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 use of a washer to make the seal is actually pretty old-fashioned in comparison to modern faucets, but it’s the type that you often find in an older home.
Ball, cartridge, and ceramic-disc faucets, known as being “washerless” faucets, don’t use washers for the off-and-on action, though they do have O-rings and neoprene seals to prevent leaking.
The fundamental problem with a compression faucet is that the rubber washer or seal wears out over time. When this happens, the tap drips or drools.
Among the various faucet tap technologies in use, compression-style faucets have been around the longest. They are also the least expensive type.
With a compression faucet tap, you turn the handle to raise or lower a stem. At the stem’s base, a seal or washer opens or closes the water’s passageway (the valve seat).
Some newer types of compression faucets lower and raise the washer without grinding it into the valve seat. For example, American Standard’s economy NuSeal faucets lower and lift the rubber washer vertically without rotating it. Because it doesn’t grind the washer against the seat, the washer lasts longer.