How does a percolater work?

In the bottom of the percolator's stem is a loose disc called the "pump". As the bottom heats, the pump begins to jump up and down. In doing so, it pumps hot water up the tube, which spills out of the top of the tube into the basket, where the grounds are. The hot water falling through the grounds makes coffee. When the drip type "Mr. Coffee" machine came into widespread use in the early seventies, the percolator was immediately displaced. It survives today as the huge "coffee urn" used at church socials, picnics, etc.