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A spring check valve is designed to allow flow in one direction while preventing reverse flow. It features a single inlet and outlet and requires correct spring selection to function properly. Each spring check valve, like all check valves, has an arrow on its side indicating the direction of flow. Often referred to as non-return or one-way valves, spring check valves utilize a spring and pressure on a disc to close the valve and stop backflow.
For a check valve to operate correctly, it must have a differential pressure with flow moving from high to low pressure. The high pressure on the inlet side, known as the cracking pressure, enables the flow to pass through the valve and overcome the strength of the internal spring.
Check valves, in general, are designed to allow media to flow in only one direction. The mechanism used for checking can take various forms, such as a ball, disc, piston, or poppet (a mushroom-shaped head). Spring check valves specifically prevent reverse flow when the pressure in a system decreases, slows, stops, or reverses, thus protecting pumps, equipment, and machinery.
Swing check valves allow flow in one direction and automatically close when the cracking pressure decreases. They are a form of butterfly valve with a disc that covers the valve opening. The disc is attached to a hinge such that the disc can swing open or close when it is struck by the flow of the media. On the side of the valve body is an arrow that indicates the direction the flow must be as it enters and exits the valve.
The pressure of the flow pushes the disc or door open, allowing the media to pass through. When flow attempts to move in the reverse direction, the disc closes due to the force of the liquid or media pushing against it.
Swing check valves operate without external power. Fluid or media flows through them unobstructed. These valves are typically installed horizontally in pipelines but can also be installed vertically as long as the flow direction is upward.
For a spring-loaded check valve to function properly, it requires upstream pressure, known as cracking pressure, to remain open. The required cracking pressure depends on the valve type, construction, spring characteristics, and its orientation in the pipe. Cracking pressure specifications are typically measured in pounds per square inch gauge (PSIG), pounds per square inch (PSI), or bars, where one bar equals 14.5 psi.
When upstream pressure falls below the cracking pressure, back pressure becomes a factor, causing the flow to attempt moving from the outlet to the inlet. In response, the valve automatically closes, stopping the flow.
An axial flow silent check valve features a disc held in place by a spring, which centers the disc to enable smoother flow and immediate opening and closing. The spring and disc are positioned centrally within the pipeline, allowing the flow to pass around the disc. This differs from swing check valves or other spring-loaded valves, which lift the disc entirely out of the flow path, resulting in a fully open pipe.
Axial flow silent check valves are more expensive than traditional spring check valves and swing check valves. However, their higher cost is offset by their longevity, often exceeding three years before replacement is necessary.
The unique design of an axial flow silent check valve is illustrated below, showing the valve in the open position with fluid flowing through. Similar to spring check valves, axial flow check valves begin to close when upstream pressure drops. As pressure decreases, the valve gradually closes.
A ball spring check valve utilizes a ball as its sealing element, positioned near the inlet orifice. The sealing seat is conically tapered to direct the ball into it, forming a positive seal. When the flow’s cracking pressure exceeds the force of the spring holding the ball, the ball is pushed away, allowing flow to pass through. As the cracking pressure decreases, the spring moves the ball back to close the inlet.
In-line spring check valves, also known as nozzle or silent check valves, feature a stem and disc construction along with a spring. They open when the cracking pressure exceeds the spring force, allowing the flow to push the disc open. As the inlet pressure decreases, the spring pushes the disc against the orifice to close the valve.
Lift spring check valves are placed in lines where globe valves are used as flow control valves. They can be used in horizontal or vertical lines and are recommended for use with steam, air, gas, water, and vapor lines. Flow enters below the seat of the valve and lifts the disc or ball off the seat. When the flow reverses or stops, the disc or ball is forced onto the seat by gravity and the backflow.
Certain check valves are designed to close abruptly if fluid flow reverses. This abrupt closing, known as slamming, happens when fluid flow stops or changes direction quickly. Swing check valves often experience slamming as the fluid flow ceases or reverses, while spring check valves are engineered to close before this reversal occurs, thereby reducing or eliminating slamming.
A no-slam check valve incorporates a spring that counteracts the pressure of the flowing fluid. When the fluid flow is vigorous, the spring compresses, gently retracting the disc in a smooth and quiet manner. As the flow diminishes or halts, the disc gradually moves back towards its seat before any reverse flow happens.
Spring-loaded Y check valves operate on the same principle as in-line spring check valves. However, their design features a spring and disc arranged at an angle resembling the letter Y. A key advantage of Y spring check valves is that they allow for inspection and maintenance without the need to disassemble them from the pipeline.
In the diagram, you can see that one side of the Y configuration includes a removable seal positioned above the spring and disc.
Swing check valves are among the most widely used and versatile types of check valves. While they share a similar function with spring check valves—preventing backflow—their operating mechanisms are distinct. All check valves, including swing types, serve the automatic function of halting reverse flow.
Swing check valves are particularly suited for systems incorporating gate valves, as they exhibit a minimal pressure drop. There are two primary configurations of swing check valves: Y-pattern and straight-body.
Composition disc swing check valves are designed to handle abrasive materials, minimizing wear and damage to both the seat and the disc. These valves feature a durable non-metallic ring on the disc, which ensures a more secure seal. The composition discs are built to withstand erosion and can effectively close even with solid particles present, without harming the valve. They are also easy to repair and require less force to achieve a proper seal.
Dual plate swing check valves, also known as butterfly, folding, or split check valves, feature a disc divided into two segments that open along their centerline with the upstream flow. When flow direction changes, these segments close against the seat seal. Their compact and lightweight design makes dual plate swing check valves ideal for applications with restricted space.
Straight swing check valves feature a circular disc that pivots on a hinge pin and is oriented horizontally. The valve opens when upstream pressure forces the disc to swing open. When the pressure decreases, the valve closes. The seat of a swing check valve is equipped with a seat ring where the disc rests to form a tight, uniform seal when closed. The seating surface is angled slightly to facilitate opening at lower pressures, ensure a positive seal, and minimize shock during closure.
Tilting disc swing check valves are designed to remain open at low flow velocities while closing rapidly to prevent backflow. These valves feature a dome-shaped disc that floats with the flow, lifting off the seat to open the valve. As the flow diminishes and slows, the disc settles back onto the seat, effectively blocking any reverse flow.
A Y swing check valve shares a similar design with an in-line swing check valve but includes an additional feature for easy access without needing to remove it from the pipeline. The Y-shaped structure permits flow through one leg, much like an in-line valve. When the disc swings upward with the upstream flow, it shifts to the other leg of the Y, which has an access point for maintenance or inspection.
Check valves are essential for preventing backflow within a piping system. They operate by opening in response to the flow of material through the system, with pressure from the upstream side causing the valve to open and reverse flow causing it to close. Among the different types of check valves, swing check valves are the most prevalent due to their affordability and effectiveness.
Typically, check valves serve as a safety mechanism to reduce system stress and prevent slamming. They come in various designs to suit different applications and operational needs. Swing and spring check valves are particularly popular for their reliability, ease of installation, and low maintenance requirements.
Swing check valves are limited to horizontal flows or vertical upward flows due to the swing nature of their disc. Since they cannot support downward flow, there is a limit to the applications where they can be used. Regardless of this disadvantage, they can handle large flow capacity. Swing check valves offer low resistance to flow and flow pressure.
Swing check valves are constructed with all components enclosed within the valve body, ensuring that there is no penetration through the body and preventing external leaks. The valve features a single-piece design that maintains a secure seal. The disc in a swing check valve can rotate up to 360 degrees and includes fine-tuning adjustments. It relies on gravity to close when there is no flow.
While swing check valves are versatile and commonly used, they may not be suitable for all piping configurations.
One frequent issue with swing check valves is the noise generated during closure, particularly in models with a metal-to-metal disc seat, which can produce a clanging or ringing sound.
Swing check valves are commonly found in applications such as toilet systems, firefighting equipment, and flood prevention in sewage systems.
The primary advantage of swing check valves is their affordability, making them a budget-friendly option for various projects.
However, a significant drawback of swing check valves is the potential for water hammer—a pressure surge or shock wave caused when fluid flow is abruptly stopped or redirected. This phenomenon creates a banging or knocking noise in the piping system and can lead to pressure spikes that may exceed the system's design limits, posing a risk to the integrity of the piping system.
Spring check valves provide greater flexibility compared to swing check valves and are suitable for a range of applications, including both horizontal and vertical orientations. The spring mechanism maintains the disc in position during pressure drops, allowing for flow in any direction. The disc is forced to seal the valve opening by the pressure of the spring.
In contrast to swing check valves, which are passive in operation, spring check valves offer resistance to flow and require the flow pressure to exceed the spring force to open the valve.
Spring check valves operate smoothly and quietly. They respond to pressure changes rather than flow changes, which means they can close before reverse flow occurs, helping to prevent water hammering.
Due to their ability to mitigate water hammer, spring check valves are often referred to as silent check valves and significantly reduce operational noise.
The adaptability of spring check valves makes them suitable for various piping configurations, provided the appropriate spring is selected. They are an excellent choice for challenging installations involving tight spaces, unique dimensions, or unconventional pipe directions.
Spring and swing check valves must be constructed from materials that can handle the specific pressures and conditions they encounter. Selecting the appropriate materials involves considering factors such as the type of media, pressure levels, corrosion resistance, and operating temperature.
Material selection also takes into account the expected wear and tear on the valve and the overall cost. Some durable materials may be more costly, affecting the final product's price.
Iron is a commonly used material for manufacturing spring and swing check valves due to its availability and affordability. It provides good shock absorption but lacks resistance to corrosion.
Brass check valves, whether for swing or spring types, can handle high pressures and temperatures effectively. They are more cost-effective than steel and can be easily shaped and adapted to various check valve designs. Brass check valves are compatible with connections to copper, brass, plastic, aluminum, and welded steel.
Bronze is an ideal material for manufacturing check valves due to its excellent properties. It offers high ductility to resist cracking, good corrosion resistance, and remains cost-effective.
Stainless steel is frequently chosen for making swing and spring check valves due to its excellent corrosion and rust resistance. These properties make it a versatile and reliable material for various check valve applications.
Monel is known for its resistance to seawater and caustic solutions. It is strengthened through cold working, offers high tensile strength, and is weldable. Monel also resists corrosion and is suitable for use in non-oxidizing chlorine solutions and marine environments.
Monel is a trademark name for a series of nickel-copper alloys, including grades such as 400, 401, 404, K500, and R405. These alloys also contain small amounts of iron, manganese, carbon, and sulfur.
Inconel benefits from the inclusion of molybdenum and niobium in its nickel-chromium alloy, which imparts exceptional strength and fatigue resistance. Key characteristics of Inconel include high tensile strength, creep resistance, fracture toughness, and excellent weldability, facilitating ease of processing. Unlike Monel, which contains copper, Inconel features chromium as a primary element, enhancing its properties.
The combination of nickel and chromium in Inconel provides outstanding resistance to oxidation and high-temperature corrosion.
The main attraction of PVC check valves is their lightweight, sturdiness, resilience, and abrasion resistance. As a plastic, PVC is not susceptible to corrosion, rust, or other damaging factors common to certain metals. The exceptional durability of PVC ensures its long life of usefulness. The popularity of PVC spring and swing check valves is due to how easy they are to install.
The versatility and ease of handling of PVC allow for the production of spring and swing check valves in various sizes to accommodate diverse applications. PVC swing check valves are commonly used in pumping systems.
Swing and spring check valves can be connected to pipelines using various methods. Ensuring a leak-proof connection is crucial for effective valve operation. Common connection methods include flanged, threaded, welded, sweat, and press fittings.
Each connection type is designed to create a secure and tight seal between the valve and the piping system. Selecting the appropriate connection method is vital for the proper functioning of the valves.
Threaded connections are one of the simplest methods for attaching valves to pipes, typically used for smaller valves in low-pressure systems. These connections involve screwing the valve onto a threaded pipe, creating a tight and secure fit.
Flanged connections are highly durable and versatile, suitable for a wide range of piping systems regardless of pressure or valve size. This method uses two flanges, one on the inlet and one on the outlet, which are fastened together with bolts to create a strong and reliable connection.
Press fittings offer an alternative to welding and soldering. This method uses a hydraulic tool to compress specially designed connectors, establishing a secure connection between the spring or swing valve and the pipeline. The pressing action of the sealing element ensures a smooth, even, and dependable join. This technique is also referred to as crimping or press-connect joining.
Welded connections are designed to create a highly secure and leak-proof joint. Although this method is more costly, it provides an exceptionally tight and durable connection between the swing or spring valve and the pipeline. Welded connections are ideal for applications where leak prevention is critical, such as in high-pressure and high-temperature pipelines.
Sweat fittings involve the swing or spring check valve having openings that are slightly larger than the pipe. The valve slides over the pipe, and solder is applied to fill the gap between the pipe and the fitting. This method is commonly used with copper piping.
Check valves are designed to permit flow in only one direction and feature various stopping mechanisms in different shapes and designs. Their primary functions are to safeguard equipment, support efficient manufacturing processes, and prevent reverse flow.
Pressure changes in a pipeline can lead to flow reversal, which may damage pumps and other equipment. In response to these pressure changes, the check valve closes to prevent backflow and protect the system.
Check valves can be constructed using various spring materials, with each type performing differently under low-pressure conditions. When upstream pressure exceeds the spring force, the poppet lifts away from the valve seat, allowing gas, fluid, or steam to flow through the outlet. To ensure proper operation, it is crucial to understand both the maximum and set pressure of the system.
A vacuum breaker introduces air into a piping system to prevent flow interruption. Check valves are installed at the top of tank piping to release pressure as the tank is emptied. They are also utilized in systems with changes in elevation or temperature fluctuations.
Check valves exhibit warning signs when they are failing, such as vibrations caused by lost internal components. The most noticeable sign of failure is reverse flow. Additionally, failing check valves often produce noise known as water hammer, which occurs during their breakdown.
The main signs of failure include:
A check valve is a safety device designed to allow fluids and gases to flow in one direction. Under pressure, fluids enter the valve at the inlet and exit through the outlet. Uninterrupted flow continues until the pressure drops, or the pump is shut down...
A ball valve is a shut-off valve that allows or obstructs the flow of liquids and gases in a piping system by rotating the ball having a bore inside the valve for 90°. The ball is mounted against two seats and has a stem that connects it to the operating and control mechanism that rotates the ball...
A butterfly valve is a quarter-turn rotational motion device that utilizes a rotary disc to allow, obstruct, or control the flow of fluids in a piping system. It features a rotating disc that is situated on the passageway of the flowing media...
Diaphragm valves utilize a flexible diaphragm to obstruct, control, or isolate the flow of fluids. The diaphragm acts as the flow control element that flexes up or down to increase or decrease the fluid flow rate, respectively...
A PVC or polyvinyl chloride ball valve is a plastic on and off valve that has a rotary ball with a bore where turning the ball a quarter turn can stop the flow of a fluid. They are highly durable, cost effective and can be...