U-seal vs o-ring

[lennypl]

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?

 

[Corn]

I´d go with u-seal. It has lower friction than o-ring. Then ptfe coated bushing for lowest friction. Then you´d also need wiper seal to keep dirt out.

 

[Peter from Holland]

There is also side load on the piston then Make sure it has a significant guide as well
A standard cilinder design is not suited for any sideload and fail with that in short order
How much pressure are you estimating?

 

[lennypl]

@Corn
Thank you for your advice.
This unit is inside of fork leg, it should be clean enough to survive till "next service job".

@Peter from Holland
Lets assume 200PSI ~ 14bar.

 

[Rickyb]

O rings are commonly used every where but they are static pressure seals NOT cylinder glands. Sliding contact is not in their job description.

 

[BoxcarPete]

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.

 

[Cole2534]

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.

 

[lennypl]

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.

 

[Peter from Holland]

Look into quad rings also as a alternative

 

[Cole2534]

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.

 

[BoxcarPete]

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.

 

[mmurray70]

(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.

 

[4GSR]

I prefer to use *nerfed SPAM link* as they are a lot more reliable.

At 100 times the cost of Nitrile O-Rings!!! Plus you have to add backup rings to keep the material from extruding out of gland running clearance.

 

[Peter from Holland]

At 100 times the cost of Nitrile O-Rings!!! Plus you have to add backup rings to keep the material from extruding out of gland running clearance.

You reacted on spam probably

Peter

 

[4GSR]

You reacted on spam probably

Peter

Yes I did. Mr. E removed his post after I posted.

 

[eKretz]

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?

 

[mattthemuppet]

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.

 

[4GSR]

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

 

[mattthemuppet]

could well be Ken, I just copied what was already there My guess was that one was an oil seal and the other was a crud seal. Either way, after the rebuild I still had damping years later which was a great improvement for a shock with an air spring

 

[4GSR]

Matt,
I told you wrong. I was thinking of a Bi-directional sealing like on the piston in a double actuated cylinder. What you described is correct. My wrong.