The Weller FT fume extraction systems are supplied with a two stage filter system.
The more recent fume extractors have a three stage filter system, a pre-filter is included.

The flow rate of the fume extractors is rated for the filter.
A high flow rate can be boasted in the spec. of a filter system, but if the flow rate is too high, the dust and/or gasses may pass through the filter before being captured.

A fume extraction system is usually required to remove a harmful gas.
The production process may also create dust particles or dust may be pulled into the filter just from the surrounding workplace.

The filter needs to be able to remove the harmful gasses  and cope with the dust, the dust can, over time, prematurely block the filter.
For this reason a pre-filter is an important part of the filter system, the pre-filter protects the main filter from the dust.
When the pre-filter becomes blocked it can be replaced, a cheap filter compared to the main filter which contains the more expensive gas filter media.

The main filter has a HEPA particle filter, this catches any remaining smaller dust particles that pass through the pre-filter.
The particle filter is 99,96 % efficient.

The standard gas filter contains a media made up of 50 % active carbon  50 % Chemisorb.
Other gas filter are available for use with different processes/chemicals.
The gas filter is 95% efficient.

The MG130 fume extraction system is primarily designed for solder fume extraction.
To make the system economical the filter has filter has enough gas filter media to last 1 year.
This is based on a 5 day 8 hour shift.
This way the filter is cheaper any when changed annually which is recommended, the filter has been fully used.
The MG140 filter system is more suitable for longer shifts or heavier soldering applications.

The MG130 is supplied with a pre-filter pad to capture the larger dust particles.
  

The MG140 fume extraction system has a larger pre-filter and gas filter.
This filter system can cope with challenging processes, when a lot of dust is generated, the chemical/gasses processed are more concentrated or for longer shifts.

The pre-filter is similar to a vacuum cleaner dust bag.
Length 35cm
Width 33.5cm
Height 8cm
Volume 0.09 meter3

The main filter is designed in the same way as the MG130 main filter, only there is much more gas filter media.
The larger amount of gas filter media makes this fume extractor more economical for demanding soldering or fume applications.
As the filter lasts longer there are less filter changes lowering the cost of ownership.