Check valve
Although they are available in a wide range of sizes and costs, check valves generally are very small, simple, and inexpensive.
The bodies (external shells) of most check valves are made of plastic or metal.
For those designs without a spring, reverse flow is required to move the ball toward the seat and create a seal.
After prolonged use, such check valves can eventually wear out or the seat can develop a crack, requiring replacement.
[citation needed] There are similar check valves where the disc is not a ball, but some other shape, such as a poppet energized by a spring.
This can occur when the swing check closes and the flow abruptly stops, causing a surge of pressure resulting in high velocity shock waves that act against the piping and valves, placing large stress on the metals and vibrations in the system.
Another variation of this mechanism is the clapper valve, used in applications such firefighting and fire life safety systems.
Another example is the backwater valve (for sanitary drainage system) that protects against flooding caused by return flow of sewage waters.
A circular recess in a weight that fits over a matching narrow ridge at the rim of an orifice is a common design.
The application inherently tolerates a modest reverse leakage rate, a perfect seal is not required.
These valves often look like small cylinders attached to the pump head on the inlet and outlet lines.
The feed pumps or injectors which supply water to steam boilers are fitted with check valves to prevent back-flow.
When the facility with the slide closes for the night, the check valve stops the flow of water through the pipe; when the facility reopens for the next day, the valve is opened and the flow restarts, making the slide ready for use again.
[13] Check valves are used in many fluid systems such as those in chemical and power plants, and in many other industrial processes.
[14] In aircraft and aerospace, check valves are used where high vibration, large temperature extremes and corrosive fluids are present.
A check valve is installed on each of the individual gas streams to prevent mixing of the gases in the original source.
In 2010, NASA's Jet Propulsion Laboratory slightly modified a simple check valve design with the intention to store liquid samples indicative to life on Mars in separate reservoirs of the device without fear of cross contamination.
Check valves used in domestic heating systems to prevent vertical convection, especially in combination with solar thermal installations, also are called gravity brakes.
