Sep. 23, 2024
Check valves are found in almost every industrial application acting as one-way or non-return valves. Check valves are simple devices that perform a vital function by preventing reverse flows, therefore preventing damage and ensuring efficient operations. Different types of check valves are designed for a specific application. To help you choose the right check valve for your needs, here are a few of the most common types of check valves and their recommended applications. Follow this new blog in Linquip to find out more.
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The most common types of check valves are explained below.
Lift-check valves feature a guided disc and a similar seating arrangement as globe valves. The disc is usually in the form of a piston or a ball. There are three body patterns (horizontal, angle, and vertical) that can be installed in horizontal or vertical lines with upward flow.
When the flow enters below the seat, a disk is raised from the seat by the pressure of the upward flow. When the flow stops or reverses, the backflow and gravity forced the disk downward to set on the seat.
Lift check valves are particularly suitable for high-pressure service where the velocity of flow is high. They are commonly used in high-rise buildings, industrial and power plant applications, and water and wastewater applications. They have no external moving parts and are known to be economical and reliable. Over time, these types of check valves can have high energy costs because the disc remains in the flow stream during operation.
There are two types of lift check valves:
This type of check valve is also known as a plug check valve. It operates by controlling the flow of fluid in a piping system utilizing the linear motion of a piston within the valve chamber. Sometimes the piston has a spring attached, which helps it stay in the closed position when not in use.
The ball check valve operates simply using gravity. When there is enough pressure in the flow, the ball is lifted upward, and when the pressure is decreased, the ball rolls down and closes the opening. Ball Check Valves come in a wide range of material types and style types.
Swing check valves utilize a disc inside the valve to allow or stop the flow of the piping system. As the fluid flows through in the correct direction, the pressure forces the disc to open and stay open. As the pressure decreases, the valve disc closes, stopping the flow of the fluid from reversing. They are inexpensive and as they are automatic they do not require any external power or control to operate; only the flow direction determines the valve operation.
These types of check valves are common in applications with a high solids percentage and lower on/off cycle count.
There are two types of swing check valves we should look at:
In this type of swing check valve, the disc is attached to the inner top of the valve with a hinge that allows the disc to open and close.
This type of swing check valve is designed in a manner that allows the valve to fully open at lower flow pressure and to close quickly. It does this using a dome-shaped disc that is spring-loaded to make the valve close faster than a top-hinged valve. Additionally, the disc in this check valve floats so that the liquid flows on the top and bottom of the disc surfaces.
These types of check valves are most commonly used to prevent flooding in sewage systems and firefighting applications. They are used in systems that move liquids, gases, and other kinds of media.
A butterfly check valve is known as a dual plate check valve, folding disc check valve, double-disc, or splits disc check valve. As the name suggests, two halves of the disk move towards the centerline with the forward flow, and with reverse flow two halves open and rest on the seat to close the flow.
These types of check valves are good for low-pressure liquid systems as well as gas piping systems. Its lightweight and compact construction make it a preferable choice when space and convenience are important. Besides, it is 80 to 90% lighter than the conventional full body check valve and the cost of installation and maintenance is lower compared to other types.
A stop-check valve is basically, two valves built into one body. It can act as a globe valve for isolation or regulation purposes. Again, It can act as a check valve to prevent backflow. Contrary to other check valves, the Stop check valve has an additional external control mechanism in perpendicular or angular direction. Stop Check valves are popular in steam services like power plants, boiler circulation, steam generators, turbine cooling, and safety systems.
Diaphragm Check Valve
Diaphragm valves utilize a flexible rubber membrane that opens up when inlet pressure increases and overcomes the elasticity of the rubber. Unlike some other valve types, diaphragm valves respond at minimal cracking pressures for their opening. As upstream fluid pressure rises, the diaphragm flexes increasingly, allowing more fluid to flow.
As backpressure builds up, the diaphragm is forced against its seat, blocking the reverse flow. The valves are commonly used in low-pressure industrial piping systems and vacuum pipelines.
A spring-loaded check valve incorporates a spring to assist in closing the check valve. They are designed to close prior to fluid flow reversal. Preventing backflow eliminates the hydraulic shock also known as water hammer which is a result of the sudden fluid stoppage of flow in a fluid process system.
There are two types of Spring Loaded Check Valves: Spring Loaded in-line valves and Spring-loaded Y-valves.
These valves employ a centrally guided stem-disc assembly along with a compression spring. To open the valve, the flow pressure must be more than the spring force and cracking pressure. In that case, the flow pushes the disc allowing the flow. When the inlet pressure reduces, the spring pushes the disc against the orifice and shuts the valve.
The operating principle of Spring-loaded y-check valves is similar to in-line check valves. The only difference is that the spring and movable disc are located at an angle to form a &#;y&#; shape. The main advantage of Y-type check valves is that they can be inspected and serviced while the valve is still connected to the system.
This type of valve is an in-line ball check valve with spring assistance. This helps the valve to maintain or allow the flow only in one direction whereas block the passage in the reverse direction.
These valves are designed for installation at the bottom, or the inlet ports of multiple piping systems, and act as mechanisms that prevent gravitational backflows. The valve has a screen &#; or a filtration shield that blocks debris and foreign matter from entering the upstream line. Foot valves feature wider inlet openings as compared to upstream pipes, to minimize pressure losses. Foot valves are commonly used with hydraulic and pneumatic pumps, intake pumps and sump pumps, wells, ponds, and pools.
Duckbill check valves are flow-sensitive, variable-area, types of check valves. They get their name from their shape which consists of two flaps shaped like a duck&#;s bill. This check valve uses a soft tube that changes its shape according to the flow direction and hence, ensures the unidirectional flow of fluid inside the valve. If the fluid is flowing in a forwarding direction, the end of the soft tube changes its shape into the diverging type and allowing the fluid to pass easily. As, the fluid reverses its direction, the end of the soft tube becomes converging and restricts the fluid to enter into it.
A wafer check valve consists of two half-circle disks hinged together. The two disks fold together upon the positive flow and retract to a full circle to close against reverse flow. Wafer check valves were designed as a smaller, less expensive option from lift and swing check valves.
They are designed to fit between a set of flanges. The disc in disc check valves moves in a plane at right angles to the flow of the fluid, resisted by the spring that is held in place by the retainer. As the upstream pressure increases and overcomes the force of the spring, and the weight of the disc, the disc lifts off its seat allowing flow through the valve. The spring allows the valve to be installed in any direction. These should not be confused with a double check valve, which is an assembly that contains two distinct check valves.
Wafer check valves are ideal for services requiring low-pressure loss as the valve operation takes place at a very low-pressure difference.
Silent check valves, also called poppet check valves, are known for their quiet closure. These valves are constructed with a spring-assisted disc. Flow pushes the disc to allow forward flow. When the pump is stopped, a compression spring pushes the disc into the seat before flow reverses, hence the silent closure.
These valves are engineered to control and protect against pressure surges that can occur in water lines. They also work to prevent water hammers and reverse flow. Silent check valves are most commonly used in clean water applications with a high head.
Pneumatic check valves, or air check valves, control airflow from a compressor by letting air in and preventing it from going out. They are placed in pneumatic circuits that need airflow in one direction. They are often simply just called one-way air valves. The most common application is for an air compressor. They allow the compressor to keep certain parts pressurized and other parts de-pressurized. They can be located on a piston compressor (inlet and outlet), air receiver, discharge pipe, etc.
As their name implies, these valves close without slamming, meaning no excess pressure spikes are created since they do not rely on gravity. The disc of a non-slam check valve has an internal spring opposing the opening fluid flow pressure. When the flow of media is strong enough, the spring compresses and the valve opens; the disc is smoothly pushed back toward the seating surface in the valve by the spring as the flow decreases and stops before flow direction reverses.
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This leads to industrial valve manufacturers in the power plant industry to seek process equipment that can increase power generation efficiency and maximize power performance.
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By looking at the bigger picture, valves seem to be just a fraction of the vastness of a power station. Small as these may be, their role is pivotal to the power plant. In fact, there are many valves in a single power plant. Each of these takes different roles.
While the design principle behind most valves has not changed, the valve materials and manufacturing techniques have greatly improved. With this in mind, valves now can operate more sophistically and efficiently. This article provides insight on valves used in power plants, their significance as well as classifications.
Gate valves have a disc or wedge that acts as a gate that blocks the flow path of media. Not intended for throttling, the main role of gate valves is for isolation of media with less restriction. To fully utilize the gate valve, only use it as fully opened or fully closed.
Gate valves, together with the globe valves, belong to the isolation valve category. These valves can stop the flow of media in emergencies or when the pipeline needs maintenance. These can also connect the media to external process equipment or it can direct which path media should follow.
The bolted bonnet valve minimizes erosion, friction and pressure drop. This is due to its straight-through port design. For the pressure seal gate valves, two designs are available for high-pressure and temperature applications: the parallel disc and flexible wedge.
The bolted bonnet type is still usable in high temperature but this type can leak when the pressure increases. For applications higher than 500 psi, use the pressure seal valve because of its seal increases as the internal pressure increases.
The design also allows for minimal contact between the media and the disk. Meanwhile, the wedge design makes it less prone to sticking to the seat.
For applications are below ANSI Class 600, use the bolted bonnet gate valve. However, for high-pressure applications, use the pressure seal gate valves. High pressure can remove the bolts in a bolted bonnet type. This could lead to leakage.
The globe valve is quite similar to the gate valve but instead of a wedged disc, it employs a globe-like disk that shuts off, turns on or throttles media. Primarily, this kind of valve is for throttling purposes. The downside of the globe valve is that it cannot be used with media with high flow rates.
The globe valves, in power generation applications, are effective in controlling flow. Additionally, compared to other valves, the globe valve has a simple design, making maintenance easier. The design creates low friction that ultimately lengthens valve service life.
Considerations when choosing globe valves are the type of medium, the flow speed of that said medium and the amount of control needed from the valve. In addition to these, the seat, disc and the number of turns to open and close the valve should not also be taken for granted.
The bolted bonnet type is still usable in high temperature but this type can leak when the pressure increases. For applications higher than 500 psi, use the pressure seal valve because its seal increases as the internal pressure increases.
Check valves are anti-backflow valves. What this means is that it allows a unidirectional media flow. The 45-degree angled disc design reduces water hammering as well as can adapt to media with high velocity. Also, the design allows a low-pressure drop.
Check valves protect the entire piping system and equipment from possible damage from reversal flow. Of all valves, check valves, perhaps, take the most damage as these are often more exposed to media and other operational challenges.
Water hammering, jamming and wedging are just a few of the common issues of check valves. Choosing the right valve means more efficient valve performance.
The bolted bonnet and pressure seal tilt disc valves are more cost-effective than any check valve designs. Additionally, the tilt disc design seals more tightly than other check valve designs. Since it has a simple operation, maintaining this kind of valve is also easy.
Check valves are important additions to any application associated with combined cycle and coal-fired power plants.
Considered as more durable, more efficient and lightweight than the swing check valve, the dual check valve has springs that increase valve response time. Its role in the power plant piping system is to adapt to the sudden changes in media flow. This, in turn, often reduces the risk of water hammer.
This is a specialized kind of check valve. It is sometimes called silent check valves. The design is particularly helpful when there is a need for a quick-response against backflow. Also, when there is a constant threat for backflow, utilize this valve.
The design minimizes the effects of water hammering as well as vibrations caused by the media. It can also reduce pressure loss and provide quick response to shutoffs.
Nozzle check valves take into consideration the velocity required to open the valve. Fluid media does not need to be in high velocity to close the valve. However, the valve immediately closes when there is a great reduction in media flow. This is to reduce water hammering.
Nozzle check valves are highly customizable to suit the requirements of the powerplant. It can be designed to fit the application. It is not even dependent on the pipeline size.
Ball valves are part of the quarter-turn family. Its main feature is the ball-like structure that turns 900 to open or close. This acts as a stopper for the media.
Power plant facilities use metal-seated ball valves because these can withstand high pressure and temperature beyond F. Furthermore, metal-seated ball valves are more resilient and less prone to seat wear in comparison to their soft-seated counterparts.
Its bi-directional metal-to-metal sealing provides better shut-off capabilities compared to other valves. It costs less to repair such valves too. Since it can withstand high temperatures, it is also fire-resistant.
The butterfly valve has a wafer-like body with a thin disc that rotates bidirectionally. Being lightweight, it is easier to install, maintain and repair.
Otherwise known as HPBV, high-performance butterfly valves have two offsets instead of one. This creates a better sealing capability. It also creates less friction, leading to a longer service life of the valve.
High-performance butterfly valves are often used in water intake applications, cooling water systems and industrial wastewater applications. HPBV has the capability to withstand high pressure and temperature if the seating is metal.
This type of butterfly valve is often used for low pressure and temperature, and less severe power plant applications. With its seat typically made of high-grade rubber, it can close off the valve quite effectively in low-pressure applications.
This type is easy to install and maintain. Its simple design makes the resilient-seated concentric valves more cost-effective to install.
Triple offset butterfly valves have an additional third offset placed in the seat. This third offset reduces friction upon opening and closing of the valve. This valve also provides gas tightness and bi-directional flow. This is the most effective type of butterfly valve when high pressure and temperature are the top considerations.
It provides the best tight sealing and longer service life among all the different varieties of butterfly valves in the market.
Each type of power generation application requires a unique set of flow control needs. That being said, there is a myriad of valves in a given pipeline system in power plants. Due to the type of processes happening in a particular part of the pipe system, industrial valves for power plants also need to take different roles.
For high integrity slurry, valves need to have tight shut-off. The disc should be easily replaceable because most of the time, the slurries passing through are corrosive or abrasive. For the body, the most ideal is iron and stainless steel for the stem.
Valves used for isolation are valves that stop the flow of media due to several reasons. These fall into four categories:
1. Bonnet Gate Valve
The best bonnet gate valve should be made of cast iron. Its seat rings should also be welded to prevent potential leaks.
2. Pressure Seal Gate Valve
The two designs, wedged and parallel, should be hard-faced and have the self-cleaning capability. It should also be easy to maintain and repair.
3. Pressure Seal Globe Valve
For high-pressure services, the disc, seat rings, and the backseat should be hard-faced to ensure longer service life.
4. Bolted Bonnet Globe Valve
The bolted bonnet globe valve is often used for throttling services, the ideal valve of this type must be cast with thicker sections in areas where there is more stress. To ensure that there are lesser leakage potentials, the seat ring must be welded.
These valves protect the counterflow. Valves of this type should have hard-seated surfaces and anti-corrosive bearings. In addition to these, the valve should have large diameter hinge pins so there is room to absorb the movement of the media.
Valves belonging to this category include the following:
There are also special applications for certain valves. This depends on the type of energy resource as well as the needs of the power plant.
Industrial valves used in power plants often undergo intense pressure and stress. Knowing the right kind of valve ensures better and optimal power generation applications.
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