Valve Sealing for Industrial Success - Global O-Ring and Seal

Summary

• Effective sealing in valves prevents leaks, ensures reliability, and maintains performance in various industries.
• Choosing between static and dynamic seals and understanding different seal types ensures compatibility of valve motion, pressure, and fluid characteristics.
• Compliance with regulatory standards and proactive maintenance help prevent seal failures, improve valve longevity, and support safe, efficient operations.

Introduction

Effective sealing is essential for valve applications to maintain optimal system performance and prevent leaks, contamination, and pressure loss. Seals support safety and efficiency by ensuring valves can operate reliably under various environmental conditions, from extreme pressures to corrosive chemicals. The proper seal can help avoid costly downtime, maintain system integrity, and prolong the lifespan of both valves and associated components.

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Valve Sealing Requirements

Valves have standard sealing requirements to ensure reliable performance, but different types of valves have unique sealing needs due to their specific designs and functions. The following list outlines five common valve types’ unique sealing needs and challenges.

• Gate Valves require seals that can handle linear motion as the gate moves up and down to control flow, often under high-pressure conditions. However, they face challenges sealing large surfaces and maintaining integrity under high pressure. Seal wear can also occur due to repeated opening and closing cycles, compromising seal performance.
• Ball Valves use seals that accommodate rotational motion and withstand friction and wear to ensure a tight shut-off and prevent leaks. The primary challenge is seal deformation due to rotational friction, requiring seals to be durable enough to maintain consistent contact with the ball surface while resisting wear.
• Butterfly Valves use seals that must handle a rotating disc. The sealing element must be flexible yet durable to maintain a consistent seal during rotation. Challenges for butterfly valves include dealing with uneven pressure distribution across the seal, especially in high-pressure applications. Ensuring flexibility and durability is vital to effective sealing.
• Check Valves require sealing solutions that prevent backflow and respond quickly to pressure changes to ensure one-way flow without leakage. The main challenge is maintaining a proper seal under frequent and rapid changes in pressure. The seal must be responsive and capable of preventing leakage even under fluctuating conditions.
• Global Valves require seals for linear motion, similar to gate valves, but with more precise control to regulate flow. The seal must handle throttling and resist erosion from fluid flow. Challenges include erosion and damage due to throttling, as the high-velocity fluid flow can degrade the sealing element over time, impacting its effectiveness.

Cost and maintenance considerations are crucial for long-term valve performance, as selecting the right sealing solution can significantly reduce maintenance frequency and complexity. High-quality seals may have a higher initial cost but provide savings through reduced downtime, extended lifespan, and improved system efficiency. Proper material selection and seal design can also help reduce energy loss, leakage, and system inefficiency costs, making them a vital aspect of overall valve management.

Dynamic vs. Static Sealing in Valves

Static seals are used where there is no movement between the sealing surfaces, such as in flanges or stationary valve parts. They are typically used to maintain a tight seal where components remain fixed. In contrast, dynamic seals are used in applications with relative motion between surfaces, such as rotating or reciprocating shafts within valves. Dynamic seals must accommodate friction and wear while maintaining a reliable seal to prevent leakage. Static seals are often more straightforward in design, while dynamic seals are more complex due to the demands of movement.

Aspect Static Seals Dynamic Seals Application Stationary parts, flanges Moving parts, rotating or reciprocating shafts Movement No movement between surfaces Relative movement between surfaces Wear Resistance Less wear, minimal friction High wear due to friction Complexity Simple design, easy installation More complex design, careful selection Typical Usage Pipe joints, valve covers Valve stems, rotating shafts

Both static and dynamic seals present their own challenges and require careful consideration when selecting the appropriate solution. Static seals generally face fewer issues due to the lack of movement, but maintaining a proper seal under extreme pressure or temperature fluctuations can be difficult. Dynamic seals, by contrast, are exposed to continuous motion, which leads to wear, frictional heat, and risks like extrusion and chemical compatibility. When selecting seals for either application, it is essential to consider the specific operating conditions. Static seals must withstand pressure and tolerate chemical exposure or temperature variations, while dynamic seals should have excellent wear resistance, low friction, and the ability to maintain integrity under repeated motion, considering factors such as movement type, speed, and pressure.

Common Seal Types for Valve Applications

Seals used in valve applications come in various forms, each with strengths and applications. The following list outlines the common types of seals used in valves and their specific uses:

• O-Rings are among the most commonly used seals in valve applications due to their simplicity, versatility, and cost-effectiveness. They are suitable for static and dynamic sealing and can handle various temperatures and pressures. O-Rings are used in ball, gate, and butterfly valves, providing a reliable seal against leakage.
• T-Seals are used primarily in high-pressure environments, where o-rings alone may not suffice. They feature a T-shaped cross-section and are often reinforced with backup rings to prevent extrusion under high pressures. T-Seals are well suited for applications that require enhanced sealing performance, particularly in hydraulic systems and other high-pressure valves.
• U-Cups are designed to provide effective sealing for applications involving pressure from a single direction. Their U-shaped cross-section enables them to react to pressure changes and provide a tight seal, making them ideal for valve stems and pistons. U-Cups are particularly useful in valves where enhanced pressure sealing is needed.
• V-Rings are used in dynamic sealing solutions, particularly in rotary applications. They are designed to fit around shafts and create a seal that prevents contaminants from entering the system while retaining lubricant. V-Rings are often used in valve stems and other rotating components, providing an effective barrier against dirt, dust, and other contaminants.

Each seal type plays an essential role in valve applications, ensuring the valve operates efficiently and effectively under various conditions. Proper selection of the seal type is critical to ensuring the longevity and reliability of the valve, minimizing maintenance needs, and reducing the risk of failure.

Preventing Common Seal Failures in Valve Applications

Valve seals can fail for various reasons, leading to leaks, reduced performance, or complete valve failure. Understanding the common types of seal failure and implementing strategies to prevent them is essential for maintaining valve integrity and ensuring efficient operation.

• Extrusion: Extrusion occurs when the seal material is forced out of its groove due to high pressure, especially in dynamic sealing situations. This can lead to partial or complete failure of the seal. Selecting seals with appropriate hardness and using backup rings to support the seal can help minimize the risk of extrusion.
• Compression Set: Compression set refers to the permanent deformation of a seal material after prolonged compression. This occurs when the seal loses its elasticity and fails to return to its original shape, resulting in leakage. Selecting materials with good compression set resistance and avoiding excessive compression during installation is essential to prevent compression set.
• Wear in Dynamic Seals: Dynamic seals are subjected to continuous movement, leading to wear and tear over time. The friction between moving surfaces can cause gradual degradation of the seal material, resulting in reduced sealing effectiveness. Using low-friction materials, proper lubrication, and selecting seals designed for dynamic applications are key strategies for addressing wear.
• Chemical Incompatibility: Chemical incompatibility occurs when the seal material reacts with the fluid or media in the valve and leads to degradation, swelling, or cracking. Choosing a material compatible with the specific chemicals in the application is crucial to prevent this type of failure. Material selection should be based on a thorough understanding of the chemical environment and its potential impact on the seal.

Proper installation and regular inspection are essential to prevent seal failures. Care must be taken during installation to ensure the seal is not damaged or pinched. Using the right tools and following manufacturer guidelines can help prevent issues. Regular inspection and maintenance also help identify potential problems early, allowing for timely intervention to prevent failure.

By understanding the common causes of seal failure and implementing effective preventative measures, valve performance can be maintained, minimizing downtime and ensuring the longevity of both the seals and the valves.

Regulatory and Industry Standards for Valve Standards

Compliance with regulatory and industry standards is critical for ensuring the safety and reliability of valve systems. Using seals that meet these standards helps prevent failures, reduce liability, and maintain the system’s performance over time. Non-compliant seals can increase leakage risks, contamination, and costly downtime. Ensuring compliance supports the valve’s longevity and contributes to overall operational efficiency and safety. Various standards define the quality, dimensions, and material properties required for seals to perform effectively in challenging environments.

The American National Standards Institute (ANSI) and ASTM International provide guidelines covering material requirements, design specifications, and performance criteria of seals. These standards ensure that seals are reliable, consistent, and capable of withstanding the pressures and environmental conditions found in industrial settings. Compliance with ANSI and ASTM standards helps ensure compatibility, reliability, and consistency across different valve systems and applications.

Different industries, such as chemical processing, water treatment, food and beverage, and pharmaceutical manufacturing, may have specific requirements for valve sealing. For instance, seals used in food and beverage applications must meet FDA standards for safety and compatibility with food products, while seals used in pharmaceutical applications must meet stringent cleanliness and compatibility requirements. Understanding the specific industry requirements is crucial to selecting the appropriate seal for each valve application.

By adhering to these regulatory and industry standards, manufacturers and operators can ensure that their valve seals are safe, effective, and reliable, helping maintain system integrity across various sectors.

Conclusion

Sealing in valve applications is a complex but vital aspect of maintaining efficient and safe operations across various industries. From understanding the difference between static and dynamic sealing to selecting the appropriate seal type for a given application, each decision significantly impacts valve performance. Addressing common seal failures through proper selection, installation, and regular maintenance is crucial for minimizing risks and ensuring longevity. Additionally, compliance with regulatory and industry standards helps guarantee that the seals used are suitable for their intended environments, ultimately contributing to the overall reliability of the valve system.

By taking a comprehensive approach to valve sealing—considering requirements, challenges, material compatibility, and industry standards—operators and manufacturers can achieve reliable, efficient, and long-lasting valve performance that supports operational goals and reduces maintenance costs.

What Are Valves and How Do They Work? 

At their most basic, valves are devices that work to control, regulate or direct flow within a system or process.

They often feature a range of characteristics that help to define their ideal application.

However, whether you’re looking to control flow, provide safety in a system that is piping liquids, solids, gasses or anything in between, there are likely stainless steel valves available to help.

Valves provide several functions, including:

• Starting or stopping flow based on the valve state
• Regulating flow and pressure within a piping system
• Controlling the direction of flow within a piping system
• Throttling flow rates within a piping system
• Improving safety through relieving pressure or vacuum in a piping system

Valve Opening Methods Explained

While many valves accomplish similar goals, how they do so mechanically can vary.

How a valve opens and closes will not only impact the overall performance but also determine how much control you have over the flow and how quickly the valve can operate.

Most valves fit into one of three categories:

• Multi-Turn valves: Think of these valves like a screw or piston. You crank the handle and the plug, plate, membrane, or other controlling obstruction moves into the path of the pipe blocking access. Depending on the valve, these can have higher or lower differentials allowing you to open or close them at various speeds.
• Quarter turn valves: Quarter-turn valves offer a full range of motion in a 90-degree turn of the handle. This makes them ideal for situations where precision isn’t as important as rapid action and easy opening or closing.

On top of the mechanical motion involved with a valve, also consider the method of actuation. In most cases, valves fall into one of three categories:

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• Manual Valves: Typically adjusted by hand, these valves use handwheels, hand levels, gear wheels, or chains to actuate.
• Actuated Valves: Often connected to electric motors, air or pneumatic systems, hydraulic systems, or solenoids, these valves allow remote control and automation for high-precision or large-scale applications.
• Automatic Valves: Some valves activate when a specific flow condition is met. Examples include check valves closing during backflow or pressure release valves activating when an over-pressure condition is detected.

Common Valve Types and Their Applications

Valves feature a range of characteristics, standards, and groupings the help to give you an idea of their intended applications and expected performance. Valve designs are one of the most basic ways to sort the huge range of valves available and finding a good fit for a project or process.

Common types of valves include:

You might also see valves classified by function instead of design.

Common functional designations and their common design types include:

• Isolation Valves: Ball, butterfly, diaphragm, gate, pinch, piston, and plug valves
• Regulation Valves: Ball, butterfly, diaphragm, globe, needle, pinch, and plug valves
• Safety Relief Valves: Pressure release and vacuum relief valves
• Non-Return Valves: Swing check and lift check valves
• Special Purpose Valves: Multi-port, float, foot, knife gate, and line blind valves

Valve Sizing Explained: Keeping Things Flowing

While valves might be a small part of your piping process or system in terms of space, they’re often a substantial portion of the design and build budget. They also have a significant impact on long-term costs and overall system performance.

Choosing a proper valve size is essential to both optimizing costs and ensuring safe, accurate, and reliable operation.

The first thing to consider is the overall size of the valve -- both in terms of physical dimensions and in terms of internal size and flow rates (CV).

Choosing a valve that does not fit properly in the space required could result in added costs. Choosing a valve which does not provide the ideal flow rate can lead to inaccurate flow control at the least and complete system failure at worst.

For example, if your valve is too small, it could cause reduced flow downstream while creating back-pressure upstream. If the valve is too large, you’ll find that flow control is drastically reduced the further you move from fully open or fully closed.

When choosing the proper size, be sure to consider both the connector diameter and the overall flow rate of the valve compared to your needs. Some valves offer excellent flow while others constrict flow and increase pressure.

This means sometimes you must install a larger valve to adjust for flow than the adapter diameter alone might imply.

Valve End Connections: The Key to a Good Fit and Proper Operation

With sizing and design out of the way, it’s also important to consider valve end connections.

While the most obvious implication here is choosing an end connection compatible with your piping, there are also functional characteristics to common end types that might make one valve more suited to your needs than another.

Common valve connections and ends include:

• Screwed or Threaded: Often used in instrument connections or sample points
• Flanged: The most common ends for piping use
• Butt Welded: Typically used in high-pressure or high-temperature operations
• Socket Welded: Commonly used on small bore piping where threaded connections are not permitted
• Wafer and Lug: Often used for compact valves installed in systems with limited space

Valve Materials: Ensuring Safety and Long-Lasting Performance

Depending on your intended use, the materials with which your valves are made might be a critical aspect in ensuring safe operation and reducing maintenance and replacement costs over the life of your operation.

Stainless steel valves are excellent options in a range of processing environments, including those involving corrosive media (such as chemicals, saltwater, and acids), environments with strict sanitation standards (such as food and beverage manufacturing and pharmaceuticals), and processes involving high pressure or high temperatures.

However, if you are processing solvents, fuels, or volatile organic compounds (VOCs), choosing a valve material from a non-sparking material -- such as brass, bronze, copper, or even plastic -- is often a better option. In addition to selecting the correct body material, internal (wetted) trim parts should be evaluated for chemical compatibility as well. If your valve contains elastomers, they should also be evaluated for their chemical compatibility as well as pressure and temperature limitations.

Valve Standards: Meeting Compliance and Regulatory Concerns

Depending on your intended usage, you might find that valves must adhere to particular standards to meet regulatory requirements for safety, sanitation, or other concerns.

While there are too many standard organizations and potential regulations to cover in detail, common general standard organizations include:

• CSA Group (CSA)
• The American Society of Mechanical Engineers (ASME)
• The American National Standards Institute (ANSI)
• The American Society for Testing Materials International (ASTM International)
• The Manufacturers Standardization Society (MSS)
• The International Organization for Standardization (ISO)
• The Public Health and Safety Organization (NSF)
• NACE International (NACE)
• The American Petroleum Institute (API)
• American Water Works Association (AWWA)

There are also industry-specific standards to consider.

Major standards organizations by industry include:

• ASHRAE Valve Standards
• ASME BPVC Valve Standards
• ASSE Valve Standards
• ISA Valve Standards
• NFPA Valve Standards
• SAE Valve Standards

Final Thoughts

Choosing the right valve for your project might seem complex. However, by starting with general characteristics -- such as valve design, valve size and actuation method -- you can quickly limit your options to determine the best valves for your needs.

Whether you’re designing a new processing system or looking to make upgrades to or maintain an existing system, Unified Alloys’ selection of valves and fittings can help you find the ideal solution for your application and usage environment. As a leading provider of stainless steel alloys, valves, flanges, and more, our experts have helped industries across Canada and North America for more than 4 decades. Need assistance or have a question? Contact us for personalized help.

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