To enable well pressure to be isolated and released from the lubricator without closing wellbore valves.
The main body in the shape of a cross has a vertical full bore section to allow movement of wireline tools in and out of the wellbore.
The horizontal ends of the cross often referred to as ram housing contain rams, with inner and outer seals. These rams can be rotated in and out of the housing with handles fastened to threaded stems for closing and opening ram bodies.
An equalizing assembly is located on the side of the main body with a bleed off port on the opposite side, and located 90 degrees from ram housings. By opening an allen wrench operated valve seat the equalizing assembly allows pressure to be returned to the lubricator from the wellbore with rams closed.
BOP are fitted with compatible hand unions for installation with surface equipment. Wireline BOP’s seal and hold pressure from below only.