How do turning ceramic discs control a faucet?

A ceramic-disc faucet valve can change water flow without lifting a rubber washer up and down. Inside the valve, two hard, very smooth ceramic faces press against each other. One disc stays fixed while the handle turns the other. Openings, often called ports, pass through the discs.

When a port in one disc lies over a port in the other, their shared open area forms a passage. The water supply’s pressure pushes water through that passage toward the spout. Turning the movable disc changes the overlap. When solid ceramic covers the opening completely, the continuous passage disappears and the valve closes.

The illustration uses two matching quarter-circle ports, one in each disc. Their shared area decreases as one rotates through a quarter turn: full overlap becomes partial overlap, then no overlap. Real cartridges can have several ports with different shapes. The example teaches the changing passage rather than reproducing a particular faucet.

The discs’ close, smooth contact helps prevent water slipping between their faces. The valve controls a path; it does not create the supply pressure. A larger opening does not guarantee a flow rate directly proportional to its area, because pressure and resistance elsewhere in the plumbing also matter. Mixing cartridges add arrangements that combine hot and cold supplies.