Ball valves, as the name implies, are stop valves that use a ball to stop or start a flow of fluid. The ball, shown in figure 6-1, performs the same function as the disk in other valves. As the valve handle is turned to open the valve, the ball rotates to a point where part or all of the hole through the ball is in line with the valve body inlet and outlet, allowing fluid to flow through the valve. When the ball is rotated so the hole is perpendicular to the flow openings of the valve body, the flow of fluid stops.
Most ball valves are the quick-acting type. They require only a 90-degree turn to either completely open or close the valve. However, many are operated by planetary gears. This type of gearing allows the use of a relatively small handwheel and operating force to operate a fairly large valve. The gearing does, however, increase the operating time for the valve. Some ball valves also contain a swing check located within the ball to give the valve a check valve feature. Figure 6-2 shows a ball-stop, swing-check valve with a planetary gear operation.
In addition to the ball valves shown in figures 6-1 and 6-2, there are three-way ball valves that are used to supply fluid from a single source to one component or the other in a two-component system (fig. 6-3).