What is Check Valve and How Does Its Work?

What is Check Valve?

A check valve sometimes referred to as a non-return valve, reflux valve, retention valve, foot valve, or one-way valve is designed to let fluid (whether liquid or gas) move through it in just one direction. This simple but essential component plays a key role in many systems, ensuring that flow occurs as intended and preventing backflow.

Structurally, a check valve is what’s called a two-port valve. It has two openings: one where the fluid enters, and another where it exits. There isn’t just one style of check valve out there; in fact, there are several different types, each suited to particular uses across countless applications.

You’ve probably encountered check valves without even realizing it, since they’re tucked away inside many everyday household devices. Though these valves come in all sorts of shapes, sizes, and price ranges, most are actually quite compact, simple in design, and relatively inexpensive.

One notable thing about check valves is that they operate automatically. They don’t require any active control from a person, nor do they usually have external handles or stems. Typically, the outer casing or “body” is made from either plastic or metal, depending on what the valve is being used for.

A key principle to understand when it comes to check valves is something called “cracking pressure.” This refers to the minimum pressure difference required between the inlet and outlet for the valve to open and allow flow. Check valves are usually designed with a specific cracking pressure in mind, so they can be chosen or specified according to the needs of a particular system.

How does a check valve work?

A check valve is a straightforward yet essential component in fluid systems, designed to permit the flow of fluids in only one direction. Typically, these valves feature two ports one serving as the entry point for the fluid, and the other as the exit.

Because they restrict flow to a single direction, check valves are often referred to as “one-way valves” or “non-return valves.” Their primary function is to prevent backflow, ensuring that fluid moves only where it’s intended.

The operation of a check valve depends on a difference in pressure across the valve. For the valve to open, the pressure on the inlet side must exceed the pressure on the outlet side. If this condition isn’t met such as when the outlet pressure rises above the inlet, or the inlet pressure drops too low the valve closes automatically.

The mechanism by which a check valve closes can vary based on its specific design, but unlike many other types of valves, check valves don’t require manual intervention or external devices like handles or actuators. They function independently, responding directly to the system’s pressure conditions.

Check valves are frequently used in scenarios where preventing backflow is critical. They offer a cost-effective and simple solution to problems that could arise if fluids were allowed to reverse direction in a system.

For instance, backflow can introduce contaminants into clean sections of piping, potentially compromising the entire system. Take a sewer line, for example a non-return valve in this context ensures waste flows out but cannot return and contaminate upstream areas.

Additionally, check valves are vital in protecting sensitive equipment that is designed to handle flow in only one direction. A good example is a reverse osmosis filter: water must only pass through the filter one way, so a one-way valve is installed downstream to ensure this happens.

To accommodate the diverse needs of different systems, check valves come in a range of sizes, materials, and designs. This versatility means there is a suitable option for virtually any application where backflow prevention is necessary.

Types of Check Valves

Check valves are available in the following designs:

• Swing Check Valves
• Tilting Disk Check Valves
• Wafer Check Valves
• Disk Check Valves
• Piston Check Valves
• Ball Check Valves
• Duo-Check Valves
• Non-Slam Check Valves

1. Swing Check Valve

Swing check valves come in two main designs: the straight body and the y-pattern. What makes these valves distinctive is the way the disk hangs inside the valve, attached to a hinge pin.

When fluid moves through, the disk lifts and allows flow, and when the flow stops, it drops back down, sealing against a seat that’s actually built right into the body of the valve.

You’ll usually see swing check valves used for pipe sizes of two inches or larger. They’re pretty versatile in terms of installation—you can put them in either horizontal or vertical piping without much hassle.

That said, they’re not the best choice if you have a system with pulsating flow. One thing to keep in mind is that, compared to lift check valves, the swing check’s disk takes a little longer to close. That’s just because it has a longer way to travel and its own inertia to overcome.

2. Tilting Disk Check Valve

Tilting disk check valves offer a different approach. These are designed to fit snugly between two pipe flanges, which makes them a great space-saving option, especially for bigger pipes. Like swing checks, you can install them in either horizontal or vertical lines.

Where tilting disk valves really shine is in how quickly they respond. They close much faster than swing check valves, which makes them especially useful if you’re dealing with pulsating flows or compressible fluids. Their quick action helps prevent backflow problems that can happen when flow conditions are less predictable.

3. Wafer Type Check Valve

Wafer type check valves are popular partly because of how compact and lightweight they are. With their short face-to-face dimensions, they can easily fit between companion flanges, which makes installation straightforward and space-saving something engineers and plant operators really appreciate when dealing with tight setups.

These valves are versatile when it comes to compatibility; you can mount them between either weld neck or slip-on flanges, and they work across various flange standards. This flexibility makes them a go-to option for different piping systems.

What sets wafer check valves apart is how well they handle situations where minimizing pressure loss is critical. Thanks to their design, the valve opens and closes even with a minimal pressure difference across the disc. The combination of an eccentric disc shaft and a precisely matched seat ensures a tight seal that prevents any backflow when the media reverses direction.

Because of their slim build and reasonable cost, wafer check valves are quickly becoming the default choice in many industrial applications. When people need an efficient, reliable, and cost-effective check valve, this is often the style they choose.

4. Disc Check Valve

A single disc check valve sometimes called a wafer type disc check valve comes together from four main parts: the body, the disc, a star-shaped guide, and a spring. Each component plays its part in keeping fluid flow in check.

The way these valves operate is pretty straightforward. Fluid pressure pushes the disc open, allowing flow in the intended direction. As soon as the flow stops, a spring snaps the disc shut, preventing any chance of reverse flow. This automatic action is essential for protecting pumps and maintaining system integrity.

One thing people find handy about these disc check valves is their sandwich-style, wafer-thin design. You can slip them between virtually any standard of flanges, and you’re not limited by the orientation of your pipeline they’ll work even if the fluid is moving downwards in a vertical setup.

That makes them a practical choice for engineers who value both flexibility and reliability in their piping systems.

5. Piston Check Valve

Piston check valves are commonly used to safeguard pumps and related equipment by permitting fluid flow in only one direction, thus preventing backflow caused by backpressure.

These valves are typically constructed with globe-style bodies, which results in a higher pressure drop across the pipeline. This particular design not only ensures a secure seal but also enables the valve to respond swiftly to closure signals.

However, it’s important to note that metal-seated piston check valves might not achieve a completely leak-proof seal in gas systems, systems with minimal backflow pressure, or when handling fluids containing particulate matter.

6. Ball Check Valve

Ball check valves have carved out a unique niche, performing reliably in both water and wastewater settings. Their straightforward operating principle makes them especially suitable for smaller pumps and systems operating at low head pressures.

While considering the use of ball check valves, it’s worth thinking about installing a roll-bar for additional safety. These valves are more prone to slamming due to the long stroke and high inertia of the ball. When subjected to high pressures and dynamic conditions, the risk of severe slamming increases.

7. Dual Plate Wafer Check Valve

The dual plate wafer check valve stands out thanks to its two spring-loaded plates, which are mounted on a central hinge pin. As the flow diminishes, these plates—assisted by torsion springs—snap shut before the flow can reverse.

Collectively, these features contribute to the dual plate design’s reputation as an efficient and adaptable solution.

Often known as a silent check valve, it’s favored for its ease of installation between standard gaskets and flanges, making it both economical to fit and maintain.

This valve is manufactured to meet API 594 and API 6D standards, and is tested according to API 598. You may also hear it referred to as a butterfly check valve.

8. Non-Slam Check Valve

A conventional swing check valve can close rapidly under gravity, sometimes causing pressure surges or “shock waves” in the pipeline—stresses that the system must then absorb.

To counteract this, non-slam check valves have been developed. Unlike their gravity-dependent counterparts, these valves use a spring to assist in closing the disc as the velocity of upstream fluid decreases.

By the time the forward flow ceases, the disc is fully closed, minimizing the chance for reverse flow and greatly reducing the forces that typically cause water hammer on either side of the valve.

How do you choose the right check valve?

Selecting the right check valve isn’t just a matter of picking one off the shelf it requires some careful thought about your specific situation. Here’s what you’ll want to keep in mind:

• Material Selection: The material of the valve is important because it needs to withstand whatever is flowing through your pipes—whether that’s a particular gas or liquid. It’s worth double-checking that the valve’s construction is up for the job, considering both the system and the type of media involved.
• Performance Needs: Think about what the valve has to handle on a day-to-day basis. What are the typical pressure and temperature ranges in your system? Make sure your choice is up to the task, especially if you’re dealing with extreme conditions.
• Type and Size: It’s not just about finding a valve that fits; you’ll want one that matches your flow conditions and any specific control requirements. In more hazardous environments, safety becomes even more important, so take time to get the sizing right—it can make a big difference in overall system performance.
• Maintenance Considerations: No one wants to be constantly fixing or replacing valves. Consider how often the valve will need attention and whether it’s likely to get clogged or jammed. Picking a reliable model upfront can save you headaches down the road.
• Special Features: Check valves aren’t one-size-fits-all, and there are some extra details to factor in. These might include how fast the valve needs to respond, whether it should stay normally open or closed, the orientation of installation (vertical or horizontal), the direction of flow, and even the density of the fluid passing through.

How do you prevent check valves from failing?

One tricky thing about check valves is that you usually can’t see what’s going on inside, so catching problems early isn’t always easy. Still, there are some telltale signs to watch out for, like vibration (sometimes called “chattering”), unexpected reverse flow, parts wearing out faster than expected, or even unusual noises (think water hammer). Leaks are another obvious red flag.

To keep your check valves working smoothly, consider these simple steps:

• Make sure you’re using the right size for your system
• Do regular inspections to check for buildup or debris
• Install the valve correctly (don’t skip the manual!)
• Swap out old or worn valves before they fail

At the end of the day, check valves play a key role in making sure your piping system runs efficiently and safely. Putting a little extra thought into selection and upkeep goes a long way toward keeping everything flowing as it should.

Applications of Check Valve

On the basis of the work function of the check valves, it can be used for the following different applications;

• To prevent the backflow of fluid creating damage to the system.
• To ensure the prevention of contamination due to backflow of the fluid.
• To avoid the siphoning action in a pipeline.
• To maintain the vacuum seal.

Advantages of Check Valves

• Prevent backflow
• Able to endure high- and low-pressure conditions
• Perform as a backup and safety system
• Able to be used horizontally and vertically
• Self-actuated
• Fast acting.
• Protect pumps and compressors from damage caused by backflow
• Reduce downtime and loss of production
• Prevent water hammer
• Reduce sudden valve failure
• Lower maintenance costs
• Few moving parts
• Smaller footprint
• Able to cope with variable flow conditions
• Do not require power to operate
• Horizontal Check Valve

Disadvantages of Check Valves

• Do not operate in pulsating systems
• Closing element can slam closed causing damage and wear
• Operate in a completely enclosed system
• Impossible to check if they are open or closed
• Internal parts cannot be checked
• Disks can get stuck in the open position.
• Noise from slamming disks
• Water hammer
• Reverse flow problems

Common Problems with Check Valves

Water Hammer

Water hammer is one of those issues that can catch people off guard if they aren’t familiar with fluid systems. Basically, it happens when there’s a sudden change—usually a quick stop—in the flow of a gas or liquid.

Imagine a valve snapping shut in an instant: that abrupt halt can create a shock wave, which often results in loud noises and even vibrations running through the pipes. If left unchecked, these surges can actually damage the piping system and sometimes lead to expensive repairs.

A practical way to avoid water hammer is by using check valves that close quickly, since these can help absorb those pressure spikes before they cause trouble.

For example, silent check valves are designed to close rapidly and smoothly, making them a smart option for minimizing noise and vibration.

Reverse Flow

Reverse flow is another headache for anyone dealing with pumps and fluid systems. When fluid starts flowing in the wrong direction, it can force a pump to spin backward—which isn’t just inefficient, but can actually cause lasting damage to the equipment.

Tight-fitting, fast-closing check valves are a reliable solution here. They’re able to snap shut before the flow has a chance to reverse, protecting the pump in the process.

Spring-assisted check valves, in particular, stand out because their design lets them react almost instantly, reducing the risk of reverse flow before it becomes an issue.

Oversizing

Oversizing check valves is a surprisingly common mistake and often leads to a problem known as “chattering.” This is when the valve repeatedly opens and closes, which isn’t just noisy—it can eventually lead to valve failure.

The root of the problem is usually that the valve isn’t sized correctly for the application. To avoid this, it’s important to make sure the check valve matches the system’s requirements, so the disk remains stable when open and can form a complete seal when closed.

Getting the sizing right goes a long way toward preventing chattering, fluttering, and unnecessary wear on the valve over time.

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