From FestoWiki - english
Jump to: navigation, search

Symbol Filter.png

Compressed air must always be so clean that it cannot cause any malfunctions
or damage.Contamination accelerates wear on sliding surfaces and sealing elements.
This can affect the function and service life of pneumatic
components. Because all filters also represent flow resistance,
for economic reasons compressed air should
only be as clean as necessary

Filter types

Compressed air filters remove particulate and droplets of moisture from the air. Particles >40 ... 5 μm (depending on the grade of filtration) are retained by a sintered filter. Liquids are separated with the aid of centrifugal force. The condensate which accumulates in the filter bowl must be emptied from time to time, because it would otherwise be drawn in by the air flow.


Centrifugal separators

The centrifugal separator is a type of coarse prefilter for water droplets and larger dust or dirt particles (larger than 50 μm). To put it simply, the centrifugal separator works like an air spinner. A whirl insert is installed in the air flow (from top to bottom), which causes the air to rotate rapidly. The resulting centrifugal forces cause the heavier particles - water and coarser dirt - to be spun radially towards the outer walls, from where they run into a collecting container, the so-called filter bowl with condensate drain





Prefilters are basically fine strainers.They are almost always round and flow takes place through them from the outside to the inside. Particles, and, to a lesser extent, oil and water, are collected on the surface. The pore size of the filter determines the particle size which can be filtered. These filters are re-usable, as they can be cleaned. With a filtered particle size of between 25 and 40 μm, these filters are generally sufficient for "normal" requirements.



Micro-filters (coalescing filters) are filters for high demands. The residual oil content is reduced to a value of 0.01 mg/m³ - this equals class 1 of the compressed air qualities - and the air is then practically oil-free. Dirt particles are filtered out to 0.01 μm which also corresponds to class 1. The filters consist of a pleated fleece material, which is made up of many individual fibres. With micro-filters, the air flows from the inside to the outside. Oil and water are gradually forced outwards and part of the condensate can thus leave the filter again. This increases the lifetime of the filter.



Activated carbon filters

On activated carbon filters, the hydrocarbons are bound to the activated carbon through adhesion. The activated carbon is therefore not re-usable. Hydrocarbons, odours and flavours which were not removed by the micro-filters, are filtered out at this point. An activated carbon filter must always be positioned downstream of an air dryer and a micro-filter. With adsorbers, a micro-filter even needs to be positioned downstream, as the compressed air can draw in extremely fine carbon particles that are smaller than 1 μm.


Water in compressed air

The only correct way to remove excess water from compressed air is to use an air dryer. If a dryer cannot be used, there is the option of removing at least part of the water from the compressed air via filters. To do so, we recommend the use of a filter combination with at least a 1 µ prefilter and a subsequent 0.01 µ filter.

Bowl guards

According to DIN ISO 4414 Chapter 8.4.1, non-metal filter and separator housings must be equipped with a burst protection feature.