Category Archive: Check Valves

Once Upon a Time This Valve Worked Well

Our process had to be shut down again.  It seems that the original valve is no longer up to the task.  Should I continue to simply repair the valve or should I look for another solution?  Up until now, it was far easier to repair the valve and/or replace it in kind … but my process efficiencies are going down and I need to find a solution.  Where do I start?

Changing Conditions

I pull out the valve data sheet and take a look at the original conditions.  Wow! I can see immediately that things have changed –

  • The plant has aged nearly 20 years;
  • We replaced the pump on that line 5 years ago;
  • We have modified the piping in the area of the valve;
  • We changed the fluid chemistry;
  • Instead of operating continuously, the plant is now cycling

Every time conditions change, we need to review the impact upon the control system.

Aging Systems

As a system ages, it does not get any cleaner.  Whether it is due to pipe scale or there is other sediment in the system, a valve that worked in a clean system may not work as well in the older system.  We have periodically been pulling the valve with cage style trim in order to drill open the passages.  We have also noticed that the valve trim is wearing out more quickly.  The valve simply requires more maintenance.

New Pump

Installing a new pump can change how the system operates.  A new pump generally means that we have a new pump curve to work with.  The new pump curve means that the flows and pressures have changed from the original specification.

Modified Piping

We added a new branch line.  A closer look reveals (I use my 20D2 rule of thumb) that the new line may have lowered the flow rate through the control valve.  Is it possible that the control valve is no longer properly sized?  The trim in an oversized control valve erodes more quickly than the trim in a properly sized valve.  Alternately, if the valve is undersized, I may be seeing high velocity erosion which also negatively affects trim life.

Changing Chemistry

Although we have always maintained our chemistry within recommended boundaries, we can see that our targets have changed over the years.  Newer technology allows us to more closely hit the mark.  Is it possible that this has tipped the balance and we are now seeing erosion-corrosion in the valve since the originally specified materials are no longer noble enough?

Cycling vs. Base Loading

When we changed from a base loading operation to a cycling operation, we started to strain our control valves.  Now they operate more frequently and often work in the low end of the range.  By changing the operation, I now need to have a valve that is suitable for severe service when previously I could use a standard valve.

The DFT HI-100™ control valve can be a good choice when conditions change.  It deals well with dirty fluid, can be sized properly for the new conditions, is not subject to erosion corrosion and is designed to perform well in the most severe services.

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.New Call-to-action

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.

Axial Flow Check Valve Video

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.

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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.

Diagram of hydraulic pump: cylinder, piston, inlet valve, outlet valve, reservoir, motor, pump housing

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.

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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.

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