Nitrile O'Rings

[robwilk]

I have to put some O'Rings around a test tube on Stirling engine to seal it in the main cylinder do you think Nitrile O'Rings will stand the temperature if not what should I use .
Thanks for looking.

Rob......

 

[deverett]

Not sure what temperature you are expecting, but if you are at all worried about the heat degrading Nitrile rings, go for Viton. That is the best heat resistant material.

Dave
The Emerald Isle

 

[steamboatmodel]

When I worked in the Hydraulic/Pneumatic industry there was a caution issued about Viton O rings, I didn't save a copy but I copied this a while back from one of the forums when Viton O rings were mentioned.
"They have 2 issues that might make them less than ideal:
1) If overheated (405 degC) they release Fluorine gas, which immediately dissolves in atmospheric water to form HF hydrofluoric acid - this destroys metals, glasses and people and is hazardous even in o ring quantities
2) Viton is physically weak by elastomer standards
3) its VERY expensive (but that may not be a problem)

Nitrile will probably be fine - the 100 degrees is the PERMANENT temperature it will stand to work 24/7 with no loss of elasticity or other properties. We don't mind replacing a o ring each year. Nitrile is hopeless in air (ozone) and especially ozone but both of these are limited in a steam engine

My strong preference would be silicone, where the temperature is immaterial (I use it in CO2 motors at minus 20 or so). It ccan be made hard enough to reduce friction (about 75 to 80 shore A if interested) and the oils used will just make it swell temporarily

hope this is helpful,
I have probably given the impression that viton has its problems - I don't use it . Leave it for aerospace where it is essential, and the maintenance chaps know its habits"

Regards,
Gerald.

 

[doc1955]

When I worked in the Hydraulic/Pneumatic industry there was a caution issued about Viton O rings, I didn't save a copy but I copied this a while back from one of the forums when Viton O rings were mentioned.
"They have 2 issues that might make them less than ideal:
1) If overheated (405 degC) they release Fluorine gas, which immediately dissolves in atmospheric water to form HF hydrofluoric acid - this destroys metals, glasses and people and is hazardous even in o ring quantities
2) Viton is physically weak by elastomer standards
3) its VERY expensive (but that may not be a problem)

Take a look at page 9 of this PDF if you use viton o rings you should be aware of this and take precautions.
Saafty Specs

 

[Kermit]

A one page primer of types and specs.

View attachment sealmaster.pdf

 

[Sparticusrye]

I've used Viton extensively in my work. But, mostly in gas turbines where the synthetic oils will destroy all other materials. I've never had an issue with them, but they are only used downstream in oil systems away from excessive heat. High heat areas usually have alloyed metal seals and fine tolerance surface finishes. I'd avoid them for small applications and definately wouldn't use them in a superheated steam system.

Stick with the Nitrile for a stirling engine, there shouldn't be any issues as stirlings don't generally run extremely hot. An if its just to seal two mating surfaces then silicon works. (I've used the table mats from the galley on the ship for this, cooks hate you for a second when they find big holes in the table mats).

James

 

[robwilk]

Thanks for you help . That clears it up for me I will stick to Nitrile. My concerns were brought up by the plans I have on them it says when fitting the power cylinder to the main cylinder you must use solder because it will get hotter than loctite can stand as these orings are in the same part I became concerned. Possibly the parts wont get as hot as the plans suggest.
If you want to see the plans i am working on they are in the download section.
http://www.homemodelenginemachinist.com/index.php?action=tpmod;dl=item270

Rob......

 

[Stan]

I have built several test tube type engines and just use the ordinary O rings that come in the red box selection from Harbor Freight. The characteristic of glass that makes Lamina engines work, is that glass conducts heat very poorly. With the engine you are building, you should be able to hold the end of the test tube in your fingers when the burner flame is under the center of it. The thermal conductivity of Pyrex is 1 whereas the thermal conductivity of aluminum is 250.

The other end is heat sinked in the cylinder so it should be even cooler and not damage the O ring.