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A check valve serves as an automatic safety mechanism crafted to allow fluids and gases to flow in a single direction while obstructing reverse movement. When pressure is exerted, fluids enter through the inlet, prompting the disc to lift from the valve seat, facilitating discharge through the outlet.
Flow continues as long as there is sufficient pressure to hold the disc open. When the pressure diminishes, the disc instinctively returns to its seat, halting the flow.
The pressure needed to initiate valve opening is referred to as the cracking pressure, varying from 3 psi to 350 psi based on the valve's size, purpose, and functionality.
Check valves ensure that gases or liquids flow in the appropriate direction while forming tight seals to avert leaks. By managing the flow of liquids, check valves help shield pumps and compressors from potential damage.
Check valves are known by different names according to their application and design. Frequently used names include clack, non-return (NRV), reflux, retention, and one-way valves. Despite their straightforward design and function, these valves are essential for safeguarding pumps, piping systems, and fluid flow control.
The swing check valve, illustrated in the image below, is the most prevalent type. It features a full port design that allows the disc to fully retract during fluid flow. The disc opens in alignment with the flow direction and remains open while the fluid continues to flow. When the flow decreases or ceases, gravity assists in returning the disc to the closed position.
The principal purpose of a check valve is to prevent reverse flow, which could harm pumps and other components. The closure of a check valve may cause a water hammer, where fluid forcefully strikes the closed valve. Therefore, check valves must be robust, durable, and constructed from high-grade materials to withstand these forces.
Check valves can be noisy and might need noise reduction measures. To counter this, various control strategies are employed in their design. Components such as springs, levers, or weights help manage pressure surges and prevent the valve from slamming shut.
Check valves are essential components in piping systems, designed to automatically prevent the backflow of fluids or gases. These one-way valves play a critical role in protecting pumps, compressors, and entire process lines in various industries. Check valves come in numerous varieties to suit a wide range of applications, from water treatment and chemical processing to oil and gas, power generation, and commercial HVAC systems. For example, in gardening and agricultural irrigation, check valves regulate the flow of fertilizers and water, ensuring precise distribution. In the aerospace and aircraft industries, they manage the transport of corrosive fluids, hydraulic systems, and fuel flow, maintaining operational safety and system integrity.
While the primary function of check valves—allowing flow in one direction and preventing reverse flow—remains consistent across applications, the specific types of check valves used vary according to a range of performance factors. These include required flow rate, media type, temperature extremes, line size (pipe diameter), pressure differential, installation orientation, and flow velocity. Understanding these criteria is essential for engineers and operators when selecting a check valve solution that maximizes system reliability and minimizes maintenance. The following chart illustrates different use cases and the recommended check valve for each scenario.
| Application of Check Valves | |||
|---|---|---|---|
| Type Flow | Media Type | Velocity Range FPS(m/s) | Recommended Check Valve |
| Uniform With Insignificant Reversal | Water Or Oil | 1 to 6 (0.3 to 2) | Swing Check w/ Lever and ctrl wt. |
| Steam, Water, Gas | 7 to 100 (2 to 30) | Simple Swing | |
| Uniform | Water Or Oil | 5 to 10 Max (a.5 to 3) | In-line Guided Disc |
| Pulsating | Air Or Gas | 5 to 10 Max (a.5 to 3) | In-line Guided Disc w/Cushion Chamber |
| Uniform With Normal Reversal | Water Or Oil | 7 to 10 (2 to 3) | Swing w/ Spring Assist To Close |
| Uniform With Severe Reversal | Water Or Oil | 7 to 10 (2 to 3) | Swing w/ Dashpot |
| Uniform Or Pulsating | Steam, Water, Or Gas | 8 to 160 (2.5 to 50) | Tee- Or Inclined- Pattern Lift |
| Uniform Or Pulsating (Severe Revesal) | Steam, Water, Or Gas | 10 to 160 (3 to 50) | Tee- Pattern Lift w/ Dashpot |
| Uniform | Steam, Water, Or Gas | 12 to 250 (4 to 75) | Tilting Disc |
| Uniform Or Pulsating | Steam, Water, Or Gas Or Oil | 20 to 250 (6 to 75) | Wye-Pattern Lift |
| Uniform Or Pulsating (Severe Revesal) | Wye-Pattern Lift w/ dashpot | ||
Choosing the optimal check valve type is critical for efficient and safe fluid or gas handling within an industrial, commercial, or municipal system. Key selection criteria include the type of media being conveyed (liquids, gases, slurries, or corrosive chemicals), pipe diameter, pressure gradient, maintenance needs, compatibility with existing pipelines, and installation orientation (vertical or horizontal). Additional factors like required cracking pressure (the minimum upstream pressure needed to open the valve), material compatibility (stainless steel, brass, PVC, cast iron), and operational environment (temperature fluctuations, potential for water hammer) should also be addressed. Evaluating these considerations helps engineers and maintenance personnel prevent system failure, reduce downtime, and extend the lifespan of both the check valve and connected equipment.
Check valves are available in an extensive selection—from standard valve designs offered at home improvement retailers to highly specialized or custom-engineered configurations used in critical process industries. The rapid advancement of check valve technology, such as anti-water hammer features and improved low-pressure performance, further broadens the selection. While it can be challenging to categorize every variant, virtually all check valves share a set of standardized characteristics, including unidirectional flow, low maintenance requirements, and availability in multiple materials suitable for diverse working conditions.
Below are the most commonly used check valve designs, each offering unique operational benefits and suiting particular industry requirements. Understanding the differences helps users make informed choices and streamline the specification, procurement, and installation processes for new or replacement valves.
A swing check valve is a classic, self-activating non-return valve engineered to prevent fluid backflow or allow flow in only one direction. It incorporates a disc that pivots on a hinge, swinging away from the valve seat as forward flow passes through the system. When flow ceases or reverses, the disc swings back onto the seat, forming a tight seal and blocking any backflow. In high-performance and critical infrastructure, swing check valves are prized for their ability to minimize turbulence and maintain a consistently low pressure drop.
Lever and weight swing check valves are best suited for systems where water hammer—a surge of pressure caused by sudden flow changes—might pose a risk, whereas lever and spring-assisted designs excel in high-pressure and high-flow velocity pipelines. Regardless of configuration, it’s important to regularly inspect, lubricate, and clean the disc mechanism to ensure reliable, leak-free operation across the lifespan of the swing check valve.
Wafer check valves are compact, lightweight check valves with a slim disc that pivots or flexes to regulate flow. When the process media moves in the intended direction, the disc lifts off its seat, allowing unimpeded passage. If the flow reverses, a return spring or gravity quickly seals the disc against the seat, preventing backflow. This rapid closure helps to significantly minimize water hammer and its associated piping stress.
The space-saving design of wafer check valves is especially advantageous in small-bore pipe systems, tight equipment skids, or piping layouts with limited clearance. Wafer check valves are also frequently specified for handling solid-bearing or semi-solid media, such as wastewater, slurry, and pulp applications in water treatment, food processing, or paper manufacturing. Their combination of durability, versatility, and ease of installation makes them a popular choice for engineers seeking effective inline backflow prevention.
A tilting disc check valve utilizes a disc mounted near its center, allowing fluid to flow on both sides—over and under the disc. This prevents abrupt closures and reduces water hammer, which is common in pipelines subject to frequent flow reversals. Unlike a swing check valve that depends on inertial force, the tilting disc valve responds to moderate changes in flow rate, providing stable operation over a wide range of flow conditions. These valves are often specified for power plants, petrochemical systems, and high-flow water distribution networks where reliability and smooth operation are prime concerns. The streamlined geometry ensures a low pressure drop at normal flows, but users should consider pressure losses at higher velocities when specifying tilting disc check valves.
Ball check valves employ a spherical ball inside the valve body that moves up and down to obstruct or permit forward flow. The conically shaped valve seat guides the ball, utilizing gravity or spring loading to control flow direction. The weight and material composition of the ball can be customized to system specifications, ensuring resilient sealing even when exposed to high pressures or variable temperatures.
Upon reversal of flow, the ball returns to its seat, effectively sealing off the line and preventing contaminant ingress or unwanted fluid return. With pulses of sufficient system pressure, the ball is momentarily lifted, enabling forward flow until conditions stabilize and the ball closes again. Ball check valves offer simple, robust, and low-maintenance backflow protection ideal for vertical lines, slurry movement, sewage and wastewater treatment plants, and applications where particulate solids are present.
A butterfly check valve, commonly identified as a dual disc, folding disc, double disc, or split check valve, utilizes two half-discs mounted on a central shaft. These discs open toward the pipe’s centerline when fluid is flowing forward, creating minimal flow resistance. When reverse flow occurs, the halves quickly collapse, sealing the valve and preventing backflow. This short travel results in reduced slamming and quieter operation, making butterfly check valves an excellent choice for minimizing pressure spike noise in heating, ventilation, air conditioning (HVAC), and fire protection systems. Their wafer-thin construction and ease of installation make butterfly check valves a favored solution in modern, space-constrained infrastructure.
The flow for lift check valves, sometimes called piston check valves, enters beneath a disc or ball. System pressure rises until it lifts the disc or ball, allowing fluid to pass upward. When flow weakens, reverses, or the upstream pressure drops below the cracking threshold, gravity (and sometimes assisted by a spring) forces the sealing element back onto the seat, halting backflow. Lift check valves perform best in high-pressure, high-flow velocity applications such as boiler feedwater lines, steam systems, and oil transmission networks. Their vertical orientation and tight shutoff characteristics offer excellent protection for expensive pumping equipment.
Silent check valves, also referred to as spring-assisted or poppet check valves, are engineered to eliminate water hammer and pressure shock. These valves are designed to close quietly and rapidly before any reversal of fluid flow occurs, thereby reducing the potential for system stress or damage. Silent check valves are widely used in potable water supply, hydronic heating, and clean process applications where noise and sudden pressure surges must be strictly controlled. Their spring-loaded mechanism ensures dependable sealing and prevents system-wide disturbances.
Duckbill check valves are flexible, elastomeric one-way valves shaped like a duck’s beak. Constructed from rubber or synthetic elastomer, the open end stretches over the outlet pipe while the opposite end maintains its original shape. Upstream fluid pressure forces the "duckbill" lips apart, allowing media to flow through; as the pressure subsides or attempts to reverse, the lips seal tightly, blocking any backflow or unwanted infiltration. Duckbill valves are commonly found in stormwater, drainage, sewage, and environmental protection installations, appreciated for their corrosion resistance, self-cleaning, and ability to handle debris with minimal clogging.
Diaphragm check valves use a flexible rubber diaphragm or disc mounted inside the valve. This element seals against a seat in the presence of reverse flow, while positive pressure from the inlet side flexes the diaphragm, opening the flow path. Diaphragm valves are prized for their quiet operation, reliable sealing on low-pressure lines, and resistance to clogging from particulates or sludge. Typical uses include pharmaceutical process lines, food and beverage systems, and applications involving aggressive chemicals or ultra-clean piping where metallic valves may be unsuitable.
A foot check valve is a specialized suction-side check valve installed at the base of a pipe connected to a pump’s intake. Structurally similar to a ball check valve, but featuring a built-in strainer or screen, it prevents debris from entering and damaging the pump. Key benefits of foot check valves include maintaining pump prime, preventing siphoning, and protecting irrigation, firefighting, and municipal water supply systems from contamination. During operation, the pump draws fluid upward through the pipe and foot valve; when the pump stops, gravity would typically cause backflow—however, the foot check valve’s self-activated closure halts this reverse movement, ensuring the pipeline remains full for immediate restarting and reduced downtime.
Pneumatic check valves, often called air check valves or compressed air non-return valves, are designed to regulate airflow within pneumatic circuits. They allow incoming air from a compressor but prevent it from venting backward, making them essential in automation equipment, process controls, and air-powered tools. Pneumatic check valves help maintain pressure stability, optimize energy efficiency, and protect sensitive equipment from accidental depressurization or contamination by backflow.
To choose the ideal check valve, carefully assess factors such as valve material compatibility (stainless steel, bronze, PVC, etc.), installation orientation (horizontal or vertical), allowable pressure drop, and system maintenance requirements. Consider the media's corrosiveness and temperature, the risk of water hammer, local regulatory standards, and ease of future maintenance or replacement. Consulting with check valve manufacturers or experienced distributors can help ensure long-term reliability, safety, and regulatory compliance in your fluid control or process system.
Since the invention of the self-sealing valve in the early 20th century, check valves have become essential for addressing backflow issues across various industries. Any sector involved in transporting products through pipelines relies on check valves within their systems.
Check valves are cost-effective devices that help prevent waste and protect equipment. They ensure that fluids traveling through piping networks are not lost due to poor handling. By automatically stopping liquid flow when pressure drops or flow decreases, check valves block backflow and retain the fluid within the system.
Check valves in pumps is one of their more common uses.
Parallel Pump System � In a parallel pump system, a check valve prevents the duty pump from pumping into the standby pump.
.jpg "Parallel Pump System with Check Valves (NRV)")
Pressure Relief � Spring loaded check valves are used in gas applications for low pressure conditions. If the pressure in the system rises above the cracking pressure, the check valve safely releases the gas.
In the pharmaceutical industry, check valves are essential for fluid movement, as they regulate pressure to ensure product quality, efficiency, and production. Only sanitary check valves are suitable for this application, as they must be easily cleanable without disassembly and feature silent closing with a tight seal.
Orifice check valves are employed in the hydraulic systems of landing gear actuators. During gear retraction, fluid flows to raise the gear. When extending the gear, the check valve regulates the flow out of the actuator to prevent uncontrolled dropping. In addition to landing gear systems, check valves are also used in aircraft hydraulic, fuel, and pneumatic systems.
In an irrigation system, check valves are positioned near the source to prevent backflow and siphoning of irrigation water, ensuring that water does not flow back into the source.
Check valves are found in vehicles that were made before the invention of the electronic injection system. Old car fuel pumps have a check valve located at the pump‘s inlet and one at the outlet, They are designed to force the fuel to flow in the correct direction. When the check valve goes bad, the fuel pressure goes down.
Water in a home should only move from the supply line and out through a fixture or from a drain to the sewer. Check valves are located in homes to prevent cross connection or backflow. They come in several varieties including ball and swing check valves. Domestic check valves can be seen below on a diagram of a hot water system for a home.
In heating boilers, check valves prevent hot water from circulating when the thermostat is not active. They stop water from returning to the boiler, which helps avoid excessive pressure buildup. Additionally, in a home heating system, a check valve ensures that boiler water does not flow into the domestic water supply, protecting it from contamination used for drinking, bathing, or cooking.
Liquid fuel check valves are engineered to work with various fuels, including jet fuel, hydraulic oil, synthetic oil, and air. They are designed to ensure stable operation from the valve's initial crack to full flow. The valve features an inverted spool with an integrated pressure sensor to maintain balance and stability, keeping a consistent delta pressure within the valve. This design allows for smooth and uniform valve opening.
To understand how a check valve functions, it's crucial to first examine its construction. A basic check valve consists of four key components: the body, seat, disc, and cover, as illustrated in the diagram below.
Depending on the design and function of the check valve, additional components such as springs, balls, stems, and hinge pins may be incorporated into the basic elements.
Swing check valves feature an unguided disc that swings open fully when flow pressure is applied. They are available in various sizes and designs to suit different applications.
Lift check valves use a guided piston that rises when flow enters the valve. The seat has a barrel design and is secured with screws and seals. The valve's opening matches the size of both the inlet and outlet.
Tilting check valves are designed to address some issues associated with swing check valves, which have been the most common type. They can stay open at low flow velocities and close swiftly when the flow stops. They are particularly effective in high-velocity applications.
The folding disc check valve features a split disc design and a wafer body pattern with a soft seat. The discs are held in place by a pivot rod and open in response to the flow pressure. Springs on the discs assist in closing the valve.
Vertical check valves are also known as spring check valves A spring keeps the disc pressed against the seat in a vertical or spring check valve. The valve remains closed due to the spring until sufficient pressure is applied to compress the spring and open the valve. While the pressure is maintained, the valve stays open and the spring remains compressed. When the pressure drops, the spring pushes the disc back onto the seat, shutting off the flow. Vertical and spring check valves are known for their reliable backflow protection.
Check valves are typically constructed from durable materials to endure high-pressure conditions. Common materials used in their manufacture include PVC, CPVC, bronze, brass, iron, and stainless steel.
Polyvinyl Chloride (PVC): PVC is corrosion resistant and flexible. The smooth surface of PVC allows the check valve parts to move easily.
Chlorinated Polyvinyl Chloride (CPVC): CPVC has the same qualities as PVC but is able to endure high temperature applications.
Bronze: Bronze can be used for low and medium pressure applications, be cast in complex configurations, and is corrosion resistant.
Brass: Brass has the same abilities as bronze as well as the same machinability and is less expensive than bronze.
Cast Iron:Cast iron check valves are used for hot and cold water, HVAC, steam, gas, and utility services due to its excellent corrosion resistance.
Ductile Iron:Ductile iron has more than 3% carbon so it can be bent and shaped easily. It is stronger than cast iron and is easier to form into check valves.
Iron: Iron is used for steam, water, oil, and gas applications. It can endure a wide range of temperatures and pressures. Its excellent performance balances its high cost.
Stainless Steel: Stainless steel is corrosion resistant, durable, and can be used in harsh conditions, including chemical applications.
Polypropylene (PP):PP is used to make check valves due to its exceptional resistance to corrosion, which is superior to CPVC and PVC.
Polyvinylidene Difluoride (PVDF):PVDF plastic is used in applications where exceptional purity and resistance to acids, solvents, and hydrocarbons are a necessity.
Cast Steel:Cast steel is used to produce check valves due to its sudden impact resistance without deforming, breaking, or bending. It can also be easily shaped to any type of check valve.
The major benefit of check valves is their ability to perform without having to be monitored or controlled. Their basic design allows them to be inserted into a pipe‘s flow and be able to control the flow without being managed.
Regardless of their many benefits, check valves are like any other type of mechanism and have drawbacks.
Water hammer is caused by a pressure surge when there is a sudden stop in the flow of a gas or fluid and the valve suddenly closes, which causes noise and vibrations. Water hammer can damage the system and lead to costly repairs
Water hammer can be mitigated by using check valves that close quickly, thereby preventing pressure surges and shock waves. Silent check valves are one effective solution to address this issue.
Reverse flow can be damaging and costly, as it may cause a pump to spin in the wrong direction. This issue can be addressed with tightly fitting, fast-closing check valves. Spring-assisted check valves, in particular, are beneficial because they react quickly to prevent reverse flow.
Some check valve systems experience chattering due to frequent opening and closing of the valve, often caused by an oversized valve. Proper sizing is crucial when installing a check valve to ensure it fits the application. The disc must remain stable when open and create a complete seal when closed to prevent issues like fluttering, repeated cycling, and potential valve failure.
Improper installation and assembly of a check valve can lead to future issues. The initial step is to select the appropriate check valve for the application, considering factors such as flow capacity, positioning, and orientation. Installing a check valve too close to a pump, for example, can result in turbulence and potential damage to the valve.
Check valves should be installed at least several straight pipe diameters upstream from circulators, elbows, tees, and strainers to avoid turbulence and prevent the disc from rattling against the seat.
A spring check valve is a valve that ensures unidirectional flow and prevents reverse flow. They have a single inlet and outlet and must be placed in proper orientation to function correctly. On the side of a spring check valve, and all...
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...