Ceramic Pump Piston — Sales and Instrument Support

Ceramic piston for an HPLC pump head. The piston reciprocates through the high-pressure seal on every stroke, so its surface finish - not its strength - is what keeps the pump sealed. Pistons are made from hard, chemically inert ceramics (sapphire, alumina or zirconia depending on the pump) for exactly that reason.

A piston does not wear out in normal use. It gets damaged, almost always by buffer salt that was allowed to crystallise on the shaft when the instrument was shut down without a water flush. Those crystals score the piston, and a scored piston then cuts every new seal that is fitted to it.

The rule that saves the repeat visit

If the piston is scored, replace the piston and the seal together. Fitting a new seal to a damaged piston buys a few weeks at most, and the second failure looks identical to the first.

Check by wiping the piston clean and looking along it under a good light; scoring is visible as fine longitudinal lines and can often be felt with a fingernail. Clean pistons with water and a lint-free wipe - never with an abrasive.