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A single check valve, also known as a one-way valve or non-return valve, finds its utility in a wide range of applications where unidirectional fluid flow control is essential. This valve allows fluid to flow in one direction while preventing backflow. Here are some common scenarios where a single check valve is used:
Sump Pumps: In residential and commercial settings, sump pumps use a single check valve to prevent pumped water from flowing back into the sump pit. This maintains the pump's efficiency and prevents flooding.
Water Treatment Systems: Single check valves are employed in water treatment plants to ensure that treated water flows towards distribution lines while preventing the ingress of untreated or contaminated water.
Irrigation Systems: These valves help control the flow of water in irrigation systems, allowing water to reach plants and crops while preventing the backflow of irrigation water into the main supply.
Fuel and Oil Transfer: Single check valves are used in fuel and oil pipelines to ensure that fluids flow in one direction only, preventing contamination and maintaining the integrity of the supply.
Air Compressors: In pneumatic systems, single check valves enable the one-way flow of compressed air, preventing backflow that could disrupt the system's operation.
Fish Tanks and Aquariums: Aquarium air pumps and water circulation systems utilize single check valves to maintain consistent water flow and prevent damage to equipment.
Hydraulic Systems: Single check valves are crucial in hydraulic systems to control the movement of fluids in one direction, ensuring precise operation of cylinders and actuators.
HVAC Systems: HVAC units use single check valves to regulate the flow of refrigerants or air in heating and cooling systems, ensuring efficient operation.
Laboratory Equipment: Single check valves are employed in laboratory setups to control the flow of gases and liquids, preventing cross-contamination and ensuring accurate experiments.
Steam Systems: Single check valves are used in steam systems to ensure that steam flows in the desired direction, preventing condensate from returning and affecting the process.
Fire Sprinkler Systems: Single check valves are integrated into fire sprinkler systems to allow water flow in the event of a fire while preventing backflow that could contaminate the water supply.
Boilers: In steam boiler systems, single check valves help maintain the correct flow of steam and prevent reverse flow that could lead to damage.
Automotive Systems: Single check valves are found in automotive components such as vacuum systems, emission control systems, and brake boosters.
Water Wells: Single check valves are used in water well systems to ensure that water flows from the well into the distribution network without the risk of backflow.
Chemical Processing: Single check valves play a role in managing the flow of chemicals and fluids in various industrial processes, preventing unintended mixing.
In essence, a single check valve is a versatile component that ensures fluid flow in one direction, making it a critical element in diverse systems and applications. Its ability to prevent backflow and maintain fluid integrity contributes to the efficiency, safety, and reliability of various processes.
Check valves are used in many different applications. For example, they are often placed on the outlet side of a pump to protect the pump from backflow. Centrifugal pumps, the most common type of pump, are not self-priming, so check valves are essential to keep water in the piping. In addition, check valves are often used in HVAC systems (heating, ventilation, and air conditioning systems.) HVAC systems are used, for example, in large buildings where the coolant is pumped to too many floors. Here, check valves are installed to ensure that the coolant does not back up.
When selecting a check valve, it is important to perform a cost-benefit analysis of the particular system. Often the focus is on reducing cost while obtaining the lowest possible pressure loss, but with check valves, greater safety equals higher pressure loss. Therefore, to ensure that the check valve properly protects the system, each system must be evaluated individually, and factors such as water hammer risk, acceptable pressure loss, and the financial consequences of installing a check valve with too much safety must be considered for the margin against water hammer. See How to Choose the Right Check Valve for more details.
There are several types of check valves available for water and wastewater applications. They work in different ways but serve the same purpose. AVK offers a wide range of swing check valves, ball check valves, tilting disc check valves, tilt seat check valves, nozzle check valves, and silent check valves. The most common types of water and wastewater check valves are swing check valves and ball check valves.
Swing check valves: Swing check valves are fitted with a disc that swings on a hinge or shaft. The flap swings from the seat to allow positive flow, and when the flow stops, the flap swings back to the seat to stop reverse flow. The weight of the valve flap and return flow has an effect on the closing characteristics of the valve.
Ball Check Valves: Ball check valves function by means of a ball that moves up and down inside the valve. The seat is machined to fit the ball, and the chamber is tapered to guide the ball into the seat to seal and stop reverse flow.
A check valve is a device that allows fluid to flow in only one direction. They have two ports, one for the media inlet and one for the media outlet. They are often referred to as "check valves" or "check valves" because they only allow the medium to flow in one direction. The main purpose of a check valve is to prevent backflow through the system.
Check valves work on differential pressure. They require the pressure on the input side of the valve to be higher than the pressure on the output side in order to open the valve. When the pressure on the outlet side is higher (or the pressure on the input side is not high enough), the valve will close. The closing mechanism is different depending on the valve type. Unlike other valves, they do not require handles, levers, actuators, or manual labor to function properly.
They are typically installed in applications where backflow would cause problems. However, because they are check valves, they are an inexpensive, effective and simple solution to potential problems. If the backflow is contaminated, the backflow can cause problems and therefore contaminate the upstream media. For example, the sewer will have a check valve to ensure that waste can leave but not re-enter the system. They can also be used if the backflow would cause damage to upstream equipment and would only allow media to flow in one direction. For example, reverse osmosis filters only allow water to pass in one direction, so a check valve is installed downstream to prevent this. A variety of sizes, designs, and materials are available to ensure that there is a check valve for every application.
Check valves require a minimum upstream pressure (the pressure difference between the inlet and outlet) to open the valve and allow flow through it. The minimum upstream pressure at which the valve opens is called the check valve "opening pressure." The exact opening pressure will vary depending on the design and size of the valve, so make sure your system is capable of generating this opening pressure and is suitable for the application.
If the upstream pressure is below the opening pressure or if there is backpressure (flow trying to flow from the outlet to the inlet), the valve will close. Depending on the design of the check valve, the closing mechanism can be changed. In short, the backpressure pushes the gate, ball, diaphragm, or disc against the orifice and seals it. Depending on the design, the closing process can be assisted by springs or gravity.
Because check valves operate in only one direction, it is critical to know the proper installation orientation. Typically, there is an arrow on the valve housing to indicate the direction of flow. Otherwise, you will need to check the valve to ensure it is installed in the intended flow direction. If it is backward, the flow will not be able to pass through the system, and the build-up of pressure may cause damage.
Depending on the design of the check valve, they will operate slightly differently. The most common type of check valve is the spring-loaded inline check valve. However, we will discuss several types below.
Inline spring-loaded check valves are common, easy to understand, and simple in design. When fluid enters the valve's input port, it must have enough pressure (force) to overcome the opening pressure and spring force. Once overcome, it pushes the valve flap, opening the orifice and allowing flow through the valve. When the input pressure is no longer high enough or when back pressure exists, the back pressure and spring push the valve disc toward the orifice and seal the valve closed. The short travel distance between the spring and the disc allows for fast closing response times. This valve design also prevents pressure fluctuations in the line and, therefore, also prevents water hammers. Common types of spring-loaded inline check valves are also known as "nozzle check valves" or "silent check valves." They can be installed vertically or horizontally. However, because they are connected in series with the system, they must be completely removed from the line for inspection and/or maintenance.
Spring-loaded y-type check valves operate very similarly to inline spring-loaded check valves. The difference is that the spring and removable disc are positioned at an angle. This creates a "y" shape, hence the name of the valve. It works exactly the same as a straight valve, but because the moveable assembly is at an angle, it can be inspected and serviced while still connected to the system. However, they are larger and take up more space in the system.
Ball check valves use a free-floating or spring-loaded ball that rests on a seal seat to close the orifice. The seat is usually tapered to guide the ball into the seat and create a positive seal, thus preventing reverse flow. When the fluid pressure on the inlet side exceeds the opening pressure, the ball is removed from its seat, and flow is allowed to occur. When the inlet pressure does not exceed the opening pressure, or when backpressure is present, the ball will close by back pressure or spring, effectively closing the orifice.
Diaphragm check valves consist of a rubber diaphragm that flexes to open when inlet pressure increases. Typically, these types of valves have a free-floating, self-centering diaphragm that keeps them normally open (NO). This means that there is no "opening pressure"; however, they can be normally closed (NC) and then require inlet pressure to overcome the diaphragm's elasticity. Because the inlet pressure is "minimum," the medium can still pass through. As the inlet pressure increases, the diaphragm will bend open more to allow flow through. If there is back pressure (or if it is a normally closed diaphragm check valve), the diaphragm will be forced against the opening and will seal it to prevent any backflow.
A lift check valve consists of a pilot disc that is raised (lifted) from the valve seat to allow media flow. It requires an opening pressure to overcome gravity and/or spring, and the guide holds the flap in a vertical line so that the flap can be repositioned and properly aligned, and sealed. Most commonly, poppet check valves require the media to make a 90-degree turn, but inline or tilting poppet check valves are also available. When the inlet pressure is reduced below the opening pressure or when backpressure is present, the valve will close by gravity, by springs, and/or by the use of backpressure. If there is no spring to assist in closing, the installation is oriented with respect to gravity to ensure that the disc swings closed by gravity.
Swing check valves are also commonly referred to as "tilting disc" check valves. They consist of a disc on a hinge (or trunnion) that swings open under inlet pressure. As inlet pressure decreases or backflow occurs, the disc swings closed. If there is no spring to assist in closing, the mounting direction is related to gravity to ensure that the disc swings closed by gravity.
Stop check valves are typically spring-loaded Y-check or lift check valves, but they have a manual override feature. This allows them to be used as normal check valves and prevent backflow. However, there is an external mechanism available to override it and hold the valve in the open or closed position. Thus, the valve can be used as two valves in one. They are commonly used in power plants, boiler cycles, steam generators, turbine cooling, and safety systems.
Butterfly check valves and wafer check valves can be used interchangeably. They consist of a hinge and a butterfly or wafer-type disc on a spring. When the inlet pressure exceeds the opening pressure, both sides open. When the inlet pressure decreases or backflow occurs, the spring (or backpressure) on the hinge closes the valve disc, effectively sealing it. This valve type allows direct flow with minimal obstruction.
Duckbill valves allow fluid to flow through a hose that has a natural flat shape at the end. This flat shape resembles a duckbill, hence the name check valve type. Flow opens the flat end of the duckbill, allowing fluid to pass through. When pressure is removed from the inlet side, the duckbill end returns to its flattened state, thereby shutting off the flow.
Bottom valves are simply a one-way valve type that is combined with an inlet-side filter and installed at the end of a section of pipe/hose because they have no connection point for the input. Common types of check valves included in bottom valves are inline spring assisted or inline ball check valves, so they allow only one-way flow and close with spring assist. They have a filter on the inlet side to prevent debris from entering the check valve and thus clogging or damaging something downstream. They are typically installed at the end of pump suction lines in water wells, tanks, or any other application where the suction line is located below the pump. As such, they can be used to keep the pump started, prevent fluid backflow, and keep debris out of the line.
Brass check valves offer excellent performance in applications where air, water, oil, or fuel are used. However, it is not resistant to seawater, pure water, or chlorinated water. They are less heat and corrosion resistant than stainless steel and are typically used in smaller, low-pressure applications.
Stainless steel check valves offer superior corrosion resistance, heat resistance, low-temperature resistance, and excellent mechanical properties. For applications that do not require high durability or resistance, stainless steel is not typically a cost-effective solution compared to PVC or brass check valves.
PVC check valves are often used in irrigation and water management systems. They are resistant to most corrosive media such as seawater, acids, alkalis, chloride solutions, and organic solvents. However, they are not resistant to aromatic and chlorinated hydrocarbons and typically have a maximum temperature of approximately 60°C.
Polypropylene check valves are used for water, corrosive media, and liquid foods. They are resistant to most corrosive media, such as inorganic acids, alkalis, and aqueous solutions that rapidly corrode metals. However, they are not resistant to concentrated acids and oxidizing agents and typically have a maximum temperature of approximately 80°C.
When selecting a check valve for your application, the following criteria need to be considered.
Material compatibility with the medium
Line size of the connection point
Maximum pressure and opening pressure requirements
Installation direction horizontal or vertical
Size of the envelope
Accessibility requirements for inspection and maintenance
Temperature (external and media)
Because of the function of check valves, they are typically used in a variety of applications for one of four different reasons.
To protect downstream equipment from backflow damage
To prevent contamination due to backflow
To prevent siphoning
To maintain a vacuum seal
Because of their function, they are used in almost every industry. They are used in common household appliances such as dishwashers, washing machines, and wastewater lines. For industrial purposes, they are used in boilers, furnaces, gas systems, pumping applications, or vacuum systems. They are also often used as aquarium check valves in water and CO2 lines. The two most common check valve applications are for water and air, so these applications are discussed in more depth below.
Check valves are used in many water applications, such as potable water and wastewater applications, and are referred to as one-way water valves. For potable water applications, they ensure that any media from the environment (the outlet side of the valve) does not enter the system with safe and clean potable water and contaminate it. For wastewater applications, they ensure that wastewater does not re-enter the system and cause spillage or additional contamination. For pumping applications, bottom valves are typically used to ensure that no debris enters the pipeline and to maintain internal pressure for the start-up. Duckbill valves can also be used for discharge on water lines. Sump pump check valves ensure that water discharged when the pump is shut down does not return to the sump pump due to gravity.
Pneumatic check valves or air check valves allow air to flow in and prevent it from flowing out. They are often referred to as one-way air valves. The most common application is in air compressors. They allow the compressor to keep some parts pressurized and other parts depressurized. They can be located on piston compressors (inlet and outlet), air receivers, discharge lines, etc.
The check valve symbol points to the direction in which flow is allowed, and the vertical line indicates that backflow is not allowed.
The primary purpose of a check valve in a system is to prevent backflow, which could damage equipment or contaminate upstream media.
Common check valve problems are noise, water hammer, vibration, backflow, seizure, leakage, and component wear/damage. To prevent problems, it is critical to properly specify the check valve for the application and media. The two most common problems due to improper specification are backflow and water hammers. For these two problems, a quick closing check valve should be used. If the check valve does not close fast enough, backflow may occur, and water hammer can occur if pressure fluctuations occur, causing shock waves within the media.
If a check valve acts quickly, it can prevent water hammer. This prevents pressure fluctuations that can create shock waves throughout the medium. These shock waves can damage equipment, pipe supports, and even rupture pipes due to vibration.
Check valves need to be installed in accordance with the inlet and outlet, usually indicated by arrows on the valve body. Since they allow flow in only one direction, they will not work properly if they are installed backward. On the horizontal or vertical side, it depends on the type of valve design you have. If it has a spring, any direction will work. If it does not have a spring, gravity will affect the operation of the check valve, so making sure you understand the internal components will ensure that you install it properly in either a horizontal or vertical manner.
When a check valve does not work, it allows backflow. The three possible causes of this are sticking, leaking, or slow closing. If there is no filter in the line, dirt or debris may become trapped between the disc and the valve body, keeping it open. The valve disc or seat may be damaged or torn due to wear on the material or corrosive media, preventing a proper seal and allowing backflow. If the valve closes too slowly, a minimum amount of backflow will enter before proper sealing occurs. Make sure gravity helps the design and/or that your spring is fast enough to close the valve quickly.
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