To get the medium through the filter cloth, you can rely on gravity only, which is done in so called gravity bed filters, or you can use additional force, using a pump. In pressure filters, and with bag or cartridge filters, pump pressure is used to push the medium through the filter cloth.
In vacuum filters, the pump is placed after the filter medium and helps to pull the medium through the cloth. But an effluent pump can only run if there is sufficient fluid on the clean side of the cloth (in the clean chamber), which limits the capabilities and performance of this type of "vacuum" filters.
The exhauster or vacuum pump, in the Q-Filter® sucks air out of the clean chamber, creating under pressure on the clean side of the filter cloth. It can achieve -200 mbar underpressure which is equal to a water column of 2 meters above the filter media! That makes it possible to remove much more dirt, and much finer particles, using less m2 of filter cloth!