This sandbox article is a collection of things we might want to add to Blowout preventer. We need better drawings, especially the annular preventer. The level of detail needed is what we have in Figure 3, enough to understand the mechanism, but not a complete machine drawing.
There are three types of blowout preventers: annular preventers, shear rams, and pipe rams. Annular preventers and pipe rams make a tight seal around the outside of a drill pipe. Shear rams (aka blind rams) cut through the drill pipe and seal everything, including whatever might be coming up inside the drill pipe.
Both annular preventers and pipe rams close around the pipe, but annular preventers have more of a vertical motion, so they loosen slightly if the drill pipe is being pushed downward, as might be necessary in a snubbing or well kill operation.[1] Shear rams are used as a last resort, because they destroy the drill pipe and limit options for further work.