O-rings provide excellent service in low power drive belt assemblies because they are inexpensive, easy to install, and the use of tensioning devices are not required.
When using O-rings as drive belts, certain design considerations should be observed such as maintaining between 8% to 12% stretch on the seal inside diameter. Also, the pulley grooves should be round and match the O-ring's cross section in depth and width while ensuring that the pulley diameter at the bottom of the groove is no less than 4 times the O-ring cross section.
Ethylene Propylene (peroxide cured) is the primary elastomeric choice because of the low stress relaxation, good flex life, abrasion resistance, and high temperature resistance. However, poor resistance to petroleum-based lubricating oil limits its application range.
Polyurethane, unlike EP, demonstrates excellent resistance to petroleum-based lubricating oils while maintaining high abrasion resistance, tensile strength, and flex life. Stress relaxation (loss of tension), however, is relatively higher and the service temperature limit (to 130°F) is somewhat lower, when compared to EP.
Neoprene is generally specified when service temperatures exceed the limit of Polyurethane (to 175°F) and possible contact with petroleum fluids. Abrasion resistance is good, but EP displays superior flex life and stress relaxation properties.
HNBRs are now being used for their superior tensile strength and oil resistance.