What Does a Check Valve Do: Everything You Need to Know

What Is a Check Valve?

A check valve, also known as a non return valve or a one way check valve, is a critical component in fluid systems designed to allow flow in only one direction while preventing backflow. This essential device automatically opens when fluid flows in the intended direction and closes when flow attempts to reverse, making it one of the most important safety and efficiency components in any piping system. 

How a Check Valve Works

The operation of a check valve is very simple yet highly effective. When fluid flows in the intended direction, it creates pressure against the valve's internal mechanism, which opens when the inlet pressure exceeds the valve's cracking pressure. This cracking pressure is the minimum pressure differential required to open the valve and allow fluid flow to begin.

As fluid continues to flow forward, it maintains the valve in an open position, allowing unrestricted passage through the valve body. The valve remains open as long as forward pressure is maintained and flow continues in the correct direction. This design ensures minimal pressure drop across the valve during normal operation, maximizing system efficiency.

When forward flow stops or reverses, the pressure differential changes dramatically. Without adequate forward pressure to keep the valve open, the internal mechanism closes automatically. Many check valves incorporate spring mechanisms that assist in closing, ensuring rapid response to changing flow conditions. This automatic closure effectively blocks reverse flow, preventing backflow that could damage pumps, contaminate clean fluids, or cause water hammer effects that stress piping systems.

Types of Check Valves

Understanding the various types of check valves available helps you select the optimal solution for your specific application. Each type offers unique advantages and is suited to different operating conditions, fluid types, and performance requirements.

Swing Check Valve

Swing check valves feature a hinged disc that swings away from the valve seat when forward flow creates sufficient pressure. These valves are among the most common types of check valves due to their reliability and relatively low pressure drop characteristics. The disc pivots on a hinge pin, allowing it to swing freely in response to flow conditions.

Ball Check Valve

Ball check valves utilize a spherical ball that moves within the valve body to control flow direction. When forward flow occurs, the ball is pushed away from the inlet seat, allowing fluid to pass around it. When flow reverses, the ball returns to the inlet seat, creating a tight seal that effectively blocks reverse flow. 

Diaphragm Check Valve

 Diaphragm check valves employ a flexible diaphragm that deflects in response to pressure changes, controlling flow direction through the valve. When forward pressure exceeds the diaphragm's resistance, it deflects away from the seat, allowing flow to pass. When pressure reverses, the diaphragm returns to its seated position, blocking reverse flow.

Lift Check Valve

Lift check valves feature a disc or poppet that moves vertically within the valve body, lifting away from the seat when forward flow creates adequate pressure. The disc's movement is guided by internal structures that ensure proper alignment and sealing when closed.

Dual-Plate (Wafer) Check Valve

Dual-plate check valves, also known as wafer check valves, feature two hinged plates that open and close in response to flow conditions. These valves are designed to fit between pipe flanges, making them compact and suitable for installations with limited space.

Key Components of a Check Valve

Understanding the essential components of a check valve helps in selection, installation, and maintenance of these critical system elements. Each component plays a vital role in the valve's operation and overall performance.

Valve Body and Seat

The valve body forms the primary structure of the check valve, containing all internal components and providing the connection points to the piping system. The body must withstand system pressure and provide smooth flow passages that minimize turbulence and pressure drop during operation.

The valve seat is the sealing surface where the valve's closure mechanism makes contact when blocking reverse flow. The seat's design and surface finish are critical for achieving tight shutoff and preventing leakage. High-quality seats are precisely machined and may incorporate special coatings or materials to enhance sealing performance and durability.

Disk or Poppet Mechanism

 The disk or poppet is the movable component that opens and closes to control flow direction. Its design varies depending on the valve type but always serves the fundamental function of responding to pressure changes to allow or block flow.

In swing check valves, the disk is typically circular and hinged, while ball check valves use a spherical element. Lift check valves employ guided disks or poppets that move vertically, and diaphragm valves use flexible membranes that deflect in response to pressure.

Spring Mechanism (in Some Types)

Many check valve designs incorporate spring mechanisms that assist in closing the valve when forward flow stops or reverses. Springs provide additional force to ensure rapid valve closure and maintain sealing pressure even under low or no-flow conditions.

Spring-assisted check valves typically respond faster to flow changes than gravity-operated designs, reducing the potential for reverse flow and water hammer effects. The spring force must be carefully calibrated to provide adequate closing assistance without significantly increasing the valve's cracking pressure.

Springs used in check valves must be corrosion-resistant and capable of millions of cycles without fatigue failure. Material selection and design are critical for long-term reliability in various fluid environments and operating conditions

Benefits of Using a Check Valve

Incorporating check valves into fluid systems provides numerous advantages that improve system reliability, efficiency, and safety. Understanding these benefits helps justify their use and guides proper application. 

Prevents Backflow and Damage

The primary benefit of any check valve is preventing backflow that could damage sensitive equipment or contaminate clean fluids. Pumps are particularly vulnerable to reverse rotation caused by backflow, which can damage impellers, seals, and bearings. Check valves installed downstream of pumps protect these expensive components from reverse flow damage. 

Maintains Pressure in the System

Check valves help maintain system pressure by preventing pressure loss through reverse flow. In elevated systems, check valves prevent gravity-induced backflow that would reduce pressure at critical points. This pressure maintenance is essential for consistent system performance and proper operation of downstream equipment.

In pumping systems, check valves maintain prime by preventing fluid from draining back through the pump when it's not operating. This feature reduces startup time and energy consumption while protecting the pump from dry running conditions that could cause damage.

Protects Equipment and Increases Safety

Beyond preventing backflow damage, check valves contribute to overall system safety by reducing water hammer effects and pressure surges. When pumps stop suddenly, the momentum of flowing fluid can create dangerous pressure spikes. Check valves that close quickly help minimize these transient pressure effects. 

Choosing the Right Check Valve

Selecting the appropriate check valve for your application requires careful consideration of multiple factors that affect performance, reliability, and cost-effectiveness. A systematic approach to valve selection ensures optimal results.

Factors to Consider: Flow Rate, Pressure, Media Type

Flow rate requirements directly impact valve sizing and type selection. High flow rates may require larger valves or specific designs that minimize pressure drop, while low flow applications might need valves with low cracking pressures for reliable operation. The valve must handle maximum expected flow rates without excessive pressure loss.

System pressure affects both valve selection and material requirements. High-pressure applications require robust valve designs and materials capable of withstanding operating pressures with adequate safety margins. The valve's pressure rating must exceed maximum system pressure under all operating conditions.

Media type influences material selection, valve design, and sealing requirements. Corrosive fluids require chemically resistant materials, while abrasive media might need hardened components or special designs that minimize wear. Temperature, viscosity, and other fluid properties also affect valve selection. Having a properly fitting valve cover oil cap is also an important consideration. Valve cover adapters are also available to ensure a proper fit.

Material Options: Brass, Stainless Steel, PVC

Material selection significantly impacts valve performance, durability, and cost. Brass check valves offer good corrosion resistance and are cost-effective for many water and mild chemical applications. They're easy to machine and provide reliable service in moderate temperature and pressure conditions.

Stainless steel valves provide superior corrosion resistance and strength, making them suitable for demanding applications involving aggressive chemicals, high temperatures, or high pressures. Various stainless steel grades are available to match specific corrosion resistance requirements.

PVC and other plastic materials offer excellent chemical resistance for many applications while providing cost advantages over metal valves. These materials are particularly suitable for water treatment, chemical processing, and other applications where metal corrosion is a concern.

Size and Installation Requirements

Proper valve sizing ensures adequate flow capacity while maintaining reasonable pressure drop. Undersized valves create excessive pressure loss and may not provide reliable operation at low flow rates. Oversized valves may have higher cracking pressures and slower response times.

Installation requirements include orientation, space constraints, and accessibility for maintenance. Some valve types require specific installation orientations to function properly, while others can operate in any position. Available space and maintenance access requirements may limit valve type options.

Installation and Maintenance Tips

Proper installation and maintenance are crucial for reliable check valve operation throughout their service life. Following best practices ensures optimal performance and minimizes unexpected failures.

Proper Valve Orientation Matters

Many check valves require specific installation orientations to function correctly. Swing check valves typically must be installed horizontally with the hinge pin level to ensure proper disc operation. Installing these valves in vertical positions can cause the disc to hang open or fail to seal properly.

Lift check valves generally require vertical installation with flow upward, allowing gravity to assist in valve closing. Installing these valves horizontally or with downward flow can result in poor sealing or failure to close completely.

Flow direction must be carefully observed during installation, with arrows or other markings on the valve body indicating the correct flow direction. Installing a rollover valve backward renders it completely ineffective and can cause system damage.

Cleaning and Inspection Best Practices

Regular inspection and cleaning help identify potential problems before they cause system failures. Visual inspection should look for signs of corrosion, wear, or damage to valve components. Any visible deterioration indicates the need for repair or replacement.

Cleaning procedures depend on the valve type and application. Some valves can be cleaned in place, while others require removal for thorough cleaning. Debris accumulation on valve seats or moving components can prevent proper sealing or cause premature wear.

How to Identify Valve Failure

Common signs of check valve failure include unusual system noises, pressure fluctuations, or evidence of reverse flow. Water hammer effects that weren't previously present may indicate that a check valve isn't closing properly or quickly enough. Regular monitoring of system performance helps identify gradual valve degradation before complete failure occurs. 

Why Every Flow System Needs a Check Valve

The importance of check valves extends beyond specific applications to fundamental system protection and performance optimization. Even simple fluid systems benefit from properly applied check valves that prevent backflow and protect equipment.

Conclusion

Understanding what a check valve does and how to properly select, install, and maintain these critical components is essential for anyone working with fluid systems. Investment in quality check valves and proper system design pays dividends through improved reliability, reduced maintenance costs, and protection of expensive system components. The automatic operation and proven reliability of check valves make them indispensable components in modern fluid systems, providing peace of mind and system protection that justify their use in virtually every flow application. To learn more reach out to our Redhorse Performance team today.