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Richard Treacy
Grand Master
Username: richard_treacy

Post Number: 2178
Registered: 4-2003
Posted on Sunday, 25 July, 2010 - 05:47 pm:   Edit PostDelete PostView Post/Check IP

In the Technical Library, you will now find a tutorial on material's qualities. See Page 202:

http://rrtechnical.info/miscellaneous/miscellaneoust.html

and select MT16.

Incidentally, the section MT01 O-Ring Compatibility Table has proven quite useful to many and is linked to the new tutorial page. I have even seen it pinned to the wall in several non-RR/B garages still sporting its RROC(A) origins. The tutorial is aimed to give a slightly more detailed insight as to why certain materials are most suited to our applications.

RT.
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Dave Puttock
Experienced User
Username: ariel

Post Number: 21
Registered: 5-2010
Posted on Friday, 12 August, 2011 - 09:51 pm:   Edit PostDelete PostView Post/Check IP

Richard, perhaps you can clear my confusion.
I keep two types of rubber sheet in my workshop. EPDM -I use for water & air, Nitrile -I use for oils.
So when I needed to make a new gasket for the petrol tank sender, I thought I'll just check compatability before I cut it out of Nitrile.
I went to the above reference and I was supprised to see that NBR scored a 4 (poor) for resistance to fuels and yet at the bottom the description of NBR suggests that it is popular because of its good resistance to oil and fuel.
So which is it ?
Same confusion arises with flexible fuel lines which I always thought were Nitrile
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Richard Treacy
Grand Master
Username: richard_treacy

Post Number: 2374
Registered: 4-2003
Posted on Friday, 12 August, 2011 - 11:02 pm:   Edit PostDelete PostView Post/Check IP

Thanks, Dave.

I take the point and shall look into it as I am certain that Nitrile/NBR/Buna-N is the correct material for petrol applications.

Section M01 http://rrtechnical.info/miscellaneous/oring.pdf shows that Nitrile/NBR is good for petroleum fuels, as does the description in thelower part of M16 http://rrtechnical.info/miscellaneous/elastomers.htm as you point out. The table at the top of M16 is apparently incorrect, but I shall double-check before correcting the table.í
Ď
RT.
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Richard Treacy
Grand Master
Username: richard_treacy

Post Number: 2375
Registered: 4-2003
Posted on Sunday, 14 August, 2011 - 02:39 pm:   Edit PostDelete PostView Post/Check IP

Dave,

I'll update M16 with a few notes. There are numerous petroleum fuels and petroleum fuel blends. Pure petroleum fuel is absolutely fine with Nitrile.

However, Nitrile hates aromatics (benzene, toluene and xylene for example) which are contained in most petroleum pump fuels. In those applications with a high aromatic content (whatever high means), Viton is the better choice as long as temperatures do not drop much below freezing where there is movement. By movement, that includes some o-rings where they are sealing a slide joint which flexes. Viton is great with petroleum, benzene, toluene, xylene and methanol. Nitrile is fine with ethanol (as in E10 and the coming E80 pump fuels) but suffers slightly with methanol.

Nitrile is probably fine with modern low-octane petroleum blends as they do not have much aromatic content. The quantity of aromatics is still quite low and probably poses no problem compared to high benzene fuels in the old days.

I use 98 RON exclusively on my cars, and none has suffered with over 10 years of those fuels, including 8 years of V-Power 100 octane in Europe. Those fuels have the highest aromatic content in pump fuel, so I donít believe that the aromatic concentration is enough to upset Nitrile which is used extensively in the fuel systems.

The danger is that the refiners are nowadays adding all sorts of additives and aromatics, possibly largish quantities of xylene, especially to the high-octane fuels (98 or 100 RON), and the quantities change daily with market conditions determining which to use and how much to reach the RON required. For example, Shell in Australia has dropped its highly-aromatic 100 RON V-Power (formerly Optimax) Racing fuel and we only have 98 RON V-Power, but that stuff is still loaded with aromatics. Worse still are the various aftermarket fuel and oil additives which are almost pure aromatic mixes (injector cleaners, octane boosters, tappet silencers etc). I never touch those additives.

RT.

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