Check valve or non-return valves, installed in pipeline systems to allow flow in one direction only. They are operated entirely by reaction to the line fluid and therefore do not require any external actuation.
There are a number of reasons for using check valves, which include: Protection of any item of equipment that can be affected by reverse flow, such as water meter, strainers and control valves.
Prevention of flooding.
Prevention of reverse flow on system shutdown.
Prevention of flow under gravity.
Relief of vacuum conditions.