Category Archive: Check Valves
Cryogenic valves are intended for use in extremely cold applications, the term cryogenic generally is applied to temperatures below -50oC. Valves for cryogenic service have to be constructed of materials that retain their ductility at these very cold temperatures as well as special gaskets and seals that are suitable for extremely cold temperatures. Industries that deal with liquefied and compressed natural gas, as well as liquid Oxygen, Nitrogen or Helium rely on these specialty valves frequently to move cryogenic liquids and gases safely and reliably.
Usually, cryogenic check valves use the pressure of the fluid flow to push the valve into an open position, which allows gas the media to flow through. When fluid flow pressure decreases, the valve will close again and form a seal in order to prevent leakage through the valve.
Special Cleaning and Concerns
Cryogenic valves require special cleaning and degreasing by the valve manufacturer. This is accomplished with special solvents to degrease and remove any organic contaminants, and often by using ultrasonic cleaning solutions. Some services like oxygen or chlorine service require very high levels of cleanliness to insure that no organic materials or lint fibers are present after cleaning. Properly cleaned and certified valves are placed in double sealed polyethylene bags to insure that the valve remains cleaned until it is time to install the valve.
Operators should always thoroughly inspect cryogenic valves before installing them. This is critical to ensure that no oil or grease has been accidently introduced into the valve. Some specialized lubricants are approved for oxygen service; their presence may be allowable, but this varies by application.
As mentioned earlier, cryogenic valves must also be kept free of lint. Generally speaking fibers greater than 1/8” in length are not allowed to be present in the cleaned valve. In many cases, absolutely no fibers or lint can are allowed to be present regardless of length. Debris like this can prove dangerous in oxygen systems. Many industry professionals utilize blacklight testing to help detect fibers.
Finally, inspectors must regularly check cryogenic valves and oxygen systems for both internal and external leakage. Internally, leakage can be prevented by ensuring that the proper valve is in place and that it has a well proven sealing design. Cryogenic conditions in particular require robust seals to boost longevity. External leakage is also a significant concern. Often times weld end designs are required. These can be in the form of butt weld ends or socket weld ends on the valves.
How DFT® Can Help
DFT® offers high quality, In-Line, Axial Flow designed check valves as well as a full line of severe service control valves. Our customers often specify weld-end valves for a greater sense of security, but flanged and wafer-style valves are also used. DFT’s GLC, WLC and BNC model check valves and our HI-100 model control valves are suitable for a wide variety of cryogenic applications.
Learn More About DFT’s Valve Solutions
With over 75 years of experience in valve manufacturing, DFT is proud to offer our clients world-class products at affordable prices. Our certified, knowledgeable staff helps customers overcome obstacles and create custom solutions that will maximize the potential of their valve systems. If you would like to learn more about cryogenic valves, keep an eye out for our upcoming eBook, “Cryogenic Valves 101.”
Check Valve Installation & Piping Design Guidelines
As a follow up from our webinar “Solutions to your check valve problems”, we are sharing, in this post, a few of the questions received from the audience. A variety of questions came in which are answered here by our host Arie Bregman, vice president and general manager of DFT® Inc and a 35-year industry veteran, who is an active member in the U.S. Valve Manufacturers Association (VMA), serving on the group’s education, training, and technical committees.
During the webinar Arie discussed the different factors that go into a well-functioning piping system and ways to prevent water hammer and related issues before they become serious, time-consuming problems. Many times valve problems are not a function of the valve at all, but problems with the piping system design, valve location, poor installation practices or selecting the wrong valve for the application. In the webinar you will hear about check valves within piping design, best practices of installation, choosing the right check valve for the application and even a section on gasket installation best practice.
If you missed this webinar, you can now view it on demand from the DFT website, just click this link.
Below, our talented host answers some common questions regarding check valve applications to help you find the right type and fit.
Q: Can you explain leakage rates for various types of check valves?
A: All of our check valves must meet one of the two most common standards for valves: MSS SP61 and API 598. To test leakage rates, we usually perform the test with either air or water, although water tends to be the more difficult medium. If you’re using your valve in an application that involves gas, you might want to choose the MSS SP61 standard and use gas testing.
Q: Can I use check valves with 50% caustic soda solution? If so, what the minimum temperature?
A: It may be a challenge to use any check valve with such a solution because the caustic soda will likely cause the parts to gradually bind. If you need to use a caustic soda solution, however, we recommend using a special coating such as Xylan on any internal parts that will need to be able to move relative to one another.
Q: How closely does a full bore gate valve approximate a straight pipe? Can this count towards the straight pipe run recommendation?
A: Although a full bore gate valve will have a fairly high flow coefficient, it will still cause flow turbulence. Therefore, you should still place it after the check valve if you plan to use it in place of a straight pipe.
Q: What is the effect on pressure drop for an axial flow check valve?
A: A pressure drop will result in higher flow resistance in an axial flow check valve than it would in a swing style check valve because of the internal pressure within the flow stream. Greater flow resistance, however, isn’t necessarily a problem, particularly if the volumetric flow rate through the collective piping system is also high. You simply need to ensure that the differential pressure created by the axial flow valve enables the valve to completely open at normal flow conditions.
Q: Can you provide a ranking of check valve types from the smallest to the largest pressure drop in the fully open position?
A: Unfortunately, this type of ranking isn’t possible because of the number of variables among the valves. Generally, the highest coefficient by line size would be with a swing style valve, followed by tilting disc, double door (dual plate), and then axial flow valves.
Q: How does cracking pressure relate to pressure drop across the valve?
A : The cracking pressure will be the absolute minimum pressure loss that the valve will experience when in operation. If you need a more precise estimate of the amount of pressure that will be lost, you must do valve-sizing calculations for your specific application.
For more than 70 years, DFT® Inc. has helped customers find and install the right check valves for their unique applications. From world-renowned DFT® Silent Check Valves to the innovative DFT HI-100® Control Valves, we have the products you need and a team of valve experts with decades experience in a range of industries, including power generation, petroleum, construction, chemical processing, steam, water treatment and many more
New Webinar From DFT®: Solutions to Your Check Valve Problems — Important Valve Installation and Piping Design Guidelines
Even one minor mistake in an otherwise well-designed piping system can cause serious, high-maintenance problems — such as water hammer — that can damage pumps and other components. At DFT®, we’ve seen best-case scenarios, and we’ve seen catastrophes, especially involving the installation and maintenance of check valves.
To help understand the many factors that go into a well-functioning piping system and to prevent water hammer and related issues before they become serious, time-consuming problems, we’ve created a comprehensive webinar, “Solutions to Your Check Valve Problems — Important Valve Installation and Piping Design Guidelines.” This presentation will review installation, maintenance, and piping design tips, as well as key guidelines to keep in mind to ensure the most efficient installation and use of check valves.
The upcoming webinar will explain the basics of piping design and the fundamentals of valve sizing, with an emphasis on sizing check valves for specific application conditions, rather than selecting a valve based solely on line size.
- Date — May 23, 2018
- Time — 2 p.m. EDT (11 a.m. PDT)
- Duration — 1 hour
- Presenter — DFT®
- Speaker —Arie Bregman, vice president and general manager of DFT® Inc. A 35-year industry veteran, Bregman is active in the U.S. Valve Manufacturers Association (VMA), serving on the group’s education, training, and technical committees. He also is a member of the VMA Board of Directors. Bregman holds a Master of Science degree in mechanical engineering from Worcester Polytechnic Institute in Worcester, Mass.
- Learn general check valve and piping design rules
- Understand how piping design can impact valve reliability and maintenance costs
- Explore best practices and review check valve installation and valve maintenance guidelines
- Learn how to choose the best check valve for your application
- Hear about common valves myths vs. reality
Typically used to restrict fluid flow to a single direction, check valves play an integral role in all types of liquid networks. At DFT® Inc., we’ve been manufacturing top-quality check valves and control valves since 1943. The DFT® Model WLC® Wafer Style Check Valve, a spring-assisted, lightweight model, offers a number of unique advantages over traditional valves.
The dual/center-guided design improves stability, while the disc and seat arrangement ensure a tight shutoff, eliminating the risk of reverse leakage and, therefore, preventing potentially dangerous water hammer. In fact, these valves are ideal for use in systems with a high risk of water hammer. Offering consistent, reliable operation and ensuring low maintenance costs, the WLC® product line can be used for a wide range of pressure/temperature combinations, making these valves ideal for applications involving liquids, gases, and steam.
Wafer Style Check Valves
As mentioned, DFT®’s wafer style check valves are specifically designed to prevent water hammer and reverse flow. Take this recent project as an example:
One of our clients approached us for assistance with an application involving raw water intake; the valves they were using were causing water hammer, and they needed an alternative solution to ensure optimal operational efficiency and reduce the risk of costly maintenance needs and downtime. We replaced the valves with our WLC® models and later assessed the facility during a routine maintenance operation. The water hammer had been completely eliminated. Simply by switching to these check valves, the client was able to fix an issue they had been dealing with for years, significantly reducing the risk of mechanical failure and ensuring optimal cost efficiency.
The WLC® check valves are available in a variety of ASME classes, and can be utilized in pipes of different line sizes. These valves can also be manufactured with a range of different materials for various types of applications. DFT®’s WLC® models meet stringent industrial standards, such as MSS-SP 61(for seat leakage) and MSS 126 and API 594 (for face-to-face dimensions).
Versatile, reliable, and lightweight, the WLC® line of check valves is specifically designed to reduce the risk of water hammer and its various related issues. Allowing for low maintenance requirements and consistent service, these valves available at DFT® serve as ideal solutions for a huge range of industries and applications.
To learn more about these unique valves, download our WLC® cut sheet today.
Used to restrict fluid flow to a certain direction, check valves are employed in the vast majority of industrial processes. At DFT® Inc., we provide a wide range of check valves for use in diverse industrial applications. Our spring-assisted in-line check valves, for instance, are specifically designed to prevent water hammer by eliminating the risk of reverse flow. And, if sizing is done to account for flow rather than line size, these high-performance valves will operate reliably and efficiently for years, without the need for extensive maintenance.
In-Line Check Valves
The experts at DFT® often help clients assess their unique check valve requirements; our check valve sizing program allows us to easily determine required valve sizes before actual setup, eliminating the risk of design errors and delays. DFT® check valves can be installed in-line in any orientation; valve operation will not be hampered in any way by the specific orientation chosen, provided the flow direction is in line with the valve design (as indicated by an arrow on the valve casting).
However, for a downward flow, these check valves need to be modified slightly to support the additional weight of the disc and any static head that may be involved. While silent check valves can be employed in vertical piping or in installations requiring constant controllable pressure, swing valves should only be used in horizontal pipe runs, in which minor flow variations are expected.
When using swing check valves, users are afforded limited pressure control, as there is less control over valve opening and closing. Therefore, this type of valve is usually employed in less sensitive, large-scale pipelines carrying liquids, gases, or steam. To allow for enhanced performance, these swing check valves can be replaced by our GLC® Silent Check Valves or Excalibur® Silent Check Valves. These silent check valves have only one moving part and allow for greater flow variability than a conventional style swing check valve. Also, because the DFT Axial Flow Check Valves have so few moving components, they are more resistant to wear and tear and can maintain a longer lifespan.
However, the GLC® model is not considered a “dead-end” service valve. It is essential that the upstream, or seat end, of the valve be connected to the line until the pressure is relieved from the downstream end. The seat end of the valve must always remain bolted to the mating flange when the valve is exposed to downstream pressure in order to avoid possible blowout of the internals, as the retaining screws do not account for direct exposure to downstream pressure. In addition to eliminating water hammer, appropriately sized silent check valves can greatly improve system safety, protect critical system components like pumps, and improve overall system life while reducing maintenance costs.
DFT® check valves are specially designed to improve the efficiency and safety of your industrial processes, and our team of experts is ready to assist in identifying the ideal model for your specific needs.
To learn more about our valve solutions, and why it may be beneficial to replace your current valves with DFT® non-slam check valves, download our new eBook, “Non-Slam Check Valves vs. Swing Check Valves.”