Here are two pictures of pages from my welding textbook from college,
showing the internals of the valves, and specifying that Oxygen valves
are to be opened "all the way".  Acetylene valves, however, are customarily
opened a quarter turn only.

WeldValve0.txt	This File

WeldValve1.jpg	Oxygen

WeldValve2.jpg	Acetylene

-Chris Daniel