Pumping up rear shocks at home

[maico police]

Good 'ol Nathan. Spotted another conspiracy theory.
Ever felt your shock reservoirs after a decent ride or race? Feel that heat in there?? Hmmmm? 

I'm sure nitrogen won't be such an issue in the new air forks as they certainly won't be charged to the same level as a shock is.

I can't imagine a bike shop that doesn't have a bottle of nitrogen. Most people who are half serious about dirt bikes have one.

This suggestion is right up there with home made air filters, shocks that are the wrong length for your bike and cheap oil in your gear box.
Insane.......

[GMC]

Don’t know much about shocks but I do know that when welding an enclosed frame tube the air pressure buildup inside the tube is enough to push out through the weakest point which is the molten weld pool.
It doesn’t take a lot of welding to build the air pressure up to the point that it wants to push out through the molten metal.

[Nathan S]

Good 'ol Nathan. Spotted another conspiracy theory.
Ever felt your shock reservoirs after a decent ride or race? Feel that heat in there?? Hmmmm? 

I'm sure nitrogen won't be such an issue in the new air forks as they certainly won't be charged to the same level as a shock is.

I can't imagine a bike shop that doesn't have a bottle of nitrogen. Most people who are half serious about dirt bikes have one.

This suggestion is right up there with home made air filters, shocks that are the wrong length for your bike and cheap oil in your gear box.
Insane.......

Good old Ross. Spotted another opportunity to argue with Nathan.

The bit where you can feel the reservoir with your hand shows that it's not all that hot. so what's the increase in pressure from 20*C to, say, 80*C?
Then remember that the change you could possibly feel is the ratio of the reservoir diameter to shock shaft diameter - sod all, like I said before.

Here's another thought: Lots of MTB fork and shocks run on compressed air, usually from hand pumps. Do you ever hear of them having problems with changes in pressure or oxidisation?
How can this be?!

Nitrogen is the best. My point is that it is nothing like essential, and the arguments against using something else are mostly about mental (and emotional?) conditioning, not physics or engineering or even feel.

[Nathan S]

Could work. The squeaky Ross Nimmo voice you get from inhaling it would be a bonus too.

[3858]

Don't start talking about yourself in the third person Nathan or you won't be able to use my Nitrogen bottle anymore....

[Nathan S]

Nathan doesn't like that idea...
 

[Montynut]

Non-emulsion shocks keep the oil and the important innards seperate from the pressurised gas.
In a bladder reservoir shock, the gas is only in contact with a rubber bladder and the inside of the reservoir cap: the only thing to worry about is the CTE, which we've established is a non-issue.

Rubber contains natural oils (otherwise would it perish?). Oxygen is highly reactive with almost everything. Even to store industrial and electronic equipment such as generators, transformers, cables, motors etc etc etc air is displaced by nitrogen to stop all oxidation caused by oxygen content of the air. If you store almost any items in a sealed container some or all of the oxygen is consumed over time therefore there must be some form of reaction taking place. The heat cycling within a shock would assist any oxidation.

I think I'll still be getting shocks charged with nitrogen regardless of the expert theory outlined here.

Over to you Nathan for the LAST word

[vmx42]

Bugger, I was hoping to have the last...

[eric318]

Oh lord, what have I started... ??

Hey, I have a MIG welder with a bottle of mix CO2/Helium. May be I can use that to pump my shocks!

[Nathan S]

Come on Greg... Tell me how much oxidisation you'll get from the oxygen in a shock reservoir. Be lucky to be a litre in there (at atmospheric pressure...).

That seperator bladder you're worried about: If you left it sitting on a shelf, with no/minimal UV exposure, how many years would you expect it to last before it was oxidisation damaged it noticably? And that's with an essentially infinite supply of O2 doing its best to wreck it...

Nitrogen is the best choice, but the sky will not fall if you use air.

[Montynut]

Bugger, I was hoping to have the last...

Impossible if Nathan is involved check every thread better still try for the last word. You will not live long enough

[maico police]

Apart from the discussion about what damage the moisture from the air is going to do to seals, bladders etc, the preasure from the air building up would have to be placing a lot of pressure on your shaft seal (via the oil that the bladder is compressing) and surely playing havoc with the overall performance of the shock.

I'm waiting for the all-time pearler when you tell us that you're wasting your time adding oil to the fuel of a two-stroke.

It can't be far away.....

[JohnnyO]

Bugger, I was hoping to have the last...

Impossible if Nathan is involved check every thread better still try for the last word. You will not live long enough

Haha ain't that the truth!!

[Nathan S]

Apart from the discussion about what damage the moisture from the air is going to do to seals, bladders etc, the preasure from the air building up would have to be placing a lot of pressure on your shaft seal (via the oil that the bladder is compressing) and surely playing havoc with the overall performance of the shock.

I'm waiting for the all-time pearler when you tell us that you're wasting your time adding oil to the fuel of a two-stroke.

It can't be far away.....

Your trolling skills are beyond my ability to ignore ignorance.

I assume you finished high school, Mont?
I also assume you did some sort of science back then? Or were you too busy with your interpretative dance electives?
Now, using those high school science skills, explain to me about how "air builds up" in a shock reservoir. I've given you a big fat hint on how to work it out the pressure rise due to a change in temperature - if you try hard, I'll even tell you how much it will alter the effective spring rate (pro tip: sod-all).

You can keep taking digs at me if you want, but I've can back up what I'm saying with science and experience - not just vague 'gut feeling' and fear of the unknown...

[eric318]

If I remember well the first law of thermodynamics tells us PV=NrT.
So with only T changing say by a factor 4, P will also go up 4x.
Do I get this right?
But this regardless of the gas...