O-Ring Permeation Coefficient Chart 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)
FKM Viton ® A
FKM Viton ® GF
Markez ® FFKM