Check valve

Check valve, also known as a one-way valve or non-return valve, is a type of valve that allows fluid (liquid or gas) to flow through it in only one direction.

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Swing Check Valve

Flap Check Valve

Ball Check Valve

Silent Check Valve

Foot Valve

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Working Principle

Normal Flow (Forward Flow):

When fluid (liquid or gas) flows in the correct direction (forward), it pushes against the valve mechanism (e.g., a disc, ball, or diaphragm).The force of the fluid overcomes the resistance of the valve mechanism, causing it to open.The fluid passes through the open valve with minimal restriction.

Reverse Flow (Backflow Prevention):

When the fluid attempts to flow in the opposite direction (reverse), it pushes against the valve mechanism from the wrong side.This force causes the valve mechanism to move to the closed position, effectively sealing the valve and preventing any backflow.The valve mechanism remains closed as long as there is reverse pressure, ensuring that no fluid can flow back through the valve.

Components of a Check Valve

Body: The main structure that houses the internal components of the valve.

Valve Mechanism:

Disc or Plate: In swing and lift check valves, the disc moves to allow or block flow.

Ball: In ball check valves, a ball moves away from or against a seat to control flow.

Diaphragm: In diaphragm check valves, a flexible diaphragm opens or closes to permit or block flow.

Seat: The surface against which the valve mechanism seals to prevent backflow.

Spring (Optional): Some check valves have a spring to help close the valve mechanism more quickly or to provide additional sealing force.

Types of Check Valves and Their Working Principles

Swing Check Valve:A disc or plate swings on a hinge or shaft.Forward flow pushes the disc open; reverse flow pushes it closed against the seat.

Lift Check Valve:A disc moves vertically within a guide.Forward flow lifts the disc off the seat; reverse flow causes the disc to drop and seal against the seat.

Ball Check Valve:A ball rests on a seat, usually with the help of gravity or a spring.Forward flow pushes the ball away from the seat; reverse flow pushes the ball back onto the seat, sealing the valve.

Diaphragm Check Valve:A flexible diaphragm deforms to allow forward flow.Reverse flow pushes the diaphragm back to its original position, sealing the valve.

Stop-Check Valve:Combines a check valve with a stop valve function.Can be manually closed to stop flow in either direction, or it operates automatically to prevent backflow.

Flow Dynamics

Pressure Differential: Check valves rely on a pressure differential to operate. Forward flow must create sufficient pressure to open the valve mechanism.

Flow Velocity: The velocity of the fluid can also influence the opening and closing of the valve. Higher velocity generally helps open the valve, while lower velocity or reverse flow assists in closing it.

By ensuring unidirectional flow, check valves protect systems from potential damage caused by backflow and maintain the integrity of various processes. Their simple yet effective design makes them indispensable in many applications across different industries.

Application

Check valve is used in various applications to ensure that fluid (liquid or gas) flows in only one direction. This one-way flow is crucial for protecting equipment, maintaining process integrity, and preventing contamination. Here are some common uses of check valves:

Plumbing Systems:

Preventing Backflow: Ensures that water flows in the intended direction, preventing contaminated water from flowing back into clean water supply lines.

Protection of Water Heaters: Stops the backflow of hot water, which could damage the heater or other components.

Pumping Systems:

Maintaining Pump Prime: Keeps the pump primed by preventing the backflow of the fluid, which is essential for the proper functioning of the pump.

Preventing Damage: Protects the pump from damage caused by reverse flow.

Industrial Processes:

Chemical Processing: Prevents the backflow of chemicals, ensuring that processes run smoothly and safely.

Petrochemical Plants: Maintains the correct flow direction of various fluids and gases, protecting sensitive equipment.

HVAC Systems:

Air Conditioning and Refrigeration: Ensures the proper flow of refrigerants, enhancing system efficiency and preventing damage.

Heating Systems: Prevents backflow in boiler systems and other heating applications.

Water Treatment Plants:

Ensuring Proper Flow: Maintains the direction of water flow through various stages of treatment.

Protecting Equipment: Prevents reverse flow that could damage pumps, filters, and other equipment.

Automotive Systems:

Fuel Systems: Prevents the backflow of fuel, maintaining pressure and ensuring proper engine operation.

Brake Systems: Ensures the correct flow of brake fluid, contributing to the safety and effectiveness of the braking system.

Medical Devices:

Infusion Pumps: Ensures that medications flow in the correct direction through the tubing.

Respiratory Equipment: Maintains the proper flow of gases in ventilators and other respiratory devices.

Fire Protection Systems:

Sprinkler Systems: Prevents the backflow of water, ensuring that the sprinkler system remains ready to operate in the event of a fire.

Benefits of Using Check Valves

Preventing Contamination: Stops contaminants from flowing backward into clean areas.

Protecting Equipment: Prevents damage to pumps, compressors, and other equipment caused by reverse flow.

Maintaining System Efficiency: Ensures that fluids and gases flow in the intended direction, improving overall system performance.

Safety: Reduces the risk of accidents caused by reverse flow in critical applications like chemical processing and fuel systems.

By ensuring unidirectional flow, check valves play a vital role in maintaining the safety, efficiency, and reliability of many systems across various industries.

Installation

Take water check valve as example.

In a piping system, it is crucial to install check valves properly to ensure their effectiveness and the system’s normal operation. Here are some common installation locations and guidelines:

After water pumps:At the pump outlet,Installing a check valve after the pump outlet can prevent water from flowing back into the pump when the pump stops, protecting the pump from damage caused by backflow and maintaining system pressure.

Before water tanks:On the inlet pipe, Installing a check valve on the inlet pipe of a water tank can prevent water from the tank from flowing back into the water supply system.

Between high and low water levels:Between high and low water tanks: If the system has high and low water tanks, install a check valve on the outlet pipe of the high water tank to prevent water from flowing back into the low water tank.

To prevent contamination:On the inlet pipe of residential or commercial buildings: Installing a check valve on the main water pipe entering a building can prevent water from inside the building from flowing back into the municipal water supply system, preventing contamination of the public water supply.

Before boilers or water heaters:On the cold-water supply pipe: Installing a check valve on the cold-water supply pipe of a boiler or water heater can prevent hot water from flowing back into the cold-water system.

After sprinkler systems:After sprinkler heads: In a fire protection sprinkler system, install a check valve after each sprinkler head to prevent water from flowing back into the sprinkler pipes when the system is not in operation.

In summary, check valves should be installed in all critical locations where backflow can occur. When installing them, it is also important to choose the right type of check valve (swing, lift, wafer, etc.) and ensure the correct installation direction (usually indicated on the valve body). Regular inspection and maintenance are also critical to ensure that check valves work properly.

Installation steps and considerations for check valves

Preparation before installation

Select the right check valve: Choose the right type and size of check valve based on the needs of the piping system.

Selecting the right check valve requires consideration of several factors, including the needs of the piping system, fluid characteristics, installation location, and operating environment. Here are some key factors and steps to consider when selecting check valves:

Key factors in selecting a check valve

Type of fluid:

Liquid: water, oil, chemicals, etc.

Gas: air, steam, gas fuel, etc.

Select the appropriate material and design based on the fluid.

Fluid temperature and pressure:

Understand the operating temperature and pressure range of the system and choose a check valve that can handle these conditions.

Different materials and designs of check valves have different temperature and pressure limits.

Flow requirements:

Select the size of the check valve based on the flow requirements of the system to ensure it can handle the maximum flow rate of the system without causing excessive pressure loss.

Installation location and space:

Consider space constraints and select the right type and size of check valve.

Ensure that the installation location of the check valve is easy to maintain and inspect.

Connection method:

Threaded connection: Suitable for small diameter pipes.

Flange connection: Suitable for large diameter pipes and easy to disassemble and maintain.

Welded connection: Suitable for high-pressure systems to ensure a tight seal.

Special requirements:

Water hammer prevention: Select a check valve with a slow-closing function.

Noise control: Choose a check valve with low noise design.

Corrosion protection: For corrosive fluids, select a check valve made of corrosion-resistant materials.

Common check valve types and characteristics

Swing Check Valve:

Suitable for liquid piping systems such as water, oil, etc.

Low fluid resistance, suitable for large diameter pipes.

Not suitable for pulsating flow and high-frequency opening and closing.

Lift Check Valve:

Suitable for high-pressure and high-velocity fluids.

High fluid resistance, suitable for small diameter pipes.

The installation position should be horizontal or vertical (fluid flows from bottom to top).

Wafer Check Valve:

Compact structure, light weight, suitable for limited space applications.

Easy to install, typically used for large diameter pipes.

Can be used for both liquid and gas piping systems.

Spring Check Valve:

Suitable for horizontal and vertical installation, suitable for systems that frequently open and close.

Sensitive response, suitable for low-pressure and low-flow systems.

Ball Check Valve:

Suitable for fluids containing solid particles, the ball can clear impurities.

Suitable for sewage, slurry, and other systems.

Selecting the size of check valves

Determine the pipe diameter:

Select the appropriate size of the check valve based on the nominal diameter (DN) of the pipe.

Calculate flow and pressure loss:

Select the appropriate check valve specifications based on the flow and allowable pressure loss of the system.

Check the flow and pressure loss curve provided by the manufacturer.

Summary of selection steps

Determine fluid characteristics: including fluid type, temperature, and pressure.

Select the appropriate type of check valve: Choose the appropriate type of check valve based on the system requirements.

Determine pipe size and connection method: Select the check valve size and connection method that match the pipe.

Consider special requirements: such as water hammer prevention, low noise, corrosion resistance, etc.

Consult professional advice: If in doubt, consult check valve manufacturer or a professional engineer.

By following these steps, you can choose the right check valve for your specific piping system requirements to ensure the system operates properly and remains stable over the long term.

Check the check valve: Before installation, check the appearance and internals of the check valve to ensure there is no damage or debris.

Clean the pipes: Remove dirt and debris from the pipes to prevent blockages and damage to the check valve.

Installation steps

Determine the installation direction:Ensure that the check valve arrow points in the direction of fluid flow (usually indicated by an arrow on the check valve).

Turn off the water:Close the water source in the piping system and drain the water from the related pipes.

Cut the pipes:Accurately measure and cut the pipe according to the length and connection method of the check valve. Make sure the cut is smooth and without burrs.

Connect the check valve:

Threaded connection: Apply a sufficient amount of sealant to the pipe threads or wrap the pipe with sealing tape, then tighten the check valve in place.

Flange connection: Align the check valve flange with the pipe flange, fix with bolts, and tighten evenly.

Welding connection: Ensure the welding area is clean, then weld the check valve to the pipe.

Wafer connection: Place the check valve between the pipe flanges and tighten with long bolts.

Check alignment and fastening:Ensure the check valve is aligned with the pipe to avoid uneven stress or deformation.Tighten all connections to ensure there is no looseness.

Verify the installation is correct

Turn on the water:Open the water source in the piping system, gradually pressurize, and observe whether the check valve and its connections are leaking.

Test the check valve function:Forward flow test: Slowly turn on the water source to ensure the water flows smoothly through the check valve.

Reverse flow test: Turn off the water source, then try to pressurize downstream of the pipe and check if water flows back from the check valve upstream.

Check for leaks:Carefully inspect the check valve and its connections for water leakage. If there are leaks, tighten the connections or replace the sealing materials.

Operational check:Repeatedly open and close the water source to ensure the check valve works properly in both forward and reverse flow.

Regular maintenance:After installation, regularly check the operation of the check valve, remove impurities, and ensure it operates stably over the long term.

By following these steps, you can ensure the correct installation and proper operation of the check valve. If you have questions or encounter complex situations, it is advisable to consult a professional pipe installer or relevant technical support from Judberd

The Impact of Check Valves on Water Flow

Check valves do indeed have an impact on water flow in a piping system, primarily in terms of changes in flow rate and pressure. Different types of check valves have different effects on water flow, as detailed below:

1,Swing Check Valve

Characteristics:Fluid flows through the valve and the valve flap rotates open like a door.When the valve is open, fluid resistance is low.

Effects on water flow:

Flow rate: The long rotational path of the valve flap minimally impacts flow rate.

Pressure: Low pressure loss occurs when the valve is fully open. Suitable for high-flow piping systems.

2,Lift Check Valve

Characteristics:Fluid flows through the valve and the valve flap moves vertically up and down.Suitable for high-pressure systems.

Effects on water flow:

Flow rate: The short vertical path of the valve flap results in minimal changes in flow rate.

Pressure: As fluid must pass around the valve flap, there is significant pressure loss, particularly when the valve is partially open. Suitable for small-diameter, high-pressure systems.

3,Wafer Check Valve

Characteristics:Compact design and installed between pipe flanges.Suitable for situations with limited space.

Effects on water flow:

Flow rate: The wafer design results in a short path for fluid to flow through, minimizing the impact on flow rate.

Pressure: Overall pressure loss is low, but specific values depend on the design and fluid characteristics. Suitable for large-diameter, low-pressure systems.

4,Spring Check Valve

Characteristics:Valve flap closes with the force of a spring and can be installed horizontally or vertically.Responsive and suitable for systems that frequently open and close.

Effects on water flow:

Flow rate: The presence of the spring and valve flap has some impact on flow rate, though this is typically minimal.

Pressure: The spring provides additional closing force, leading to a moderate level of pressure loss. Suitable for low-pressure, low-flow systems.

5,Ball Check Valve

Characteristics:Fluid flows through the valve and the ball moves to open or close the passage.Suitable for fluids containing solid particles.

Effects on water flow:

Flow rate: The presence of the ball has some impact on flow rate, particularly at the start of opening.

Pressure: Due to the need for the ball to overcome fluid resistance, there is significant pressure loss. Suitable for sewage and slurry systems.

Comparison of Pressure Loss

Swing Check Valve: Low pressure loss, suitable for high-flow systems.

Lift Check Valve: High pressure loss, suitable for high-pressure, low-flow systems.

Wafer Check Valve: Moderate pressure loss, suitable for large-diameter, low-pressure systems.

Spring Check Valve: Moderate pressure loss, suitable for low-pressure, low-flow systems.

Ball Check Valve: High pressure loss, suitable for systems handling fluids containing solid particles.

Conclusion

Different types of check valves have their own characteristics in terms of design, and each has a different impact on flow rate and pressure. When selecting a check valve, it is necessary to consider various factors, including the specific requirements of the piping system, fluid characteristics, flow rate, and pressure. Proper selection and installation of check valves can ensure the normal operation of the system and minimize unnecessary pressure loss and flow rate impact.

Relationship Between Check Valves and Water Hammer

Water hammer is a pressure surge or wave caused when a fluid in motion is forced to stop or change direction suddenly. This phenomenon can cause significant damage to pipelines, valves, and other components. Check valves, depending on their design and application, can either exacerbate or help mitigate water hammer. Below is a discussion of how different types of check valves interact with water hammer:

1,Swing Check Valve

Characteristics:The valve disc swings open when fluid flows in the desired direction and closes when the flow reverses.

Impact on Water Hammer:

Potential for Water Hammer: Swing check valves can exacerbate water hammer because the disc can slam shut if the flow reverses rapidly.

Mitigation: To reduce water hammer, the swing check valve should be installed with dampening mechanisms or be part of a system with controlled flow changes.

2,Lift Check Valve

Characteristics:The valve disc moves vertically to allow or block flow. It is often used in high-pressure applications.

Impact on Water Hammer:

Potential for Water Hammer: The lift check valve can cause water hammer if the disc rapidly closes due to a sudden flow reversal.

Mitigation: A lift check valve with a spring-assisted closure can help reduce the risk of water hammer by providing a controlled closing action.

3,Wafer Check Valve

Characteristics:This valve is compact and installed between two flanges. It uses either a single disc or a dual-plate design.

Impact on Water Hammer:

Potential for Water Hammer: Wafer check valves, especially those with a single disc, can contribute to water hammer if the disc closes quickly.

Mitigation: Dual-plate wafer check valves are better at mitigating water hammer as the plates tend to close more gently and evenly, reducing the pressure surge.

4,Spring Check Valve

Characteristics:A spring mechanism assists in closing the valve, ensuring quick and reliable operation. Suitable for horizontal and vertical installations.

Impact on Water Hammer:

Potential for Water Hammer: The spring mechanism can help in preventing water hammer by ensuring that the valve closes smoothly and quickly, reducing the chance of a pressure surge.

Mitigation: Spring check valves are generally effective at mitigating water hammer because the spring controls the disc’s movement, preventing sudden closure.

5,Ball Check Valve

Characteristics:A ball moves up and down within the valve body to open or close the flow path. Often used in applications with particulate matter.

Impact on Water Hammer:

Potential for Water Hammer: The ball can cause water hammer if it drops rapidly into the seat, especially in systems with high flow velocities.

Mitigation: To minimize water hammer, ball check valves should be used in systems with steady, non-turbulent flow, or designed with cushioning mechanisms to slow the ball’s movement.

General Recommendations for Mitigating Water Hammer with Check Valves

Slow-Closing Valves: Choose check valves designed to close slowly, such as those with spring-assisted or dampened closures, to minimize the sudden stop of fluid flow.

Proper Sizing: Ensure the check valve is properly sized for the system to avoid excessive flow velocities that can increase the risk of water hammer.

Installation Position: Install check valves in appropriate positions within the system to manage flow changes effectively. Vertical installations may sometimes help reduce water hammer.

System Design: Incorporate surge tanks, air chambers, or other pressure relief devices within the system to absorb the pressure waves caused by water hammer.

By understanding the relationship between check valves and water hammer, and choosing the appropriate type for your specific application, you can effectively mitigate the risks associated with water hammer in fluid systems.

Common Problem Caused by Check Valve, Reason and Solution

Take water check valve as example

While check valves are effective in preventing backflow in a piping system, they can sometimes cause common problems. These issues are typically caused by improper installation, selection, or operation. Here are common problems caused by check valves, the reasons for them, and the solutions:

Water Hammer

Reasons:Check valves close quickly, causing fluid to stop suddenly and create a pressure wave.There are drastic changes in flow rate in the system, leading to pressure fluctuations.

Solutions:

Slow-Closing Check Valve: Select a check valve with a slow-closing function to slow down the valve closing speed and reduce water hammer.

Buffer or Shock Absorber: Install buffers or shock absorbers in the piping system to absorb pressure waves.

Throttle Valve: Install throttle valves at critical locations to control fluid velocity and reduce pressure fluctuations.

2,Valve Jamming or Failure

Reasons:Impurities or particles accumulate in the pipe, causing the valve flap to jam.The check valve material is not suitable for the fluid, leading to corrosion or wear.

Solutions:

Regular Cleaning and Maintenance: Regularly inspect and clean check valves to ensure there are no impurities inside the valve.

Proper Material Selection: Choose check valve materials that are corrosion-resistant and wear-resistant based on fluid characteristics.

Strainer or Filter: Install strainers or filters before check valves to prevent impurities from entering the valve.

3,Noise Issues

Reasons:Check valves generate impact noise when closing, especially in high-flow or high-pressure systems.The valve flap vibrates or resonates, creating noise.

Solutions:Low-Noise Check Valve: Select check valves designed for low noise, such as double-disc or check valves with silencers.

Install Shock Absorption Pads: Install shock absorption pads at the connection between the check valve and the pipe to reduce vibration transmission.

Adjust Flow Rates: Reduce valve flap vibration by adjusting system flow rates.

4,Frequent Opening and Closing of Valves

Reasons:Fluid flow in the system is unstable, causing check valves to open and close frequently.The check valve spring is too tight or loose, causing valve instability.

Solutions:

Stabilize Flow Rates: Add buffer tanks or pressure stabilizers to the system to stabilize flow rates and reduce the frequency of check valve opening and closing.

Adjust Spring Tension: Adjust the spring tension of the check valve according to system requirements to accommodate fluid flow characteristics.

Use Appropriate Valves: Select check valves that are appropriate for system flow rates and pressures to avoid unnecessary opening and closing actions.

5,Excessive Pressure Loss

Reasons:Improper check valve selection with excessive resistance.Valve size mismatch causing excessive pressure loss when fluid passes through.

Solutions:Correct Selection: Choose the appropriate type and size of check valve based on system flow rates and pressure requirements.

Optimize Piping Design: Optimize piping layouts to reduce unnecessary bends and reductions, lowering pressure losses.

By correctly selecting and maintaining check valves, these common problems can be effectively avoided, ensuring the normal operation and long-term stability of your water piping system.

Operation of Check Valves and Opening/Closing Pressures

Take water check valve as example

Check valves are automatic valves that do not require manual operation. They rely on fluid pressure and flow to automatically open and close to prevent backflow. Different types of check valves have different opening and closing pressures. Here are specific explanations for common check valve types:

Swing Check Valve

Operation:Automatic. The valve flap is pushed open by fluid flow; the valve flap closes under the action of gravity and backflow pressure when fluid flows back.