The water system in your home is a complex network of piping and valves. While the piping tends to require little to no maintenance most of the time, plumbing valves are a different story. These small valves are located everywhere from under your sinks to behind your toilets, from your water heater to your icemaker, from your dishwasher to your clothes washer. Also known as cut-offs, stops, or shut-offs, these valves all perform the same function: stopping the supply of water to a certain fixture or area of the home. There is a large valve one on your main water line close to where it enters the home, next to your PRV (see" Pressure Valves" section), allowing you or your plumber to shut off the water to your entire home, allowing maintenance of the system. While all performing the same function, these valves are constructed in several ways and are used in specific locations throughout the house.
"Stops" is the name generally given to the valves located under sinks and behind toilets. These small, usually brass valves are used to cut off the supply of water to one fixture. They function on a simple shaft and rubber washer system, and often fail after repeated use. Small, slow drips are usually the first sign of an impending problem, and the valve should be immediately replaced.
Gate valves and ball valves are heavier-duty units used to isolate water at specified points of your plumbing system. They are in-line valves, meaning they are installed between two points of a waterline. Gate valves are usually made of brass, and employ a multi-turn handle to open or close a thick brass "gate" inside the valve body, thereby cutting off the supply of water. These valves are often found on water mains, above water heaters, and on various lines throughout the home. Ball valves are also generally made of brass, and are operated using a lever-type handle that swivels a core-less brass "ball" inside the valve body. Because of this design, ball valves require only 90 degrees of rotation to operate, rather than the multi-turn gate valves. While both types of valves function well, gate valves are more prone to failure after many years due to their construction, which employs a threaded brass rod to operate the gate. These rods often corrode and break, rendering the valve useless.
Another type of in-line valve found in some homes (and on most water meters) is called a check valve. This component of the plumbing system uses a one-way "door" inside the valve, which allows water to pass through the valve once, and never flow back through. These valves are generally used to eliminate the possibility of contaminants that have entered the water in the home from passing back out to the county or city lines. Two types of "doors" are employed in a check valve. The first functions just like a door in your home, swinging on a hinge inside the valve, opening and closing with water flow. The other, known as a spring-check, uses a plate attached to a spring that opens and closes with pressure, allowing water to flow around its edges, closing the valve when pressure is equalized.
Just like any other mechanical item with moving parts, these valves fail on occasion. Add to that the presence of water, a highly corrosive