Though there are hundreds of different styles, colors, and shapes of faucets, the working mechanisms of nearly all can be grouped into four main types: cartridge, compression, ball, and disc. These names refer to the parts that actually control the flow of water through a faucet. The type of valve you choose will make a difference in a faucet's price, how well it works, and how long it will last.
Three of these—cartridge, ball, and disc faucets—are mixing faucets. They normally have a single handle or control, though cartridge and disc types are also made with two handles. The compression faucet has two controls, one for hot, the other for cold.
Cartridge faucets have a hollow metal or plastic cartridge insert that seals against the spout or faucet body. Depending on how a series of holes in the cartridge align with the stem, water is mixed and controlled. Drips usually mean the cartridge needs replacing.
Compression faucets have two separate handles. When the handle is turned, it raises or lowers a washer or seal that closes against a valve seat at the base of the stem to restrict water flow through the faucet body when you turn the handle off. The other three types don't use washers for the off-and-on action, though they do have O-rings and neoprene seals to prevent leaking. These types of faucets are referred to as "washerless."
Ball faucets have a single lever that operates a rotating, slotted metal ball. The slots in this ball align with hot and cold water inlet seats in the faucet body to regulate the amount of incoming water allowed to reach the mixing spout.
Disc faucets utilize two discs—a movable upper disc and a fixed lower one. When the movable disc is turned from side to side or lifted and lowered against the lower disc, it regulates the flow of water through inlet and outlet holes. If this type of faucet leaks, the culprits are usually the inlet and outlet seals or sediment buildup in the inlets. The handle should be in the "on" position when repairing a disc faucet to prevent cracking the replacement seals.
Because washers and seals wear out with use—resulting in the familiar drip, drip—washerless faucets are generally favored. If you have a faucet that leaks or drips, chances are good that the washers, seals, or O-rings have become worn and simply need to be replaced. If you do the work, be sure to turn off the water to the faucet first, using the shutoff valves beneath the sink.
