This is the same check valve used in all of our valve cover breathers originally equipped with a check valve. It is offered as a replacement part in case the original valve is misplaced. This valve will not fit valve cover breathers that are not specifically machined to accept the valve.
This part is CNC-machined from high-grade composite material, and should never require replacement unless lost or damaged.
When properly installed, the channel-side faces up, and the flat side of the valve faces down.