O-Ring Permeation Coefficient of Common Materials

Permeability or permeation of gases through an O-ring varies by material type; material hardness; degree of squeeze; presence or absence of lubrication; size of O-ring cross section; and the pressure, temperature and type of gas being sealed.

Typically, harder compounds containing more carbon black feature lower diffusion rates. Increased seal squeeze results in decreased permeability. Externally lubricated O-rings can decrease permeability.

FKM Viton® O-Rings are commonly used in vacuum applications due to lower permeation which impacts vacuum pump-down time and the ultimate vacuum level achievable. O-Ring permeation can also affect the accuracy of sensitive sensor and test equipment. O-Ring outgassing or leaching of internal substances can also impact sensor effectiveness. Marco Rubber offers FKM Viton® O-Rings with an additional post cure or vacuum baking resulting in lower outgassing O-Rings.



Q = K A (P1 - P2) / D

Q is the permeation rate (cm3/sec)
K is the permeation coefficient (cm3 cm/sec cm2 atm)
A is the area (cm2)
P1 – P2 is the pressure gradient (atm)
D is the thickness (cm)



Permeation Coefficients (10-8 sccm - cm/sec - cm2 – atm)

Material

He

H2

H2O

N2

CO2

Buna-N

8

2.5

760

0.1

25

EPDM

25-30

16-18

 

6-7

85

Silicone

250

75-450

8,000

200

2,000

Fluorosilicone

140

80

 

40

400

FKM Viton® A

9-22

1-2

40

0.05-0.7

5

FKM Viton ® GF

30

3

 

2

 

Markez® FFKM

60-80

6-8

90-100

8-12

 

KEL-F

 

0.1

 

0.1

0.5

PTFE

 

0.4

 

0.14

0.12

Polyimide

1.9

0.1

 

0.3

0.2

New Customer Hotline: 800-775-6525

Existing Customer Specialist: 603-468-3600 or repeat customers

Marco Rubber & Plastics
PO Box 1150
Seabrook, NH 03874

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