EPCO

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required with conventional systems. He had several design parameters: the O-ring always had to be backed up by a secondary seal; the O-ring must be smaller than the groove it fit into. There must be a mechanism for minimizing any gap that may occur due to axial movement and the desidgn needed to involke elasticity of assembly and sustain high unit loading.

Williamson saw a need to change the design of typical SAE fittings. To understand why, Aichele says one needs to understand how SAE straight or adjustable thread O-ring boss fittings work.

With standard SAE fittings, the SAE J514 port has internal female threads and either a 12- or 15-degree taper at the outer edge. There's a large O-ring below the head of the plug that becomes a gasket in assembly and during pressurization axial force pushes the components together to form a seal.

Problems with leaking arise when the O-ring is damaged in operation. What can happen during pressurization is the O-ring gets extruded into the interface where it forms an extruded portion, which creates a leak path. The fitting must be disassembled, the O-ring replaced and then reassembled.

"The O-ring can be nibbled or damaged in that area," says Aichele. "And that particular design is also extremely vulnerable to vibration. When vibration occurs it is possible for that component to start backing out and once it does that, the O-ring can be extruded in that area and the seal lost."

The answer

What the inventor did to correct O-ring extrusion, thus eventual leaking, was to add an extenison underneath the head of the plug that has a taper that corresponds to the design of the SAE J514 port. Below the taper on the plug, he created recess, with the cross-section area of that recess being greater than the cross-sectional area of the O-ring that rests there. The fitting enters the first few thousandths of an inch of the port forming metal-to-metal contact, which is the fitting's primary seal. Since the seal is internal, no spot facing on the external surface of the port is necessary.

"The primary seal when you tighten the plug is metal-to-metal contact," Aichele says. "The tighter you tighten it, the more that taper engages, developing maximum gap minimization."

The design puts no pressure on the O-ring, eliminating the potential for O-ring damage. The main reason for this is that
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