A one-way valve is a device that only allows fluids to flow in one direction. They have two ports, one as input for fluids and the other as output for fluids. Because they only allow fluid to flow in one direction, they are usually called “one-way valves” or “check valves.” The main purpose of the one-way valve is to prevent backflow in the system. The following figure shows an example of a one-way valve.
The one-way valve relies on a pressure differential to operate. To open the valve, they need more pressure on the inlet side of the valve than on the outlet side. When the outlet pressure is high (or the inlet pressure is not high enough), the valve closes. Depending on the type of valve, the closing mechanism is different. Unlike other valves, they do not require handles, levers, actuators or humans to work properly. They are usually installed in programs that cause backflow problems. However, since they are not return valves, they are a cheap, effective and easy solution to a potential problem. If the return stream is contaminated, the return stream can cause a problem and, therefore, contaminate the upstream fluids. For example, a sewer line does not have a return valve to ensure that waste can be removed but not re-entered into the system. They are used if the reverse current damages the upstream equipment, which only causes the media to flow in one direction. For example, a reverse osmosis filter can only pass water in one direction, so a one-way valve is installed downstream to prevent this. There are different sizes, designs and materials to ensure there is a check for each application.
How one-way valve works
One-way valve cracking pressure
The one-way valve requires a minimum upstream pressure (pressure differential between inlet and outlet) to open the valve and flow through it. This minimum upstream pressure at which the valve opens occurs is called the “cracking pressure”. Specific cracking pressure varies depending on the design and size of the valve, so make sure your system can generate this cracking pressure and it is suitable for use.
Close the one-way valve
If the upstream pressure never falls below the cracking pressure or there is a return pressure (the current is trying to move from the outlet to the inlet), the valve will close. Depending on the design of the one-way valve, the closing mechanism can be changed. In short, the return pressure pushes a gate, ball, diaphragm, or disc toward the orifice and seals it. Depending on the design, the closing process can be assisted by a spring or gravity.
Install one-way valve
Since a one-way valve only works in one direction, it is important to know the correct orientation. Often, there is an arrow on the valve body that indicates the direction of flow. Otherwise, you need to make sure that the valve is installed in the desired flow direction. If it is reversed, the current cannot move through the system and the increased pressure leads to damage.
Types of one-way Valve
Depending on the design of the one-way valve, they will work slightly differently. The most common one-way valve is an in-line one-way valve that has a spring. In this section, we describe the different types of one-way valves.
One-way disc valve
One-way disc valves are common, easy to understand and have a simple design. The following figure shows an example of a one-way disc valve and shows the main components that the arrows indicate the direction of flow. When current enters the valve inlet port, it must have sufficient pressure (force) to overcome the cracking pressure and spring force. After overcoming it, it pushes the disc, opens the hole and allows the flow to flow through the valve. When the inlet pressure is no longer high enough, or there is a return pressure, then the pressure and spring of the disc are pushed towards the orifice and the valve closes. The short-distance spring for the disc allows for a quick reaction to close. This valve design also prevents pressure on the line and thus prevents the occurrence of water hammers. Common types of one-way disc valves are also called “nozzle control valves” or “silent noises”. They can be installed vertically or horizontally. However, as they are compatible with the system, they must be completely out of line for inspection and / or maintenance.
One-way valve Y
One-way valves are very similar to disc one-way valves. The difference, as you can see in the figure below, is that the spring and the movable disc are at an angle. This creates an “y” shape, hence the name lion. It works exactly like a line valve, but since the moving parts are 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.
Check even the ball
A ball valve uses a free-floating or spring-loaded ball that rests on a sealing sheet to close the hole. The sealing seat is typically a tapered cone to guide the ball into the seat and create a positive seal, thus stopping the reverse flow. When the liquid pressure at the inlet exceeds the crack pressure, the ball separates and allows flow to occur. When the inlet pressure does not exceed the crack pressure or there is a return pressure, the ball closes with a return pressure or through a spring and effectively closes the orifice.
The one-way diaphragm valve consists of a rubber diaphragm that flexes as the inlet pressure increases. Typically, these valves have a self-centered floating diaphragm, which allows them to open normally (NO). This means that there is no “cracking pressure”, however, they can be closed normally (NC) and then require an inlet pressure to overcome the tension of the diaphragms. The figure below on the left shows an open diaphragm valve because there is a “minimum” inlet pressure and fluid is still passing through it. As can be seen in the middle of the figure below, as the inlet pressure increases, the diaphragm opens further and allows more current to flow. If back pressure is created (or a one-way diaphragm valve is normally closed), the diaphragm is forced to face the orifice and seal it to prevent backflow, as shown in the figure below. Seen on the right.
One-way push valve
A one-way pressure valve consists of a guided disc that rises (rises) from the valve seat to provide fluid flow. It needs cracking pressure to overcome gravity or a spring, and the guide holds the disc in a vertical line so that it can reposition the disc with the correct alignment and seal. Normally, one-way pressure valves require a 90-degree rotation of the circumference, as shown in the figure below, but there are also one-way pressure valves that are aligned or at an angle. By reducing the inlet pressure below the cracking pressure or the presence of return pressure, the valve closes by gravity, spring and / or by using return pressure. If there is no spring to help close, gravity orientation is important to ensure that the disc is cut by gravity.
One-way swing valves are also commonly referred to as “sloping disc” valves. They consist of a disk mounted on a hinge (or tripod) that opens with inlet pressure. The disc is disconnected as the inlet pressure decreases or the flow returns. If there is no spring to help close, gravity orientation is important to ensure that the disc is cut by gravity. The figure below shows an example of a one-way swing valve.
One-way stop valve
The one-way stop valve is typically a y-check valve or an elevator check valve, but has a manual undo feature. This allows them to act as a natural one-way valve and prevent the flow from returning. However, there is an external mechanism that can be used to replace it and keep the valve open or closed. So this valve can act as two valves in one unit. They are commonly used in power plants, boiler circulators, steam generators, turbine coolers, and safety systems.
Butterfly or wafer
One-way butterfly valve or one-way check valve can be used instead of each other. They consist of a butterfly or wafer-style disc mounted on a hinge and spring. When the inlet pressure exceeds the cracking pressure, the two sides open, as shown in the figure below. When the inlet pressure decreases or there is a backflow, the spring on the hinge (or rear pressure) closes the disc effectively. These types of valves allow direct flow of fluid with minimal obstruction. You can also read the article on butterfly milk for more information .
Ductile one-way valve
The ductile one-way valve allows flow through a soft tube with a naturally smooth end at the end, as shown in the figure below. This flat shape is similar to a duck’s beak, hence the name of the one-sided lion. The flow opens the smooth end of the ductile and allows liquids to pass to the left as shown below. When the pressure is removed from the inlet, the end of the dock excavator returns to its flat position thus shutting off the flow as shown in the figure below.
One-way foot or foot valve
The one-way foot valve is simply a one-way valve in combination with a strainer at the inlet, which is mounted at the end of part of the pipe / hose because their inlet has no connection point. The most common types of control valves in a foot valve are linear springs or in-line check valves, so they only allow flow in one direction and help close with a spring. They have a strainer at the inlet to prevent debris from entering the one-way valve, which can block or damage something downstream. They are usually installed at the end of the pump suction line of a water well, fuel tank or any other application where the suction line is located below the pump. Therefore, they can be used to hold pumps, prevent liquids from siphoning, and prevent fluid from leaking out of the line. The following figure shows an example of foot milk.
One-way brass valves have excellent properties for applications that use air, water, oil or fuel. However, it is not resistant to seawater, purified water or chlorinated water. Compared to stainless steel, they are less resistant to heat and corrosion and are usually used for smaller applications with low pressure.
Stainless steel has corrosion resistance, heat resistance, low temperature resistance and excellent mechanical properties. For applications that do not require high durability and strength, stainless steel is usually not a cost-effective solution compared to PVC or brass control valves.
PVC (polyvinyl chloride)
PVC one-way valves are frequently used in irrigation and water management systems. They are resistant to corrosion by most corrosive substances such as seawater, acids, bases, chloride solutions and organic solvents. However, they are not resistant to aromatic hydrocarbons and chlorine, and the maximum temperature is usually around 60 ° C.
Polypropylene valves are used for water, aggressive environments and liquid food products. They are resistant to most corrosive substances such as inorganic acids, bases and aqueous solutions that quickly corrode metals. However, they are not resistant to concentrated acids and oxidizing agents, and the maximum temperature is usually around 80 ° C.
Criteria for selecting one-way milk
To choose a one-way valve, you should consider the following criteria according to your plan:
- Compatibility of materials with the environment
- Line size for connection points
- Maximum pressure and crack pressure
- For installation horizontally or vertically
- Installation dimensions
- Access requirements for inspections and repairs
- Temperature (external and fluid)
One-way valve applications
Because of how the one-way valve works, they are usually used in different applications for one of four different reasons:
- Protect equipment downstream, causing back damage
- Prevent backflow contamination
- Avoid siphoning
- Keep the 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 sewers. For industrial purposes, they are used in boilers, furnaces, gas systems, pumping applications, or vacuum systems. They are also often used in water and CO2 lines as aquarium check valves. Two of the most common applications of check valves are related to the weather, so they are discussed in more depth below.
Check one-way valve for water
Check valves are used in many cases, such as drinking water and wastewater, and are easily called one-way taps. For drinking water applications, ensure that no medium (milk outlet side) can enter and contaminate the system with safe drinking water. For wastewater applications, they ensure that wastewater cannot re-enter the system and cause additional flooding or contamination. For water pumping applications, foot valves are often used to ensure that no debris enters the line and to rotate the internal pressure for primary purposes. Duct valves can also be used to drain water lines. Tank pump check valves ensure that gravity-drained water does not return to the tank pump when the pump is switched off.
Pneumatic check valve
Pneumatic check valves or air check valves allow air flow inside and prevent it from shutting off, they are called one-way air valves. The most common application is for air compressors. They allow the compressor to compress certain components and compress other components. They can be mounted on a piston compressor (inlet and outlet), air intake, drain pipe, and so on.
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