As air can be hot, wet and dirty, air preparation is a crucial process and air used in compression lines should flow through a filtering, regulating or lubricating process (FRL).
A coalescing filter is used in compressed air systems to remove oil droplets and fine particles, down to 0.01 micron in size. As unwanted oil can stick to moving parts and slow down pneumatic cylinders, a coalescing filter is an important part of air preparation. In conjunction with a general purpose filter, which can draw out water and larger particles, a coalescing filter drains oil droplets into a bowl.
How does a coalescing filter work?
A coalescing filter removes oil by forcing air through an element. When the air changes direction and bumps into itself, it forces any oil to coalesce, or stick together. This creates drops which are caught on an outer sock and gain mass, being forced down into an attached bowl by gravity. The oil is then drained away otherwise it could get back into the system and contaminate it.
How do I select a coalescing filter?
When it comes to choosing the correct coalescing filter, there are a few features you should consider, including the type of material the bowl is made from. With a choice of metal or polycarbonate – which are transparent – you should also consider the following:
- Substance exposure: A polycarbonate bowl cannot be exposed to incompatible substances. In this instance, a coalescing filter with a metal bowl should be selected.
- Temperature and pressure: Metal bowls can be exposed to lower temperatures and higher pressure than polycarbonate bowls.
Other features to look for when selecting the appropriate coalescing filter are:
- Automatic or manual drain: Coalescing filters are available with a manual or an automatic drain option. Automatic drains require a minimum of 0,35 bar (5psi) in order to close. As manual drains have to be checked regularly, ‘fit and forget’ automatic drains are generally the preferred option in many systems.
- Air purity class: Coalescing filters can remove oil to 0,01 mg/m3, with particle removal down to 0,01, in line with ISO 8573-1.
- Visual service indicator: Most coalescing filters are fitted with indicators which turn from green to red when the filter elements need replacing.
- Size and weight: Coalescing filters with polycarbonate bowls are generally lighter in weight.
Types of coalescing filters
IMI Norgren has a range of coalescing filters compatible with Excelon Plus and Olympian Plus products. These are available with manual or automatic drains, and with metal or transparent bowls, depending on what the application requires.
Typical applications of coalescing filters
Coalescing filters are commonly found in applications ranging from paint spraying and food preparation to the manufacture of paper materials.
Do I need anything else to make a coalescing filter work?
In addition to fittings, tubing and brackets, a general purpose filter is essential, and should be fitted upstream of the coalescing filter. To keep a coalescing filter running effectively, it should be maintained and serviced annually, or when visual service life indicator turns to red.