Originally Posted by onehundred80
Max
I think you will find that 3" O-Ring which is 76,2 mm and .139" which is 3.53 mm is really a metric 75 mm x 3.50 mm. ( 2.952" x .138")
The Metric O-Ring would be snug in the groove, the 3" O-Ring would be looser - too loose?.
I would question the use of Viton O-Rings as they seem like over kill temperature wise. Nitrile O-Rings are good for continuous service at 225 -250 degrees F. depending on what specific composition the material is. The use of the Viton O-Rings would be money wasted in the filter makers eyes.
I have to admit that I have had none of these in my hand so my observations are strictly based on O-Ring use on other applications.
I figured some Canuck (or Euro) would chime in here- There was no metric equivalent shown in my quite old Parker O-ring Design Guide and none on the McMaster-Carr website. The 3 smaller ones are quite common and available.
A M3.5 X 75 will work and is correct.
As for material selection, Viton is definitely indicated for these temps and materials/fluids (synthetic oils).
Buna-N (Neoprene) is typically a third choice in this application.
Please use this:
About Resistance of O-Ring Materials
The cost differential is very small. $1 each for Buna and $1.50 each for Viton. (Inch size)
Temp chart:
Materials are listed in order of least to most expensive.
Nitrile (Buna-N, NBR)
–30°F to 250°F (–34°C to 121°C)
EPDM (Ethylene Propylene, EPM)
–70°F to 300°F (–57°C to 149°C)
Neoprene (Chloroprene, CR)
–35°F to 225°F (–37°C to 107°C)
Silicone (VMQ)
–65°F to 450°F (–54°C to 232°C)
Viton (Fluorocarbon, FKM)
–15°F to 400°F (–26°C to 205°C)
Polyurethane (AU, EU)
–40°F to 180°F (–40°C to 82°C)
Fluorosilicone (FVMQ)
–100°F to 350°F (–73°C to 177°C)
Aflas (Tetrafluoroethylene Propylene, FEPM)
25°F to 450°F (–4°C to 232°C)
Kalrez (Perfluoroelastomer, FFKM)
–15°F to 600°F (–26°C to 316°C)