Check valve vs. check flap where to use it
Introduction: Key Difference Between Check Valve and Check Gate in Practice
In the world of heating, plumbing, and technical engineering, we often come across the term "check valve." At first glance, it may seem like it refers to one and the same type of device, but an experienced technician knows that this term includes two fundamentally different solutions with specific applications, operational properties, and consequences of incorrect selection. When we talk about the check valve, we mean a device that works on the principle of a spring and a spherical or flat closure, while the check gate uses gravitational force and rotation around a hinge. Although both are designed to prevent the reverse flow of liquid or gas, their use in the system is dictated not only by the pipe diameter but also by pressure, flow rate, media viscosity, and hygiene cleanliness requirements.
Our experience at atria.sk shows that the most common mistake during the reconstruction of older apartment buildings or in the construction of new single-family homes is the inappropriate selection of the type of check closure. A frequent case is the installation of a heavy metal check gate in a small apartment water distribution system, which leads to excessive noise, vibrations, and premature wear of seals. On the contrary, the use of a delicate check valve in an industrial cooling system with high flow can cause excessive hydraulic losses and reduce the efficiency of the pump. This article aims to provide a comprehensive guide that will help you understand the mechanism, calculation parameters, and practical scenarios where each valve is used. We will focus not only on theoretical differences but also on specific examples from installation practice, such as how to correctly integrate these valves into the system together with other components, such as high-quality ball valves with drainage.
Physical Principles and Structural Differences
To understand why a check valve is not the same as a check gate, we need to look inside their functions. Both valves are passive, meaning they do not require an external energy source to operate—they function automatically based on the pressure difference at the inlet and outlet. The difference lies in how they overcome the resistance of reverse flow.
Mechanics of a Check Valve (Check Valve)
A check valve is a type of valve that contains a closure (a ball, disc, or cone) that is pressed against the seat by a spring or its own weight. In the case of standard sanitary check valves, which you find in apartments and single-family homes, the spring version is dominant. When the flow is in the forward direction, the water pressure overcomes the spring force and opens the closure. As soon as the flow stops or the pressure at the outlet increases (for example, when the pump is turned off), the spring immediately pushes the closure back against the seat and creates a hermetic seal.
A key feature of a check valve is its ability to respond very quickly to changes in the direction of flow. Thanks to the spring, there is no opening delay, which is critical in systems where pump start-up cycles are frequent. An advantage is also the possibility of adjusting the opening force (spring) according to the working pressure in the system. A disadvantage, however, is the higher hydraulic resistance compared to a gate, because the water has to flow through a smaller opening and overcome the spring resistance even during normal operation.
Mechanics of a Check Gate (Swing Check Valve / Butterfly Check)
A check gate operates on a different principle. Its core is a rotating plate (disc) mounted on a hinge. When the flow is forward, the water pressure pushes the disc into the open position. When the flow stops or the pressure at the outlet drops, the disc returns to the closed position either by its own weight (gravity) or with the help of a spring (in the case of low-angle gates). Most often, in industrial and large distribution systems, gates without springs are used, where the return is caused by gravity, provided they are properly mounted.
The main advantage of a check gate is its low hydraulic resistance when fully open. The disc completely swings into the flow and creates almost a direct passage for the water. This means less pressure loss and lower energy consumption for pumps. However, the response to reverse flow is slower than with a spring-loaded valve. The disc has to physically swing back, which takes a fraction of a second longer, which can lead to so-called "water hammer" (hydraulic shock) in extreme cases if the system is not properly dimensioned.
A significant difference is also the spatial requirement. Check valves are often compact and can be installed even in tight spaces where there is not enough room for the disc of a check gate to rotate. On the other hand, check gates require a certain length of pipe to allow the disc to open and close freely, which can be a problem in narrow distribution systems.
Hydraulic Properties and Impact on the System
One of the most important questions that designers and installers ask is: "What impact does this valve have on the overall pressure in the system?" Here, the difference between a check valve and a check gate is most clearly expressed. Each valve causes hydraulic losses, which are manifested as a pressure drop (so-called pressure loss Δp).
Pressure Loss in a Check Valve
A check valve typically has a higher flow coefficient Kv (or a lower resistance coefficient ξ). When water flows through a check valve, it has to change direction, pass through the tight space between the closure and the valve body, and overcome the resistance of the spring. At low flow rates, this resistance is relatively small, but at high flow rates, the check valve can become a significant limiting factor. For example, when using a check valve in a system with high flow (such as heat recovery or large heat pumps), the pump may not be able to achieve the required performance, as part of the energy is spent overcoming the resistance of the valve.
In practice, we have seen cases where the installation of a check valve with a low Kv value (for example, for small flows) into the main water supply line in a residential house caused the pressure in the system to drop below the critical limit when multiple taps were opened simultaneously, leading to unstable operation of the boiler or heat pump. Therefore, when selecting a check valve, it is crucial to consider the Kv parameterization, which indicates how many liters of water will flow through the valve with a pressure drop of 1 bar.
Pressure losses in check valves
A check valve, especially if properly mounted and dimensioned, offers significantly lower hydraulic losses. When the disc is fully open, it creates only a small obstruction in the flow. This is why check valves are preferred in industrial piping systems, where flows are high and energy efficiency is important. However, with small flows, it can happen that the pressure is insufficient to fully open the valve, which leads to vibrations and noise ("ticking"). This phenomenon is called "fluttering" and can damage the valve body and surrounding piping.
Therefore, when selecting a check valve, it is necessary to ensure that the minimum operating flow in the system is sufficient to keep the valve in a fully open position. If you have a system that operates with a variable flow (e.g., with a frequency converter), you must verify that the selected valve will remain stable even at the minimum pump speed.
Practical applications: Where to use a check valve and where a check valve?
Theory is nice, but practice is decisive. As a professional, I have seen hundreds of installations over the years where errors in this area became apparent only after several months of operation. Let's look at specific scenarios that will help you make a decision.
1. Domestic plumbing and apartments
In this area, the check valve clearly dominates. Why? Because flows in apartments are relatively small, pressures change quickly (when a tap is opened), and space is limited. A check valve is indispensable in two situations:
- Backflow preventer: If you have separate water sources (e.g., a well, a cistern) connected to the public water supply, it is a legal requirement to install a check valve or even a more complex backflow preventer to prevent contamination of the public network by your water. In this case, the valve must be able to react immediately and hermetically.
- Protection of pumps and water heaters: When installing a pump for water supply or hot water recirculation, a check valve is essential to prevent reverse flow of water after the pump is turned off, which could cause the pump to restart or damage the motor.
In this segment, light check valves are ideal, which do not burden the piping and have sufficient capacity for normal apartment flows. For example, the model Light check valve EURA - 1/2"FF; Kv 4,27 is perfect for standard apartment connections, where it ensures safety without unnecessary pressure losses. For larger flows within the house, for example on the main supply, the model Light check valve EURA - 3/4"FF; Kv 7,11 is more suitable.
2. Heating and heating systems
In heating, the situation is slightly different. While check valves are still used in small systems, in larger systems (e.g., multi-story buildings, industrial facilities), we more often encounter check valves. The reason is the need to minimize hydraulic losses in long piping and to protect pumps from reverse flow during shutdown.
However, in heating it is important to remember temperature and pressure. Standard plastic check valves are not suitable for systems with high temperatures. You must use valves made of stainless steel or brass with durable seals. In heating, special check valves with adjustable settings are also often used, which allow setting the exact point at which the valve opens.
It is important to mention that when installing check valves in heating, it is necessary to combine them with a ball valve with drainage. This type of valve not only allows closing the supply, but also enables safe drainage of the system before repair. For example, Ball valve water - with drainage - 1/2"FF; lever is ideal for smaller branches, while Ball valve water - with drainage - 3/4"FF; lever is suitable for larger flows. Without such a valve, you would have to deal with draining the entire system during pump repair or replacement of the check valve, which is impractical and risky.
3. Industrial installations and sewage
In industry and drainage, the choice is related to the viscosity of the medium and the content of solid substances. Spring-loaded check valves are often unsuitable here, as the spring can get stuck due to deposits or corrosion. On the contrary, check valves (especially those with an elastic seat or special design) are preferred here. They are more resistant to dirt and have a longer service life under harsh conditions.
In drainage systems, special valves are used that prevent the reverse flow of sewage and odors. Here, not only the function is critical, but also the hygienic aspect. Incorrect installation can lead to the valve not sealing properly and allowing gas emissions into the interior.
4. Heat recovery systems and solar collectors
In these systems, stability and protection against freezing or overheating are important. Check valves are often used here to separate individual circuits. It is important that the valve can withstand high temperatures and pressures that can occur in a stagnating solar system. In this case, valves with high resistance and the possibility of manual opening are often selected.
Mounting aspects and common installation errors
Even the best valve will fail if installed incorrectly. Proper installation of a check valve or check valve is key to the safety and functionality of the system. Let's look at the most common errors we have recorded.
Direction of flow
The simplest, yet most common mistake is the installation of the valve in the wrong direction. Most check valves and check valves have an arrow on the body indicating the direction of flow. Installation in the opposite direction means that the valve will constantly block the flow or will be non-functional. In spring-loaded check valves, this is obvious, while in check valves, the direction is sometimes harder to determine if it is not clearly marked. Always verify the direction of flow before starting installation!
Placement and distance from the pump
There is a rule that applies to most systems: the check valve should be placed as close as possible to the pump, on the outlet side. This prevents water from flowing back into the pump and protects it from damage. If the valve is too far away, water can flow back and the pump can restart, leading to frequent starts and premature motor wear.
However, with check valves, it is necessary to maintain a certain distance from the pump to ensure sufficient flow stabilization. Placing the valve too close can cause turbulence and vibrations that can damage the valve. The recommended distance is usually at least 5-10 times the pipe diameter.
Horizontal vs. vertical installation
This is a key difference between these two types of valves. Spring-loaded check valves can be installed in any position – horizontally or vertically. On the contrary, check valves, which operate on the principle of gravity, must be installed in a horizontal position with the disc oriented upwards (so that it can close under gravity). If installed vertically, the disc may not close properly, leading to water leakage back.
In our practice, we have seen cases where check valves were installed vertically in a heating system, which led to the valve not closing after the pump was turned off and water returning into the boiler, causing pressure and temperature problems. Therefore, when selecting a check valve, it is always necessary to verify whether it is suitable for the installation orientation.
Integration with other valves
A check valve or flap should not be installed alone. It is always necessary to equip it with shut-off valves on both sides for maintenance and service. Here come the ball valves into play. Ideally, ball valves with drainage should be used, such as for example Ball valve for water - with drainage - 1"FF; lever, which will allow safe drainage of the system before replacing the valve. Without such a valve, you would have to deal with draining water from the entire system, which is impractical and risky.
Another important element is the filter. A filter should always be installed before the check valve to prevent dirt from entering the valve, which could cause it to jam. The filter should also be equipped with a shut-off valve for easy maintenance.
Maintenance, fault diagnosis and extending the service life
No valve is immune to wear. Check valves and flaps are constantly exposed to the effects of water, pressure and temperature changes. Their maintenance is therefore key to the long-term functionality of the system.
Common signs of faults
- Leakage: If you hear water flowing or see a leak after turning off the pump or during pressure changes, it means that the valve or flap seal is no longer tight. Causes may include deposits, corrosion or damaged sealing.
- Jamming: If the valve or flap does not react to pressure changes, it may be jammed by dirt. In this case, it is necessary to clean the system and check the condition of the filter.
- Vibrations and noise: If the flap or valve vibrates or makes noise, it may be due to a water hammer or incorrect sizing. In this case, it is necessary to check whether the valve is correctly dimensioned and whether it is necessary to add vibration dampers.
Maintenance and cleaning
Regular inspection and maintenance should be part of the annual system service. With check valves, it is important to check the condition of the spring and the seal. If the spring is weakened or damaged, the valve will no longer function properly. With flaps, it is necessary to check the condition of the disc and the stem to see if they are damaged by corrosion or deposits.
It is always better to replace an old valve with a new one than to try to repair an old one that has already reached the end of its life. New valves, such as for example Check valve EURA light - 1/2"FF; Kv 4,27, are designed to provide long-term and reliable operation.
Valve replacement
When replacing a check valve or flap, it is important to follow the sequence and ensure safety. First, it is necessary to close the water supply using ball valves, drain the water from the system and then dismantle the old valve. When installing a new valve, it is important to pay attention to the correct flow direction and the tightness of the connections.
We recommend using high-quality sealing materials and properly tightening the connections to prevent leaks. When installing check valves in heating systems, it is important to pay attention to temperature and pressure to avoid damaging the valve.
Specific parameters for dimensioning: Kv value and pressure conditions
When selecting the correct valve, it is often necessary to go deeper than just the type (valve vs. flap). The key technical data that determines functionality in the system is the Kv value. This value indicates the water flow in m³/h that flows through the valve at a pressure drop of 1 bar. With check valves, the Kv value often changes depending on the spring opening. If you choose a valve with too low a Kv value for a large system, it will become a "bottleneck" that limits the pump performance and increases energy consumption. On the other hand, with check flaps, the opening pressure is also important. If this pressure is too high, the flap may not open completely at low flows, which leads to system instability.
The importance of filter protection before the valve
One of the most common, yet often overlooked mistakes during the installation of check valves is omitting a filter before the valve. Check valves are sensitive to mechanical impurities – sand, rust or corrosion from the piping. Even a small particle can get between the sealing surface and the seat, creating a microscopic gap. As a result, the valve may close, but it will not seal properly. This is even more critical for check discs, as impurities can jam the stem, preventing its movement and leaving the disc either permanently open (risk of reverse flow) or permanently closed (blocking the flow).
We always recommend installing a Y-filter or a mesh filter directly before the check valve or disc. The filter should have sufficient flow capacity to avoid significant hydraulic losses, but at the same time it must capture particles larger than 0.5 mm to 1 mm (depending on the specific model). In systems with high levels of impurities (e.g., old piping, recovery from a well), it is advisable to use filters with a denser mesh and to regularly inspect them. Without this protection, you significantly reduce the lifespan of the valve by several years and risk the non-functionality of the entire safety component.
Material specifications and temperature conditions
While standard check valves for cold water are often made of brass with rubber seals, the situation changes in heating systems and solar collectors. High temperatures (above 70 °C) and the chemical properties of glycol mixtures can quickly degrade standard rubber, leading to loss of sealing.
In these cases, it is essential to use valves with EPDM or Viton seals, which are resistant to heat and chemicals. Another important difference is the construction of the body itself. In heating systems, check valves are often made with ceramic seats or fully constructed from stainless steel (inox) to prevent corrosion and lime deposits. On the other hand, industrial-scale check discs may have a body made of cast iron with anti-corrosive coating, which would be unsuitable for a small apartment system due to the risk of leakage and installation difficulties.
Difference in reaction to hydraulic shock (Water Hammer)
One of the critical factors in selection is the valve's ability to withstand hydraulic shock, which occurs when the flow of liquid is suddenly stopped (e.g., when a pump is suddenly turned off or a valve is closed). This phenomenon creates a pressure wave that spreads through the piping and can damage not only the valves, but also the piping and connecting components.
Check valves have an advantage in this regard due to the spring. The spring mechanism allows for very fast closure (often in the order of milliseconds), which helps absorb the energy of the pressure wave and minimizes its impact on the system. This is an ideal solution for systems with short and rigid piping, where the risk of water hammer is high.
Check discs, on the other hand, have a heavier disc and higher moment of inertia. When the flow is suddenly stopped, the disc may open slightly later than the pressure wave has stabilized. If the disc is too heavy or not properly balanced, it can hit the seat with great force, causing the characteristic "thud" sound and long-term wear of the seat. Therefore, in systems prone to water hammer, it is recommended to either use a check valve or a special dampered check disc with smooth closing and an integrated impact damper.
Hygienic aspects and surface treatments
For sanitary applications, such as drinking water, the hygienic cleanliness of the valve surface is crucial. Check valves intended for drinking water must meet strict standards (e.g., current regulations on drinking water), which prohibit the release of substances into the water. The surface must be smooth, without cavities where bacteria (e.g., Legionella) could settle.
FAQ: Frequently asked questions about check valves and discs
1. Can I use a check disc instead of a check valve in a residential water system?
Generally yes, if the disc is properly sized and installed in a horizontal position. However, a check valve is safer and reacts faster to reverse flow, which is important in apartments. In addition, check valves are more compact and easier to install in tight spaces.
2. Why does my check valve get stuck?
The most common cause is the presence of impurities in the system that get between the closure and the seat. The solution is to install a filter before the valve and perform regular system maintenance. If the spring is damaged, the valve needs to be replaced.
3. What is the difference between a check valve and a check disc in heating systems?
Both types are often used in heating systems, but it depends on the pipe diameter and flow rate. For small systems, check valves are suitable, while for larger systems, check discs with lower hydraulic resistance are suitable.
4. How often should I replace a check valve or disc?
There is no fixed interval, but we recommend regular inspection at least once a year. If signs of wear or leakage are found, the valve must be replaced.
5. Can I use a check valve for oil or other viscous liquids?
Yes, there are special check valves designed for oils and other viscous liquids. It is, however, important to select a valve that is compatible with the medium and has suitable seals.
6. Why is my check valve vibrating?
Vibration can be caused by water hammer or incorrect sizing. Check whether the valve is correctly sized and whether it is necessary to add vibration dampers.
Conclusion: The key to success is correct selection and installation
Choosing between a check valve and a check ball valve is not just a matter of price or availability. It is a decision that will affect the safety, efficiency and longevity of your system. Check ball valves are ideal for standard residential and household installations, where fast response and compactness are important. Check valves, on the other hand, are preferred in industrial systems and large distribution networks, where low hydraulic loss and resistance to impurities are crucial.
The key to success is understanding the characteristics of both types of valves and their correct application in a specific scenario. Do not forget the importance of proper installation, maintenance and integration with other valves, such as ball valves and filters. With this knowledge, you will be able to design and implement a system that will operate reliably and safely for many years.
Please remember that at atria.sk we have a wide range of high-quality valves, including check ball valves and check valves, approved for various applications. If you are unsure about the selection, do not hesitate to contact our experts, who will be happy to help you with the selection and installation. Your safety and satisfaction are our priority.
Do you have a question on this topic?
Having trouble deciding or dealing with a specific situation in your home? Write to us – we are happy to help.