Check valves are two-way valves, which means they have two openings in the body, for a fluid to enter and the second for the fluid to exit. There are different types of valves used in a variety of applications.
Check valves are available in a wide variety of sizes and costs and are usually very small, simple and / or inexpensive. Check valves work automatically and most are not controlled by a person or any external control, accordingly, most do not have any valve handle or stem. The bodies (external shells) of most check valves are made of plastic or metal.