Want to see all the Valve Designs

[TeamJackal37]

I would like to see all the Valve Designs. and Why are there 2 "X" Valve (one is in the center and other is alittle higher than the center) and What year was it Designed. Please post some pictures. I would like to know the Background of these Valves.

[MANN]

there is a search button. use it