SUBJECT : Selecting the correct elastomer (O- ring) for your mechanical seal application 4-9

This paper is to be used with the O-ring selection guide you'll find in the chart and data section of this web site. The guide is an attempt to select the fewest number of elastomers that will give you satisfactory sealing of most of the chemicals we find in the process industry. As you can see from the selection, most of the chemicals can be handled by either fluorocarbon (Viton/ Fluorel) or Ethylene Propylene.

The following paragraphs describe the codes used in the chart.

Keep in mind that this o-ring selection chart is only a guide to help you in selecting the correct elastomer for your mechanical seal application. It was created from published information, various industry guide lines and many years of practical experience by field sales and engineering people. Most mechanical seals use at least one dynamic elastomer, so even small amounts of swelling or chemical attack is almost always un-acceptable. When using this chart please keep the following in mind:

The degree of carbon and elastomer attack is determined by the chemical concentration and temperature. The higher the concentration and the higher the temperature, the more likely the attack.

Plant experience is your best protection, but if you have no experience in handling these chemicals it would be wise to immersion test both the black o-ring and carbon face prior to installing a mechanical seal. You could duplicate the temperature by placing the test vessel in an oven, or on a hot plate when practical.

Temperature range F.
Temperature range C.

Flurocarbon (Viton ®)

-15 to 400

-25 to 205

Ethyle propylene

-70 to 300

-55 to 150


-20 to 450

-30 to 230

Kalrez ®

0 to 500

-20 to 260


-45 to 300

-45 to 150

Buna N

-65 to 225

-55 to 105

Buna S

-75 to 250

-60 to 120

Ethylene Propylene Rubber (EPR) is the first choice in most water and water based applications, but the variance noted above can cause premature O-ring failure. If you have any doubt about your water, conduct an o-ring immersion test prior to installing the mechanical seal.

The four step procedure for selecting the correct elastomer:

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