Why are the o-rings used with Zero-Leak Gold Plugs smaller than the o-rings used in comparable size SAE J514 plugs?

The o-rings used with Zero-Leak Gold Plugs are all standard metric sizes and are avialable in Buna Nitrile 70 durometer as standard and in Viton, EP, etc. materials as special order.

The Zero-Leak Gold Plug o-ring is located under the head of the ZLGP in a recess that has a cross sectional area that is greater than the cross sectional area of the o-ring. The smaller ZLGP o-ring allows it to perform its secondary seal function with less than a 100% port fill rating while its SAE counterpart requires more than 100%. The fact that their fill rate is greater than 100% may be factor that is conducive to o-ring nibbling and extrusion.

The convergence of the tapers of the port and the ZLGP invoke maximum gap minimization and high unit loading at that point. This feature prevents the o-ring from passing between the ZLGP and the wall of the port. Should the metal-to-metal seal fail and therefore require the o-ring (back up seal) to make the seal, the small diameter o-ring is sufficient to make the seal.

The fact that the ZLGP o-ring does not have any sealing pressure applied to it unless the primary metal-to-metal seal fails, allows the ZLGP o-ring to have a longer useful life than the SAE J514 plug o-ring, which is under constant sealing pressure of the fluid it is attempting to contain. The ZLGP o-ring won't take a set, be nibbled by the threads of either the ZLGP or port, nor will it be extruded. All of these problem conditions may exist with o-rings used with the old style, o-ring dependent SAE J514 plugs.