Author Topic: O ring application guide  (Read 5186 times)

Offline CR

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O ring application guide
« on: March 25, 2010, 09:12:43 AM »
I've always been a firm believer in Buna N as the go to O ring material and always wondered at the populist trend to use Silicone in applications where it is quite possibly least well suited.  

http://www.parker.com/literature/ORD%205700%20Parker_O-Ring_Handbook.pdf
The single best educational  resource available
I have their hardcover and was unaware that they  also publish a PDF version.
The nice thing about the PDF is it's searchable

here's a much smaller guide
http://www.sealdynamics.com/o-ring-reference.pdf


Purusing them you will quickly come to the conclusion that good old black Buna-N (nitrile)  is the most useful, cheapest, and most reliable O ring going  with a  GoZillion (to the tenth power) of duty hours in all industries.   Buna N  is able to tolerate a wide temperature range under a very diverse set of duty applications from sliding seals to static and is excellent for assemblies which must be disassembled often.  Buna N is also  very cheap.

Silicone on the flip side is expensive,  and when you squeeze it in a static compression it  can  get a tear started  from the ridges in things like tanks and kettles.  Once the tear starts, propagation is fast.  Silicone  takes a set from compression loading  it has very low friction tolerance and is a terrible material for frequent disassembly  precisely because of it's friction intolerant character.
Silicone leaks gasses faster too. ( though  pretty much all O ring gas transpiration rate is so trivial as to be insignificant.)
In fact Silicone's only  real advantage is thermal resistance.    

But who needs more thermal resistance  than Buna N offers?
It seals satisfactorily for five minutes at 538°C (1,000°F) and at 149°C (300°F) for 300 hours.

Buna N is the default material of all generic O ring producers.  You can  bet, for dead certain, that whenever you see a package of black O rings that they are Buna N, unless the package says otherwise.  This is exactly because of Buna N's incredible performance characteristics, extensive range of applications,  and  enormous history.     They want their O rings to have the broadest application capacity for the money and Buna is cheap cheap cheap.  


Over 20 years ago  I was part of a group touring  Parker's  O Ring  factory.   I asked why so many were black.  The answer was that  rubber-like and rubber products  are  black is  because there's so much carbon through out the process that  in order to make the products any other color they'd have to run super clean facilities and take extra measures to exclude carbon  from the whole chain of production  as is done for other polymer products.   He told me that we'd pay a lot more for pretty colored O rings.

Since then,  the carbon has been found to slow the rate of gas transpiration through O rings.  Prolly because  the carbon  absorbs the gas.   The cost of making pretty colored O rings remains  high.  


 
« Last Edit: March 25, 2010, 09:17:34 AM by CR »

Offline Pirate Point Brewer

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Re: O ring application guide
« Reply #1 on: May 09, 2010, 05:25:16 AM »
CR,

Wow!  That's a lot of data!  We just got around to following up on this post.
We're really happy to read this about Buna-N as they are the easiest to find and the least costly.
We've used them in the MLT and worried about temp. So we're glad to read that our fear was unfounded.

Thanks

Preston
In Fall and Winter, we burn wood in the fireplace and brew beer.
In Spring & Summer, we're on the water or walking the beach!
 Then back at the dock we create a reason to brew!

Offline CR

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Re: O ring application guide
« Reply #2 on: May 12, 2010, 07:36:41 AM »
Buna N is a marvelous material.
The higher the black carbon ratio the more impermeable to oxygen  the it becomes - up to a point of course.

Offline Pirate Point Brewer

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Re: O ring application guide
« Reply #3 on: May 12, 2010, 02:31:46 PM »
CR,

Thanks again for the info. I've been waiting for a drip from the MLT for a while now. Maybe I won't worry so much.  The Princess told me drips aren't all bad .... she married one and things have worked out .... so far.  Boy, when ya get .... ya just get it!

Preston
In Fall and Winter, we burn wood in the fireplace and brew beer.
In Spring & Summer, we're on the water or walking the beach!
 Then back at the dock we create a reason to brew!

Offline CR

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Re: O ring application guide
« Reply #4 on: May 19, 2010, 01:31:31 PM »
shameless bump

there ought to be a way to make some things sticky.


 

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