The ACS twist-to-lock vented flush fuel cap is machined from 6061 aluminum billet. The sealing element for the cap is an easily replaceable viton “O” ring. The bottom of the cap is secured to the bottom of the ring by a safety chain to prevent loss of the cap during flight. the mounting ring may be welded, riveted, bolted or molded onto the tank. The bottom side of the mounting ring has 6 center drilled marks (they do not go through) to aid in drilling an evenly spaced 6 hole pattern if required.

The venting feature of the cap is a gravity controlled ball valve and air labyrinth designed to do the following:

• Allow the entry and exit of air without pressure buildup when the face of the cap is pointing up
• Restrict the entry of water when the face of the cap is pointing up
• Allow the entry of air when the face of the cap is pointing down
• Restrict the exit of fuel when the face of the cap is pointing down