Burette, Rotaflow

Quick Answer: A Rotaflow burette is a graduated glass burette fitted with a screw-action valve: a PTFE spindle turns in a threaded glass body to open or close the flow. The valve gives very fine control, down to part-drops, and needs no grease.

A Screw Valve Instead of a Turning Plug

Most burettes control flow with a tapered plug turned through a quarter turn between open and closed. The Rotaflow pattern works differently. Its glass valve body is threaded, and a PTFE spindle with a sealing tip screws into it; turning the knob advances or withdraws the tip from a seat, so the opening grows gradually over several turns. That gradual opening is what lets titrant be released in a steady trickle, in single drops or in fractions of a drop.

Fine control is most useful in titrations whose end point is gradual or easy to overshoot. In an EDTA titration for water hardness, Eriochrome Black T changes from wine red to blue only slowly near the end, and in an iodine-thiosulfate titration the last blue of starch must be discharged by the final drop. With a Rotaflow burette the analyst can add part-drops and rinse them in from the tip with a wash bottle.

Because nothing in the valve is greased, there is no film to contaminate the titrant or block the tip, and alkaline solutions do not seize it. The valve can be opened fully for fast filling and draining of cleaning water. Capacity and graduation interval are not stated in the listing.

Applications

• EDTA complexometric titrations for calcium and magnesium hardness in water
• Iodometric titrations with sodium thiosulfate and starch indicator
• Accurate acid-base work where part-drop additions sharpen the end point
• Titrations with alkaline titrants that would seize a glass stopcock

Specifications

Care & Handling

• Close the valve with light finger pressure only; screwing the spindle hard onto its seat deforms the PTFE tip and causes leaks.
• Back the spindle out slightly before storage so the tip is not held compressed against the seat.
• When cleaning, unscrew the spindle completely and rinse the thread, where fine particles collect.
• Replace a spindle with a cut or flattened tip rather than tightening harder to stop a drip.

Why Choose LabEquip

Analytical chemistry and water-testing laboratories prefer the Rotaflow burette for demanding titrations in which a single drop decides the result. LabEquip lists it in the chemistry lab equipment range; share the capacity and number required via the LabEquip contact page.

Frequently Asked Questions

How does a Rotaflow valve differ from a PTFE key stopcock?

A PTFE key stopcock is a tapered plug turned through a quarter turn from closed to fully open. A Rotaflow valve is a screw: several turns take it from closed to open, so the flow changes gradually and very small amounts can be delivered.

How do I add half a drop?

Open the valve just enough for a drop to form on the tip, close it, then touch the tip against the inside wall of the flask and rinse the liquid down with a little distilled water from a wash bottle.

Why does the valve drip even when closed?

The PTFE tip may be worn, scratched or dirty, or a particle may be caught on the seat. Clean the spindle and seat, and replace the spindle if the tip is damaged; do not overtighten to stop the drip.

Does a Rotaflow burette need grease?

No. The PTFE spindle seals against the glass without lubricant, which keeps grease out of the bore and tip and avoids contaminating the delivered liquid.

Is it slower to use than a standard burette?

Opening takes a few turns rather than a quarter turn, so the start of a titration can take slightly longer. Most users run in the bulk of the titrant quickly and then use the fine control near the end point.

Can the burette be used with strong alkalis?

Yes. The valve does not depend on a ground glass joint, so alkaline solutions do not cause seizing. Rinse the burette with distilled water after use, as alkali left in contact with glass for long periods slowly etches it.

Last Updated: September 2026