Ball valves are valued for their longevity and their ability to work perfectly after years of disuse. Inside a ball valve, a sphere usually made of brass, chrome-plated brass, or stainless steel has been drilled through from one end to the other. Attached to the top of the sphere is a lever whose range of movement is just a quarter turn. Move the lever parallel to the pipe, and the opening in the sphere aligns with the water flow. Move it perpendicular to the pipe, and a solid section of the sphere blocks the flow. You can control the flow by moving the lever between 0° and 90°. A partially open ball valve, however, can leave the silicone or PTFE seats on either end of the ball susceptible to deformity from uneven pressure.
One advantage to quarter-turn valves such as ball valves is that they can be shut off quickly. The disadvantage is that this makes water hammer more likely. For that reason, it’s best to turn the lever on a ball valve slowly. The levers themselves give ball valves two advantages over wheel-operated valves: First, it’s much easier for persons of all abilities to move a lever than to turn a wheel. Second, it’s possible at a glance to tell if a ball valve is open. Ball valves have one potential disadvantage over wheel-operated valves: Because shutting off the water flow means turning the lever perpendicular to the pipe, a ball valve may not work in certain tight locations.