Imhoff Cone

June 25, 2003                                                                                                                                                                                                          ISSUE #139

An Imhoff cone is very useful lab instrument.  We use it to compare the amount of suspended solids that will settle out of liquids.  For example, the cone is used to compare the amount of settleable solids in the filtrate from a Fiber Filter against the amount in the feed into 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 two different discharge cone 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 18" tall.  Because the cone is very pointed (about 10o), the bottom 2" end of the cone holds only 10 ml.  In comparison, the top 2" holds 200 ml.

When a liquid is allowed to sit in the cone, the suspended solids settle to the bottom (pointed end) 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.

Vincent buys Imhoff cones from James Griffin at BC Scientific in Oldsmar, Florida  813-854-4373.  The box they come in is labeled "Wheaton, Millville NJ, #990750 1,000 ml."