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 a 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.