Powered by Outside

Dropper cartridge O-rings , what materials?Nitrile?FKM?Other?

PB Forum :: Mechanics' Lounge
Dropper cartridge O-rings , what materials?Nitrile?FKM?Other?

 Post Message | Latest Comment
Author Message
flag miguelcurto
Posted: Sep 21, 2022 at 10:44 Quote
Hi,

I'm in the process or trying to salvage a btoken Oneup dropper cartridge following tthis

Although I still haven't opened it, the author (which I assume has good knowledge of this) says there's usually two parts responsible for the malfunction: a o-ring and a spring . I've assumed it s probably the o-ring because it compresses without being actuated and doesn't retain position as well.

photo

My real question is: from other thread in Singletrack forums I'm guessing most forks and droppers o-rings are probably Nitrile and I'm wondering if there's a better rubber material for those, not even remotely familiar with the subject but IF its a common issue the o-ring in question breaking, is there a more suited compound?

Sourcing the o-ring from here https://www.o-ring-stocks.eu/

I can see several compounds that are more expensive than Nitrile and some are described to cope better with mechanical stress:

photo

photo

Any one with the know-how wanna give advice, plz?

Also: If you happen to know an european site to look for the spring (5mm OD - 9mm long) plz let me know.

Tks
flag BenLow2019
Posted: Sep 21, 2022 at 12:07 Quote
A quick search of "best o-ring for hydraulic oil" showed that Flurocarbon (Viton) o-rings may be suited for the harshest chemicals and temperatures and might be the best bet for you. Looking at the chart you provided that would cross to the FKM-FPM o-ring.

Good luck.
flag miguelcurto
Posted: Sep 21, 2022 at 15:20 Quote
BenLow2019 wrote:
A quick search of "best o-ring for hydraulic oil" showed that Flurocarbon (Viton) o-rings may be suited for the harshest chemicals and temperatures and might be the best bet for you..

Tks, but that's not what i want to know, wich one has better mechanical resistance? Not exactly clear by what I've look around, could be HNBR (Automotive Grade Nitrile?) but isn't available in this size on the sources I looked around.


I dismounted both ends of the cartridge (quick and easy) and after that the top of the actuator valve.A quick look seems to pinpoint the culprit, exactly the same that's supposedly known to break, spring is fine.

photo

That o ring slides up and down on a small shaft, and looks like it's not "strong enough".
flag M0rd4c4i
Posted: Sep 22, 2022 at 6:57 Quote
Whatever you try, try using a higher shore hardness o ring. That should put up with more stresses.
flag miguelcurto
Posted: Sep 23, 2022 at 0:52 Quote
M0rd4c4i wrote:
Whatever you try, try using a higher shore hardness o ring. That should put up with more stresses.

I'm having a crash course on O Rings, this is all new to me, do you happen to know if are there any disadvantages in using a harder compound like 90A?

I could be talking rubbish but if Viton is supposedly a better compound and by the looks of it usually a different colour (non-black) one has to wonder why isn't more commonly used for critical parts in forks and droppers like cartridges.
flag kemo-725
Posted: Sep 23, 2022 at 1:02 Quote
Viton would not offer a performance advantage on these applications, Viton s main advantage is in chemical compatibility
which is not an issue on forks and seat posts, just make sure you are not buying cheap O rings from poor suppliers ,
flag miguelcurto
Posted: Sep 23, 2022 at 3:50 Quote
That's about what I was thinking, been at a specialized store this morning, ended up buying Nitrile (NBR) 90 O-rings per recommendation of shop employee, they also had Viton (FPM) 80 and he said the NBR 90 ones would be more resistant.
The advantage of Viton is being more chemical and temperature resistant.

Still, looked around some more a while ago and found a NZ store that seems to know this stuff and state the PolyUrethane ones are tougher,
But could be they are refering to this ones being 90 Shore vs NBR 70:
photo



https://www.marcorubber.com/Buna-N-vs-Polyurethane/material-type/14v19

bigquotesAdditionally, Buna-N has a significant advantage when considering wear resistance. Also, Buna-N has a significant advantage when comparing heat stability. Furthermore, Polyurethane has a slight advantage when comparing short term resilience

photo

My take from this is Nitrile 90 should be the one to go for (maybe with the exception for Polyurethane O-rings but can't source those locally) as they all seem to have about the same Wear Resistence and what I'm fitting as replacements. Would be nice to know if that's what most brands spec.
flag M0rd4c4i
Posted: Sep 23, 2022 at 12:04 Quote
Fluropolymers such as FKM and FFKM have different chemical tolerance and better mechanical resilience, but I think one of the main reason they're not used where it's possible is that they're more expensive.

And shore hardness of 90 isn't a problem really, may be a little more difficult to install that's all.
flag miguelcurto
Posted: Sep 26, 2022 at 6:57 Quote
In this particular case the faulty o-ring isn't fitted anywhere, it just goes inside the shaft that controls the valve, its really a very tiny one.There's a metal washer on top of it that when the actuator gets depressed backs into that o-ring.

photo

I did replace it with a 90A Nitrile, filled with Rockshox 5w oil following the instructables (link at the start) and dropper is working now,altought noticeable slower,will change to 2.5w ASAP, needs further testing to see if it holds.
But the author says its a common issue and one has to wonder just how many of this dropper faulty cartridges could be avoided with a tougher (?) o-ring like PolyUrethan.

This article has good quality photos on that valve (but doesn't show the o-ring):

Found this one from Peter Verdone as well, curious it was exactly the same o-ring at fault.
flag ka81
Posted: Oct 1, 2022 at 13:42 Quote
In 99% it's NBR70.
flag miguelcurto
Posted: Oct 2, 2022 at 5:56 Quote
ka81 wrote:
In 99% it's NBR70.

That would be my guess, one was to wonder: don't know about other brands but every single OneUp dropper failed cartridge I've read about that decided to inspect it is either the valve oring or the spring, how many RMAs/warranty returns could be avoided by specing a tougher oring/spring?

Kudos on them to actually make them serviceable, altought not advertised it's pretty easy and straightforward to fix them.
flag cxfahrer
Posted: Nov 1, 2022 at 23:40 Quote
I used the 4.9*1.78 in NBR70 and until now it works. Thinner (e. g. 1.5) O-rings did not work longer than 10 times up and down, and then got sucked in.
In my TranzX post it does not fit really well, sometimes the post comes back up. It is the same construction, but every measure is a little bit different, e. g. the IFP uses O-rings instead of X-rings.

I guess there must have been a lot of trial and error testing when TranzX developed that cartridge many years ago. Would be interesting to find out.
  • Previous Page
  • Next Page

 


Copyright © 2000 - 2026. Pinkbike.com. All rights reserved.
dv65 0.008172
Mobile Version of Website