Category Archive: Check Valves
The Importance of Good Information About Valves
Proper valve selection is critical for ideal operation of any system. Improper valve selection can cause system underperformance or failure. The greatest problem when selecting valves is incorrect information.
Often, we may only have access to incomplete or dated information regarding valve applications. Do we know enough about the system the valve will be used in or the main purpose of its use? This “bad information” can create a situation where the theoretical situation does not match reality.
Good Information is Key
“Bad information” comes in many forms. Original design specs might be difficult to obtain, and having those specs does not guarantee success. Occasionally, specs aren’t properly updated. Information that was good at first can fail to incorporate changes in process conditions. If the actual pressure, temperature, flow-rates or the media is different than that which was used to select the valve, it may fail or fail to work properly.
When choosing a gate, globe, ball or check valve, we always want the valve to be operating in the full open or closed position. Control valve selection, however, targets 40% to 60% open for normal flows. When most control valves operate below 20% open or over 80% open, they can lose their ability to control properly.
What information is required to properly size a valve? Fluid type, operating pressures and temperatures upstream and downstream of the valve, and the flow rates associated with these conditions are required information to have.
Knowing What is the Right Valve for the Application
There are many different types of valves available. They do not all work the same way or for the same purposes. Each valve type has its advantages and disadvantages.
For proper control valve selection, it is important to understand how the valve is used to control system flow. For example: is the system tuned for a constant set point, or is it set to modulate a variable flow over time? The layout of the piping system and locations of reducers and elbows also impact valve performance.
Often, choosing what seems to be the most efficient valve might not be the best valve for application. Replacing a valve “in kind” with an upgraded version of an older valve might actually do more harm than good.
Poor Performance – Get Good Information
Unfortunately, the blame for poor performance often lands on the installed valve when it is actually bad information that caused its failure. Simply repeating the bad information to select a different valve is doomed to have the same results. When DFT Inc. is asked to troubleshoot an installation, we start by collecting all of the available information and check for “bad information” concerning flow conditions and application mismatches with respect to the installed valves.
Take the time to get good information. Fortunately, the information is more readily available today than it has been in the past through trending information. If you can provide actual system operational information, your chance for success increases significantly.
Watch DFT Valves’ ALC® Axial Flow Check Valve in Action
Check valves are instrumental for regulating fluid flow within a given valve system. When properly chosen and installed, check valves are meant to operate seamlessly throughout their design life; improper check valves can lead to harmful complications—such as water hammer.
Water hammer is one of the most common problems befalling check valves. Simply put, water hammer is the generation of shock waves that occur when a liquid comes to a sudden stop inside a pipe. These high-pressure shock waves persist until the energy of the surge dissipates; during that time, shock waves can cause serious damage to pipe lines, joint gaskets, pressure gauges, and other components.
Valves that close on reversing flow and back pressure are major contributors of water hammer; these valves include swing check valves, tilting discs checks, and double door check valves. Water hammer can lead to poor productivity due to failures, so it’s vital to use check valves designed to combat this issue.
DFT Valves’ ALC® axial flow check valves are an ideal choice to reduce the effects of water hammer. The DFT Valves team created a short video to demonstrate how beneficial this check valve can be to your system.
DFT Axial Flow vs. Double Door Check Valve
In this video, we demonstrate the difference between our ALC® check valve and a double door check valve on the psi of a pump valve application. This specific application is 15 psi, and the double door valve causes a pressure spike that nearly reaches 60 psi. Due to this pressure imbalance, we replaced the double door valve with our axial flow check valve.
Once the ALC® check valve is installed, you can immediately notice the pressure stabilize within the pump’s system. The psi goes from zero, back up to 15 without any pressure spike as the ALC® valve cycles.
Benefits of the ALC® Check Valve
The DFT ALC® valve is designed specifically to prevent water hammer and reverse flow. Lightweight and compact, these valves can fit between mating flanges with ease. ALC® valves are useful for a variety of applications that involve liquids, gases, or vapors. Other benefits of these valves include:
- Simple to maintain
- Can be installed horizontally or vertically
- Body material can be carbon, stainless steel, or other materials.
- Custom sizes can be made to your specifications
- Meets several industry codes and standards, including ANSI, MSS, and ASTM
To learn more about choosing a DFT check valve that is best suited for your application, contact us today.
The Importance of Accurate Check Valve Sizing
Check valves are among a system’s essential components. For greatest efficiency and maximum protection, however, check valves must be properly sized in order to work at their highest level.
A properly sized check valve will make a system reliable and provide the longest service with the minimal amount of manual attention. Proper sizing will eliminate disc fluttering whether the valve’s disc is in the stable and fully open position against the internal stop, or in the fully closed position against the seat.
Properly sized check valves also contribute to overall cost savings. Appropriate sizing increases the lifespan of the valves, but also improves the longevity of pumps and other related components on the same system. Check valves that are sized correctly function well, and in the process enhance the safety of processes and applications.
Examples of Check Valves
There are a variety of types and styles of check valves. These are applied to a number of processes.
- Ball checks: Ball checks control the movement of flow by using a “ball” inside the body. The ball can freely rotate, resulting in a wearing and wiping action that is suited very well to handle viscous materials. Ball checks can also be spring-loaded to safely lock a system.
- Dual plate: Dual plate valves are made of two spring-loaded semicircular plates with a hinge in the center. These valves are known for their excellent flow capacity, due to their lightweight nature and compact face-to-face dimensions. Their compact size means they need less manual attention, support, and valuable real estate in a system.
- Piston Check: Piston check valves feature a body-guided or stem-guided disc that operates within the body bore. This ensures that the disc and seat are properly aligned when the valve closes. They are available in T pattern and Y pattern body designs. The latter usually have a higher flow coefficient than T pattern bodies.
- Swing Check and Tilting Disc: Swing check valves or tilting disc valves are designed with a hinged arm at the top of the valves. Gravity and reverse flow are the chief mechanisms responsible for closing this valve. These valves come with a variety of connections, such as socket weld, flanged, threaded, ring type joint or butt weld end connections.
- Spring Assisted In-Line/Axial Flow Check: These valves are also sometimes referred to as Nozzle Check or Silent Check Valves. Their primary design function is to prevent reverse flow and reduce or even eliminate water hammer. The mechanism behind this is a spring-assisted disc, constructed in line with the flow with a short travel distance, which acts as a fast-closing valve. These valves can be installed in any position, with either vertical or horizontal pipe runs, and is available with a number of different styles and end configurations.
Correct Sizing Means Best Fluid Handling
Before purchasing valves, be sure to consider a number of factors that go with it, chief among them proper sizing. Properly sized valves will prevent malfunctions and ensure that a system operates reliably and efficiently. All related system components will last longer and safety—both for the workers and the valves—will be enhanced.
Check valves play a central role in fluid handling systems, and it is crucial to ensure that they are properly sized. Consulting a qualified professional and carefully considering your options will help you choose the best check valve, and ultimately help your bottom line. The best valve choice gets you the most out of your systems and equipment for the longest possible and most efficient performance.
Design Elements to Consider when Selecting a Check Valve
Check valves perform a crucial function in pumping systems by permitting the forward flow of water when open, and preventing reverse flow when shut. When selecting a valve for your water and wastewater pumping system, you will likely want one that not only executes this task, but also does so efficiently.
Check valves should minimize energy consumption and also protect the system from pressure surges caused by water hammer. They should also suit your particular application. The two common types of check valves to examine are silent or in line check valves and swing check valves.
3 Common Problems in Check Valve Selection
Did you know that, unlike other types of valves, check valves continue to work if a plant loses electricity, air, manpower, or all of the above? They come in a wide variety of sizes, materials, and end connections, and can be used in countless applications.
So why is it that they’re often improperly sized or selected? It’s because check valves are only as good as their application. Oftentimes the problems with a check valve are not related to the valve itself, but application and other factors. So when you’re problem solving or replacing a check valve, keep these three common problems in mind:
Water Hammer
Water hammer is one of the most common check valve problems. Water hammer is a pressure surge that’s caused when a liquid or gas is forced to stop or change direction suddenly, and often occurs when a valve is suddenly closed at the end of a pipeline system. This can result in both noise and vibration, which can in turn lead to damage and additional maintenance or repair costs.
Water hammer can be prevented, however, by using a faster-closing check valve that stops the pressure surges and shock waves that can damage and rupture equipment. Our silent check valves in particular are known for their effectiveness in preventing and in many cases eliminating water hammer.
Reverse Flow
Reverse flow is another common check valve problem and can be extremely costly, especially when it occurs at the discharge of a pump, causing the pump to spin backwards.
