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About Check Valves

Check valves, also referred to as “non-return” or “one-way directional” valves, are very simple devices that allow fluid, air or gas to flow in only one direction. When the fluid moves in the pre-determined direction, the check valves open. Any backflow is prevented by the moveable portion of the valves. 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 check valves.
 
Check valves are indispensable. Domestically, check valves are found in many devices such as faucets, toilets and dishwashers. Without check valves, fresh water would be impossible and common plastics would be unheard of. Industries use check valves 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 check valves may also be precision-designed for highly sophisticated systems.
 
As aforementioned, check valves use different means of preventing backflow. Swing disc check valves are typically used with liquids, such as slurries, that can easily damage the valve seat. These check valves and custom check valves 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. Custom check valves featuring ball mechanisms have many uses in a wide variety of applications. Custom check valves are more resistant to plugging than other check valves, and thus can be used to handle even fluids that deposit gummy residue. Check valves may also utilize a plunger, which is spring-loaded and usually used to prevent backflow of pressurized gases, or backpressure. A poppet in check valves is spring-loaded and typically installed in systems that require prevention of backpressure.
 
The versatile custom check valve is often made of a wide variety of materials. Some check valve manufacturers exclusively manufacture plastic check valves. Other check valve manufacturers, check valve distributors, and check valve suppliers provide brass check valves, electroless nickel plated brass check valves and stainless steel check valves. The components of check valves can be made of different materials, such as cast iron check valves or bronze check valves, depending upon their application. Many leading check valve manufacturers may also be construct their products out of Teflon. Elastomer products can also be used to make check valves.

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Featured Articles

“Silent Treatment – Valve Technology Upgrade at Mt. Horeb, WI Wastewater Treatment Plant Operates Quietly and Efficiently.”
http://www.valmatic.com/articles.html#article1

“Dynamic Flow Testing of Check Valves”
http://www.engineering.usu.edu/cee/faculty/rahm/check.html

Types of Check Valves

• Ball Check Valves are valves where liquids can flow only one way. The pressure from the liquid forces the ball to move, when the pressure from the fluid stops the ball also stops and the valve closes.
  
• Double Check Valves consist of at least two independently acting check-valves. They are typically used in liquid services.
  
• Foot Valves are often used in conjunction with a pump. The valve aids in pumping water and helps prevent backflow.
  
• Hydraulic Check Valves prevent backflow in hydraulic systems, typically using a ball or a poppet.
  
• Plastic Check Valves can be used for industrial purposes or for lower grade home use, such as in a swimming pool or aquarium. Typically, they are used when resistance to corrosion is needed.
  
• Pneumatic Check Valves allow fluids to flow in one or two ways. When the fluid is allowed to flow more than one way it is often metered.
  
• Relief Valves relieve excess and potentially dangerous pressure from piping systems or closed-top vessels and are normally closed until the set pressure is reached.
  
• Sanitary Check Valves are used when the fluids contained in the pipes need to remain germ free. These check valves are often used for medical, food, or dairy purposes.
  
• Silent Check Valves have a spring-operated return mechanism. They eliminate the shock of sudden reversal of flow, making them a favorite for use in clear liquid systems.
  
• Swing Check Valves use outside levers to slow down the flow of materials through a pipe. The lever pulls the disk into the flow which causes the flow to stop more quickly.
  
• Wafer Check Valves are often used for liquid services. The check valve is made of two half-circle disks hinged together. With positive flow, the two disks fold together to allow materials to flow through the pipe. With reverse flow, they retract to a full circle to restrict flow.