Imhoff Cone

May 20, 2003

An Imhoff cone is very useful lab instrument. We use it so compare the amount of suspended solids that will settle out of liquids. For example, the cone is used to compare the amount of settlable solids in the filtrate from a Fiber Filter against the amount in the feed to the filter machine. Similarly, we can use a pair of Imhoff cones to compare the amount of suspended solids that will settle out of the press liquor from a screw press when it is operated at various discharge door air pressures.

A laboratory centrifuge can be used in the same way, in the same applications above described. The advantage of the Imhoff cone is that it is more convenient to use when doing field testing at a remote location.

An Imhoff cone is simply a cone-shaped plastic container. It holds one liter, with the side of the cone graduated in milliliters. The cone is about 14" tall. Because the cone is very pointed (about 15º), the bottom 2" end of the cone holds only 20 ml. In comparison, the top 2" holds 300 ml.

When a liquid is allowed to sit in the cone, the suspended solids settle to the bottom within a few minutes. Since the cones are made of clear plastic, it is easy to see the level marks between the settled solids, the clear liquid, and floating solids (if any). Typically we will see that anything from 2 ml to 500 ml of thick solids will settle on the bottom, with clear liquid above. Measurements we would be interested in would be a comparison between the feed to a machine compared to the filtered liquid, or the difference in settleable solids between samples run with two different meshes of filter cloth.

We generally use Imhoff cones in pairs so that two samples can be easily compared.

Issue 139