Check valves differ significantly from gate and globe valves. Check valves are designed to prevent backflow. Backflow simply means the flow that has reversed itself within a pipe and begins to flow backward. There are many designs of check valves, but the two most common types are the swing check and the lift check. Check valves do not use handwheels to control the flow of a commodity but instead use gravity and the pressure of the commodity to operate the valve.

Check valves are used in gas lines where it is important to assure that gas can only flow in one direction. They are not recommended for use as the primary means of shutoff but as a backup should the primary shutoff valve fail. They are commonly used in systems on the purge gas inlet line to assure that process gas will not back up into the purge gas supply. This is especially important if a common purge gas reservoir supplies many gas delivery systems.

In some systems, many different gases may be vented into a common header. If this is the case, separate check valves should be installed on the vent lines for the separate gases to assure they will not be able to mix in the system. Check valves can also be used on the process gas delivery line to prevent any backup of gas from the process into the gas supply system. They can also be placed directly after the cylinder to prevent any backup and contamination of the cylinder.

Many check valves are only designed to seal bubble tight and not provide a high leak integrity. Parts inside check valves are subject to wear and check valves should be checked frequently for proper operation.