Check Valve

Uses of check valve:
Check valves are best suited for moderate velocity applications.
They are often part of common household items.
They work automatically.
They do not have any valve handle or stem.
They are self-activating safety valves.
They permit gases and liquids to flow in only one direction.
They prevent liquid flow from reversing.
They are used in many fluid systems like in chemical and power plants, and in many other industrial processes.
They are capable of mixing multiple gases into one gas stream.
Check valves are installed in irrigation sprinklers and drip irrigation emitters to keep the lines from draining when the system is shut off.
Working of a check valve:
There is a hinged ball or door which is placed inside the valve. With the pressure coming upstream the ball is held open. On the other hand, when the pressure increases on the downstream side, it forces the ball or door to close which stops any back flow. An important factor in check valves is the cracking pressure. This is the minimum upstream pressure at which the valve will operate. Typically the check valve is designed in such a way to specify a specific cracking pressure.