Check valves allow fluid to flow in a system in only one direction. They are operated by the flow of fluid in the piping. A check valve may be of the swing type, lift type, or ball type. Figure 13-24 shows a swing check valve and a lift check

Figure 13-23.-Typical seawater ball valve.

Figure 13-24.-Check valves.

valve. Check valves may also be built into globe valves or ball valves.