Month: July 2024

Here are 5 Essential Steps to Installing an O-Ring

Step 1: Choose the Right O-Ring

The initial step in O-ring installation involves ensuring that you have the right ring for the job. O-rings are available in a diverse array of sizes, materials, and hardness, with each type tailored to a specific application. Whether you require standard O-rings, miniature O-rings, or custom O-rings, here’s the essential information to consider when selecting the most suitable fit:

• Size: Using the right O-ring size for each assembly is critical. If it’s too small, the O-ring could tear or break. Alternatively, if an O-ring is too large, it won’t provide adequate sealing, making it essential to find the just-right-sized option for your application. O-ring sizing is often measured by its inner diameter (ID), outer diameter (OD), and cross-sectional diameter (CS). 
• Material: Each O-ring material has different properties that make it better suited for certain conditions, such as the temperature, fluid compatibility, and other conditions the seal will encounter. A few of the most common compounds include nitrile (buna n), ethylene propylene (EPDM), fluoroelastomer (FKM, Viton®), Neoprene®, silicone, perfluoroelastomer (FFKM), polyurethane, and aflas.
• Hardness: The hardness of the O-ring is another factor to consider when choosing the right fit for your application. Hardness represents resistance to compression and abrasion and is measured in durometer units. Most O-rings can be molded in a wide range of compounds in hardnesses from 40 to 95 Shore A.

Step 2: Clean the O-Ring and Surfaces

• After selecting the appropriate O-ring based on its size, material, and hardness, it becomes crucial to clean both the O-ring and the surfaces between which it will be installed. Any dirt, dust, or other contaminants can potentially lead to O-ring leaks or failure. A comprehensive cleaning process, typically involving a clean cloth and a basic solution of soap and water, is often adequate. However, depending on the specific conditions, you may find it necessary to utilize a more specialized cleaning solution.

Step 3: Lubricate the O-Ring

In most cases, you must apply lubricant before installing the O-ring. Lubricating the O-ring facilitates easier installation and reduces the risk of elastomer damage from tearing, twisting, pinching, cutting, and abrasions. Applying a thin film of lubrication to fill any gaps or spaces between the O-ring and the mated part helps the ring slide smoothly. Additionally, lubricant decreases the surface tension between the surfaces, allowing for a tighter fit. It’s important to note that when install an O-ring on a standard female gland, lubricant should be applied after positioning the O-ring.

The choice of lubricant depends on factors such as material, system fluid compatibility, and service temperature. 

Step 4: Install the O-Ring

Now, let’s proceed with the O-ring installation. Start by placing the ring in the groove between the two surfaces, ensuring proper centering and alignment at both ends. Subsequently, carefully stretch the O-ring evenly over the surface, being mindful to avoid pulling from either side, twisting, or causing any damage. Exercise caution during stretching to prevent overstretching the O-ring beyond its maximum elongation, as this could result in breakage and tearing during assembly or use.

Once the O-ring is positioned, use a flat tool to press it into the groove until it is fully seated. If the installation is in a confined space, a tool with a smaller profile, such as a flat screwdriver, may be necessary to carefully position it. Instead of rolling, slide the O-ring down the shaft to prevent spiraling, thereby reducing the risk of leaks and contamination in the final assembly.

When dealing with O-rings paired with threaded parts, gently guide the O-rings over the threads to avoid tearing. To provide additional protection for the O-ring and threads, consider using lubricant and covering the threads with masking tape as a precautionary measure.

Step 5: Check the Installation

After installing the O-ring, make sure to seat it properly and check for leaks. For example, when installing an O-ring in a hydraulic system, run the system and inspect for leaks using UV dye. However, if you are installing an O-ring in another system, you might need to perform a different leak test.

O-Ring Installation Tips for Success

• Avoid forcing O-rings over sharp corners and jagged features. This can cause tiny tears that may not be visible but can compromise the seal’s performance.
• Follow ISMAT’s O-ring storage and cleaning recommendations to prevent damage and promote the best results.

O-rings can fail for various reasons, typically related to environmental conditions, material properties, installation issues, or operational stresses. Here are some common types of O-ring failures and their causes:

1. Compression Set

• Description: The O-ring becomes permanently deformed and fails to return to its original shape after being compressed. The cross-section of the O-ring becomes less circular and may take the shape of the groove/gland.
• Causes:
  • Excessive temperature exposure
  • Long-term static load
  • Improper material selection

2. Extrusion and Nibbling

• Description: Portions of the O-ring material are forced into the clearance gap between the mating surfaces, leading to nibbling or tearing. The edges of the O-ring will have a chipped or nibbled appearance. 
• Causes:
  • High pressure
  • Large clearance gaps
  • Inadequate material hardness

3. Abrasion

• Description: The surface of the O-ring wears away due to friction against mating surfaces. The sliding surface of the O-ring will have lacerations and a grazed finish.
• Causes:
  • Rough or poorly finished surfaces
  • Inadequate lubrication
  • Movement between the O-ring and sealing surfaces

4. Chemical Degradation

• Description: The O-ring material deteriorates due to exposure to incompatible chemicals. The O-ring may exhibit a number of blisters, cracks and discolouration due to chemical attack.
• Causes:
  • Contact with aggressive chemicals
  • Use of unsuitable O-ring material for the chemical environment

5. Thermal Degradation

• Description: The O-ring material degrades due to exposure to excessive heat or cold.
• Causes:
  • Operating beyond the temperature limits of the material
  • Inadequate heat dissipation

6. Explosive Decompression

• Description: Rapid decompression causes trapped gas within the O-ring to expand, leading to blistering or rupturing.
• Causes:
  • Rapid pressure changes
  • High-pressure gas environments

Explosive decompression (ED) is a specific failure mode for O-rings that occur when they are exposed to high-pressure gas environments followed by a rapid decrease in pressure. This can cause the gas absorbed or trapped within the O-ring material to rapidly expand, potentially leading to blistering, cracking, or rupturing of the O-ring. Here are details on this type of failure and how to mitigate it:

Mechanism of Explosive Decompression Failure

1. High-Pressure Gas Exposure: The O-ring is exposed to a high-pressure gas environment. Gases can permeate the O-ring material during this period.
2. Rapid Pressure Drop: When the external pressure is rapidly reduced, the gas trapped inside the O-ring attempts to escape quickly.
3. Internal Stresses: The rapid expansion of gas within the O-ring creates internal stresses that can lead to blistering, cracking, or rupture.

Symptoms of Explosive Decompression Failure

• Blistering: Visible blisters or bubbles on the surface of the O-ring.
• Cracking: Radial or circumferential cracks in the O-ring material.
• Rupturing: Complete breakage or tearing of the O-ring.
• Swelling: Noticeable swelling or deformation of the O-ring.

Causes

• Rapid Depressurization: The primary cause is a rapid decrease in external pressure.
• Material Permeability: Materials with high gas permeability are more susceptible to ED.
• High-Pressure Gas: Certain gasses, such as nitrogen or carbon dioxide, can exacerbate the problem.

Mitigation Strategies

1. Material Selection:
   1. Use ED-resistant materials. Fluorocarbon (FKM), Hydrogenated Nitrile Butadiene Rubber (HNBR), and perfluoroelastomers are known to have better resistance to explosive decompression.
2. Design Considerations:
   1. Minimize the rate of pressure drop if possible to allow the gas to escape gradually.
   2. Ensure proper groove design to avoid trapping gas.
3. Preconditioning:
   1. Precondition O-rings in the high-pressure environment before operation to reduce the amount of gas absorbed.
4. Surface Treatments:
   1. Apply surface treatments or coatings that reduce gas permeability.
5. Regular Inspection and Maintenance:
   1. Regularly inspect O-rings for signs of ED damage and replace them as needed.
6. Pressure Management:
   1. Implement controlled decompression procedures to reduce the risk of rapid pressure drops.

7. Installation Damage

• Description: The O-ring is damaged during installation, leading to cuts, nicks, or overstretching.
• Causes:
  • Improper installation techniques
  • Sharp edges or burrs in the groove or mating surfaces

8. Over compression

• Description: Excessive compression of the O-ring leads to flattening and material extrusion.
• Causes:
  • Incorrect groove design
  • Excessive tightening of mating surfaces

9. Weather and Ozone Cracking

• Description: The O-ring surface cracks due to exposure to ozone or ultraviolet (UV) light. The earliest signs of this type of O-ring failure begins with discolouration leading to subsequent cracking. 
• Causes:
  • Outdoor or high-ozone environments
  • Use of materials not resistant to ozone or UV light

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10. Swelling

• Description: The O-ring swells excessively, altering its dimensions and leading to seal failure. The O-ring may swell or increase from its original dimension consistently across the seal or in localized areas.
• Causes:
  • Absorption of fluids
  • Incompatible material with the sealing environment

11. Spiral Failure

• Description: The O-ring twists in its groove and develops spiral cuts or cracks. The O-ring will have a spiraling pattern around its exterior, with deep cuts at 45° angles where the highest stress levels are apparent.
• Causes:
  • Dynamic applications with reciprocating motion
  • Improper O-ring lubrication
  • Misalignment

If you are facing such O-ring failures, contact ISMAT to help find a solution for them. Our team of engineers will help you identify the right material to use with aggressive chemicals and harsh environments. They are also trained to study gland designs and suggest the accurate O-ring dimensions to use. You can also check out our O-ring Installation Guide that can help you in reducing O-ring failures. 

What is Sealing?

A seal is a device used to prevent the leakage of fluids or gasses between two surfaces. Seals are designed to create a barrier between two parts of a machine or system to prevent the escape of fluids or gasses, or to prevent the entry of contaminants into the system. 

Understanding the Types of Mechanical Soft Seals in Trunnion Mounted Ball Valves

Trunnion Mounted Ball Valves (TMBVs) are critical components in various industries like Oil & Gas and Pharmaceutics, due to their ability to control high-pressure and high-flow applications. These valves rely on a variety of soft seals to ensure optimal performance and leak prevention. In this blog, we will explore the different types of mechanical soft seals used in TMBVs, focusing on O-rings, backup rings, valve seats, seat rings and Valve Packings for static applications, and quad rings for dynamic applications. We will delve into their functions, the materials they are made from, and their specific roles within a TMBV.

1. O-Rings

Description

O-rings are circular elastomeric rings that create a seal at the interface of two or more parts. When installed, they deform under pressure to effectively seal gaps and mating components. After deflection, O-rings revert to their original shape, maintaining a sealed condition. They are one of the most common types of seals used in various mechanical applications, including TMBVs.

Reasons for Use

O-rings provide an effective and reliable seal with simple design requirements. They are versatile, cost-effective, and easy to install and maintain.

Materials

• Perfluoro elastomer: Excellent resistance to aggressive chemicals such as, hot organic and inorganic acids, caustics, amines especially hot amines >70°C, ketones, aldehydes, esters, ethers, alcohols, fuels, solvents, sour gases, hot water, steam, ethylene propylene oxide and mixed process streams.
• HNBR Rubber (HNBR): Excellent resistance to oils, vegetable oils, greases, glycol based coolants, hydrocarbon oils and sour gases.
• Fluorocarbon (Viton): Excellent resistance to chemicals, hydrocarbon oils, sour gases, steam and high temperature resistance upto 200°C.
• Aflas (FEPM): Good for water and steam applications.
• Fluorosilicone: Excellent resistance to heat, chemical degradation, high tensile and tear strength compared to silicone, excellent low temperature flexibility.

Application in TMBVs

O-rings can be used in both static and dynamic applications:

1. Static Seals: These do not move except for pulsation caused by cycle pressure. Examples include axial, radial, dovetail, and boss seals

• Axial: Squeezed axially in the groove like a flat gasket.
• Radial: Squeezed radially between the inside (ID) and outside (OD) of the groove.
• Dovetail: Retained in the face seal during assembly and maintenance.
• Bosstail: Used for sealing straight thread tube fittings in a boss.

1. Dynamic Seals: Sit inside a groove between rotating surfaces, providing a leak-tight seal.

In TMBVs, O-rings are commonly used in static applications to seal the valve body, ensuring that no fluid leaks between the valve components. They are placed in the grooves of the Seat Ring and are compressed to form a tight seal.

2. Backup Rings

Description

Backup rings are ring-shaped components made from rigid materials that support O-rings or other seals to prevent extrusion and deformation under high pressure. The two main types of Backup Rings are: 

• Scarf Cut Backup Ring
• Solid Backup Ring
• Spiral Backup Ring
• Contoured Rubber Backup Ring

Reasons for Use

Backup rings enhance the performance of O-rings by providing structural support, especially in high-pressure applications. They help maintain the integrity of the seal by preventing extrusion into the clearance gaps.

Materials

• Polytetrafluoroethylene (PTFE): High chemical resistance and low friction.
• Reinforced PTFE (RPTFE): Enhanced mechanical strength and wear resistance.
• Peek: High temperature and chemical resistance with excellent mechanical properties.
• Fluorocarbon (FKM) : High chemical and temperature resistance.

Application in TMBVs

Backup rings are used in conjunction with O-rings in static applications. They are typically placed on the low-pressure side of the O-ring, providing additional support to maintain a reliable seal.

3. Valve Seats

Description

The ball valve seats are critical surfaces responsible for sealing the fluid inside and uniformly distributing the seating stress. In soft seat ball valve designs, either an elastomer or polymer is used as the seal and is inserted into a metallic seat ring. Valve seats interface with the ball and are responsible for stopping the flow of fluid when the valve is closed.

Reasons for Use

Valve seats provide a primary sealing function within TMBVs, ensuring a tight shut-off and preventing fluid leakage. They must withstand the mechanical stress and wear associated with valve operation.

Materials

• PTFE: Offers excellent chemical resistance and low friction.
• Reinforced PTFE (RPTFE): Enhanced mechanical strength and wear resistance.
• Peek: High temperature and chemical resistance with excellent mechanical properties.

Application in TMBVs

Valve seats are located around the ball in the valve body. When the valve is closed, the ball compresses against the seats, creating a tight seal that stops the fluid flow.

4. Seat Rings

Description

The primary function of a ball valve seat ring is to provide a sealing surface against which the ball (the spherical closure element) can press to stop fluid flow. When the ball valve is in the closed position, the seat ring ensures that there is no leakage by creating a tight seal. In the open position, the seat ring ensures minimal resistance to fluid flow. This dual role is vital for the proper functioning of the valve, ensuring both effective shutoff and smooth operation.

Reasons for Use

It forms an essential part of the sealing mechanism that ensures the valve can shut off fluid flow effectively and maintain a tight seal under various operating conditions.

Materials

The choice of material for seat rings depends on the application requirements, including pressure, temperature, and the nature of the fluid being handled. Common materials include:

1. PTFE (Polytetrafluoroethylene): Known for its excellent chemical resistance, low friction, and high temperature tolerance, PTFE is a popular choice for seat rings in chemical and pharmaceutical industries.
2. Reinforced PTFE (RPTFE): This is PTFE combined with fillers like glass or carbon to enhance its mechanical strength and wear resistance. RPTFE is used in more demanding applications.
3. Peek (Polyether Ether Ketone): PEEK offers high temperature and chemical resistance with excellent mechanical properties, making it suitable for high-performance applications.
4. Elastomers (e.g., Nitrile Rubber, EPDM): For applications involving lower temperatures and pressures, elastomers provide good flexibility and sealing performance.
5. Metal: In some high-pressure or high-temperature applications, metal seat rings are used for their strength and durability. Metal seats can be overlaid with softer materials to improve sealing performance.

Application in TMBVs

In ball valves, seat rings are positioned in the valve body and form a seal with the ball. When selecting seat rings for a ball valve, several factors must be considered:

1. Fluid Compatibility: The material must be compatible with the fluid being handled to prevent degradation or chemical attack.
2. Temperature and Pressure: The seat ring material must withstand the operating temperature and pressure conditions without deforming or failing.
3. Mechanical Wear: Materials should have good wear resistance to ensure long service life, especially in applications involving frequent cycling.
4. Regulatory Requirements: In certain industries, seat ring materials must comply with regulatory standards, such as FDA regulations for food and pharmaceutical applications.

5. Quad Rings

Description

Quad rings, also known as X-rings, are four-lobed seals that provide a more stable seal compared to standard O-rings. They are designed to resist rolling or twisting in dynamic applications.

Reasons for Use

Quad rings offer improved sealing performance in dynamic applications due to their unique design, which provides multiple sealing surfaces and reduces friction. They also have better resistance to twisting and extrusion.

Materials

• Nitrile Rubber (NBR): Suitable for oil and fuel resistance.
• Fluorocarbon (Viton): High chemical and temperature resistance.
• EPDM: Suitable for water and steam applications.

Application in TMBVs

In TMBVs, quad rings are used in dynamic applications such as stem seals or shaft seals. They provide reliable sealing under the movement of the valve stem or shaft, ensuring no leakage during valve operation.

Conclusion

Trunnion Mounted Ball Valves rely on a variety of mechanical soft seals to ensure optimal performance and reliability. O-rings, backup rings, valve seats, seat rings, and quad rings each play crucial roles in maintaining a leak-free environment within the valve. The choice of materials for these seals depends on the specific application requirements, including pressure, temperature, and chemical exposure. By understanding the functions and applications of these soft seals, we can appreciate the complexity and precision involved in designing high-performance sealing solutions for TMBVs.