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A check valve, also known as a non-return valve, reflux valve, retention valve, foot valve, or one-way valve, is a type of valve that allows fluid (liquid or gas) to flow in only one direction.
Check valves have two openings in their body—one for the fluid to enter and one for the fluid to exit. They can be used in a very wide variety of applications; they are also found in common household items. Despite being available in different sizes and being of different costs, check valves are generally small, simple, and inexpensive. They operate automatically so do not require manual control like using a valve handle. The majority of check valves have bodies made of plastic or metal.
A key aspect of check valves is the cracking pressure, which is the minimum pressure difference between the inlet and outlet that allows the valve to function. The check valve can be designed and specified for a specific cracking pressure.
A check valve is a plumbing valve that allows fluid to flow in only one direction. It usually consists of two openings, through which the fluid enters and exits. Its operation is based on the principle of "pressure differential." This mechanism shuts the valve when the pressure is greater on the exit side. There are various designs for this mechanism.
Selecting the correct check valve is very important for any application. There are many factors to be considered based on the fluid media, pipe size, pressure differential, velocity of the fluid, and the type of pumping mechanism to ensure proper and safe operation of the system that needs to be protected equipment. The set-up is a mask with a water-based cleaning agent.
Check valves are available in many varieties, from the standard to the specially made and those designed for very specific applications. New valves are constantly being developed; therefore, it is difficult to give a complete listing. Nonetheless, some descriptive factors apply to all check valves.
A swing check valve is an automatic valve intended to prevent backflow or ingress of flow in the reverse direction. It typically consists of a disk that swings on hinges out of the way from the valve seat to allow forward flow. In some designs, when the flow stops, the disc swings back into place stopping reverse flow. Returning forces may have to be enough to keep light disks in place. The swing check valves provide less turbulence and low pressure drop.
Swing check valves that are appropriate to be used in situations where a water hammer might occur are those with a lever and weight; those with a lever and spring are suitable for high-pressure, high-velocity flow applications. Regular maintenance of any swing check valve is crucial, irrespective of whether it is the disc type.
Wafer check valves have a slim plate that pivots in the force of fluid to either impede or allow the flow. This makes the plate rise from its seat position. On movement of fluid in the opposite direction, it closes tightly for shut-off sealing and to prevent any blowout flow. In many cases, a spring or lever is attached to the plate to help close it quickly and thus reduce chances of water hammer.
Wafer inspection valves are ideal for use in small piping systems and systems that handle solids or semi-solids because of their slender, short, reduced design.
A swing check valve disc, unlike the tilting disc check valve, is centered on the shaft. This allows for fluid to pass entirely over the top of the disk. These valves are most often used in applications where flow is frequently reversed. A swing check remains open because of the velocity of flow; a tilting disc remains open because of flow itself. The small disc has an insignificant weight and its center-of-gravity location is close to the hinge pin. It offers very low pressure drop at low flow rates and higher pressure drop at high flow rates
Ball check valves use a ball that rolls up and down within the valve to stop the flow of fluid. The seat of the valve is designed for this purpose, to house the ball and it consists of an area of geometry converging inwards (commonly referred to as a cone) at the centerline that would guide the traveling ball back towards its seat. Balls are sometimes made heavy depending on conditions or likelihood during water hammer.
To keep the current from going in the opposite direction, the ball is forced back onto the seat. When pressure is adequate, the flow lifts the ball out of its path. When pressure builds up, force balls to unseat holes against flow and allow free passage of allowed by reverse-flow. Conversely, as pressure drop balls descend and are directed back towards their seats again.
Poppet check valves, commonly referred to as silent check valves, prevent water hammer or shock by shutting down prior to the reversal of fluid flow. The advantage of utilizing a silent check valve lies in its ability to swiftly and seamlessly close, thereby safeguarding the surrounding materials from any potential harm.
Rubber or synthetic elastomer duckbill valves resemble the beak of a duck. The valve's open end is stretched over the outlet of the supply line, while the other end maintains its original shape. When there is upstream pressure, the duckbill lips are pushed open, enabling the flow. With higher pressure, the lips open even wider, but they flatten and close as the pressure decreases.
Air check valves, also known as pneumatic check valves, regulate the movement of air from a compressor by allowing air to enter while blocking its exit. These valves are utilized in pneumatic systems that require unidirectional air flow.
Industrial check valves are typically manufactured using strong materials that can endure high-pressure situations. PVC, CPVC, bronze, brass, iron, and stainless steel are commonly employed in the production of check valves
Polyvinyl Chloride (PVC): PVC is resistant to corrosion and has flexibility. The sleek surface of PVC enables easy movement of the check valve components.
Chlorinated Polyvinyl Chloride (CPVC): CPVC possesses the same characteristics as PVC but can withstand high temperatures.
Bronze: Bronze is suitable for applications with low and medium pressure, can be molded into intricate shapes, and is resistant to corrosion.
Brass: Brass shares the same capabilities as bronze, including its machinability, and is more cost-effective.
Cast Iron: Check valves made of cast iron are utilized in various services such as hot and cold water, HVAC, steam, gas, and utilities due to its exceptional resistance to corrosion.
Ductile Iron: Ductile iron contains more than 3% carbon, allowing for easy bending and shaping. It possesses greater strength than cast iron and can be readily formed into check valves.
Metallic Element: The metallic element, iron, finds utility in steam, water, oil, and gas applications. It exhibits remarkable endurance in the face of varying temperatures and pressures. Despite its high cost, it delivers exceptional performance.
Stainless Steel: Stainless steel boasts corrosion resistance and durability, making it suitable for use in harsh conditions, including chemical environments.
Polypropylene (PP): PP is employed in the production of check valves due to its outstanding resistance to corrosion, surpassing that of CPVC and PVC.
Polyvinylidene Difluoride (PVDF): PVDF plastic finds application in scenarios where utmost purity and resistance to acids, solvents, and hydrocarbons are imperative.
Cast Steel: Check valves are manufactured using cast steel owing to its ability to withstand sudden impacts without deformation, breakage, or bending. Additionally, it can be easily molded into any desired check valve configuration.
