Engineering: Section 4: Installation:

INSTALLATION PROCEDURE
The assembling area should be free of sharp edges, burrs, machining traces, threads, etc. The surface finish of the groove should be at least 32 micro-inches and a clean light lubricant can be applied to the ENCAP-O-SEALTM Teflon® encapsulated O-ring to minimize abrasion. It should be noted that the elasticity of the rubber core material within the ENCAP-O-SEALTM Teflon® encapsulated O-ring is impaired by the less flexible FEP/PFA encapsulation. To improve flexibility for difficult installations (over shaft, piston, etc.), the ENCAP-O-SEALTM Teflon® encapsulated O-ring can be heated to approximately 150C/250F (boiling water, oil bath, hot air). This softens the O-ring and allows it to be stretched. *See Diameter Stretch.

DIAMETER STRETCH
Stretch occurs when the inside diameter (I.D.) of the seal is smaller than the gland I.D., requiring extension of the seal diameter for installation and fit. It is generally recommended that an ENCAP-O-SEALTM Teflon® encapsulated silicone O-ring not be stretched more than 20% during installation and ENCAP-O-SEALTM Teflon® encapsulated Viton® O-ring not be stretched more than 8% during installation. This recommendation is frequently difficult to follow, particularly with smaller diameter O-rings. In those cases, where the recommended installation stretch is exceeded, sufficient time should be allowed for the O-ring to return to its normal diameter before closing the gland. *See Installation Procedure.

The designer should be aware that any time an I.D. of an O-ring, in its installed state, is stretched greater than 3%, seal life will be compromised.

Diameter stretch for rectangular glands:

Stretch % = [(Groove I.D. – O-ring I.D.) / (O-ring I.D.)] x 100%