Check valves, also known as non-return or one-way valves, are designed to allow fluid to flow one way in a pipeline. They’re constructed of a clapper which hangs from a hinge, the clapper shaft or pin, which is mounted to the underside of the bonnet, inside the valve body. The basic design of a check valve inhibits backflow in a line. Because of their simple design, check valves generally operate without automation or human interaction and instead rely on the flow velocity of the fluid to open and close. This means they generally do not have a method of outside operation, like a handle or lever. The minimum upstream pressure required to operate the valve is called the “cracking pressure”. Check valves are generally designed specifically with this number in mind and, depending on the size and style of check valve, this number is 1 psi to 5 psi.
Parts of a check valve:
Types of Check Valves:
Horizontal Swing Check Valve
Operates in the horizontal position.
Piston Check Valve
Works up and down providing a very strong, firm seal under high pressure conditions.
Ball Check Valve
Uses a ball rather than a clapper.
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.
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.