or planned as part of a routine maintenance schedule.
For optimum equipment protection, coalescing filters should be located as close to the application point of use as possible to ensure no additional liquid condensation occurs. For general plant compressed air conditioning, the filters should be located on main compressed air lines at the point where the pressure is highest and the temperature is lowest to ensure the maximum amount of water is in a liquid state to maximize removal efficiency of the filter.
Coalescing filters are ideal for the continuous removal of liquid and particulate contaminants, to the sub-micron level, from compressed air systems, and for protecting sensitive equipment and instrumentation from damage and malfunction.
For additional information read about compressed air filter installation recommendations. You can also refer to the compressed air filters section of the Parker Balston compressed air and gas treatment product catalog.
This post was contributed by Allan Fish, Compressed Air and Gas Treatment Product Manager, and Judy Silva, Compressed Air and Gas Treatment Technology Team Member - Parker Hannifin.