Vacuum filtration usually involves a rotary vacuum drum onto which filteraid is applied to form a filtercake. This vacuum drum rotates very slowly while partially submerged in the liquor to be filtered. A vacuum is drawn over the whole surface area of the filtercake and as the drum rotates the filtercake comes into contact with the liquor. The vacuum action draws the liquor through the filtercake where suspended solids are trapped.
The filtrate passing through the filtercake is thus clear and free of suspended solids. The solids trapped on the surface of the filtercake are then cut off by an advancing knife as the drum rotates. Vacuum filtration is usually used in applications where the suspended solid content is between 5-20%.