The word "percolate" is a process where fluid gradually passes through a permeable substance with the inference that a liquid emerges from the union with a different quality than what originally existed before the percolation process.
The percolator coffee pot functions by utilizing the natural rising action of bubbles created by boiling water at the bottom of a pot.
A hollow pump stem tube ensures a concentration of these bubbles will crowd in together, forcing water in an upward motion through the tube.
This tube then sprays water over the spreader cover, which thoroughly disperses the water over the ground coffee, saturating it. The spreader cover is designed with holes of various sizes to evenly saturate the coffee. The spreader also serves the dual purpose of preventing ground coffee from splashing up into the rest of the pot.
As the water boils in larger rolls, it will also splash up through the bottom of the coffee basket affecting the coffee from both sides, as the water will also be flowing down through the coffee and through the bottom of the basket into the rest of the boiling water.
The water will continue to go through this cycle over and over. This makes the coffee stronger and stronger, by infusing the bean oils more and more thoroughly with the water, until the coffee pot is removed from the heat.
In order to be a percolator coffee pot, the pot must have the internal features of an upright pump stem tube and a basket to hold the coffee and for the water to pass through. The tube usually sits upon a stand and the coffee grind basket rests upon the tube. The basket has a perforated spreader cover to put on top of it.
Some form of lid, often made of glass or plastic for viewing the coffee color and determining readiness, sits atop it all. The pump stem tube goes through the basket and through the spreader cover and holds those pieces secure.
This pot may be made of metal which can be set over a fire to heat, or it may be made of glass and the water may be preheated prior to pouring it into the percolator coffee pot. It also might be made of any number of materials, but be electric so that it heats up simply by plugging the cord into an outlet.
A paper filter is not needed in a percolator coffee pot grind basket. But if all grinds escaping into the pot are to be completely avoided, a customized percolator filter must be used.