Plasticizer extraction can affect all seals, especially those used in fuel systems. Plasticizer is initially added to an O-ring compound in order to augment its flexibility and resilience. If plasticizer is extracted (chemically removed) by system fluids, the seal’s flexibility and resilience both suffer. The O-ring hardens, small cracks start to appear in the stressed area of the cross-section, and the seal’s overall volume decreases.

This loss of volume (shrinkage), coupled with the aforementioned hardening, is typically accompanied by a loss in retained sealing force, i.e. the seal will leak. The best available solution is to use a seal material that is still compatible with all elements of the system but that contains little or no extractable plasticizer. Figure 136 is an example of O-ring failure due to plasticizer extraction.