Shutoff valves, or stops, for water piping have a variety of control mechanisms. Each mechanism type has its advantages and disadvantages, and understanding those pluses and minuses will help you decide where to use each one. For example, some valve mechanisms restrict flow by as much as 50 percent. This is a real concern in certain situations. The main house valve, for instance, should not restrict flow, because a reduction there could affect the performance of the entire system. In contrast, the smallbore compression valves under sinks have little effect because the faucets they serve restrict flow in the first place.
Gate valves, along with some ball valves, allow an unrestricted flow of water. As the name implies, the control mechanism is an internal gate. Turn the handle to the left, and the gate rises out of its seat. Turn it to the right, and the gate moves downward, slicing off the flow. The sliding gate makes gate valves larger than other valves.
Like most full-bore water valves, gate vales are not meant to be used frequently. They can't survive the wear and tear that a faucet endures on a daily basis. If the gate valve has a serious nemesis, it's hard water. Calcified minerals can encrust the mechanism, rendering it inoperable. Forcing the valve can break the stem from the gate. In most cases, replacement is the best option.
Because of their full-flow design, gate valves are used close to the beginning of the water piping system, usually near the meter or pressure tank.
Ball vales are available in flow-reducing and larger fulflow versions. The mechanism in these valves is a hollow nylon or metal ball that pivots in the valve body. Opposing sides of the ball are open. When you rotate the valve against the flow, the closed sides of the ball stop the water. Ball valves are easy to use because is takes only one-quarter turn of the handle to open or close them. In addition, they are generally more durable than gate valves. The are certainly less vulnerable calcification. Ball valves can be used anywhere a gate valve might be used.