Why don't Zero-Leak Gold plugs leak?

Zero-Leak Gold plugs use both a metal to metal and elastomeric seal in their design. The metal to metal seal is accomplished by allowing the standard design geometry of the 12 or 15 degree taper that is present at the entry of the SAE J1926 port (see SAE port drawings at our site) to engage the corresponding taper located under the head of the Zero-Leak Gold plug. As the ZLG plug is engaged in the port the tapers converge and develop maximum gap minimization between the mating surfaces of the ZLG plug and the port. This same contact point, by the very nature of the fact that only several thousandths of an inch of both the ZLG plug and port come in contact, becomes the recipient of high unit loading which supports the metal to metal seal.

The o-ring acts as a back up seal to the primary metal to metal seal. The back up seal is made possible by the o-ring resting in an area under the head of the ZLG plug that has a cross sectional area that is greater than the cross sectional area of the o-ring being retained. There is no pressure applied to the o-ring as long as the metal to metal seal is performing. If for some reason the metal to metal would fail, the o-ring acts as the back up seal and prevents a leak.

The size relationship of the recess and the o-ring prevent the o-ring from being nibbled by the threads of either the plug or the port as may be the case with standard SAE J514 o-ring only style plugs.

The gap minimization feature of the metal to metal seal does not allow the o-ring to be extruded from the interface. The extrusion of the o-ring in standard SAE J514 style plugs is a common problem because vibration, pressure spikes, temperature changes can cause the SAE plug to begin to back out. When the backing out begins this process is supported by the pressure being contained. At some point the plugs back out far enough for the o-ring to begin to extrude out of the interface with a leak path being established.