A simple description is that when the lever is raised, it unseats the "seal" letting water into the barrel from the hot and cold supply lines, which then goes to the spout. Moving the lever right or left increases the cold or hot water coming into the barrel. Further movement adjusts the flow of hot or cold water until reaching the desired temperature. Of course, pushing the lever down seats the seal, shutting of any water flow into the barrel. Hope this is the explanation you are looking for rather than how to reapir such a faucet...