Buchner Funnels

The flat perforated base of the funnel should be slightly smaller than the filter paper disc so the paper covers the holes completely and folds up slightly at the edges against the funnel wall. Check the funnel's base diameter against your filter paper stock before ordering to avoid a poor seal or wasted paper.

A Buchner funnel needs a side-arm (Buchner) flask with a compatible neck size to seal against, usually via a rubber stopper or filter adapter cone. Confirm the neck size and stopper fit before buying, since a poor seal will let air leak in and slow or stop the filtration.

A small electric or hand-operated vacuum pump provides more consistent suction than a water aspirator and does not risk contaminating your filtrate with tap water. Match the pump's vacuum rating to the volume and viscosity of liquid you typically filter for reliable, repeatable results.

Always break the vacuum seal, by opening a release valve or disconnecting the tubing at the pump, before lifting the funnel off the flask. Removing it while still under vacuum can cause the filtrate to be sucked back through the filter paper, disturbing your collected solid.

A regular filter funnel relies on gravity alone and has a conical shape that channels liquid through a folded filter paper cone. A Buchner funnel has a flat, perforated base and is designed to be used under vacuum, pulling liquid through a flat filter paper disc far faster than gravity filtration for the same volume.

You need a Buchner flask, also called a side-arm or vacuum flask, which has a thick-walled body to withstand reduced pressure and a side arm that connects to vacuum tubing. The funnel seals into the flask's neck using a rubber stopper or a purpose-made filter adapter cone.

Slow filtration is usually caused by an air leak at the stopper seal, filter paper that has torn or does not sit flat against the base, or a vacuum pump that is not generating enough suction. Check each of these in turn: reseat the stopper, replace the filter paper, and verify your pump is working correctly before troubleshooting further.

Yes, porcelain is chemically inert and resists virtually all common laboratory organic solvents, making it a safer long-term choice than plastic funnels which can soften, swell, or degrade with repeated solvent exposure. Always check that your filter paper and any tubing in the vacuum line are also solvent-compatible.

Remove and discard the used filter paper first, then rinse the funnel with an appropriate solvent or water to clear the perforated base of any trapped residue. A soft brush can help clear the small holes if they become blocked. Dry thoroughly before storage to prevent residue from hardening in the perforations.