Check valves are two-port valves, meaning they have two openings in the body, one for fluid to enter and the other for fluid to leave. There are various types of check valves used in a wide variety of applications. Check valves are often part of common household items. Although they are available in a wide range of sizes and costs, check valves generally are very small, simple, 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.
Design and Manufacture：ASME B16.34, API 6D
End Flange Dimension：ASME B16.5
Face to Face and End to End：ASME B16.10
Pressure-Temperature Ratings：ASME B16.34
Inspection and Test：API598, API600 or API 6D
Wall Thickness Dimension：API 600, BS 1868