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1. What Is Cracking Pressure?

   May 21, 2021 4:38 pm Comments Off on What Is Cracking Pressure?

   What Is Check Valve Cracking Pressure?

   Cracking pressure refers to the inlet pressure level at which the first sign of flow is present. It can also be described as a measure of the pressure differential between the inlet and outlet ports of the valve when flow is initially detected. Specifically, cracking pressure is the least differential pressure that the valve experiences during flow.

   Check valves are frequently used with liquids, but they are also found in many industrial applications handling media such as steam, gas, slurries, and mixed-phase flows. In relation to cracking pressure, pressure drop is another, somewhat related aspect of pressures within a valve to keep in mind. Pressure drop is the difference in pressure between both the valve’s inlet and outlet. Once the cracking pressure is reached, the valve starts to open, which facilitates the flow of the contained media. As the flow rate decreases, the valve then starts to shut.

   The cracking pressure will depend on the check valve design. It’s usually measured in pounds per square inch (psi), pounds per square inch gauge (psig), bar or kPa (their metric equivalents), or both.

   Why Is Understanding Cracking Pressure Important?

   

   When choosing a check valve for a particular application, it’s important to know the valve’s cracking pressure. This specification is the initial indication of flow, but the valve won’t be fully open when it reaches cracking pressure. You’ll need to select the most appropriate valve with the right internal component design to achieve the required cracking pressure and overall pressure differential.

   It’s also important to keep in mind that a check valve is designed to control flow in only one direction and is available with a specific normal cracking pressure. As the fluid flows through the valve and the pressure becomes greater than the cracking pressure, the disc moves off the seat, and the valve opens compressing the spring. When a check valve is oversized for the expected flow, it creates low flow (low velocity) conditions. Changing the spring to a lower cracking pressure can be one way to reduce chattering while improving the stability of the valve.

   What Happens When the Incorrect Cracking Pressure is Selected?

   Cracking pressure can have a significant impact on the compatibility of a check valve with its intended application. Certain issues can occur if the cracking pressure is too high or too low.

   • Too high. High cracking pressure causes a higher pressure drop across the check valve. If the cracking pressure is too high, the valve may not open fully or at all. When the check valve isn’t fully open throughout normal flow, it may pop or chatter, which can lead to premature wear.
   • Too low. Low cracking pressure can reduce the valve’s closing speed. If the cracking pressure is too low, the valve may also be unable to close entirely in the vertical flow down position because of the stem and disc weight overcoming the opposing force of the spring.

   Get Check Valves with the Correct Cracking Pressure at DFT®

   To ensure consistent flow and avoid premature wear, it’s important to choose the right check valve for your specific application. If you need help finding the correct check valve with the right specifications, DFT® carries a wide variety of check valve products to meet your application’s requirements. We offer a selection of threaded/socket weld check valves, vacuum breaker check valves, restrictor check valves, sanitary check valves, and more.

   For help finding a check valve with the right cracking pressure for your needs, contact us today or request a quote to start your order.

2. Effective Check Valve Selection and Placement for Industrial Piping Systems

   March 23, 2021 9:38 pm Comments Off on Effective Check Valve Selection and Placement for Industrial Piping Systems

   When planning a check valve installation, the primary goal is to achieve a valve and piping system that offers the longest service life at the lowest cost. Accomplishing this goal while also ensuring that the system operates effectively and efficiently requires several considerations.

   As a world-class manufacturer of high-quality check and control valves, DFT® understands the challenges of choosing the optimal valve for a piping system. To facilitate the selection process for our customers, we put together the following guide outlining how to choose and implement the right valve.

   

   Principles of Piping Design

   In general, optimal piping system designs follow three basic principles:

   1. There must be a 5-10x nominal pipe size (NPS) of straight pipe on either side of the valve, i.e., both the upstream and the downstream sides of the valve.
   2. The minimum pressure to open a check valve is referred to as the cracking pressure. However, to fully operate a valve, the system requires twice the differential pressure.
   3. While many styles of check valves will work in horizontal piping, only axial flow (“silent”) check valves are suitable for use in vertical piping. Whenever possible, a horizontal line is preferred since it rules out gravity, but vertical piping must be considered for flows that require up or down transport.

   Common Piping Design Mistakes

   Following the above principles facilitates the proper configuration of check valves in a piping system with minimal need for maintenance and maximum reliability. However, many industry professionals may find it challenging to navigate the nuances of pipeline design. Some of the most common mistakes made when designing a pipeline involve:

   Valve Location

   As mentioned in Principle #1, valves should have enough clearance—i.e., straight pipe—on either side from other pipeline components, such as pumps, elbows, expansion joints, and other valves, to function properly. When positioned upstream, these components can cause turbulence, which affects the performance of the check valve and can cause increased wear and, consequently, failure. The same can be said of other types of valves, such as ball valves and control valves; they perform best when the media flow is laminar, not turbulent.

   Axial flow check valves can be installed close to the inlet of an isolating value if it is full port and fully open.

   Flow Conditions

   As outlined in Principle #2, there must be enough pressure to keep the valve fully open under minimum, normal, and maximum flow conditions. It is not enough to match the valve size to the pipe; it is necessary to do the sizing calculations to pick the right sized valve for the given flow conditions.

   Vertical Pipe Runs

   Avoid using swing check valves in vertical pipes. The downward flow keeps the valve open, and the upward flow leads to water hammer from the disc slamming against the seating. As specified by Principle #3, use only axial flow check valves in vertical pipes. The strong spring of the axial flow check valve avoids water hammer by ensuring that the valve closes before the reverse flow happens.

   Choosing the Best Check Valve for Your Application

   There are several factors to keep in mind when choosing a valve for a piping system. These selection considerations include:

   Valve Location

   As required by Principles 1 & 3 above, the location of a valve is important; horizontal piping is preferred for all valves except axial flow check valves, and there must be sufficient straight piping on either side of the valve.

   Valve Size

   Check valves remain open only when there is sufficient pressure in the line. Therefore, the pressure available with minimum flow must be considered along with maximum and normal flow conditions while selecting the valve. This is the requirement per Principle #2 above.

   Valve Material

   When choosing a valve material, the main focus is on choosing one that is compatible with the characteristics of the piping and requirements of the application (i.e., temperature, pressure, corrosion resistance, etc.). This generally results in the body material of the valve matching the flange material of the pipe. For example, a carbon steel line typically features a carbon steel valve body. Carbon steel is the most commonly employed valve material, with cast iron and stainless steel following close behind.

   Types of Valves Used in Industrial Piping

   Valves find use in a variety of industrial piping system applications. Typical applications include:

   • Preventing reverse flow (check valves)
   • Managing the flow of process fluids, including concentrated acids and bases
   • Redirecting flow from one line to another
   • Restricting flow for system balancing purposes
   • Controlling cooling rates to regulate temperature
   • Stopping flow during a system failure

   Industry professionals employ a wide range of valves to fulfill the above functions, depending on the requirements and restrictions of their unique application. Some of the most common valve types used are:

   • Check valves have a disc, stem, or a similar moving part that closes if the flow reverses or stops.
   • Ball valves are the most common type of valve and feature a ball with a round hole in the center. When aligned with the pipe, the valve is ON. When turned 90°, it is OFF.
   • Diaphragm valves are used for precise flow control, especially when the media contains solids.
   • Flanged valves use bolts to secure the connection and a gasket to seal the joint.
   • Gate valves turn flow ON and OFF with a vertical disc that moves up and down.
   • Globe valves regulate flow with a disk that moves relative to a stationary ring seat.
   • Needle valves are similar to a globe valve, but they use a tapered plug for finer flow control.
   • Relief valves are safety valves that prevent excessive pressure buildup in the system.
   • Wafer valves in general have a smaller footprint in the system.

   In addition to the valves listed above, there are many other types available, each of which is suitable for varying industrial applications.

   If you need a valve for your pipeline, DFT®, Inc. delivers. With over 75 years of experience manufacturing high-quality check valves and control valves, we can provide you with a valve solution that meets your needs. Check out our product page to find out about our valve offerings or contact us today with your questions or project specifications.

3. DSV® Sanitary Check Valves in the Pharmaceutical Industry: Explore Our eBook

   October 20, 2020 2:40 pm Comments Off on DSV® Sanitary Check Valves in the Pharmaceutical Industry: Explore Our eBook

   In sanitary manufacturing applications that employ the use of fluid systems, such as in the pharmaceutical industry, regulating fluid flow and pressure is essential to maintaining high product and production quality. Common issues—such as backflow, water hammer, and cleanliness – significantly affect the overall effectiveness and efficiency of the system. For these situations, DSV® sanitary check valves serve as an ideal solution.

   Why Are DSV® Sanitary Check Valves Important?

   Unlike other check valves available on the market, DSV® sanitary valves meet 3A sanitary standard and are designed for use in applications with high sanitation requirements. As such, they are ideal for the manufacturing operations of products intended for consumption or direct contact with consumers, where unsanitary conditions can result in illness or injury. 316L stainless steel offers the corrosion resistance needed to prevent the contamination of process fluids.

   By eliminating crevices and cavities from the valve design and achieving smooth, polished finishes on internal and external surfaces, we minimize the risk of material and bacteria buildup in our valves. We test 100% of our check valves before shipping them out to customers.

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   Get Your Free Copy:

   A Guide to DSV® Sanitary Check Valves in the Pharmaceutical Industry

   
   

   Download Now

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   Additional Information on DSV® Valves

   Construction

   The valve consists of seven main components: body, seat, disc, spring, guide, clamp, and body gasket. Both the disc and seat are lapped to ensure tight shutoff capabilities.

   

   For full valve construction, check out our eBook.

   Types

   • Horizontal Valves. The horizontal valve models are suitable for use in horizontal piping lines that require a self-draining valve.
   • Vertical Valves. The vertical valve models are designed for use in vertical piping lines or horizontal piping lines that do not require a self-draining valve.

   Key Features

   • Meets 3A Standard 58-02
   • 32 Ra or 15 Ra finish
   • Clean-in-Place Design
   • And more…

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   Download Now: All key features found in our eBook!

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   Applications

   • Condensate lines
   • Evaporators
   • Vacuum breakers
   • Purified Water
   • And more…

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   Download Now: All applications listed in our eBook!

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   A DFT® DSV® Sanitary Check Valve Success

   A major engineering firm contacted us on behalf of several pharmaceutical companies. The firm needed to find a check valve solution for their noncorrosive medical waste drain system. The check valve needed to operate at 20 psig or less with a flow of 3 GPM, have sanitary end connections, provide tight shutoff, have a low cracking pressure to open and be able to be steam cleaned in place.

   The check valve had to withstand high temperatures, as the firm used 330°F steam to clean the entire medical waste process system 3 times a day. The valve also needed an extremely smooth finish to maintain sanitary conditions.

   Responding to the challenge, a DFT® 2 inch DSV® vertical check valve was specified. Designed to prevent flow reversal, this non-slam, full-body valve came equipped with a 0.1-psi cracking pressure spring. We also designed it with tri-clamp connections for ease of disassembly. The product was so successful that… Get the full story in our eBook!

   For additional information about our DSV® valves and how they suit the needs of the pharmaceutical industry, download our eBook today.

4. Why Do DFT® Axial Flow Check Valves Inherently Reduce Water Hammer?

   April 23, 2020 6:16 pm Comments Off on Why Do DFT® Axial Flow Check Valves Inherently Reduce Water Hammer?

   Hydraulic shock—more commonly known as “water hammer”—occurs when the flow within a pipe is suddenly forced to change direction, which creates a pressure wave that can be characterized by a loud knocking or banging sound. In piping and process systems, water hammer often happens upon closing a valve to stop or redirect flow. It’s important to take steps that will reduce water hammer or mitigate its effects, as repeated waves of pressure can cause significant wear on pipes and joints over time. Even without wear, a strong enough pressure wave may still burst weak threads or seals.

   The best way to stop water hammer is to bring the flow to a stop before it reverses direction. This may be achieved using a valve, but the valve in question must be able to respond very quickly to the change in flow rate through the piping system. In this blog post, we will examine why the DFT® Axial Flow Check Valve is the best choice to halt water hammer of the 3 most common types of check valves:

   • Swing check valves
   • Double-door check valves
   • Axial flow check valves

   The time it takes for a valve to go from full open to full closed relies heavily on the distance the disc must travel. If the valve must respond quickly, it stands to reason that a shorter distance can be traversed in less time. The following illustration compares the travel distance for the above valve types.

   

   To simplify the explanation, we’ll use nominal pipe size (NPS) to represent the inside diameter (ID) of the pipe in all examples in this blog.

   How Swing Check Valves Close

   Swing check valves contain a disc that is hinged above the ID of the pipe, so the distance the swing check disc travels is ¼ of the circumference of the circle, where the radius of the circle is the NPS. If circumference is πD, then ¼ of this would be πNPS/4 or 1.57 NPS.

   How Double-Door Check Valves Close

   The disc used in a double-door valve is comprised of two halves hinged along the split. Each half of the disc travels through an arc, which can be represented by ½ NPS. Therefore, the distance that each half of the double-door disc travels is half the distance of the full disc in the swing check, or πD/8 or 0.785 NPS

   How DFT® Axial Flow Check Valves Close

   In general, axial flow check valve discs travel ¼ NPS (0.25 NPS) from a fully open position to a fully closed position. Given that a swing check valve disc must travel almost six times that distance to close, it stands to reason that an axial flow check valve disc can close much faster. By adding a spring to the disc, the disc can close before the flow reverses to avoid the water hammer effect.

   Preventing Water Hammer With DFT® Axial Flow Check Valves

   Water hammer poses a risk in most piping and process piping systems. Without proper solutions in place to mitigate hydraulic shock, these systems are at risk of bursts, leaks, or excess long-term wear. This makes it especially important to use check valves that can reverse flow without creating a damaging hydraulic pressure wave. To do this, the disc within a check valve must be able to close as quickly as possible.

   DFT® Axial Flow Check Valves are designed with fast closure in mind. The spring-loaded discs in these valves go from fully open to fully closed with a significantly shorter travel distance than other check valve types. With this short distance and fast closure capabilities, the overall valve closure time is significantly reduced. This naturally mitigates the risk of water hammer.

   For more information about our check valves and how they can prevent water hammer in your system, please request a quote.

5. New Webinar From DFT®: Solutions to Your Check Valve Problems — Important Valve Installation and Piping Design Guidelines

   May 16, 2018 2:13 pm Comments Off on 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.

   Webinar Details

   • 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.

   Key Takeaways

   • 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

   Register Today

   DFT® has solutions for your check valve problems. Register for our webinar today!