Check valves, also referred to as "non-return" or "one-way directional" valves, are very simple valves that allow fluid, air or gas to flow in only one direction. When the fluid moves in the pre-determined direction, the valve opens. Any backflow is prevented by the moveable portion of the valve. A swinging disc, ball, plunger or poppet moves out of the way of the original flow. Since these devices are slightly larger than the through hole, the pressure of backflow will cause them to tightly seal, preventing reversal of flow. Gravity or a spring assists in the closing of the valve.
Check valves are indispensable in every area of life. Domestically, they are found in devices such as faucets, toilets and dishwashers. Without them, fresh water would be impossible and common plastics would be unheard of. Industries use them to control flows of all types—from the thinnest gas to radio active materials, from molten metal to highly corrosive materials. Check valves can range in size from less than an inch in diameter to 30 feet across. The simplest check valves can be purchased at the local hardware store, but they may also be precision-designed for highly sophisticated systems.
Check valves are indispensable in every area of life. Domestically, they are found in devices such as faucets, toilets and dishwashers. Without them, fresh water would be impossible and common plastics would be unheard of. Industries use them to control flows of all types—from the thinnest gas to radio active materials, from molten metal to highly corrosive materials. Check valves can range in size from less than an inch in diameter to 30 feet across. The simplest check valves can be purchased at the local hardware store, but they may also be precision-designed for highly sophisticated systems.
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Last Updated: January 10, 2007
Last Updated: January 10, 2007
What are Check Valves?
As aforementioned, check valves use different means of preventing backflow. Swing disc valves are typically used with liquids, such as slurries, that can easily damage the valve seat. They may be installed either vertically or horizontally, but a lever and counter-balance is recommended when vertically installing swing disc valves. Ball check valves use a ball with a small hole in the middle, which can be either free-floating or spring-loaded. These valves have a wide variety of applications. They are more resistant to plugging than other valves, and thus can be used to handle even fluids that deposit gummy residue. A check valve may also utilize a plunger, which is spring-loaded and usually used to prevent backflow of pressurized gases, or backpressure. A poppet in a check valve is spring-loaded and typically installed in systems that require prevention of backpressure.
Because check valves have so many applications, they are made of a wide variety of materials. Some companies exclusively manufacture plastic check valves. Other companies produce check valves made of brass, electroless nickel plated brass and stainless steel. The components of valves may be made of different materials, such as cast iron or bronze, depending on the application. Specialized valves may also be constructed of Teflon. Elastomer products may also be used to construct valves.
Because check valves have so many applications, they are made of a wide variety of materials. Some companies exclusively manufacture plastic check valves. Other companies produce check valves made of brass, electroless nickel plated brass and stainless steel. The components of valves may be made of different materials, such as cast iron or bronze, depending on the application. Specialized valves may also be constructed of Teflon. Elastomer products may also be used to construct valves.
