Sealing Elements Technical Handbook O-rings
6. Compound Selection Hydraulic and Transmission Oils and ACN content High ACN content with a low plasticizer level provides excellent resistance to petroleum oils. Low ACN content with high plasticizer level gives better flexibility at lower temperatures. A peroxide-cure provides the best compression set resistance at elevated temperatures. These properties are important for use in hydraulic applications. ERIKS has several NBR compounds with high ACN content for the extreme demands of heavy equipment, for automatic transmission fluid (ATF), crude oil, as well as NBR with low ACN content for flexibility at very low temperatures. Silicone Fluids Silicone fluids are chemically very stable. Referring to fluid compatibility tables, all types of seal elastomers, except silicone rubber, may be used for silicone oils and greases. There are some exceptions; however, silicone fluids have a tendency to remove plasticizers from elastomer compounds, causing them to shrink. The effect is most severe with low viscosity fluids and high temperature applications. Because of this, military nitrile compounds and any other nitriles with a low temperature limit below -40°F (-40°C) should not be used to seal silicone fluids, because low temperature nitriles must contain plasticizers. Other compounds should be tested before being used to be certain they will not shrink more than one or two percent. Silicone rubber has a poor chemical compatibility rating in contact with silicone fluids. This is because silicone rubber tends to absorb silicone fluids, resulting in swelling and softening of the O-ring. Occasionally, however, it is desirable to seal a silicone fluid with a silicone rubber O-ring. This combination is generally acceptable if the viscosity of the silicone fluid is 100,000 centistokes or more, and if the maximum temperature will not exceed 150°C (300°F).
Summary of the resistance for mineral and biological degradable oils Mineral oils Type: H H-L H-LP H-LPD H-V
Elastomer to use
Waterbased oils Type: HFA (>80% water) HFB (40% water) HFC (35% water) HFD-R HFD-S
Elastomer to use
Biological oils Type: HETG HEPG HEES
Elastomer to use
NBR, FKM, HNBR, AU NBR, FKM, HNBR, AU NBR, FKM, HNBR, AU NBR, FKM, HNBR, AU NBR, FKM, HNBR, AU
-5° +55°C - NBR, FKM, AU -5° +60°C - NBR, FKM, AU -20° + 60°C - NBR -20° + 150°C - EPDM (aeronotique) -20° + 150°C - FKM
for agriculture up to 80°C: AU, NBR, HNBR for protected waterareas up to: 80°C AU, NBR, ANBR, FKM* +80°C: HNBR, FKM* (*only peroxide cured FKM’s) up to 80°C: AU, NBR, HNBR, FKM +80°C: HNBR, FKM* (*only peroxide cured FKM’s)
98 All the information in this documentation has been compiled with the greatest of care. Despite this we can bear no responsibility whatsoever for any errors present in the documentation. The recommendations are intended as guidelines.
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