Contact pressure of elastomer seals on the surfaces to be sealed, which arises when the seal is installed. To that end either –– as in lip seals — the lips are designed to be undersized or oversized, which is then to be stretched or –– as in compact seals and O-rings — the seal body changes shape and is compressed during installation (Figure V 41).
The pre-load is an elementary requirement for the suitability of a seal for its function by ensuring the initial sealing effect, which is then amplified under increasing pressure by the automatic sealing.
Figure V 41: Generating pre-load with O-rings