What is the difference between oil seal and O ring?

by：DMS Seals

    

2023-04-28

When it comes to industrial machinery, there are countless small components that keep the larger systems running smoothly. Two of these essential parts are oil seals and O rings. While they may seem similar at first glance, they serve different functions and have unique properties that make them suitable for specific applications. In this blog post, we'll explore the difference between oil seals and O rings, including when to use each one. Whether you're a seasoned mechanic or just starting out in the industry, understanding these two critical components is essential for maintaining efficient machinery operations!

What is an oil seal?

An oil seal, also known as a shaft seal or grease seal, is a mechanical device that prevents the leakage of lubricants and fluids from machinery components. These seals are typically made from rubber or other elastomeric materials, including silicone and Viton庐. The design of an oil seal consists of two primary parts: the sealing lip and the metal casing. The sealing lip is responsible for creating a tight barrier between moving machine parts while allowing necessary movement to occur.

One example of where you would find an oil seal in action is in automotive engines. Oil seals play a critical role in keeping motor oils within their intended compartments and preventing contamination by outside elements such as dirt and debris. In addition to cars, these seals can be found anywhere that rotating equipment meets stationary parts - such as industrial pumps or hydraulic cylinders.

Oil seals come in various sizes to fit different types of machinery components accurately. Choosing the right size and type for specific applications ensures optimal performance and longevity for your equipment.

What is an O ring?

An O ring, also known as a rubber seal or toric joint, is a mechanical gasket in the shape of a loop. It's commonly used to prevent leaks between two connecting parts by sealing them tightly together.

The name 'O ring' comes from its circular shape that resembles the letter O. They're usually made from rubber or elastomers and come in different sizes depending on their application.

O rings are versatile and can be found in many industries like automotive, aerospace, plumbing, pharmaceuticals, and more. They can be used to seal liquids, gases or even vacuum applications.

One of the benefits of using an O ring is its simplicity compared to other seals. Its design allows it to create a tight seal with minimal force applied which reduces friction and wear on components over time.

O rings play an essential role in many industries where preventing leaks is critical for safety and efficiency purposes.

The difference between oil seals and O rings

Oil seals and O rings are two different types of sealing components commonly used in various industrial applications. While both serve the purpose of preventing leaks, there are some significant differences between them.

Oil seals, also known as shaft seals, are designed to prevent oil or other fluids from leaking out of a rotating shaft. They consist of a metal casing with a rubber lip that makes contact with the shaft surface. Oil seals usually require some form of lubrication to function efficiently.

On the other hand, O rings are circular elastomers typically made from rubber or silicone materials. They're often used in static sealing applications such as pipe connections or hydraulic systems. Unlike oil seals, they don't require any lubrication since their design allows them to create an effective seal without rubbing against moving parts.

One key difference between these two sealing components is their application range; oil seals have higher pressure resistance compared to O rings which make them ideal for high-pressure environments like engine parts while O-rings work well for lower-pressure assemblies like valves and pipes.

Understanding the differences between these two types of sealing components can help you choose the right one for your specific application needs based on factors such as pressure requirements and potential wear and tear issues over time.

When to use an oil seal or an O ring

When it comes to choosing between an oil seal and an O ring, there are a few factors to consider. Firstly, the size of the gap that needs sealing is important. If the gap is small, then an O ring may be more suitable as it can fit into tight spaces easily. Oil seals are typically used for larger gaps and provide better protection against leaks.

Another factor to consider is the type of fluid or material that needs sealing. Oil seals are designed specifically for use with oils and lubricants, while O rings can work with a wider range of fluids including water and gas.

Temperature also plays a role in determining which type of seal to use. Generally speaking, oil seals are better suited for high-temperature applications while O rings perform well at lower temperatures.

Cost is another consideration when deciding between these two types of seals. O rings tend to be less expensive than oil seals but may not offer the same level of protection against leakage.

Ultimately, whether you choose an oil seal or an O ring will depend on your specific application requirements and budget constraints.

Conclusion

Oil seals and O rings are both important components in preventing leaks and ensuring the efficiency of machines. While they may seem similar in terms of their function, there are clear differences between the two.

Oil seals offer more comprehensive protection against leaks due to their design and materials used. They can also withstand higher pressure and temperatures compared to O rings. On the other hand, O rings are more versatile and can be used in a wider variety of applications.

When deciding whether to use an oil seal or an O ring, it is important to consider factors such as operating conditions, material compatibility, and cost-effectiveness. Consulting with a trusted supplier or engineer can help ensure that you choose the right sealing solution for your specific needs.

In summary, understanding the differences between oil seals and O rings is crucial for selecting the appropriate sealing component for any given application. By taking these factors into account during product selection process, you can optimize machine performance while minimizing maintenance costs in the long run.

Rotating shaft seals can be found in virtually every facet of daily lives—household appliances, cars and trucks and across industries. Though often treated as a commodity product, their failure can result in costly downtime and lost productivity. Despite their use in countless applications, many still have basic questions about how to use them. Here are some frequently asked questions.

1. What is a retainer plate (cover plate), and why is it required with an all-rubber split seal?

A cover plate is a piece of metal (or other hard material) installed after the oil seal has been placed into the housing bore. The cover plate pushes on the back side of the oil seal and compresses it into the housing. All-rubber split seals require cover plates because this style does not have an outer reinforcement to help retain the seal, so it needs compression inside the housing to ensure the best possible sealing capability.

2. Which direction should the lip face when installing my oil seal?

A single lip seal is unidirectional and will only seal in one direction. The primary sealing lip should always be facing or pointing toward the media that needs to be sealed. The media being sealed is usually a grease or oil lubrication, but it could also be a chemical media that needs to stay inside of a tank. If the seal is to function as an excluder and keep out contamination, the seal should face out towards the contaminant, which could be dirt and dust or chemical washdown. Sometimes seals will either have a secondary lip or dual opposed lips to keep dirt or contamination away from the bearing system and/or the media being sealed.

3. Which rubber material should I select for my oil seal?

Proper material selection is essential for good sealing performance. One of the factors that drives elastomer selection is the application temperature. A common rubber used in many sealing applications with mild operating conditions is nitrile (NBR), which is generally rated for use up to 200 F (continuous). Nitriles offer low cost and good wear resistance but will harden and/or crack if used at elevated application temperatures. At temperatures higher than 200 F, some choose carboxylated or hydrogenated nitrile (HNBR), which are generally rated for use up to 300 F (continuous). Another type of elastomer used at higher temperatures would be a fluoroelastomer (FKM), rated for use up to 400 F (continuous). However, in exchange for the higher temperature capability, the cost of these materials will be higher than the standard nitrile.

Aside from temperature considerations, some applications contain chemical media that might require a more compatible material like fluoroelastomer (FKM) or even polytetrafluoroethylene (PTFE), which can be impervious to many chemicals. It is important to note that PTFE lip material is closer to a plastic than an elastomer and will have different application considerations.

4. Which lip seal material(s) should I use if my application requires FDA compliance?

The food and beverage industry often requires FDA compliant seals. This means that the lip and case materials must meet FDA standards for sanitation. Some available lip materials that are FDA compliant include FDA Silicone, FDA Viton and some PTFE formulations, to name a few. If the seal has a metal case, FDA compliance requires the use of 316SS. Additionally, much of the equipment in food and beverage applications needs cleaning or steaming when in use. The seals must withstand the cleaning chemicals and the high temperatures associated with these processes.

5. Which lip seal material or design might be recommended for an application with harsh chemicals?

Depending on the application, some applications exposed to chemical media might require a PTFE lip seal, which will be compatible with the widest range of chemicals. In addition, some PTFE lip seal designs can withstand high pressures and dry running conditions that standard elastomer seals cannot. PTFE seals can be found both with and without a metal case, and can be installed in the same groove as a traditional oil seal.

6. Should I select a seal with a metal case or rubber outer diameter (OD)?

Seals with a metal case generally have the most OD interference, or ability to remain inside the housing. The trade-off for this extremely tight fit is that housing damage might occur when a metal case seal is installed. Some users prefer a rubber OD seal because it will not scratch or damage the housing during the installation process. Changing to a rubber OD seal might also do a better job statically sealing previous housing damage caused by a metal-cased seal. Another consideration is that standard steel metal cases might oxidize or rust over time. This would not be a concern with an all-rubber or metal-encapsulated rubber OD seal.

7. I have removed my leaking oil seal from the equipment. How do I know what size oil seal I need?

When replacing a failed oil seal, do not measure the used seal, as it will give erroneous measurements. Along with the fact that different manufacturers use different design interferences, used and worn-down oil seals often suffer damage during removal. Manufacturers design oil seals to fit the user’s equipment, so all a user needs to do is provide the seal manufacturer with the equipment’s shaft diameter, bore diameter and bore depth. Also, check
the markings on the seal, as some oil seals display the equipment dimensions that it requires.

8. How are oil seals measured?

Under most circumstances, users will not need to measure the oil seal. To size the seal correctly, users only need to know the shaft diameter, bore diameter and bore depth of the equipment.

Users might need to measure the seal, though, if they are trying to verify its manufactured size. The most important dimensions on an oil seal are the inside diameter (ID), outside diameter (OD) and width (height). The ID of the seal is not measured directly, as it is difficult to do without stretching or altering the lip. The OD of the seal measures most accurately with a special piece of equipment called a pi tape. The pi tape can consider any out-of-round condition with the seal that a pair of calipers might not. The seal’s width (or height) measures best with a pair of calipers, taking a few measurements around the whole diameter.

9. Does oil seal thickness matter?

As long as the seal correctly fits the shaft and the bore diameters, there is not any sealing advantage to different seal widths. If the seal is larger in width than the actual bore depth, the only potential issue might be interference with the surrounding equipment. Conversely, if the seal width is smaller than the actual bore depth, this is usually not a problem unless the seal is an all-rubber style being compressed by a retainer or cover plate. In this case, the best practice is to take up the extra space inside the bore housing with gasket spacers to ensure correct compression on the seal by the cover plate.

10. What is the purpose of the spring used in oil seals?

The spring provides loading around the sealing circumference and keeps the sealing lip tight against the shaft surface. Some seal designs use a garter spring design, which applies pressure everywhere around the shaft. Other seal styles employ a finger spring design, which provides an independent finger action only in areas where needed. Spring dumping can happen to garter springs, as they typically rest inside a molded groove disconnected from the sealing lip. If the spring dislodges during installation, for example, it can enter the equipment at startup, often causing serious damage to expensive bearings and other equipment. Finger spring designs, however, are usually either molded in or mechanically connected to the seal so the spring will not fall off or damage the equipment.

11. How long does an oil seal last?

Seal life is difficult to determine on equipment in the field because operating conditions are unknown, and they vary considerably. Furthermore, the applications are usually not ideal (defined as clean lab-type environments, fully lubricated, low speed, ambient temps, no pressure, no misalignment or runout, no exposure to chemicals or solids, correctly sized components, etc.), and the reality is that these factors change seal life considerably.    

12. I replaced my oil seal and found the shaft grooved underneath the lip. What causes this, and what should I do?

When grooving occurs at the shaft, this is typically a result of shaft hardness and/or finish not meeting industrial recommendations of a minimum 30 Rockwell C and 10 to 20 microinches Ra. The lip materials themselves will not cause shaft grooving, however, if there is dirt or contamination in the application. It might be possible for some particles to stick underneath the lip and groove of the shaft if it is too soft. It is not recommended to install a new oil seal over shaft grooving, as this could likely result in leakage. Cover any shaft grooving with a shaft sleeve, or offset the new sealing lip to contact a surface free of grooves or scratches.

13. Should I glue the ends of my split seal back together during installation?

If the split seal needs a garter spring, there will generally be a hook or screw attachment that will pull the two split ends together. Some other split seal designs, with a finger spring, hold tightly together by the interference (or press fit) between the OD of the seal and the machined bore housing. In either case, it is generally not recommended to glue the split ends of the seals back together, as it is difficult to get the lip alignment correct. Also, the chemical compatibility of the adhesives and lip elastomer requires testing.