I'd like to try making new sealing head unit for mtb fork damper (OEM version has a lot of friction). Hobby lathe project.
Can someone help me with desingning choices?
Let me start and give some background:
- working fluid: hydraulic oil
- 10mm alu anodized shaft
- 2-4 m/s max speed or so (80-160 inch/s), longitudinal movement, zero rotation
- total 100% leak free is not needed
- significant side load, hard to estimate in numbers
- shaft will be backed up with bushing
- lowest friction is the key point
Now questions:
1. Should I go with o-ring or u-seal?
2. Is delrin ok for bushing? Is there an andvantage with maximum possible length of the bushing?
O rings are commonly used every where but they are static pressure seals NOT cylinder glands. Sliding contact is not in their job description.
Who ever told you that? O-Rings are used dynamically in applications all over the place. 200 psi isn't all that high, an o-ring with a wear band would work just fine.
You might want to consider a polyseal, but there's no reason an o-ring wouldn't do everything you need it to. With that kind of pressure, you aren't getting all that much fluid pressure activation on the seal, which is where the u-cup really shines compared to an o-ring. Delrin would be a somewhat low friction guide bushing or wear band, and they generally do alright. GF nylon is the traditional choice and would be stronger but more abrasive, teflon would be weaker but slicker.
Let me know if you want any more detailed advice, but I'd recommend grabbing a copy of the Parker book if you haven't designed an o-ring groove before. It's an excellent resource.
Let me know if you want any more detailed advice, but I'd recommend grabbing a copy of the Parker book if you haven't designed an o-ring groove before. It's an excellent resource.
Agreed! They sent me 2 hardcopies for free a few years back, just emailed them requesting one. Of course, the pdf is available online as well.
Side question- what's the limitation for the axial shaft speed of a hydraulic cylinder with urethane cup seals? I can't find a clear answer.
This is how it looks like now. Sorry for my insane drawing skills, drawing not to scale etc...
And here's how I'd like to make it. Due to other reasons making everything shorter is also needed (I transplant this damper to some other fork, whole another story). Due to lack of real estate I'd like to go with oring. U seal that I have right now is useless, massive drag. That is why I asked.
@BoxcarPete
As for designing oring groove - this is not a problem, I already went through all parker, trelleborg ans skf pages. But thank you for offer anyway.
For me most problematic is that it is hard to find comparsion of many seals in terms of friction. Moreover - I wonder why no one uses PTFE energized by oring type of seals (like those) at least no one in bicycle industry. It looks like perfect solution.
Moreover - I wonder why no one uses PTFE energized by oring type of seals (like those) at least no one in bicycle industry. It looks like perfect solution.
Most times Ive run across that question the answer has been cost. One of the times where 20% of the effort yields 80% of the result and that is sufficient.
Most times Ive run across that question the answer has been cost. One of the times where 20% of the effort yields 80% of the result and that is sufficient.
There's also space to consider. Those seals are tall in the radial direction, which might drive yet more cost into the assembly if it forces other components to upsize.
(OEM version has a lot of friction).
My advice... dont worry about a little friction. The purpose of a damper is to slow motion. Little bit of friction will never hurt.
When suspension manufacturers brag about the lowest possible friction, special materials/coatings etc etc... its all marketing bullshit. People buy it up, but it will never make a noticeable difference in the real world.
Yes I did. Mr. E removed his post after I posted.
Actually I think plastik got him first but he didn't spam clean, just banned, which left the link behind. I just did a little cleaning up afterwards...
Anyway, Lenny did you ever try one approach or the other?
I'm curious too. I rebuilt a Cannondale headshock damper a while back (new piston shaft and top cap) and the top cap had two single lip wiper seals pointing away from each other. That was a sealed unit though, no idea what the OP's is, could be open bath for all we know.
I'm curious too. I rebuilt a Cannondale headshock damper a while back (new piston shaft and top cap) and the top cap had two single lip wiper seals pointing away from each other. That was a sealed unit though, no idea what the OP's is, could be open bath for all we know.
Matt,
In my world that is done to prevent fluid lock between the seals. Ken
Introduction
O-Rings are indispensable sealing components widely used in industrial and everyday applications, such as machinery, pipeline systems, automobiles, and electronic devices. Their primary function is to effectively prevent fluid or gas leakage, ensuring stable operation of equipment. However, the process of selecting the right O-Ring is complex, requiring consideration of multiple factors, including material, size, working environment, and pressure conditions. Improper selection can shorten equipment lifespan and result in production downtime and increased costs. This article provides 9 professional tips to help you select the right O-Ring, improve sealing performance, and reduce the risk of failure.
Langnuo Mining Equipment Product Page
1. Identify Application Scenarios and Working Conditions
1.1 Differences Between Static and Dynamic Sealing
It is essential to distinguish the type of O-Ring application:
- Static Sealing: Used in stationary components, such as flanges and valves, where the O-Ring remains static. These applications require higher dimensional stability and compression resistance.
- Dynamic Sealing: Applied in components that experience frequent motion, such as pistons and pump shafts. These applications demand materials with wear resistance and low friction coefficients to endure movement and minimize damage.
1.2 Determine Working Conditions
Consider the following working conditions:
- Temperature Range: High or low temperatures directly impact the elasticity and durability of the O-Ring.
- Pressure Levels: Static and dynamic sealing have different pressure requirements, particularly in high-pressure environments where materials with superior pressure resistance are needed.
- Chemical Media: Verify whether the O-Ring will be exposed to acids, alkalis, or oils, as these substances can corrode or degrade incompatible materials.
- Special Requirements: For outdoor applications, factors like ozone and UV resistance must be considered.
2. Material Selection: Adapting to Different Media
2.1 Analysis of Common Materials
Various materials are suitable for different working environments:
- NBR: Excellent oil resistance; ideal for hydraulic and lubricating oil applications.
- EPDM: Resistant to high temperatures and ozone; suitable for outdoor and steam environments.
- FKM: Outstanding resistance to high temperatures and chemical corrosion; commonly used in chemical industries.
- PTFE: Best suited for extreme chemical environments, with excellent resistance to acids and alkalis.
- Silicone/VMQ/PVMQ : Exceptional high and low-temperature resistance, non-toxic, odorless, and highly durable against aging. Widely used in food, medical, and electronics industries, especially in environments requiring high cleanliness.
2.2 Material Application Recommendations
- Hydraulic Systems: NBR or HNBR is recommended.
- Food Industry: Use FDA-compliant Silicone or EPDM materials.
- Chemical Environments: Choose FKM or PTFE for excellent chemical resistance.
2.3 Avoiding Mismatched Materials
Using mismatched materials may result in:
- Premature Aging: High temperatures or UV exposure can accelerate hardening and reduce elasticity.
- Dissolution or Swelling: Incompatible chemical media can cause O-Rings to swell or dissolve, affecting sealing performance.
3. Accurate Sizing and Tolerance Matching
3.1 Measurement Methods
Precisely measure three key dimensions of the O-Ring:
- Inner and Outer Diameter: Use measuring tools for accurate results.
- Cross-Section Diameter: Ensure uniformity to avoid uneven sealing and potential leakage.
3.2 Size and Groove Compatibility
The O-Ring's size must match the groove dimensions, with a recommended compression ratio of 10%-30% to maintain proper sealing performance.
3.3 Importance of Tolerance
Tolerance control is critical:
- Excessive Tolerance(out of up limit): Can make installation challenging and may lead to deformation or damage.
- Insufficient Tolerance(out of low limit): Can cause loose sealing and leakage.
4. Temperature Range and Heat Resistance
4.1 High-Temperature Environments
For high temperatures up to 200°C, FKM or Silicone is recommended for reliable performance.
4.2 Low-Temperature Environments
NBR or Silicone performs well in low temperatures, withstanding conditions as low as -50°C. For even lower temperatures, contact our team for customized solutions.
4.3 Effects of Temperature Fluctuations
Frequent temperature changes can accelerate hardening and cracking, leading to sealing failure.
5. Pressure Conditions and Compression Performance
5.1 Pressure Requirements for Static Sealing
Static sealing demands O-Rings with high resistance to compression deformation to maintain long-term effectiveness.
5.2 Pressure Requirements for Dynamic Sealing
For dynamic applications, materials with low friction and high wear resistance are necessary to extend service life.
5.3 Recommendations for High-Pressure Environments
Use HNBR or FKM in high-pressure scenarios to ensure that the O-Ring resists deformation and rupture.
6. Chemical Resistance and Media Compatibility
6.1 Effects of Chemical Corrosion
For applications involving strong acids, alkalis, or organic solvents, PTFE or FKM should be used to prevent corrosion.
For more information, please visit Hydraulic O Ring Seals.
6.2 Special Requirements for Food and Medical Industries
FDA-compliant Silicone or EPDM materials are essential for ensuring safety and hygiene in food and medical applications.
6.3 Avoiding Chemical Reactions
Mismatched materials may cause chemical reactions, such as swelling, cracking, or failure, compromising the seal.
7. Wear Resistance
7.1 Wear Resistance in Dynamic Applications
For high-speed or reciprocating motion, choose materials with excellent wear resistance to enhance durability.
7.2 Impact of Friction Coefficient
Using internal lubrication formulas effectively reduces friction, extending the O-Ring's lifespan.
7.3 Regular Wear Inspection
Inspect O-Rings periodically for wear and replace them promptly to prevent leaks.
8. Proper Installation Methods
8.1 Preventing Damage During Installation
Use professional tools to avoid cutting or tearing the O-Ring during installation.
8.2 Importance of Lubrication
Applying lubricants during installation reduces friction and minimizes the risk of damage.
8.3 Ensuring Correct Installation
Verify that the O-Ring is fully seated in the groove without deformation or twisting.
9. Maintenance and Inspection Recommendations
9.1 Regular Inspection and Replacement
Check the O-Ring regularly for aging or wear and replace it based on usage frequency.
9.2 Storage Environment
Store O-Rings in a cool, dry place away from direct sunlight, high temperatures, and moisture to prevent material degradation.
9.3 Addressing Issues Promptly
Replace damaged or leaking O-Rings immediately and ensure correct installation.
Conclusion
Selecting the right O-Ring is critical to achieving effective sealing. It requires careful consideration of factors such as material, size, temperature, pressure, and chemical environment. By following these 9 professional tips, you can choose the ideal O-Ring, enhance sealing performance, and extend equipment lifespan. Whether for static or dynamic applications, proper selection and regular maintenance significantly reduce the risk of sealing failure and ensure stable equipment operation.
For more Cable Hanger Hookinformation, please contact us. We will provide professional answers.