BÃ¼chner funnel

A suction filter (also Buchner funnel ) is a filter for the mechanical separation of a suspension ( also known as suction or vacuum filtration ). The suction filter, in contrast to a hopper has a flat bottom with small openings, which are covered by a filter paper. The suspension is added to the filter paper in a suction filter, leaving behind the solids as a filter cake on the filter paper. The liquid, which is called filtrate passes into the container under the funnel. The negative pressure required for this purpose is most often created by using a diaphragm pump or a water aspirator.

Besides Funnels with filter paper, there are suction filters with a sintered glass bottom, so-called frit. These Funnels very small particles can be filtered from a suspension. This separation method are also used in small-scale production. More Nutschtechniken are pressure filters, in which - to suck instead of from below - from the top with a gas supply pressure is produced.

If a solution can be filtered, can be heated some suction filters, so that the solute does not fail. This method is usually applied to clear filtration of solutions. Likewise Funnels can be deep-frozen ( -78 ° C up to with dry ice ) to avoid decomposition of the analyte. In large-scale productions also Funnels are used with an agitator. These special suction filters are mainly used then used when the product needs to be washed. By stirring a greater contact between Produkteteilchen and washing liquid can be achieved, which makes the washing operation to some economic.

The Buchner funnel is a funnel into a cylindrical shape with an integrated screen plate. It was developed by the German chemist Ernst Büchner funnel.

It is used in conjunction with a suction flask in a chemical laboratory for vacuum filtration of solids. This end - similar to the coffee filter - a filter paper inserted, which can be subsequently removed with the solid. In the modern laboratory, it is increasingly replaced by glass filter frit, which do not Filtrierpapiereinlage.